Immunity of an insect herbivore to an entomovirus is affected by different host plants

Abstract

BACKGROUND Interactions between herbivorous insects and entomoviruses may depend on host plant, perhaps mediated through changes in herbivore innate immunity. RESULTS Caterpillars (Spodoptera exigua) fed Glycine max had high viral loads and low melanization rates together with low melanization enzyme [PO, DDC, TH] activities and gene expressions. Caterpillars fed Ipomoea aquatica had low viral loads and high melanization, gene activities and gene expressions while those fed Brassica oleracea or artificial diet had intermediate levels of each. Melanization rates were negatively correlated with viral loads and positively correlated with activity and expression of each of the three enzymes. Some diet effects on enzymes were constitutive because the same diets led to low (G. max) or high (I. aquatica) melanization related gene activities and expressions without infection. CONCLUSION Diet influences the interactions between insect herbivores and viruses by shaping the innate immune response both at the onset of infection and afterwards as viral loads accumulate over a period of days. In addition, diets that lead to low viral loads are associated with high activities and gene expressions of a variety of melanization related enzymes suggesting a common causative mechanism. © 2019 Society of Chemical Industry

Plant‐mediated effects on life history traits of entomovirus infected caterpillars ofSpodoptera exigua

“…Tri‐trophic interactions among plants, insect herbivores and entomoviruses are of increasing interest in entomology and ecology (Cory & Myers, 2004; Shikano, 2017; Wang et al., 2020). Among such tri‐trophic interactions, host plant‐mediated effects on the susceptibility of insect herbivores to entomoviruses have received particular attention (Cory & Hoover, 2006; Shikano et al., 2010; Wan et al., 2016, 2018).…”

“…(2018) and Wang et al. (2020) have reported that the differences in virus susceptibility depend on the variation in melanization enzymes of humoral immunity (i.e. phenoloxidase, dopa decarboxylase and tyrosine hydroxylase) of herbivores.…”

Plants impact cellular immunity of caterpillars to an entomovirus

“…In fact, more hemocytes denote stronger resistance against entomovirus infection and also greater immunity. In a previous study, 43 we found that S. exigua feeding on I. aquatica had the lowest mortality and the lowest viral load, followed by Brassica oleracea . This was consistent with Shikano et al 8 .…”

“…The purified NPV were diluted 100‐fold with PBS, and the NPV concentration (1.26 × 10 7 OB mL −1 ) (occlusion body, OB) was obtained by Thomas hemocytometer under a phase‐contrast microscope at 400× magnification. The virus was diluted with sterile water to a concentration of 1.26 × 10 4 OB mL −1 for this experiment to avoid excessive larval mortality 7,43 …”

“…Melanization is important aspect of insect innate immunity to defense against pathogens. In these studies, we found that the difference in the susceptibilities of S. exigua to Se MNPV raised on different plants was closely related to the amount of Se MNPV proliferation and caterpillar melanization (melanization enzyme [PO, DDC, TH] activities and gene expressions) in vivo 42,43 . However, whether this is relevant to cellular immunity is unclear.…”