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By Dr. R. S. Kaae and Patricia Kaae
Entomologists estimate there are between 2 and 14 million species of insects. Of these, slightly less than a million have been identified. Approximately 2/3 of all insects eat other insects, which means there is approximately 1.5 to 10 million species of entomophagus insects. Entomophagus insects fall into 2 large categories, mainly the predators and the parasitoids. The term parasitoid is sometime used interchangeably with the term parasite. On strictly entomological terms, a parasite is like a flea, louse or tapeworm where there is one biological group feeding internally (endoparasite) or externally (ectoparasite) on a totally different biological group with subsequent harm but rarely resulting in death. Typically there are many parasites on any one host.
On the other hand, a parasitoid is one insect feeding on another insect (same biological group) and the ultimate result is death of the host. A parasitoid is only parasitic during the immature stage while the adult is free living. Parasitoids may attack any stage of the host but the least attacked is the adult. Parasitoids have been used more often in biological control than any other agent. A notorious example of a parasitoid would be a tarantula hawk laying its egg in a tarantula with the larvae of the wasp feeding internally in the spider and eventually killing it (Figure 1)
Figure 1. Left-A tarantula hawk (parasitoid). Image courtesy of Bob Jensen. Right-Tarantula hawk capturing a spider. Image courtesy Peter Chew.
Predators are free-living organisms that feed on other animals, sometimes devouring them completely and usually rapidly. Predators may attack their prey as an immature and or adult and require the consumption of many to survive. Major predators of insects include birds, reptiles, fish, amphibians, mammals and other arthropods. Of these, the most important predators in biological control programs have been the insects and mites. It is difficult to rank which orders of insects are most important from the standpoint of predation since almost all have important species but the Hymenoptera, Diptera, Coleoptera and Hemiptera are outstanding.
Some predaceous insects are quite specific on which prey they feed and are therefore termed monophagus. Others feed on a few different types of prey (oligophagus) while most feed on a wide range of hosts (polyphagus). Being polyphagus has advantages and disadvantages. The advantage is that when the numbers of a particular species of prey in the field drops, this type of predator is not dependent on that particular species for survival and its population in the field is not generally affected. However, when the population of a particular pest species begins to increase in the field the population of a polyphagus predator does not typically correspondingly increase—the result is that this type of predatory will not typically suppress a growing population of a pest. From the standpoint of biological control monophagus predators and parasitoids are considered the most effective in controlling pest species. This is not to say that the other types of predators in a cropping situation are not important because they all add to the overall picture.
ODONATA-DRAGONFLIES AND DAMSELFLIES
These are relatively large insects that are characterized by huge protruding eyes that occupy most of the head, an elongated abdomen, well-developed wings with many veins and small hair like antennae (Figure 2). Dragonflies and damselflies can be distinguished from each other by the way they hold their wings when at rest. When not in flight, dragonflies hold their wings straight out from the body while damselflies hold their wings folded over the abdomen.
Figure 2. Left. Damselfly. Right. Dragonfly.
Dragonfly and damselfly nymphs are aquatic while the adults are terrestrial, but are usually found near water. Both stages of each are predatory.Nymphal Odonata breathe by means of gills. In damselflies the gills appear as 3 featherlike structures that protrude from the tip of the abdomen (Figure 3). Gills of dragonflies are ridged and line the rectum internally. They breathe by drawing water into the rectum and over the gills. This water is subsequently forcibly expelled out the anus, thus moving the nymph in a jet propulsion-like manner.
Figure 3. Left. A dragonfly nymph or niad. Right. Damselfly nymph.
Nymphal and adult dragonflies are predatory. The nymphs, or naiads, feed on a variety of small aquatic organisms. Typically they lie in wait for prey either on a plant or while partially buried in the mud. Even though most naiads feed on smaller insects, some of the larger species prey on small fish, frogs and salamanders. Occasionally these become major pests at trout farms.
Adult dragonflies typically feed on mosquitoes and other flying insects. Dragonflies are quite agile and fast flying. When actively seeking prey, they fly with their legs held in a basket-like fashion that allows them to trap flying insects in the air. Damselflies are much weaker fliers and normally feed on slower moving insects than do dragonflies.
Dragonflies are one of the few insects that exhibit a degree of territoriality. It is not uncommon for an individual to select a 100-to-200 yard territory along a stream and to patrol that area continuously during most of the daylight hours. Typically it will have 2 or 3 locations (twigs, etc.) along the stream that are preferred for resting. This territory is closely guarded and any other individual of the same species that enters the area is quickly chased out.
Dragonflies and damselflies usually lay their eggs directly in the water or on aquatic vegetation. These insects typically complete one generation per year and pass the winter in the egg stage. In some species adults are active for only a few weeks each year, whereas others may be seen throughout the warmer months over a period of several months.
This is an order of tiny insects (1/32 to 1/16 inch) that is characterized by their shape and the presence of rod-like wings that are fringed with elongate hairs ((Figure 4). Almost all the members of this order are phytophagus feeding on leaves, fruit and other plant parts. These insects have tiny mouthparts and typically can only feed one cell deep.
A few species are predatory, the most notorious of which is the six-spotted thrips This is an effective predator of
Figure 4. Phytophagus thrips..
ORTHOPTERA-WALKING STICKS, MANTIDS, GRASSHOPPERS
FAMILY MANTIDAE-PREYING MANTIS. The only true predators in this order are the preying mantids. These well-known insects are readily recognized by their elongate prothorax and well-developed raptorial front legs (Figure 5). In raptorial legs, the femur is swollen with large spines on the ventral margins of the femur and tibia. The tibia is also capable of being folded back on the femur forming an efficient grasping organ for their predaceous way of life. Mantids are chiefly tropical in origin with over 600 species occurring worldwide. There are only about 20 species in the United States with most occurring in the southern states.
