Extension Common Beneficial Arthropods W127 Found in Field Crops Scott D. Stewart, The University of Tennessee Blake Layton and Angus Catchot, Mississippi State University Introduction ambush bugs and the wheel bug. Although they are seldom present in large numbers, several species There are hundreds of species of insects and spiders that attack arthropod pests found in cotton, corn, can be important predators of caterpillar pests found soybean and other field crops. A few common and in many crops. Wheel bugs can grow to a length representative examples are presented herein. With of ½ inch. Assassin bugs are highly susceptible to few exceptions, these beneficial arthropods are insecticides, and thus, are more common in fields that native and common in the southern United States. have not been sprayed for pests. Scouts should be The cumulative value of insect predators and aware that assassin bugs can deliver a painful bite. parasitoids should not be underestimated, and this Description and Biology: The most common species publication does not address important diseases that of assassin bugs found in row crops (e.g., Zelus also attack insect and mite pests. Without biological species) are ½ – ¾ inch long and have an elongate control, many pest populations would routinely head, which is often cocked slightly upward. A reach epidemic levels in field crops. Insecticide long beak originates from the front of the head and applications typically reduce populations of beneficial curves under the body. Most range in color from insects, often resulting in secondary pest outbreaks. light brownish-green to dark brown. Periodically, the Therefore, insecticides should be used only when pest adult female lays cylindrical brown eggs in clusters. populations are no longer under the adequate control Nymphs are wingless and smaller than adults but of natural and biological control agents. otherwise similar in appearance. Assassin bugs can be Predatory Insects and Spiders easily confused with damsel bugs, but damsel bugs are usually smaller. Assassin Bugs Prey: Assassin bugs are generalist predators that may feed on caterpillar eggs and larvae, plant bugs, and other pest and beneficial insects. Bigger species can tackle the largest insect pests found in cotton and other crops. Big-eyed Bugs (Geocoris spp.) General Comments: These insects are a primarily predatory group of Hemiptera (“true bugs”) belonging to the family Reduviidae. Some representative members of this family include thread-legged bugs, General Comments: This is one of the more Insidious Flower Bug (Orius insidiosus) abundant and easily detected predators. It is an important predator in cotton, corn and soybeans. These insects are commonly found in pre-blooming cotton or in young corn or soybean fields after flying in as adults from surrounding vegetation. In the absence of insecticide sprays, they will remain in the field for the remainder of the season. In cotton, populations of 0 – 40 per 00 sweeps can sometimes be found, especially in fields with a minimum of early insecticide treatments. Higher populations of tobacco budworm and bollworm can be tolerated if many big-eyed bugs are present. Despite their distinctive appearance, they are sometimes mistaken for plant bugs. There are several species of big-eyed bugs, so they are sometimes referred to by their genus name, Geocoris. Geocoris punctipes is the most common species encountered and is the one described below. General Comments: This insect is often a very important predator in field crops. However, because of Description: Both the nymphs and adults are well its small size, it is commonly overlooked. Orius occurs described by their common name. The head is as wide in all major row crops, and it is present throughout as the body and the eyes are notably large. Adults are the season. It is an important predator of thrips and about 3/6 inch long and are dull grey in color with often appears in fields shortly after emergence. Quite transparent, shiny wings. The nymphs resemble the often smaller, less noticeable predators provide the adults in general body shape, but they are a distinctive greatest benefit, and this is definitely the case with metallic silver-grey in color. The eggs are white to Orius. This is one predator that all scouts need to pink in color and are shaped like a hotdog but only learn to recognize and appreciate. They often build to /5 inch long. These eggs are often found in cotton relatively high numbers on early season populations of terminals and are often mistaken for plant bug eggs. thrips and mites. When this occurs, they can be of real However, plant bug eggs are almost always inserted benefit in ‘buffering’ populations of many caterpillar into plant tissue and are rarely seen by scouts. pests during mid- and late-seasons. Prey: Both