Honeydew secretions of aphids provide sustenance for mosquitoes

By Diane Mar-Nicolle

It’s hard to imagine that hemipteran honeydew, a sugar-rich sticky liquid that is forced out of the anus of aphids and some insects as they feed on plant sap, provides essential nutrients to mosquitoes (Aedes aegypti) and many insects.

In fact, without sugar, of which honeydew is an important source, mosquitoes are unable to outlive their first few days of adulthood.

“Floral nectar is the primary source of plant sugar, but mosquitoes can locate and exploit honeydew when nectar is scarce or honeydew is particularly abundant,” says Dan Peach, a PhD candidate in SFU’s Department of Biological Sciences.

Peach and his colleagues set out to answer a question that has long stumped scientists—how are mosquitoes able to find this rather inconspicuous secretion?

The team started at the very beginning—rearing mosquitoes in the lab’s insectary. They were fed with a 10 per cent sucrose solution and blood from Peach himself.

At the same time, the group grew fava beans from seed in the SFU greenhouse and added aphids.

Peach was finally able to start his experiment a month later, when the mosquitoes and the beans had matured, and the aphid population had boomed.

The team exposed mosquitoes to traps baited with synthetic honeydew odorant blends. One blend contained the equivalent of microbe-infested honeydew, and another contained the equivalent of sterile honeydew. Odorant blends were at a dose equivalent to a plant infested with aphids.

Peach found that female mosquitoes were attracted to the honeydew expelled by aphids but not to the physical presence of aphids or to the mechanical damage inflicted on plants.

Peach says, “More specifically, we discovered that it is the smell of microbes that live in the honeydew that is critical to mosquito detection.”

The study provides the first evidence that mosquitoes use smell and air currents to help them locate honeydew via odorants.

Peach conducted this research under the supervision of Gerhard Gries, who holds several patents for creating synthetic pheromones used to lure rats and bed bugs into traps.

When asked about the possibility of creating a trap, Peach says he’s not sure whether he will personally pursue the project. However, he is pleased that “this research provides the first steps to the development of a trap lure that combines mammalian-, inflorescence- and microbe-derived odorants for trapping both sugar- and blood-seeking mosquitoes. “

The study was published in Insects.