Figure 5. A common mantid illustrating elongated prothorax and raptorial front legs.
Mantids are general predators, feeding on any insect of appropriate size (neither too small nor too large). As a rule, they are not considered too important in the natural, or biological, control of pest species. Because mantids are not host specific, the practice of buying their egg cases in order to turn the hatched nymphs loose for backyard pest control is of little, if any, value.
The praying mantis is cannibalistic with larger forms commonly eating smaller ones. The female frequently consumes the smaller male after mating. Any male mantid attempting to mate with a female approaches her with great caution since he doesn’t want to be eaten before mating. In most cases he will take several minutes to travel a few inches, especially in her immediate vicinity. Most predators, including female mantids recognize their prey by movement. In some species, once the male mounts the female and copulation begins, he has a difficult time releasing his sperm packet due to a neurological block located in the brain. However, once the male mounts the female she reaches backward and bites his head off, thus releasing block. Then the sperm packet is released and the female consumes the rest of the male.
In the United States, eggs are typically deposited on branches or bark in an egg case or mass (ootheca) (Figure 6). This is the overwintering stage or that stage of the insect that is best suited to pass the less hospitable winter months. In the spring the young nymphs emerge to grow to adults by late summer or fall.
Figure 6. The egg case of the Chinese mantid.
Being large common insects, mantids in many countries are subject to considerable folklore. In Guatemala, children are told that these insects will eat your tongue, if given a chance; consequently, it is not uncommon for a child upon seeing a mantid to slap their hands over their mouths and run as fast as they can. The translation of the Vietnamese name for mantis is heaven’s horse. There it is believed that if you see a mantid, it is considered good luck if you place a drop of honey or sugar on its head as the insect will fly to the heavens and present this gift to the gods.
The Chinese mantid is the species that has received the most attention (Figure 7). This species was introduced into the United States in 1896 for control of various insects. Today its eggs are shipped all over the United States primarily to sell to homeowner for supposedly biological control.
Figure 7. A female Chinese mantid.
FAMILY-NABIDAE-DAMSEL BUGS. This is a small family all of which are predatory in the adult and nymphal stages. As with all predatory bugs their front legs are raptorial with a swollen femur. The larger femur is needed to house the heavier musculature needed to give these legs the strength necessary to subdue their prey. Since this is such a small family there is very little difference in the appearance from species to species (Figure 8). Once characteristic that is unique to this family is that they have a latter-like arrangement of cell on the inner margin of the front wing.
Figure 8. A damsel bug, Nabis ferus, one of our most common predators found in agricultural fields.
Nabis ferus is one of the more common insect predators found in agricultural field and orchards throughout the United States. Adults are approximately 0.4 inches in length and grayish in color. Their prey includes but is not limited to aphids, leafhoppers, tree hoppers and small caterpillars.
FAMILY-ANTHOCORIDAE-MINUTE PIRATE BUGS. This is a very small family of small insects measuring 0.1 inches in length or less (Figure 9). The family as a whole can be distinguished by small break on the edge of the leathery part of the hemelyra (see arrow). The most common species in this family is Orius insidiosus that is distributed throughout the US and is commonly found in flower heads. It can be identified by the upper part of the front wing colored yellowish white with a black triangular area at the tip. The lower area of the front wing (membrane) is milky white. This insect is sometime mistaken for the chinch bug on which it preys.
Common prey include the chinch bug, false chinch bug, thrips, corn earworm (eggs and early instar larvae), walnut husk fly eggs, mites and many other small insects and eggs. These insects are abundant on corn in the eastern stares laying their eggs on the silk. Minute pirate bug are abundant in cotton field throughout the US and are considered an important predator.
Figure 9. A minute pirate bug. . Image courtesy of USDAS-ARS.
FAMILY-REDUVIIDAE-ASSASIN BUGS, CONE-NOSED BUGS. This big family is comprised of relatively large bugs (1/2 to 1+inches in length) that are mainly predatory and with a few blood-sucking forms. Assassin bugs are characterized by possessing a short beak, which terminates in a groove in the front part of the thorax. In addition the head narrow behind the eye giving the appearance of a neck like structure and with many species the abdomen is widest in the middle and tapers at either end (Figure 10). Cone- nosed bug refers to the characteristic that in many species the head is cone shaped.
Figure 10. An assassin bug illustrating the short beak and narrowing of the head behind the eyes. Image courtesy of Peter Chew, Brisbane Insects..
Many of the predatory forms are capable of and will readily inflict painful bites. The blood suckers feed on warm-blooded animals (mainly mammals) including humans. In Mexico, Central and South America they vector Chagas’ disease, a type of sleeping sickness. Most of the blood sucking assassin bugs that vectors this disease belongs to the genus Triatoma (Figure 11). This genus is well represented in the US but the disease does not occur here.
Figure 11. A blood sucking conenose (Triatoma spp.). a blood sucking form. Image courtesy of Marcelo de Campos Periera.
The spied assassin- is one of the more common assassin bugs found in cropping situations throughout North America (Figure 12). It is characterized by having many spines on the pronotum (top of prothorax) and front legs. This average sized (adult length ½ inch) bug feeds on many different agricultural pests including all stages of the Mexican bean beetle.
Figure 12. The spined assassin bug, one of the more common predators found in many crops.
Bee Assasins-Apiomeris spp. There are several species in this genus that are distributed throughout North America. The most common species is Apiomeris crassiipe, which measure around 0.6 inches body length (Figure 13). As their name implies these bugs primarily feed on bees or other insect that visit flowers for nectar and pollen. As one might expect these are active during the day and sit on flower head waiting for visitors.
Figure 13. A bee assassin, a common predator of bees and other insects that visit flowers for nectar and pollen.
