Lysiphlebus fabarum: Aphid Rancher, Butcher

Dairy farmer meets Alien: The braconid wasp Lysiphlebus fabarum harvests honeydew from aphids before literally stabbing them in the back so their offspring can develop inside of the aphids’ bodies.

There are many unlikely relationships in the animal kingdom. Personally, I’m a fan of “Bonedigger” the lion and “Milo” the dachshund, but there are some pretty odd couples in the insect world as well. I recently stumbled across a research piece studying the behavior of a parasitoid wasp that attacks black bean aphids. Interestingly enough, the wasps mimic ant behavior to effectively “coax” the aphids into a false sense of security before stabbing them with their sharp ovipositor and inserting their eggs, which hatch to feed on the aphids from the inside out. Remarkably, these behaviors involve some degree of cooperation from the aphid, and when ants are present, there’s potential for some unlikely mutualism among all three species (although, admittedly, not so much between the aphids and wasps).

Lysiphlebus fabarum forages in ant-tended black bean aphid (Aphis fabae) colonies. Primarily, the aphid is the unfortunate host to developing L. fabarum larvae. In addition, adult wasps feed on aphid honeydew secretions, which is similar to host feeding in other parasitoid–host systems. But unlike host feeding, honeydew feeding does not harm the aphids, instead requiring host cooperation.

Female L. fabarum wasps promote honeydew secretion by mimicking the anntenal drumming of ants, and employ similar antennal movements while probing potential hosts prior to oviposition. Switching between the roles of ant mimic and parasitoid overall reduce the defensive responses of aphids: kicking, thrashing, dispersing, and secreting a waxy, glue-like substance from their cornicles (these cornicle secretions can fuse mandibles, antennae, legs, etc., leading to the death of the wasp).

L. fabarum mimicking ant antennal behavior.
Image credit: Rasekh et al., J Ins Sci, 10(1)

Lysiphlebus spp. also possess cuticular hydrocarbons and lipids that identify them as aphids to help mask their presence from ants. Apparently their chemical camouflage is so good that it can be difficult for wasps to identify their conspecifics. This camouflage is an evolutionary response to ant aggression, since ants ferociously protect the aphids they tend to. And for L. fabarum, mimicry of ant behavior provides additional protection—not because the ants themselves are fooled, but because it makes aphids more inclined to secrete honeydew in the future.

So a few aphids are lost to parasitism, but the others are more productive—a benefit for hungry wasps as well as ants. In turn, ants offer protection for wasp offspring, albeit unintentionally. Ultimately there is potential for mutualism between ants and L. fabarum, as long as the wasps continue to parasitize only a small fraction of the aphid population. Of course, none of this could have happened if the parasitoid wasps didn’t take advantage of the already-existing mutualism between ants and aphids.

Further Reading:
Rasekh A, Michaud JP, Kharazi-Pakdel A, & Allahyari H. (2010). Ant mimicry by an aphid parasitoid, Lysiphlebus fabarum. Journal of Insect Science, 10(1). doi:10.1673/031.010.12601