Mortality of Cutworm Larvae Is Not Enhanced by Agrotis segetum Granulovirus and Agrotis segetum Nucleopolyhedrovirus B Coinfection Relative to Single Infection by Either Virus

Abstract

Mixed infections of insect larvae with different baculoviruses are occasionally found. They are of interest from an evolutionary as well as from a practical point of view when baculoviruses are applied as biocontrol agents. Here, we report mixed-infection studies of neonate larvae of the common cutworm, Agrotis segetum, with two baculoviruses, Agrotis segetum nucleopolyhedrovirus B (AgseNPV-B) and Agrotis segetum granulovirus (AgseGV). By applying quantitative PCR (qPCR) analysis, coinfections of individual larvae were demonstrated, and occlusion body (OB) production within singly infected and coinfected larvae was determined in individual larvae. Mixtures of viruses did not lead to changes in mortality rates compared with rates of singlevirus treatments, indicating an independent action within host larvae under our experimental conditions. AgseNPV-B-infected larvae showed an increase in OB production during 2 weeks of infection, whereas the number of AgseGV OBs did not change from the first week to the second week. Fewer OBs of both viruses were produced in coinfections than in singly infected larvae, suggesting a competition of the two viruses for larval resources. Hence, no functional or economic advantage could be inferred from larval mortality and OB production from mixed infections of A. segetum larvae with AgseNPV-B and AgseGV.A large number of baculoviruses isolated from the larvae of species of the insect orders Lepidoptera, Diptera, and Hymenoptera have been described (1). According to their occlusion body (OB) morphology, baculoviruses are distinguished into two morphological groups: the granuloviruses (GVs) with a single virion in an ovocylindrical OB (granule) and the nucleopolyhedroviruses (NPVs) with a few to many virions in a polyhedral OB (polyhedron) (2). Taxonomically, the Baculoviridae family is subdivided into four genera, the Alpha-, Beta-, Gamma-, and Deltabaculovirus genera (2, 3). Alpha-and betabaculoviruses comprise lepidopteran-specific NPVs and GVs, respectively. Many lepidopteran species are susceptible to baculoviruses from different species. Even simultaneous infections, so-called coinfections or mixed infections, of two NPVs (4), two GVs (5), and NPVs and GVs (6, 7) have been observed.Larvae of the turnip moth, Agrotis segetum (Denis & Schiffermüller) (Lepidoptera: Noctuidae), so-called common cutworms, are important agricultural pests (8). Two different alphabaculovirus isolates, Agrotis segetum nucleopolyhedrovirus A (AgseNPV-A; also called the Polish isolate) and A. segetum nucleopolyhedrovirus B (AgseNPV-B; also termed the Oxford isolate) (9-11), as well as the betabaculovirus Agrotis segetum granulovirus (AgseGV) (12), were isolated and characterized from A. segetum larvae. AgseGV was tested extensively as a biocontrol agent for the control of A. segetum in the field (13-16), and AgseNPV-B has shown its potential as a biocontrol agent under laboratory conditions (13).Both viruses were found to infect A. segetum larvae simultaneously (17), but little is known about possible in...

Natural Coinfection between Novel Species of Baculoviruses in Spodoptera ornithogalli Larvae

“…This group includes NPVs (six group 2-and one group 1-alphabaculoviruses) and GVs from Agrotis segetum [10,44], Helicoverpa armigera [45,46], Mythimna unipuncta [47,48], S. frugiperda [49,50], S. litura [32,51], Trichoplusia ni [52,53], and Choristoneura fumiferana [54]. All these GVs are of the slowly killing type and a potentiating effect has only been reported to NPVs for S. frugiperda [13,55,56]. Probably, coinfection with NPVs is an evolutionary strategy selected in some slowly killing GVs to persist and spread in nature.…”

Comparative Pathogenesis of Generalist AcMNPV and Specific RanuNPV in Larvae of Rachiplusia nu (Lepidoptera: Noctuidae) Following Single and Mixed Inoculations

“…Hackett et al (2000) found that a GV isolated from H. armigera inhibited the replication of HearNPV in H. zea larvae. Independent action was also reported: neither an increase nor a decrease in mortality was observed in mixed-virus treatments of Agrotis segetum larvae with Agrotis segetum granulovirus and Agrotis segetum nucleopolyhedrovirus B (Wennmann et al 2015). Concerning NPVs-NPVs interactions in vivo, studies focused on different strains (wild-type and/or genetically modified) of the same NPV species (Georgievska et al 2010, Virto et al 2014.…”

Cross-Resistance of the Codling Moth against Different Isolates of Cydia pomonella Granulovirus Is Caused by Two Different but Genetically Linked Resistance Mechanisms

“…To determine ODV fusion, RFUs was measured again as described. Fifty µL of labeled ODV of CpGV-M or CpGV-S were measured as a positive control to calculate the total amount of ODV (for details see [41]). Measured RFUs were corrected for background fluorescence associated with the midgut epithelial cells from control larvae fed with water.…”