Squash bugs, Anasa tristis
Squash bugs are true bugs and are distinctively shiny, slightly oval and black with copper-colored markings on the thorax and outer wings. They can be a destructive insect pest of winter squash and pumpkins. Adults and nymphs suck sap from the plants resulting in wilted vines, often prematurely killing plants. Nymphs are pale green right after hatching and turn dark grey in later instars. Late-stage nymphs have distinct dark wing pads. Nymphs and adults may occur together in large masses and both life stages are pests of vine crops.
- Squash bugs can be a destructive insect pest of winter squash and pumpkins.
- Both nymphs and adults primarily feed by sucking sap from plants causing significant damage.
- Mulches often provide protective cover for squash bugs and damage can be worse on plants that are mulched compared to those grown over bare soil.
Squash bug eggs on inside of leaf. Image credit: Whitney Cranshaw, Colorado State University, Bugwood.org.
Squash plant damage from squash bugs. Image credit: Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org
Squash bug adults mating. Image credit: Whitney Cranshaw, Colorado State University, Bugwood.org
Early stage nymphs. Image credit: Jennifer Carr, University of Florida, Bugwood.org.
Life history and habits
Squash bugs overwinter as adults under debris in the vicinity of previously infested plantings. The bugs become active during warm days of late spring and move to germinating squash. Egg laying begins around mid-June. Eggs are laid in small masses usually on the underside of leaves.
Both nymphs and adults feed by sucking sap from plants. However, their manner of feeding, sometimes described as “lacerate and flush” is quite destructive. Their feeding can kill cells and result in many feeding punctures which collapse and no longer move water leading to plant wilting. Squash bugs also feed on fruit which can result in sunken, dead areas that allow entry of rotting organisms that eventually destroy the fruit. Hard, winter squashes are the most damaged plants. Less commonly, summer squashes are damaged. Related cucurbits, such as cucumber and melons are rarely damaged.
Weather conditions appear to be very important in the severity of squash bug infestations and impact. Warm temperatures during the growing season allow most of the second-generation nymphs to successfully reach the adult stage. Mild winter temperatures allow a greater proportion of overwintering adults to survive. In small garden settings, hand picking squash bugs can be very effective. Eggs can also be easily detected and destroyed. Egg surveys should be done at least once a week during June when egg laying is likely to begin. Debris should be cleared from the base of plants. Mulch can also provide shelter for squash bugs around the base of the plant. If insecticides are applied, they should be concentrated around the base of the plant. Early season management approaches tend to have the best efficacy.
Schellman, A. 2008. Squash Bugs. University of California – Agriculture and Natural Resources. Available https://ipm.ucanr.edu/PMG/PESTNOTES/pn74144.html
Utah State University. (n.d.). Squash Bug. Utah State University – Extension. Available https://extension.usu.edu/pests/ipm/notes_ag/veg-squashbug#:~:text=Squash%20bugs%20are%20the%20primary,folded%20over%20a%20flat%20back.