Abandon Ship! Parasitoid fly larvae flee their doomed host

A new research article, published in the Proceedings of the Royal Society B discusses a unique insect endoparasitoid. This fly larva typically grows inside an aphid host until it matures and exits the aphid. However, the researchers have discovered that the larva is capable of abandoning its aphid early if the aphid is threatened by a predator. This behavior prevents the larva from going down with the ship.

The red Endaphis fugitiva larva parasitoid exiting its injured aphid host. Image adapted from Muratori et al., 2010.

Larval endoparasitism is well know among insects, with parasitoid wasps being the most common example. However, some flies also engage in endoparasitism. One such fly, Endaphis fugitiva, was describe just last year. Unlike parasitoid wasps, which inject their eggs into the body of their host insect, E. fugitiva lays its eggs on the leaves of plants with aphid infestations. The eggs hatch, and the fly larvae seek out the nearest aphid, where they use their specialized mouthparts to bore into the aphid’s abdomen. Once inside, the larva feeds off the aphid until it matures. It exits through the anus, killing the aphid, and drops to the ground. There, the larval fly forms a cocoon and metamorphosizes into an adult.

In the most recent paper, Muratori et al. have shown that the E. fugitiva larva can sense that its host is in danger and jump ship before it is consumed along with the aphid. They demonstrated that the fly larvae will exit the aphid if the aphid is injured or exposed to predation by lacewings or syrphid larva. Surprisingly, the researchers also found that early-ejecting fly larvae were still able to grow to full size and pupate into adults in the same amount of time as normal.

Muratori et al. hypothesize three possible mechanisms by which the larval fly may be able to sense its host’s imminent demise:

• Emergency cues such as stress factors in the aphid’s haemolymph could be detected by the parasitoid larva.

• Direct contact between the predators mouthparts and the parasitoid larva.

• A drop in the internal pressure of the aphid as the predator begins to suck out its internal fluids could be detected by the parasitoid larva.

Watch this video of a larval fly fleeing from its host aphid as the aphid is attacked by a lacewing (Via Nature). What a way for the poor aphid to go. Just as a predator starts sucking out your internal fluids, a massive fly larva shreds your innards and bursts out your anus.

References:

Muratori, F.B., Borlee, S. & Messing, R.H., 2010. Induced niche shift as an anti-predator response for an endoparasitoid. Proc. R. Soc. B, published online before print January 13, 2010

Muratori, F.B., Gagne, R.J. & Messing, R.H., 2009. Ecological traits of a new aphid parasitoid, Endaphis fugitiva (Diptera: Cecidomyiidae), and its potential for biological control of the banana aphid Pentalonia nigronervosa (Hemiptera: Aphididae). Biological Control, 50(2), 185-193.