–by Raymond Cloyd – Horticultural Entomology
Squash bug, Anasa tristis, females have laid eggs and various stages of the nymphs are present feeding on squash and pumpkin leaves. Squash bug adults are flattened and 1/2 to 3/4 of an inch in length. Adults are dark-brown and have wings with brown-to-black and orange markings along the outer edge of the body (Figure 1). Females lay red-orange eggs on the leaf underside and top of leaves. Nymphs emerge (eclose) from the eggs in seven to 14 days and undergo five instars (stages between each molt) before maturing to adults. First instar nymphs that emerge from eggs have a red head and thorax (middle section) and pale-green abdomen (Figure 2). Second instar nymphs have a black head and thorax and a pale-green abdomen (Figure 3).
Figure 1. Squash bug adult (Raymond Cloyd, KSU)
Figure 2. Young squash bug nymphs (Raymond Cloyd, KSU)
Figure 3. Young squash bug nymphs (Raymond Cloyd, KSU)
Nymphs tend to gather near the eggs after emerging. Older nymphs (3rd to 5th instar) are gray (Figure 4) and tend to distribute themselves over the entire plant (Figure 5). Nymphs are 3/16 of an inch long and cannot fly because they do not have fully-developed wings.
Squash bug nymphs and adults use their piercing-sucking mouthparts to withdraw plant fluids from leaves, stems, vines, and fruits. Damage to leaves appears as small, yellow specks that eventually turn brown (Figure 6).
Figure 4. Older squash bug nymphs (Raymond Cloyd, KSU)
Figure 5. Older squash bug nymphs on the stem (Raymond Cloyd, KSU)
Figure 6. Feeding damage caused by squash bug (Raymond Cloyd, KSU)
Below are the plant protection strategies that you can implement to mitigate problems with squash bugs and prevent subsequent plant damage.
- Check plants for the presence of eggs, nymphs, and adults on leaf undersides at least once per week during the growing season.
- Destroy eggs, and remove (handpick) nymphs and adults, placing them into a container with soapy water to kill them. Handpick every three to four days.
- Place a floating row cover over plants to protect them from squash bug nymphs and adults.
- Position wooden boards throughout the garden, turning them over daily to collect squash bugs hiding underneath. You can kill the squash bugs by placing into a container of soapy water.
- Apply a contact insecticide when the nymphs are present. The smaller nymphs are easier to kill than the larger nymphs. Contact insecticides are less effective against adult squash bugs because adults have a thickened waxy cuticle (skin) that insecticides cannot adhere to and penetrate. Adults are also protected from insecticide sprays by the leafy plant canopy. Weekly applications of contact insecticides may be required to maintain populations below levels that will prevent plant damage. Thorough coverage of the leaf undersides is important to manage squash bug populations.
For more information on how to manage squash bug populations refer to the following extension publication:
Squash Bug (MF3308 July 2016)
https://www.bookstore.ksre.ksu.edu/pubs/MF3308.pdf