Some parasites alter the behaviour of their hosts. The larvae of the parasitic wasp Cotesia congregata develop within the body of the caterpillar Manduca sexta. During the initial phase of wasp development, the host's behaviour remains unchanged. However, once the wasps begin to scrape their way out of the caterpillar, the caterpillar host stops feeding and moving spontaneously. We found that the caterpillar also temporarily lost sensation around the exit hole created by each emerging wasp. However, the caterpillars regained responsiveness to nociception in those areas within 1 day. The temporary reduction in skin sensitivity is probably important for wasp survival because it prevents the caterpillar from attacking the emerging wasp larvae with a defensive strike. We also found that expression of plasmatocyte spreading peptide (PSP) and spätzle genes increased in the fat body of the host during wasp emergence. This result supports the hypothesis that the exiting wasps induce a cytokine storm in their host. Injections of PSP suppressed feeding, suggesting that an augmented immune response may play a role in the suppression of host feeding. Injection of wasp larvae culture media into non-parasitized caterpillars reduced feeding, suggesting that substances secreted by the wasp larvae may help alter host behaviour.
The authors declare no competing or financial interests.
S.A.A. and C.I.M. developed the question. S.A.A., C.I.M., R.H.E., I.K. and K.F.T. developed the necessary methods and performed the studies. S.A.A. analysed the data and wrote the paper. C.I.M., R.H.E., I.K. and K.F.T. critically read and revised the manuscript.
We thank NSERC (Natural Sciences and Engineering Research Council of Canada) for Discovery Grant (RGPIN 203133-2013) funding to S.A.A.
Supplementary information available online at http://jeb.biologists.org/lookup/doi/10.1242/jeb.145300.supplemental
- Received June 27, 2016.
- Accepted September 9, 2016.
- © 2016. Published by The Company of Biologists Ltd