Effects of single and mixed infections with wild type and genetically modified Helicoverpa armigera nucleopolyhedrovirus on movement behaviour of cotton bollworm larvae

Abstract

Naturally occurring insect viruses can modify the behaviour of infected insects and thereby modulate virus transmission. Modifications of the virus genome could alter these behavioural effects. We studied the distance moved and the position of virus-killed cadavers of fourth instars of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) infected with a wild-type genotype of H. armigera nucleopolyhedrovirus (HaSNPV) or with one of two recombinant genotypes of this virus on cotton plants. The behavioural effects of virus infection were examined both in larvae infected with a single virus genotype, and in larvae challenged with mixtures of the wild-type and one of the recombinant viruses. An egt-negative virus variant caused more rapid death and lower virus yield in fourth instars, but egt-deletion did not produce consistent behavioural effects over three experiments, two under controlled glasshouse conditions and one in field cages. A recombinant virus containing the AaIT-(Androctonus australis Hector) insect-selective toxin gene, which expresses a neurotoxin derived from a scorpion, caused faster death and cadavers were found lower down the plant than insects infected with unmodified virus. Larvae that died from mixed infections of the AaIT-expressing recombinant and the wild-type virus died at positions significantly lower, compared to infection with the pure wild-type viral strain. The results indicate that transmission of egt-negative variants of HaSNPV are likely to be affected by lower virus yield, but not by behavioural effects of egt gene deletion. By contrast, the AaIT recombinant will produce lower virus yields as well as modified behaviour, which together can contribute to reduced virus transmission under field conditions. In addition, larvae infected with both the wild-type virus and the toxin recombinant behaved as larvae infected with the toxin recombinant only, which might be a positive factor for the risk assessment of such toxin recombinants in the environment.

Digital gene expression analysis of Helicoverpa armigera in the early stage of infection with Helicoverpa armigera nucleopolyhedrovirus

“…BmNPV-infected silkworms showed enhanced locomotory behavior on the 4 dpi (Kamita et al, 2005), HearNPV-infected cotton bollworm (Georgievska et al, 2010) and LdMNPV-infected European gypsy moth (Hoover et al, 2011) all exhibited climbing behavior in the later stage after NPV infection. In previous studies, two NPV-encoded genes (ptp and egt) were found to be critical to the manipulated behavior of NPV-infected lepidopteran larvae (Hoover et al, 2011;Kamita et al, 2005).…”

“…HearNPV is one of the most widely used commercialized NPV products for the control of the devastating pest H. armigera in cotton and vegetable fields (Georgievska et al, 2010;Grzywacz et al, 2000). The pathogenicity of HearNPV declines when H. armigera larvae grow larger or the inoculation dose decreases.…”

“…HearNPV has been extensively used in China for the control of this notorious pest in cotton and vegetable fields (Chen et al, 2001;Georgievska et al, 2010). HearNPV contains a single nucleocapsid packaged into a virion, which is then occluded in a polyhedron.…”

Expression, Delivery and Function of Insecticidal Proteins Expressed by Recombinant Baculoviruses

“…Toxin expression in baculovirus-infected larvae also results in larvae falling from their position on a plant and dying on the ground, while wild-type baculovirus-infected larvae tend to climb and die in a higher position on a plant [ 124 , 125 ]. The climbing behavior of baculovirus-infected larvae is thought to augment the distribution of progeny OBs from a cadaver and facilitate dissemination [ 126 ].…”

Host miRNAs are involved in hormonal regulation of HaSNPV‐triggered climbing behaviour in Helicoverpa armigera

“…Although egt exists in nearly all lepidopteran baculoviruses, its role in baculovirus‐induced tree‐top disease may not be highly conserved. In Helicoverpa armigera , infection by the egt ‐negative virus of H. armigera single nucleopolyhedrovirus (HaSNPV) resulted in lower virus yield and faster time to death in fourth instars; however, there was no effect on the death positions of larvae under controlled glasshouse conditions or in field cages (Georgievska et al., ). Larvae of Trichoplusia ni and Spodoptera exigua that were infected with Autographa californica multiple nucleopolyhedrovirus (AcMNPV) also died at the same height as larvae infected with a mutant virus lacking the egt gene (Ros, van Houte, Hemerik, & van Oers, ).…”