The wheel bug is one of the larger species of assassin bugs and is named after the half-wheel appearing structure in the top o the thorax (Figure 14). This species occurs primarily in the eastern and southern state extending down into Central America. This large assassin bug (over an inch in length) is a voracious predatory attacking a variety of insects. It is even capable of devouring a large tomato hornworm. It reportedly has a very nasty bite with the pain lasting for a day or more.
Figure 14. A wheel bug, one of the larger assassin bugs with a nasty bite.
FAMILY PHYMATIDAE-AMBUSH BUGS. These odd looking insects are sometimes placed in the same family as the assassin bugs. Most are relatively small, ranging from 0.3 to 0.5 inches in length. They can readily be recognized by the distinctive shape (Figure 15). Ambush bugs typically sit on flower head waiting for butterflies, flies bees and other insects that come for nectar and pollen.
Figure 15. An ambush bug waiting on a flower head a bee or other insects. Image courtesy of Entomology, University
FANILY-PENTATOMIDAE-STINK BUGS. Most members of this family are slightly flattened, shield-shaped and the scutellum (triangular area behind the top of the prothorax) is greatly elongated when compared to other Hemiptera (Figures 16). In the case of the stinkbugs this structure is at least half the length of the rest of the body. The name Pentomidae refers to the 5 segmented antennae.
Most members of this family are phytophagus, chiefly feeding on seeds and fruiting bodies; however, there are a few species of stink bugs that are predatory in both the nymphal and adults stages. In these cases they are typically general predators feeding on those insects of appropriate size.
Figure 16. A stinkbug attacking a phyotphagus species of stink bug. Image courtesy of Peter Chew.
FAMILY LYGAEIDAE-SEED BUGS. Most members of this family are plant feeding and include such notorious insect such as the chinch bug, false chinch bug and milkweed bug (Figure 17). Most members of this family are medium size and can readily be recognized the presence of 4 to 5 simple veins (no cells) in the membranous part of the front wing.
Figure 17. A common milkweed or seed bug. Image courtesy of Peter Chew.
There are a number of predatory species in this family but the most well known is the big-eyed bugs. This is a relatively small species (0.12 to 0.15 body length) belonging to the genus Geocoris spp. with a broad head and thorax and bulging eyes (Figure 18)
Figure 18. A big eyed bug (left) approaching dinner (insect egg). Image courtesy of ARS.
These insects are predatory in both the nymphal and adults stages feeding on a variety of pest species including but not limited to aphids, chinch bugs, leaf hoppers, Lygus bugs mites and small caterpillars. They are very commonly found in cotton, alfalfa and sugar beet fields in the western US and are considered a very important part of the predatory-parasitoid complex that keeps these insects under control. There are several species of this genus found in these fields.
Water boatmen are the most common group of aquatic insects in North America, in both the number of species and abundance of individuals (Figure 19). They are extremely common in lakes and ponds with a few species found in brackish water along the seashore. The body is elongate-oval, somewhat flattened, and usually dark gray in color. The hind legs are elongated and oar-shaped, while the front legs are scoop-shaped (arrow) and used to scrape algae, their main diet, off rocks.
The only family of aquatic Hemiptera that remotely resemble water boatmen are the backswimmers. These two families can be separated by several characteristics. Notable differences are the shape of the front legs and beak or rostrum. As discussed above, the front legs of the water boatmen terminate in the scoop-shaped tarsi. In the case of the backswimmer, the front tarsi are sharpened, which is an adaptation for their predatory way of life. Additionally, the beak of water boatmen is cone shaped, while that of a backswimmer is elongated and pencil-like in shape. An even more discernable characteristic is the shape of the body. When viewed from the front, the back of water boatmen is distinctly flattened, while that of a backswimmer is distinctly pyramid shaped or humpbacked.
Because the insects are so common in aquatic situations and are a primary convert of plant-to-animal matter, they are considered very important in food chains. In many areas of the world water boatmen are even consumed by humans. The adults are not normally consumed, as they are too crunchy; however, in the lakes of Mexico large rope mats are placed in the water and serve as a suitable substrate for egg deposition. Periodically the mats are removed and the eggs are scraped off and ground up into flour high in protein.
Figure 19. An adult water boatmen with scoop-shaped front legs. Image courtesy Charles Hogue.
The backswimmers, as you might expect, are so named because they swim on their backs. They are very similar to the water boatmen in shape, but the dorsal side of their body is more roof-like in cross section and they typically are lightly colored. In addition the tip of the front legs is not scoop shape but adapted for catching their prey, namely sharp (Figure 20).
Backswimmers are aquatic and most rest just below the surface of the water with the head angled downward. They are predaceous, feeding on other insects and, occasionally, tadpoles. They are important in the biological control of mosquito larvae. A common method used to catch mosquito larvae and pupae, is to drift up under them after releasing hold of an aquatic plant to which they have been clinging.
These insects are capable of inflicting painful bites if carelessly handled. The males of many species can produce a 'squeaking' sound by rubbing their front legs against their beaks (stridulating). This sound is associated with the backswimmer's courtship behavior.
The action of swimming on the back is due to a ventral light reaction. That is, backswimmers swim with the most lighted part of their environment on the underside, or venter, of their bodies. The importance of light in their orientation can easily be demonstrated by placing backswimmers in an aquarium with a dark board over the top and a light bulb shining through the bottom. In this case the insects will swim with their venter toward the bulb or right side up. As discussed, in nature it is to the advantage of backswimmers to swim upside down as their prey typically is on the surface of the water and they can float up in a position ready to attack.
Figure 20. Left. Backswimmer nymph. Right. Backswimmer adult.A nymphal backswimmer.
The water scorpions are a small family of very large aquatic insects with many species reaching 2 inches or more in length. All are predatory with well-developed raptorial front legs. In addition their body shape is unique and quite distinctive with the abdomen terminating in two long breathing tubes (Figure 21). The early instar nymph lack the breathing tubes. These insects occasionally leave the water and are slow swimmers. They reportedly are capable of delivering a painful bite.
