Some of the more difficult to control insects in the field often belong to the true bug group. Squash bug, stink bugs, and plant bugs belong to this group. But there are also several important groups of insect predators that belong to the true bug group. These natural enemies of vegetable pests slow the buildup of pest populations, often keeping them below their economic thresholds. Being able to recognize natural enemies is just as important as recognizing pest insects.
Characteristics of True Bugs
True bugs have piercing-sucking mouthparts that they jab into their food. They pump saliva through this beak to partially digest the food before sucking it in. True bugs also have characteristic front wings in which the half of the wing closest to the body is thickened and the outer half is very thin. They have gradual metamorphosis with the nymphal stages often feeding on the same food type as the adult. Some of the more common and important true bugs families on vegetable crops include minute pirate bugs, assassin bugs, big-eyed bugs, damsel bugs, and stink bugs (yes, there are beneficial stink bugs!).
Beneficial True Bugs
Minute pirate bugs are definitely minute; less than 1/10 of an inch when full grown. Both the adults and the nymphs are predators that feed on insect eggs and other small soft-bodied insects including aphids and thrips. They actively search plants for prey and are often overlooked due to their small size.
Big-eyed bugs are also small, but considerably larger than minute pirate bugs, about 1/8 to 1/6 inch. As their name implies, they have prominent eyes. They can be found on many types of vegetables and can be very common on beans and eggplant. When encountered during scouting they often drop from the plant when disturbed. As with minute-pirate bugs, big-eyed bugs will feed on insect eggs, small soft bodied stages, and even mites.
Despite their dainty name, damsel bugs are voracious and important predators of many insect pests. They are nearly ½ inch in length with a prominent beak in front of the head. They are tan in color, slender, with thickened front legs., These predators will on occasion bite people, given the opportunity. I have experienced this while scouting vegetable crops; the bite feels little more than like a small pinch.
Assassin bugs make up a diverse family of predaceous insects that vary in size, shape, and color. The species can range in size from less than ½ inch to almost 2 inches. They have enlarged front legs and a relatively short and thickened beak. Many assassin bugs are ambush predators; they wait for prey to approach. Some may bite if handled.
We have three species of predaceous stink bugs: the spined soldier bug, the two-eyed stink bug, and the anchor bug. The two-spotted stink bug is specialized and attacks Colorado potato beetle and close relatives, but the spined soldier bug and anchor bug attack a wide variety of insect pests. The spined soldier bug can be confused with the brown stink bug, but can be recognized by the dark marking on the transparent part of the front wings near its tail. The anchor bug is cream-colored and black or orange and black, and has a variety of markings. The body is convex with a large scutellum, which partially covers the wings. The beak of the beneficial species is thickened, usually twice the width of the plant feeding species.
Ric Bessin, Extension Entomologist