Squash Bugs

Squash bug infestations typically begin in late June and July in Illinois.  The squash bug, Anasa tristis (De Geer) (Hemiptera: Coreidae), is a perennial and severe pest of pumpkins and squash; it rarely injures cucumbers and melons in the Midwestern United States.

Identification.  The squash bug is a "true bug" in the order Hemiptera.  Like all adult Hemiptera, adult squash bugs have two pairs of wings, with the front wings hardened at the base and membranous at the tips.  Its mouthparts form a needle-like beak that arises from the tip of the head.  Adults are brownish black, with yellowish to red-orange markings; they appear oval shaped when viewed from above, and somewhat flattened when viewed from the side.  Females lay yellowish-white eggs in small clusters or masses on the upper and lower surfaces of leaves; the eggs quickly darken to a reddish brown color.  Eggs hatch to produce grayish-white, wingless nymphs with black legs.  The nymphs darken in color as they grow older, and wing pads (the beginnings of adult wings) begin to develop. 

Life Cycle.  The squash bug overwinters as an adult, and survival is greatest in plant debris, mulch, and field borders or woods.  Adults become active in the spring, mate, and females begin feeding and laying eggs in June and July.  Nymphs grow to the adult stage in 5 to 6 weeks, and new females mate and begin laying eggs immediately.  Populations are greatest during hot, dry summers.  Females that reach the adult stage after late July or early August do not mate or lay eggs but instead enter an inactive stage and seek overwintering sites.  Squash bugs may be present as nymphs or adults in pumpkins and squash from June through October.

Plant Injury.  Squash bugs use piercing mouthparts to penetrate stems, leaves, and fruit and suck sap from plants.  This direct damage may cause wilting or even kill plants if populations are great enough.  Recent research has found that squash bugs transmit squash yellow vine disease; controlling squash bugs limits the spread of this disease within fields.

Management.  Early in the season when adults move into fields and feed on young plants, watch for wilting of seedlings and apply an insecticide if wilting is observed.  Scout for eggs of the squash bug on upper and lower surfaces of leaves.  If densities exceed one egg mass per plant, use insecticides for control as nymphs begin to hatch.  Insecticides labeled for use against squash bug are most effective against young nymphs, and for commercial growers who possess a Pesticide Applicator's License, the pyrethroid insecticides (particularly Brigade, Mustang Max, and Warrior) are most effective against squash bug.  Organic growers may choose to use floating row covers to exclude squash bugs from young plants, but when row covers have to come off to allow pollination, none of the insecticides approved for use in Certified Organic production systems are truly effective against squash bugs.  See the 2014 Midwest Vegetable Production Guide for Commercial Growers for listings of registered insecticides.

(from Illinois Fruit and Vegetable News, Vol 20 No 7)