Figure 21. Left. An adult water scorpion. Right. Early instar nymph.
The water striders (adults and nymphs) are long-legged insects that run or skate over the top of water to catch their prey, mainly other insects that fall accidentally onto the surface. The front legs are short and raptorial for catching and holding their prey while feeding (Figure 22). The tarsi and other parts of the legs of these insects a covered with short hairs that are difficult to wet. Additionally, the tarsal claws are antapical referring to the fact that they are positioned on the last tarsal segment before the tip and are capable of being retracted. Therefore the claws do not protrude from the tip of the leg and do not break the surface tension of the water. This, plus the non-wettable hairs, allows these insects to walk on water. Water striders are common in quiet water where they often occur in large numbers. A few species are wingless as adults are are all nymphs
Some individuals of a species are winged and some are apterous. If a stream or pond dries up, the winged forms will attempt to fly to a new aquatic environment, while the apterous forms burrow in the mud or under stones where they remain dormant until the rainy season returns. Water striders are one of the few types of insects that can be found in the ocean. Ocean-inhabiting species are apterous as the ocean is not likely to dry up.
For any fishermen reading this text, water striders are not good bait for trout or other fish. It makes biological sense that any insect that lives on the top of water must have some mechanism for survival because, without this, they would be “sitting ducks” for any hungry fish. In the case of water striders the mechanism is simple; they don’t taste good. Water striders possess glands that produce foul tasting oil. After eating a few, fish quickly learn to associate the foul taste with the insect and ignore them in future encounters.
Figure 22. Left. Adult water striders. Right. Wingless nymph. Image courtesy Peter Chew.
The riffle bugs are similar in appearance and are found in similar habitats as the water striders. They are predatory but since they are considerably smaller than the water striders they tend to occupy the slower moving (if moving at all) areas of streams and ponds than do the latter. They also are capable of “walking on water’ and have antapical tarsal claws as the water striders. Besides size the riffle bugs can be easily distinguish from the water striders by the relative length of the hind femur. In riffle bugs when drawn straight back the length of the hind femur does not extend past the tip of the abdomen while it extends past the tip of the abdomen in water striders (Figure 23). This is also characteristic of the nymphs of both families.
Figure 23. Adult or nymph of riffle bug with relatively short hind femur .
There is no doubt where this family gets its name. They look like toads and even hop around like toads (Figure 24). In addition both the adults and nymphs have buldging eyes and a warty appearance as do toads. These predators can frequently be found along the shores of streams and lakes and are considered semi-aquatic. There are only 2 species in the United States with one occurring in the southwest and the other having a broader distribution. They have a mottled appearance and frequently carry bits of twigs, small pebbles and mud on their body both of which enhance their ability to blend into their environment.
Figure 24. Adult (Right) and nymphal toad bugs.
FAMILY-NAUCORIDAE-CREEPING WATER BUG
These moderately sized hemipterans are commonly found in slow moving streams. They are typically oval-flattened in shape with distinctive very large raptorial front legs (Figure 25). They are voracious predators which can deliver a nasty bite if carelessly handled.
Figure 25. A creeping water
FAMILY-BELOSTOMATIDAE-GIANT WATER BUGS
The giant water bug gets its name from the fact that members are very large (0.8 to over 4 inches) and aquatic. They can generally be recognized by the overall shape, color (flattened, brown to gray) and presence of well-developed raptorial front legs (Figures 26).
They commonly are found in lakes, streams and ponds and typically feed on other insects, snails, tadpoles and small fish. Some of the huge South American species are capable of preying on frogs, salamanders, mice, and even small rats. These are voracious predators and capable of delivering a painful bite if handled carelessly. They inject a poisonous fluid into their prey and suck them dry, much like a spider does. The author once dove into a swimming pool in Acapulco and was immediately bitten by the sole giant water bug present. This 4-inch creature is now pinned and can be found in our entomology museum.
Giant water bugs are strong fliers, frequently leave the water to feed and are readily attracted to lights. They also have been called the electric light bugs, toe biters and fish killers. In some U.S. species, the female lays her eggs on the back of the male who carries them around until they hatch. As in several groups of aquatic hemipterans, a giant water bug is capable of trapping an air bubble between its hemelytra and abdomen. The spiracles of the respiratory system open into this bubble. This air bubble is then carried with the adult (much like a scuba tank) and allows it to be submerged for several hours.
As one might expect, giant water bugs are a source of human food. It came as no surprise to the authors while shopping in the day market in Chiang Mai, Thailand, that there was a giant water bug stall next to the chicken and egg stall. The vendor had a large basket containing around 200 four-to-five inch long giant water bugs. Each of the bugs’ legs and beaks were tied down with a rubber band to prevent them from escaping and biting. Apparently certain oils are extracted to make a spice or the entire insect is deep-fried and consumed. They are collected from the rice fields.
Figure 26. Top. Adult giant waterbugs. Bottom. Giant waterbug nymph.
FAMILY-COCCINELLIDAE-LADYBIRD BEETLES. These are small, broadly oval, convex and often brightly colored beetles. Their head is generally not visible when viewed from above. They also appear to have 3 tarsal segments on each leg and have short-clubbed antennae. Most are considered polyphagous both in the larval and adult stages. They feed on some of our most important pest species including including aphids, mites, scales insects, thrips and mealy bugs. They following are some of the more common species.
Vedalia beetle, Rodalia cardinalis. The use of this ladybug, the vedalia beetle (Figure 27) is one of the first examples in the United States of how humans have used predators successfully to control a pest species. The cottony cushion scale was accidentally introduced into California on acacia imported from Australia. Once introduced it became a major pest on citrus and threatened the existence of this emerging industry in California. During this period (late 1880's), there were no effective pesticides available for the control of this pest.