the nymphs and adults feed on aphids, Description: Like the tarnished plant bug and big- whiteflies, mites, and the eggs and larvae of eyed bugs, Orius is a true bug and belongs to the caterpillars such as tobacco budworm, bollworm and order Hemiptera. The adults are sometimes mistaken soybean loopers. In addition, they are also predators for chinch bugs, but although they resemble chinch of plant bugs, especially the younger nymphs. In one bugs superficially, the adults are much smaller (about laboratory study, big-eyed bug nymphs consumed /6 of an inch in length). Adult Orius are black with an average of 5 tobacco budworm eggs or 76 first a white band across their backs and a white area over instar larvae during the – 3 days required to the end of the abdomen. The nymphs are elongate in complete all five nymphal instars. Late instar nymphs shape and yellowish or yellow-orange in color. They consumed approximately 0 eggs per day. Like many are often mistaken for thrips, one of their primary prey predatory insects in this order, big-eyed bugs also items. feed on nectar and directly on plants, causing little or no damage. Their populations may be affected by in- Prey: Insidious flower bugs feed primarily on thrips furrow systemic insecticides. and spider mites; and when these pests are numerous, Orius can build to notably high numbers. One reference reports that nymphs are capable of eating an average of 33 mites per day. Eggs of caterpillars, such as bollworm and tobacco budworm are also the entire length of the abdomen and this distinguishes favored prey, along with newly hatched larvae. This them from tarnished plant bug adults in which the wings predator is common in corn, where it is often found angle downward at the back third of the abdomen. searching for bollworm eggs on the silks, and it has Nymphs resemble adults, except for the lack of wings. been reported to consume as much as 54 percent of Prey: Both the nymphs and adults are predatory and the eggs. It is also an important predator of eggs and feed on a variety of prey. Almost any insect that is small caterpillars in soybeans. In cotton, Orius are smaller or slower is subject to attack, including other often found in the blooms, where their primary prey is predators. In addition to aphids and whiteflies, they flower thrips. They will also readily attack the small commonly feed on eggs and larvae of caterpillar pests larvae of various pest species that they encounter. This such as tobacco budworm and bollworm. They will makes them an important predator of bollworm and also attack plant bug nymphs. They occasionally bite fall armyworm larvae. scouts as well. Damsel Bugs (Nabis spp.) Spined Soldier Bug (Podisus maculaventris) General Comments: Like the insidious flower bug General Comments: The spined soldier bug is a and the big-eyed bug, damsel bugs belong to the order predatory stink bug that is sometimes found in cotton, Hemiptera and are considered true bugs. They are soybean and other crops. These predators can be easily predators with piercing sucking mouthparts. Damsel confused with plant feeding stink bugs such as the bugs are usually much less numerous than insidious brown stink bug. Thus, it is important that scouts learn flower bugs and big-eyed bugs, but it is not uncommon to recognize this as a beneficial insect rather than a pest. to find numbers in the range of – 6 per 00 sweeps in pre-blooming cotton. They are also important predators Description: Adult spined soldier bugs are medium in corn and soybeans. They are sometimes mistaken sized (9 – 3 mm long) and brown in color. They for plant bugs, so it’s important that scouts know the are shield shaped with a prominent spine extending difference. Damsel bugs belong to the family Nabidae outward from each “shoulder.” Unlike plant feeding and are also referred to as Nabids. species, the tips of the wings tend to extend well past the abdomen, and there is often a dark line at the wing Description: There are several species of damsel bugs tips when they overlap. These predators have a strong, that can be found in cotton. Most adults are grey to stout beak relative to plant feeding stink bugs, which light brown in color and are about 3/8 – / inch long. have more slender beaks. The beak is kept folded Adult damsel bugs do resemble plant bugs somewhat under the body unless feeding. The eggs of spined in general body shape, but they have a more slender soldier bugs are laid in a loose mass of 7 – 70 eggs. and longer body and legs. Also, the wings are flat over Each egg has a characteristic crown of “spines” that 3 rings its top. Immature (nymphal) stages are more although it can be found in row crops as well. This rounded in shape. Small nymphs have a black head predator has become well established throughout and thorax with a red abdomen.