University of Maryland Extension

Squash Bug and Squash Beetle - Double Trouble

Squash beetle adult

If squash vine borer or bacterial wilt disease don’t take out your squash plants this summer you will probably be battling an old nemesis- squash bug- and may encounter a new pest- squash beetle. The squash bug is a “true bug” with a triangular thorax (middle insect segment) and piercing sucking mouthparts that leave tiny whitish dots (stipples) on leaves where they feed. They stink when threatened or crushed, but they are not stink bugs. 

The trouble with this pest is that adults overwinter and hone in on squash plants in spring as soon as they emerge or are planted. Most gardeners don’t look for the copper to rust color egg masses laid on leaves (usually the underside), blossoms, stems, and fruits. Find and destroy egg masses and you can prevent population build-up. Ignore this pest at your peril. It can ravage plants and reduce yields.In the mid-1990s I started seeing squash beetle in Anne Arundel Co. and parts of Southern Maryland. For nearly 20 years gardeners have contacted HGIC wondering about the Mexican bean beetles (MBB) on squash, cucumber, and pumpkin plants. These pests are host specific: MBB feeds on garden bean and squash beetle feeds on squash family members. The eggs and larvae are quite similar but the squash beetle adult is larger and has 14 spots compared to 16 for MBB. Adults and larvae of both species feed on the tissue between leaf veins producing “skeletonized” leaves.Squash beetle is not a major problem- yet. It’s slow moving and easy to handpick adults, larvae and egg masses. Plants can also be protected with floating row covers applied over transplants or newly emerged seedlings (remove when plants bloom). Direct sprays of horticultural oil or insecticidal soap will kill eggs and nymphs.

Having trouble telling squash bug from brown marmorated stink bug? This article will help you make the distinction.

Squash beetle eggs on leaf underside.
Squash beetle eggs on leaf underside. 
Crush em!

Squash beetle eggs on leaf underside.
Bristly larva with black spines feed on leaf underside. 
Squash em!

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