Mechanisms of caterpillar behavioural manipulation by two virus species: spot the difference

Baculoviruses are known to manipulate the behaviour of their caterpillar hosts, by inducing hyperactivity and altered climbing behaviour. To date, however, knowledge on parasitic genes governing such behavioural manipulations is scarce. Previously we have shown that the baculovirus Autographa californica nuclear polyhedrovirus (AcMNPV) induces hyperactive behaviour in Spodoptera exigua caterpillars, and that the viral protein tyrosine phosphatase (ptp) gene is a key player in the induction of hyperactivity. However, this gene is present in only a subset of phylogenetically related baculoviruses, while it is hypothesized that also baculoviruses that do not carry ptp are able to manipulate behaviour, possibly induced by a different viral gene. We compared behavioural changes in Spodoptera exigua caterpillars induced by two baculovirus species: the generalist AcMNPV (carrying ptp) and the specialist SeMNPV (not carrying ptp). We discuss the possible (difference in) mechanism that these two viruses use to manipulate behaviour in the context of host-pathogen coevolution.