Squash Ladybugs

 Squash ladybugs? But I thought lady bugs were good?

Well, they are and they aren’t.

It ends up that there are two camps in the world of lady beetles. Most of them are voracious predators that help keep aphids in check. Mexican bean beetles (Epilachna varivestis) and squash lady beetles (Epilachna borealis) are something else entirely.

Squash lady beetle eating a squash leaf (Mangoreads) CC BY-SA 4.0

Squash lady beetles and Mexican bean beetles are vegetarians. Bean beetles prefer legumes. Squash lady beetles prefer the leaves of squash plants.  This means your butternut squash, chayote, cucumbers, gourds, pumpkins, watermelons, and zucchini are all vulnerable to this garden pest. They might eat your bean and pea plants, too.

Squash lady beetle identification

Squash lady beetles have the familiar dome-shaped body we associate with the more helpful lady beetles. But these slightly larger insects are yellow with black spots. They look a lot like spotted cucumber beetles, which have more elongated bodies.

Unfortunately, the eggs of squash lady beetles look exactly like the eggs of helpful lady beetles: yellow, oblong, and laid in clusters on the underside of leaves. The larvae look a little different. Good lady beetle larvae look like tiny alligators, while squash lady beetle larvae look more like yellow hedgehogs. The pupae are fat yellow grubs.

Damage caused by squash lady beetles

Adults, larvae, and pupae feed on leaves, usually from the underside. They have an odd way of circling the leaf as they feed, in a technique called trenching. A study at the University of Delaware found that this behavior reduces the likelihood of the plant sending out chemical defenses. Leaves end up skeletonized, with only the veins remaining. The fruit is rarely affected, but leaf damage weakens the plant, reducing crop sizes and increasing the chance of other pests and diseases taking hold.

How to control squash lady beetles

Handpicking in the middle of the day is your best control method. Heavy infestations can be treated with products containing Spinosad.

As you grow cucurbits this summer, be on the lookout for squash lady beetles.