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.

A Place to Grow? Host Choice and Larval Performance of Microplitis similis (Hymenoptera: Braconidae) in the Host Spodoptera litura (Lepidoptera: Noctuidae)

“…The genus Microplitis contains 200 species (Ernandez-Triana et al 2015) and M. similis Lyle (Hymenoptera: Braconidae) is a solitary endoparasitoid, with hosts including Agrotis ypsilon (Rottemberg), Spodoptera exigua (Hübner) and S. litura (Fabricius) (Shepard and Barrion 1998;Ranjith et al 2015). Microplitis similis was first recorded in India (Wilkinson 1930) and identified as a vector of Heliothis virescens ascovirus 3h only recently (Li et al 2016). …”

Altering of host larval (Spodoptera exigua) calcineurin activity in response to ascovirus infection

“…SfAV‐1a), HvAV‐3h appears to be a strain with a relatively broad host range. The mortalities of cotton bollworms ( H. armigera ), beet armyworms ( S. exigua ) and tobacco cutworms ( S. litura ) infected by HvAV‐3h are 94.4 ± 3.7%, 88.9 ± 3.7% and 94.4 ± 1.5%, respectively . Prior to succumbing to HvAV‐3h, infection normally leads to observed stunted growth and reduced diet consumption in the host larvae.…”

“…The mortalities of cotton bollworms (H. armigera), beet armyworms (S. exigua) and tobacco cutworms (S. litura) infected by HvAV-3h are 94.4 ± 3.7%, 88.9 ± 3.7% and 94.4 ± 1.5%, respectively. 15,16 Prior to succumbing to HvAV-3h, infection normally leads to observed stunted growth and reduced diet consumption in the host larvae. Ascoviruses appear to be sufficiently efficient to warrant consideration for development into biological insecticides.…”

Baculovirus-induced insect behaviour: from genes to brains

“…HvAV-3g is a double stranded DNA virus classified in the family Ascoviridae, that has been detected in S. exigua before (Li et al, 2016). Ascoviruses in general have a low infection rate and ascovirus transmission is dependent on parasitoids.…”

“…Ascoviruses in general have a low infection rate and ascovirus transmission is dependent on parasitoids. Infected hosts lack apparent infection symptoms (Li et al, 2016). The function of the HvAV-3g DNA metabolism protein is unknown, however, its homologue in eukaryotes seems to be involved in chromosome condensation, segregation, cohesion and DNA recombination repair (Graumann, 2001).…”