Does the solitary parasitoid Microplitis pennatulae use a combinatorial approach to manipulate its host?: Multiple mechanisms for host manipulation

Host manipulation is a strategy used by some parasites to enhance their transmission. These parasites use a combination of neuropharmacological, psychoneuroimmunological, genomic/proteomic, or symbiont‐mediated mechanisms to manipulate their hosts. Bodyguard manipulation occurs when parasitized hosts guard parasitoid pupae to protect them from their natural enemies. Bodyguard‐manipulated hosts exhibit altered behaviours only after the egression of parasitoid prepupae. Behavioural changes in post‐parasitoid egressed hosts could have resulted from their altered physiology. Previous studies have shown that gregarious manipulative parasitoids induce multiple physiological changes in their host, but the physiological changes induced by solitary manipulative parasitoids are unknown. Microplitis pennatulae Ranjith & Rajesh (Hymenoptera: Braconidae) is a larval parasitoid of Psalis pennatula Fabricius (Lepidoptera: Erebidae). After the egression of parasitoid prepupae, P. pennatula stops its routine activities and protects the parasitoid pupa from hyperparasitoids by body thrashes. In this study, we looked into the physiological changes induced by the solitary manipulative parasitoid, M. pennatulae, in its host, P. pennatula, during various stages of parasitization. We considered octopamine concentration and phenoloxidase (PO) activity as biomarkers of physiological change. We also examined whether M. pennatulae has a symbiotic virus and whether the wasp transfers it to the host during parasitization. We found that octopamine concentration was low in the pre‐parasitoid egressed host, but it was elevated after the parasitoid egressed. Phenoloxidase activity was lower in the pre‐ and post‐parasitoid egressed host than in the unparasitized host. We also detected symbiotic bracovirus (BV) in the wasp ovaries and isolated the BV virulence gene from the parasitised host. Our study suggests that solitary parasitoids also induce multiple physiological changes to influence the host behaviour to their advantage, as is the case with the gregarious parasitoids.