Figure 28. Vedalia beetle consuming the cottony cushion scale. Image courtesy of Charles Hoague.
Entomologists from the USDA, realizing that this scale was not a pest in Australia, suspected that its non-pest status there probably was due to the presence of effective biological control agents. Based on this premise a team of scientists was sent to Australia to search for predators and parasites of the cottony cushion scale. Several were found and brought back to the United States to be colonized and released. The most effective predator of these was the vedalia beetle, a ladybug. Upon introduction, this beetle soon became established throughout California and reduced the scale to a non-pest level. Since that time the cottony cushion scale rarely, if ever, becomes a pest due to the ever-present activity of this ladybug. This introduction was the first of many successful programs where biological control agents are introduced into the United States following the accidental introduction of pests.
Convergent ladybird beetle. Hippodamia convergens. This beetle is one of the most notorious species occurring throughout most of North America. The larvae (Figure 29) can daily consume its weight in aphids while the adult consumes up to 50 aphids a day. In California and other states, adults (Figure 30) commonly are sold by nurseries, department stores, and home and garden centers. Homeowners and even some cities and pest control technicians buy and release them for aphid control. Although this species can control aphids quite effectively in nature, the well-intentioned practice of mass-releasing the convergent ladybird beetle for aphid control is generally considered worthless.
Figure 29. Last instar larval convergent ladybird beetle.
The reasoning behind this statement is associated with the seasonal cycle of this beetle. In the valleys of Southern California and other states, adult and larval beetles commonly are found feeding on aphids in the spring. As the season progresses and the aphid population begins to disappear, the behavior of these beetles changes drastically. In late fall the adults fly to an elevation of about 5000 feet and follow the winds to the mountain passes. At this time the adult beetles enter into a condition called reproductive diapause. While in this stage, the beetles congregate into huge clusters (sometimes many thousands per cluster) and hang on rocks and trees. In diapause, the physiology of the beetle slows down. They do not feed or lay eggs, but are capable of movement when prevailing temperatures are above 50 degrees (F). This condition allows the beetles to survive the winter without food and in freezing conditions. In early spring they emerge from diapause and fly back to the valleys to lay eggs and resume their feeding on aphids.
Figure 30. Adult convergent ladybird beetle.
The main environmental factor that triggers these beetles into and out of diapause is day length. On a yearly cycle this is the only consistent factor in their environment. On a given date at any time of the year the amount of daylight and darkness is always consistent. Environmental conditions such as temperature on any given day of the year are inconsistent and, therefore, would be very unreliable as a triggering factor. If temperature were used, it could be disastrous to the beetles. A few hot days in December could trigger the beetles out of diapause, resulting in their flying back to the valleys where few, if any, aphids would be present.
Unfortunately, the beetles that are sold commercially are collected from the Mountain passes while they are still in the diapausing condition. When they are sold in the spring, they may still be in diapause. Of course they do not feed or reproduce. If they are released in a yard and then emerge from diapause, they follow their natural instinct and fly.
A consumer might be fooled into thinking he or she has a hard working bunch of ladybugs after such a release because a few individuals still remain in the yard. However, these probably are members of the small percentage, which have been parasitized by wasps. These unfortunate beetles never develop normally--they can't fly or feed well and do not reproduce.
The winter-collected beetles can be artificially triggered out of diapause by exposing them to the photoperiod (amount of daylight vs. darkness) normally present during the springtime. Even when this is done, apparently the beetles still require an extended flight period prior to settling down to feed and reproduce.
A considerable amount of research has been conducted in the attempt to prevent the need for this flight period. Scientists have turned the beetles in large tumblers over long time periods, attempting to simulate flight. They have even tried gluing the elytra together to prevent this flight. Nothing has been successful yet.
Multicolored Asian Lady Bug-Harmonia axyridis. This beetle (Figure 31) has a number of color phases and patterns; hence the name multicolored. It was initially introduced into the United State in 1918 for the control of a variety of insects: however, actual existing populations were not found until 1988 in Louisiana. It now occurs in many areas and has been reintroduced on a number of occasions. Some of these introductions have been accidental on imported nursery stock and others have been on purpose as a beneficial insect.
Figure 31. The multicolored lady beetle.
Mealybug Destroyer-Cryptolaemus montrouzieri. This is a very small lady beetle with the adults measuring approximately 1/16 inch in length. As illustrated (Figure 32) the head and thorax are orange-red with black elytra tipped in orange-red. This species was introduced into California from Australia in 1892 for control of mealy bugs. Unlike other lady beetles which typically pupate on leaves and stems, the larvae of this beetle often descend to leaf-litter to pupate.
Figure 32. An adult of the mealy bug destroyer, an introduced species. Image courtesy of Peter Chew.
These beetles are reared by insectaries for release in citrus field in California for control of mealy bugs and scale insects. The larval stage (Figure 33) is quite unique in that it has long waxy filaments and on occasion is confused with mealy bugs.
Figure 33. Mealy bug destroyer immature feeding on scale insects. Image courtesy of Dave Britton..
FAMILY-CARABIDAE-GROUND BEETLES. This is one of the largest families of beetles with 20,000 species worldwide and over 2,500 species in North America. These are very active, long legged, nocturnal beetles that are typically found under rocks and debris during the day. They are mostly black in color with large eyes and forward projecting sickle-shaped mandibles (Figure 34). Many have parallel lines of pits (striations) running the length of the elytra. Almost all members of this family are predatory in both the adult and larval stages and some are important enemies of slugs, snails and insect pests. Many ground beetles exude foul smelling chemical that are used to repel their enemies.
Figure 34. The head of a ground beetle illustrating the sickle-shaped mandibles and enlarged eyes.
