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Imperfection works: Survival, transmission and persistence in the system of Heliothis virescens ascovirus 3h (HvAV-3h), Microplitis similis and Spodoptera exigua.

ABSTRACT: Ascoviruses are insect-specific large DNA viruses that mainly infect noctuid larvae, and are transmitted by parasitoids in the fields. Heliothis virescens ascovirus 3h (HvAV-3h) has been recently isolated from Spodoptera exigua, without parasitoid vector identified previously. Here we report that Microplitis similis, a solitary endoparasitoid wasp, could transmit HvAV-3h between S. exigua larvae in the laboratory. When the female parasitoid wasp acquired the virus and served as a vector, the period of virion viability on the ovipositor was 4.1 ± 1.4 days. Infected host larvae were still acceptable for egg laying by parasitoids, and the parasitoids thereafter transmitted virus to healthy hosts. Virus acquisition occurred only from donor hosts between 3 and 9 days post infection. The peak of virus acquisition (80.9 ± 6.3%) was found when M. similis wasps oviposited in larvae that had been inoculated with the virus 7 days previously. When virus infection of the host took place during the life cycle of the parasitoid wasp, it caused 1- to 4-day-old immature parasitoids death in the host, whilst a small proportion of 5- to 6-day-old and the majority of 7-day-old parasitoids larvae survived from the virus-infected hosts. Viral contamination did not reduce the life span or fecundity of female M. similis.

SUBMITTER: Li SJ

PROVIDER: S-EPMC4754712 | biostudies-other | 2016 Feb

REPOSITORIES: biostudies-other

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Project description:Shortly prior to death, many species of Lepidoptera infected with nucleopolyhedrovirus climb upwards on the host plant. This results in improved dissemination of viral occlusion bodies over plant foliage and an increased probability of transmission to healthy conspecific larvae. Following applications of Spodoptera exigua multiple nucleopolyhedrovirus for control of Spodoptera exigua on greenhouse-grown sweet pepper crops, necrophagy was observed by healthy S. exigua larvae that fed on virus-killed conspecifics. We examined whether this risky behavior was induced by olfactory or phagostimulant compounds associated with infected cadavers. Laboratory choice tests and olfactometer studies, involving infected and non-infected cadavers placed on spinach leaf discs, revealed no evidence for greater attraction of healthy larvae to virus-killed over non-infected cadavers. Physical contact or feeding on infected cadavers resulted in a very high incidence of transmission (82-93% lethal disease). Observations on the behavior of S. exigua larvae on pepper plants revealed that infected insects died on the uppermost 10% of foliage and closer to the plant stem than healthy conspecifics of the same stage, which we considered clear evidence of baculovirus-induced climbing behavior. Healthy larvae that subsequently foraged on the plant were more frequently observed closer to the infected than the non-infected cadaver. Healthy larvae also encountered and fed on infected cadavers significantly more frequently and more rapidly than larvae that fed on non-infected cadavers. Intraspecific necrophagy on infected cadavers invariably resulted in virus transmission and death of the necrophagous insect. We conclude that, in addition to improving the dissemination of virus particles over plant foliage, baculovirus-induced climbing behavior increases the incidence of intraspecific necrophagy in S. exigua, which is the most efficient mechanism of transmission of this lethal pathogen.

Dataset Information

Imperfection works: Survival, transmission and persistence in the system of Heliothis virescens ascovirus 3h (HvAV-3h), Microplitis similis and Spodoptera exigua.

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