Abstract
Although the cotton bollworm Helicoverpa armigera has traditionally been controlled by application of chemical pesticides, chemical control selects for resistance, pollutes the environment, and endangers human health. New methods for controlling H. armigera are therefore needed. Heliothis virescens ascovirus 3i (HvAV-3i) is a recently identified virus of the lepidopteran larvae. We tested the effects of HvAV-3i on H. armigera larvae following oral ingestion of HvAV-3i-containing hemolymph (about 1.0 × 1010 virus genome copies per larvae) and following injection of HvAV-3i-containing hemolymph by insertion of a needle. Following oral ingestion, first-instar to fifth-instar larvae grew and developed normally. Following needle injection, in contrast, the corrected mortality of third and fourth instars was 88.9 ± 2.1 and 93.7 ± 3.4%, respectively. Food intake was significantly lower for larvae injected with virus-containing hemolymph than with virus-free hemolymph. Larvae injected with virus-containing hemolymph had extended survival times and could not complete the pre-pupal stage. These results indicate that inoculation of HvAV-3i via needle injection, but not via oral ingestion, significantly reduced the growth and development of H. armigera larvae.
Highlights
The cotton bollworm, Helicoverpa armigera Hübner (Lepidoptera: Noctuidae), is a worldwide crop pest that attacks over 200 species in nearly 20 families (Wang et al, 2009; Bird, 2017)
The mortality of needle-inoculated H. armigera larvae was significantly affected by Heliothis virescens ascovirus 3i (HvAV-3i) hemolymph dilution (F7,16 = 419.05, P < 0.0001)
The current study was consistent with that earlier study in that no mortality occurred when L1–L5 larvae of H. armigera were inoculated with HvAV-3i via oral ingestion
Summary
The cotton bollworm, Helicoverpa armigera Hübner (Lepidoptera: Noctuidae), is a worldwide crop pest that attacks over 200 species in nearly 20 families (Wang et al, 2009; Bird, 2017). Helicoverpa armigera Infected by HvAV-3i (Wakil et al, 2009, 2010; Liu et al, 2010; Zhang et al, 2012; Mironidis et al, 2013; Qayyum et al, 2015) To manage this pest, new methods of control, including biological control, are needed. Ascoviruses typically induce cell rupture and the release of vesicles containing virus particles into the larval hemolymph (Federici et al, 1990; Asgari et al, 2017). Before they die, ascovirus-infected larvae exhibit weak muscle elasticity, decreased food intake, reduced weight gain, retarded growth, a yellow body color, and molting failure (Carner and Hudson, 1983; Federici and Govindarajan, 1990; Govindarajan and Federici, 1990). The effects of HvAV-3h on noctuid larvae have been studied (Li et al, 2013), the effects of HvAV-3i on H. armigera have not been studied
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