Hunters and Searchers-Cacosoma spp. This genus contains a number of very large (up to 1 inch in length) robust beetles that have a characteritic body shape (Figure 35). A number of species either as larvae or adults or both active seek their prey in trees. Calcosoma. sycopantha was imported from Europe and introduced into the New England states for control of the gypsy moth, one of our most important forest pests. Most members of this genus prey on caterpillars and other larvae including cutworms, armyworms, tent caterpillars, boll worms, cotton leaf worm, cabbage loppers and many more. Adults typically consume more than the larvae on a daily basis with one beetle capable of devouring up to 50 caterpillars in a few week period. Some adults are long lived surviving for up to 5 years.
Figure 35. A representative of one of the many species in the genus Calosoma.
Not all ground beetles are black in color and some take on metallic coloration, chiefly green and blue. Obviously there is no way to discuss all the beneficial ground beetles as there is such a large number that attack a great variety of pest insects. In actuality we still have a lot to learn just how beneficial these insect really are.
FAMILY-MELOIDAE-BLISTER BEETLES. This is a rather small family in term of number of species but quite large in terms of the size of the individual insects. Most meloid are ¾ inches or larger, soft bodied, elongated and possess a narrow neck and deflexed head (Figure 36).
Figure 34. Typical blister beetles illustrating deflexed head, narrow thorax and elongated body.
Members of this family are both destructive and beneficial. In most cases the adults are phytophagus feeding on a variety of crops including legumes, beets, potatoes, ornamental flowers, tomatoes and others. The larval stages, depending on the species, are predatory mainly on either grasshopper egg pod in the soil or attack the young of wild bees. Some consider them as parasitoids but they exhibit characteristics of both predators and parasitoids.
These insect exhibits hypermetamorphosis, a type of complete metamorphosis. In the case of hypermetamorphosis the larval stage not only increases in size, but unlike with standard complete metamorphosis, it changes form with progressive molts. These changes are associated with their mode of life. The first instar larva is called a triungulin and is silver fish-like in appearance. This form actively seeks out the grasshopper egg pods in the soil or in the case of those forms that feed on wild bees may sit and wait on flower heads for these pollinators. Once available it attaches to the bee’s hair and is carried back to the nest. Once reaching the nest or egg pod the larva become more grublike and eventually legless with progressive molts-at this point all the food necessary for development is provided and legs are no longer needed. Those forms that feed on egg pods are quite beneficial in controlling these pests. One larva is capable of consuming a whole pod (30 eggs) during its development. Those forms that feed on wild bee larvae (Figure 35) could be considered destructive since the insects are valuable pollinators.
Figure 35. The adult blister species, a species that attacks wild bee nests in the soil.
FAMILY STAPHYLINIDAE-ROVE BEETLES. This is the largest families of beetles with over 26,000 species worldwide and about 2,800 in North America. They are easily recognized by their short elytra that only cover the first 3 abdominal segments leaving the remaining segments fully visible from a dorsal angle (Figure 36). Most are small with a parallel sided body and exhibit the behavioral characteristic of turning the tip of their abdomen upward when disturbed. The majority of these insects are predatory and a few are parasitic. These are very common insects and undoubtedly play a more important role in the biological control of pests that might be expected.
In most the larval and adult stages are predatory. Common habitats include decaying vegetation, leaf litter, fungi, compost piles and around decaying carcasses. Many are predators of a variety of fly maggots and are important in the biological control of these pests.
Figure 36. Rove beetles.
FAMILY CICINDELLIDAE-TIGER BEETLES. The name tiger beetle (Figure 37) is derived from their fierce predatory behavior, speed of movement and possibly coloration. Almost all species have elongated legs, are very fast and quickly take flight when disturbed. Members of this family can readily be identified by their characteristic appearance and coloration; many are brown with white markings. Most prominent are their large sickle shaped mandibles.
These beetles are active during the day and prefer well lit sunny locations, especially along the banks of streams, ponds and lakes. The larval stages are typically found in similar situations in vertical tunnels that can extend up to a foot into the ground. Their head and thorax are modified to form a plug at the top of their tunnel. They typically wait at the opening with their exaggerated jaws open. When a potential prey is encountered the jaws are snapped shut. Their sixth abdominal segment is somewhat swollen and bears a pair of hooks that are used to prevent them from being pulled from the tunnel during the ensuing struggle.
Figure 37. Left. A typical tiger beetles, many are brown with white markings. Right. Larval stage of tiger beetle.
FAMILY-CLERIDAE-CHECKERED BEETLES. This is a relatively small family of small to medium sized beetles. Their overall appearance and shape of the adults are somewhat distinctive. Most are brightly colored with patterns of red, orange or blues and have a large number of fine erect hairs covering the adult body (Figure 38). Both the larvae and adults are predatory typically with the adults feeding on the adult stage of the prey and the larvae feeding on the larval stage of the prey. Most are quite host specific and in certain situation are considered very beneficial.
Figure 38. An adult checkered beetle. Image courtesy of Dave Britton.
The range of prey attacked by different individual species is quite diverse. Most are quite common on conifers and attack bark beetles; however, for example there are species that attack solitary bees and hornets, European corn borer caterpillars, cheese skippers and dermestid larvae.
Chapter 6 .Neuroptera Family Identification and Biology
All the members of this order are predatory in either the immature or adult stages or both. The adults lack anal cerci and many have elongated sickle-shaped mandibles (Figure 39).
Figure 39. Neuropter adult and immature with exaggerated sickle-shaped mandibles. Right image courtesy Peter Chew.
This is a family of very large insects (frequently approaching 2-inches in length) (Figure 40). The larvae (hellgrammites) are aquatic predators typically found in fast moving streams under rocks and logs. Because of their large size and distinctive shape it is difficult to confuse the predatory adults with other Neuroptera. The males typically have huge mandible with the females
Figure 40. Typical Dobson fly (top-larvae) (bottom-male).
