Common throughout the US, The squash bug, Anasa tristis, attacks all members of the cucurbit family but are most common on pumpkins and squash. Using piercing/sucking mouth parts, feeding occurs primarily on the plant foliage. However, late in the season, squash bugs may also feed on fruit. The damage symptoms include wilting of leaves and ultimately results in leaves that appear black or dried out.
We fell into the trap of initially thinking the 2 squash bugs we found lurking in the Little Garden were stinkbug. Both insects are similar looking and both emit a distinct odor when crushed; The stinkbug, however, is not a pest of cucurbits rather, it is more commonly associated with tomatoes or various legumes such as soybeans and peas.
Squash bug adults (see image, left) are 5/8 in. long and 1/3 as wide. They are usually gray to black with the edges of the abdomen having orange and brown stripes. Nymphs are 3/16 to 1/2 in. in length. Young nymphs have a red head and legs with a green abdomen, however as the nymphs age the red color will turn to black. Late instar nymphs will be greenish-gray in color with black appendages.
Eggs are 1/16 in. long and have a yellowish brown to brick red color. Eggs are laid individually in groups of about twelve on the underside of leaves (see image, left). Each cluster of eggs is usually laid in a characteristic V shape pattern and are laid under the leaves from spring to midsummer and will take 1-2 weeks to hatch. The eggs will become darker as they get close to hatching.
Unmated adults overwinter and find shelter during the early fall under plant debris, around buildings, under rocks, etc; nymphs will die off as temperatures begin to drop. The overwintering adults will emerge in spring and will fly into fields when the plants begin to grow. Mating begins in early spring, and the females lay eggs until midsummer. After eggs hatch, it takes a total of 4-6 weeks to develop into adults. Nymphs commonly form groups at the base of the plant or under the leaves but are also seen on vines or unripe fruit. They will disperse quickly when disturbed. There is usually a decrease of adults for a period in late summer because of a lag between the death of overwintering adults and the development of new adults from the existing nymphs. There is typically one generation per year in the midwestern U.S.
Damage to Your Garden
Both adults and nymphs cause damage by sucking nutrients from leaves and disrupting the flow of water and nutrients, which can cause wilting. Initially, before wilting, yellow specks will develop on the foliage that eventually turn brown. Under heavy feeding pressure, small plants can be killed; larger plants can have many affected leaves and vines. Subsequent wilting can look similar to bacterial wilt; however, bacterial wilt is a disease spread by striped cucumber beetles and is much more detrimental. Once the squash bug population is reduced, wilted plants should recover. By contrast, plants infected with bacterial wilt will continue to decline and will eventually die. Therefore, it is important to determine which wilt is occurring, and the correct identification of the insect pests present in the field is an essential first step. Squash bugs will also feed directly on the fruit, and it has become an increasing problem in recent years. Below is an example of squash bug feeding on fruit, near harvest.
The adult squash bug is difficult to kill, so early detection of nymphs is important. The smaller the insect, the easier it is to squash and control. Control measures should also be taken when wilting occurs and the damage is attributed to squash bug and not other pests or environmental conditions. Seedlings, new transplants, and flowering plants are the most critical growth stages to monitor, as these are the stages when the most damage can occur.
There are few if any effective organic control options for squash bug besides the very effective squashing. However, natural enemies of the squash bug include Tachinid fly, Trishopoda pennipes and Sceleonids, Eumicrosoma spp. These biological control options may prove useful. Sabadilla may provide some control and is organic certified.