Hi, AmeriCorps Lynn here. This morning, an RSSA student and I were totally buggin’ out over bugs in the Greenhouse. So our broccoli and cabbage has always had a fair amount of grey aphids on them. They weren’t causing too much damage, as aphids suck juices out of leaves but have been leaving the broccoli florets pretty much alone. We had always noticed that when cleaning lettuce and other leafy veggies that there were always a few brown, large aphids that were harder to remove.
You can see one of these weird aphids on the top of this leaf. But wait! There is a hole in that aphid. What does that mean?
Upon further research, we found out that these are called aphid mummies! We are seeing biological control happen right before our eyes. Something called a parasitic braconid wasp in the Genus Aphidius is helping us control these aphids. A female wasp is using her ovipositor to lay a single egg inside an aphid nymph. When the egg hatches, the wasp larva will eat the aphid from the inside out, turning the aphid into a hard, brown mummy. The wasp larva then attaches its new casing to a leaf with a thread a silk, spins a cacoon, and pupates. The wasp then chews through the mummy to emerge as a adult wasp (I might have accidentally got a picture of the adult—look at the small black insect at the bottom of the picture above).
Organic gardening really gives us the opportunity to experience these marvelous things. If we had used an insecticide on our plants, more insects than the aphids would be harmed. Sometimes, nature has its very own way of controlling harmful pest populations. Stay tuned to hear about another biological control, the aphid midge!