These are small (app. 0.4 inches body length) fragile appearing insects with relatively large wings (in comparison to their body size) that, as in the case of many Neuroptera, are held roof-like over the body. Their body and wings are typically covered with hairs. Both the adults and larvae are valuable predators of aphids, mealy bugs, other homopterous insects and mites. The larvae are sometimes referred to as aphid wolves. Hemerobius pacificus (Figure 41) is the most common species encountered on the west coast and southwest ranging in distribution from Alaska to California and eastward to Arizona and New Mexico.
As with the green lacewing their eggs are deposited on thin, hair-like stalks, but of course are much, much smaller and not so easily detected. It is thought that these stalks give the eggs a certain degree of protection from smaller predatory insects (even their own hatching siblings) by possibly making them less accessible.
Figure 41. A brown lacewing adult-note the hairy wings.
These are a much better known group of insects than the brown lacewings. They are typically much larger (0.6 to 0.8 inch body length) and lack the hairy appearance of the body and wings of their brown relatives (Figure 42). As their name implies, most are green, although shades of yellow are also common. The adults are chiefly nocturnal while the larvae may be active during the day.
Figure 424. A green lacewing adult. Image courtesy of John Moore.
The eggs are deposited on a thin elongated stalk, again most likely for protection against predatory insects such as ants or their own hatching siblings. This engineering feat is accomplished by the use of a quick drying material that is produced by a gland on the tip of the abdomen. As an adult places a drop of this material on a leaf it quickly raises her abdomen drawing it into the thin stalk. Subsequently the egg is deposited on the stalk (Figure 43).
Figure 43. The eggs of a green lacewing on thin stalks. Image courtesy of Peter Chew.
The larval stage is predatory feeding on aphids, mealy bugs, other homopterous insects and mites. They are often referred to as aphid lions. They can readily be recognized by the sickle-shaped mandibles and the presence of prominent body tubercles ending in tufts of hairs (Figure 6E). Some species camouflage themselves by heaping bits of litter and even the dead remains of their prey on their back (Figure 44). A common name for these species is the trash carriers. The entire life cycle generally takes 5 to 6 weeks with the larvae passing through 3 instars. These insects overwinter as pupae, generally in leaf litter on the ground.
Figure 44. The larval stage of a green lacewing. Right image with larvae carrying remains of prey on back-courtesy of Peter Chew.
These rather unusual looking insects can readily be identified by their elongated prothorax (first thoracic section). In actuality this is a small family in terms of number of species and there is nothing else that “looks like them” (Figure 45). The larvae is also quite distinctive-elongated, lacking anal cerci and forward projecting mandibles.They are quite common in brushy areas where the adults are predatory on aphids and other insects. It is quite rare to see them in crops; however, it has been reported that the larvae an important predators of overwintering codling moths in Colorado. The most common species is Agulla unicolor, which occurs in the Pacific Northwest, California, Utah, Nevada and Colorado.
Figure 45. Left. The adult stage of a snakefly with elongated prothorax as indicated by arrow. Image courtesy of Univar . Right. Larval snakefly.
This is the largest group of Neuroptera in North America, occurring most commonly in the south and west. The adults are not as commonly recognized as the larval stage. Adults resemble damselflies with their stalk like abdomens, but possess elongate club-shaped antennae that are frequently hooked at tip. They are rather weak fliers and readily attracted to lights, especially in summer months (Figure 46). Their eggs are deposited in sand.
Figure 46. The adult of an antlion-note the hooked- clubbed antennae.
Antlion larvae (doodlebugs) are strange looking insects with elongate sickle-shaped mandibles and fringed lateral projections on the abdomen (Figure 47). Some larvae remain motionless on the surface of the soil or buried just beneath the surface, waiting for passing prey. When aroused, they give chase and quickly subdue the victim with their piercing jaws.
Figure 47. Antlion larvae or doodlebug.
In more notorious species, the larvae capture their prey by means of a pitfall. They construct a small cone-shaped pit (Figure 48) in the soil and remain buried at the bottom. When a passing ant or other potential prey falls in, the larva will begin to jerk its flattened head upward, throwing sand in an attempt to undercut the sloping walls of the pit. If the ant does not fall to the bottom of the pit due to the quickly eroding walls, it may be knocked down by the catapulting sand particles. Once captured, the ant is quickly pulled below the soil and consumed.
Figure 48. A few antlion pits.
This is a family of tiny insects that are characterized by their mealy or dusty appearing wings (Figure 49). They are frequently confused with the whiteflies because of their similar size (1/10 inch) and appearance. The larval stage is considered a beneficial as are one of the most efficient predators of the citrus red mite in California.
Figure 49. A dusty-wing covered with pollen. Figure courtesy of Dave Britton.
This is a small family that is rarely seen and as a consequence is of limited value from the standpoint of biological control of agricultural pests. They are somewhat similar in appearance to preying mandtids but typically considerably smaller (1 inch or less in length). As with mantids they have raptorial front legs and an elongated prothorax (Figure 50). As with all neuropterans they lack anal cerci and possess the net-like veination in their wings. Adults are chiefly nocturnal attacking a variety of insects. The larval stage is also predatory and is mainly found under loose bark and feeds primarily on wood boring insects. The few species in the United States occur in the West.
Figure 50. An adult mantispids. Bottom image courtesy of Peter Chew.
This is a very small family of little known large Neuroptera. They superficially resemble antlion adults but can be easily distinguish by the presence of a well-developed ball-like knobs on the tips of the antennae (Figure 51). The larvae are characterized by elongated sickle-shaped mandible and branched appendages lining the outer margin of the abdomen. Adults of many fly chiefly at dusk while the larvae are active predators and are found on or just beneath the soil.
