Abstract
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.
Highlights
Parasitic manipulators are parasites that alter host behaviour, leading to an enhancement of the parasite’s reproductive success (e.g. Thomas et al, 2005)
We examined this issue by studying the mechanisms by which the parasitic wasp Cotesia congregata alters the behaviour of its host, the caterpillar Manduca sexta
Are stranded wasp larvae required for host behavioural change? The number of wasp larvae emerging from each parasitized caterpillar was recorded (N=35)
Summary
Parasitic manipulators are parasites that alter host behaviour, leading to an enhancement of the parasite’s reproductive success (e.g. Thomas et al, 2005). Some parasitic manipulators have co-evolved with their hosts for millions of years (Hughes et al, 2011). These ancient interactions are often multifaceted (Thomas et al, 2010), with the parasite able to exert control over the host’s immune system and endocrine system as well as its behaviour (Beckage and Gelman, 2002). de Bekker et al, 2014; Libersat and Gal, 2014) These results are superficially surprising, because the most parsimonious method of exerting control over the host would be to attack discrete neuroanatomical and/or neuropharmacological targets
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