Last week havoc reigned as ladybugs, syrphid maggots, and parasitic wasps made a feast of the grandma aphid and her children (see Murder and mayhem in the land of aphids). If aphids weren’t such nasty pests, well, you might almost feel sorry for them. This week help arrived for many colonies of aphids under siege. Aphid bodyguards in the form of several species of ants were common in flowerbeds, gardens, and fields.
Why ants protect aphids is somewhat of a mystery but it appears to be part of a “deal” struck between primordial ants and ancient aphids more than 20 millions years ago. Aphids and ants often occur in the same locations and habitats. For eons ants have depended on plants for sources of food such as seeds, leaves, and fruits. They also find meat in the form of small insects living on plants.
Some of the most common denizens of plants are aphids and their kin. As aphids feed, they suck plant sap to gain nutrients. This process results in the production of a sugar-rich waste product called honeydew. Aphids and other sucking insects such as scales and whiteflies produce large amounts of honeydew as they feed. As ants forage on plants, they contact honeydew producing aphids and in several species a deal is struck. Ants use honeydew as a food particularly as a source of carbohydrates for energy. In return for the sweets, ants provide protection for aphids. They drive off would be attackers such as ladybugs and parasitic wasps. If you carefully watch an ant tending its aphid flock, you will see the ant stroke an aphid with its antennae. The contact will elicit the production of a droplet of honeydew from the rear end of the aphid. The ant consumes the honeydew and moves to the next aphid for another drink. Ants pass honeydew from one ant to the next and the honeydew is eventually taken back to the colony to nourish the developing larvae, workers, soldiers, and queens. As shepherds, ants are awesome. In another episode of Bug of the Week, we met an aphid assassin, the Asian multicolored lady beetle, Harmonia axyridis. I captured a larva of Harmonia and placed it on a leaf near a colony of aphids tended by field ants. The hungry ladybug larva soon found a juicy aphid and began to chow down. In less than 30 seconds one of the six legged shepherds discovered the intruder and waged war. The ant bit the ladybug larva mercilessly until it dropped from the plant. With bodyguards like this, the fate of the aphid clan is secure and grandma can rest a little easier.
The wonderful book “The Ants” by Bert Hölldobler and Edward Wilson, Harvard University Press, was used as a reference for this bug of the week.