Figure 51. Top-Adult, eggs of owl flies. Bottom-Larvae.
FAMILY-SYRPHIDAE-FLOWER FLIES. These flies often look more like bees than flies (Figure 52). They are often black with yellow bands and can frequently be seen hovering over flowers; hence, another common name for them is the hover flies. The diagnostic characteristic of the adults is a spurious vein that dissects the second cross vein in the wing.
Figure 52. A common flower fly.
While the adults of most flower flies are nectar feeders, the larval stage (Figure 53) is highly predaceous on aphids and other soft bodied insects. A close inspection of an aphid colony will frequently reveal a syrphid larva eating it way through consuming many aphids a day.
Figure 53. A typical syrphid fly larva consuming an aphid. Image courtesy of Clemson University Entomology.
Not all syrphid flies are predatory in the larval stage. A well-known example is the drone bee (Figure 54). The adult of this species closely mimics a honey bee drone. It is nearly worldwide in distribution. The larval stage is called the rat tailed maggot which is a fitting description considering its appearance. The tail functions as an elongated breathing tube. The maggots breed in putrid water and moist feces: a common location is outdoor latrines.
Figure 54. The drone bee, also known as the H-bee. Image courtesy of Dave Britton.
FAMILY-ASILIDAE-ROBBER FLIES. The adults of robber flies are typically large with a robust thorax and long tapering abdomen (Figure 55). Their eyes are normally large and bulging with a concave depression on the top of the head between opposing eyes. Hairs giving them a bearded appearance frequently surround their mouthparts.
Figure 55. A typical robber fly with robust thorax, long tapering abdomen and bearded mouthparts. Image courtesy of IO Vision, Dexter Sear.
Most species are gray in color but some are bright black and yellow and beelike in appearance. All are active predators in the adult stage and are normally found in sunny areas such as dry fields and pastures. They are quite common in the desert and other sandy areas.
FAMILY-DOLICOPODIDAE-LONG LEGGED FLIES. This is a frequently overlooked family from the standpoint of biological control. They are predatory in both the adult and larval stages and are quite common in many agricultural systems. Adults are typically small with long legs, a delicate body and frequently metallic in coloration (green, blues or copper colored). The larval stage is aquatic with the adults commonly found in cooler streams. The unknown species in Figure 56 is quite common in California frequently occurring in many cropping situations where it actively feeds on a variety of smaller economic insect pests.
Figure 56. A long legged flies. Right image courtesy of Peter Chew.
FAMILY-VESPIDAE-HORNETS, YELLOW JACKETS, PAPER WASPS. These wasps, being true social insects, have a well-developed caste system. In a typical mature wasp nest, there are many workers and one or more king and queen. Unlike some of the other social insects, there is very little difference in the appearance of each caste. In temperate climates hornets, yellow jackets and paper wasps all exhibit the same general life cycle. Their nesting cycle is annual, with only mated queens surviving the winter in a variety of protected locations--including under bark and in attics. In early spring the queen emerges and may reoccupy an old nest, or construct a new one. Regardless of which condition prevails, the queen initially deposits a few single eggs-one to each cell.
Upon hatching, the larvae are fed a variety of insect larvae (mainly caterpillars), which are captured and brought back to the nest by the adult queen wasp. The majority of these larvae will develop into adult workers, which take over the duties of expanding the nest-including collecting food and feeding the young (Figure 57). The queen continues to lay more eggs. This results in several generations within the colony, which continues to increase in size into the fall. In the late fall, new kings and queens are produced, mating occurs, and the newly mated queens will overwinter, completing the annual cycle.
Figure 57. A common yellow jacket with folded wings.
These insects are considered beneficial, as they are predatory on some pest species. Besides feeding on caterpillars, these insects are attracted to any meat source, a phenomenon, which is frequently observed by campers or diners at backyard barbecues. Adult wasps readily feed on sugar substances, including ripened fruit, honeydew and often soda pop.
The nests of hornets, yellow jackets and paper wasps are constructed of cellulose, which is collected by the adult workers from a variety of sources, including old newspapers, cardboard, weathered wood, and bark. Once collected, these materials are chewed, saliva is added and they are formed into cells basically like bee combs. In paper wasps the nest is a single layer, which is suspended upside down by a short stalk (Figure 58).
Figure 58. A paper wasp nest with a dozen or so workers hanging from the eave of a house.
Around the home, paper wasp nests typically are found under eaves, along fences, or can be found attached to trees or plants. Hornet and yellow jacket (Figure 59) nests may exist above or below ground; they are much larger than paper wasp nests, and are constructed of many layers of cells that may or may not be surrounded by a capsule-like structure. These structures may occur above or below ground.
Figure 59. Mating yellow jackets.
Questions for Continuing Education Credit
1. Generally speaking predatory insects that are host specific are more efficient in controlling the pest species that they feed upon than are general predators in controlling that pest species.
2. Dragonfly adults feed on flying insect including mosquitoes. (This was a question on Jeopardy the other night).
3. Generally speaking the preying mantis is considered very beneficial in controlling pest species.
4. Assassin bugs have two basic feeding habits depending on the species. Some are blood suckers and are capable of vectoring Chagas disease and some are general predators.
5. The release of large numbers of wild collected convergent ladybird beetles is considered an effective way of controlling aphids.
6. Blister beetles as a group are considered beneficial and harmful as some adults feed on crops and some larvae feed on grasshopper egg pod in the soil.
7. The green lacewing lays its eggs on a thin stalk and is considered a very
beneficial predator in cropping situations.
8. Many syrphid fly adults are similar in appearance to bees and the larval stage is a common predator of aphids.
9. Paper wasps, hornets and yellow jacket have the same basic biology differing mainly on construction, location and size of the individual colonies.
10. One of the chief prey of checkered beetles is bark beetles.