Granulovirus prevents pupation and retards development of Adoxophyes honmai larvae

Abstract

Abstract. Larvae of Adoxophyes honmai (Lepidoptera: Tortricidae) infected with granulovirus (AdhoGV) do not pupate; instead, they undergo prolonged larval development and die during the final stadium. Non-infected larvae, however, pupate after five larval stadia. Insect metamorphosis is regulated by fluctuations of ecdysteroid and Juvenile Hormone (JH). JH esterase activity and titres of ecdysteroid must be measured to understand fully the interaction of an insect virus and its host. JH esterase activity is consistently low in AdhoGV-infected larvae, which suggests that JH in AdhoGV-infected larvae is not degraded during the final stadium. The ecdysteroid titre in non-infected larvae showed a large peak in the final stadium before pupation, whereas that in AdhoGV-infected larvae increased from day 2 to day 5 in the final stadium, and then remained at a high level until death. Furthermore, an ecdysteroid UDP-glucosyltransferase (EGT) assay showed that this activity occurs in haemolymph from AdhoGV-infected larvae, but not in haemolymph of non-infected larvae. PCR and sequencing analysis revealed that the AdhoGV genome contains an egt gene, which encodes a protein of 445 amino acids, located approximately 1 kbp upstream from the granulin gene. These results suggest that AdhoGV-infected larvae are prevented from pupating because JHE activity is suppressed and EGT expression inactivates ecdysteroid in the haemolymph.

Entomopoxvirus infection induces changes in both juvenile hormone and ecdysteroid levels in larval Mythimna separata

“…Lepidopteran baculoviruses, like EPVs, are also known to infect fat-body cells (Federici, 1997). Reduced JHE activity is found in caterpillars infected with baculoviruses such as Adoxophyes honmai nucleopolyhedrovirus and Adoxophyes orana nucleopolyhedrovirus , Adoxophyes honmai granulovirus (AdhoGV) (Nakai et al, 2002) and Autographa californica multiple nucleopolyhedrovirus (Hajó s et al, 1999). Thus, the infection of fatbody cells and subsequent reduction in JHE activity may be a strategy used by both EPVs and baculoviruses to alter JH levels in infected hosts.…”

“…This suggests that EPVs prevent moulting and pupation by mechanism(s) that do not involve the inactivation of ecdysteroids. We previously showed that pupation is inhibited in caterpillars that are infected by either AdhoGV, a slow-killing baculovirus that possesses an egt gene, or AHEV, an EPV that does not possesses an egt gene (Nakai et al, 2002(Nakai et al, , 2004Thézé et al, 2013). In these studies, higher ecdysteroid levels were observed in AdhoGV-infected larvae than in mock-infected larvae, presumably because the glucosylated ecdysteroids accumulate in the haemolymph following inactivation by EGT.…”

“…JHE activity was measured by the method of McCutchen et al (1995) as described in detail by Nakai et al (2002) using the colorimetric substrate methyl 1-heptylthioacetothioate (HEPTAT) (Mccutchen et al, 1993). Newly moulted fourth instar larvae were exposed to 10 5 MySEV OBs larva 21 .…”

“…Haemolymph was collected from at least five MySEV-infected or negative control sixth instar larvae at 24 h intervals as described above except that the centrifugation was performed at 6000 g for 5 min to remove haemocytes. Ecdysteroid concentrations were measured by radioimmunoassay as described by Nakai et al (2002). Briefly, a 5 ml aliquot of haemolymph was mixed vigorously with 160 ml methanol.…”

Insecticidal Efficacy of Azadirachta indica, Nucleopolyhedrovirus and Chlorantraniliprole Singly or Combined against Field Populations fo Helicoverpa armigera Hübner (Lepidoptera: Noctuidae)

“…Occluded viruses (OV) initiate primary infections in midgut epithelial cells of susceptible hosts and Budded viruses (BV) spread from cell to cell in the larvae (Keddie et al, 1989;Washburn et al, 1995). The infected larvae become pale in color, which ultimately swell due to the deposition of OV's, climb upper parts of the host plants and ultimately die (Inceoglu et al, 2001;Nakai et al, 2002).…”