Effect of host plants on the infectivity of nucleopolyhedrovirus to Spodoptera exigua larvae

Abstract

Previous studies have shown that the infectivity of baculovirus to herbivores is affected by phytochemicals ingested during the acquisition of viral inoculum on the foliage of host plants. Here, we measured the effects of 14 host plant species on the infectivity of Spodoptera exigua nucleopolyhedrovirus (SeNPV) to its larvae. The order of the LD 50 values of SeNPV among the host plants was Ipomoea aquatica > Brassica oleracea > Raphanus sativus > Amaranthus tricolor > Spinacia oleracea > Vigna unguiculata > Solanum melongena > Capsicum annuum > Apium graveolens > Allium fistulosum > Lactuca sativa > Brassica chinensis > Zea mays > Glycine max, with 940.1 AE 2.26, 424.0 AE 0.60, 295.2 AE 1.13, 147.3 AE 0.63, 138.6 AE 0.22, 119.9 AE 0.07, 119.8 AE 0.02, 109.2 AE 0.18, 104.8 AE 0.62, 102.1 AE 0.66, 97.9 AE 0.22, 89.9 AE 0.32, 79.0 AE 0.13 and 64.0 AE 0.38 OBs per larva, respectively, and the values of mean time to death of virus-infected larvae were 6.21 AE 0.11, 7.12 AE 0.10, 7.33 AE 0.21, 6.97 AE 0.02, 7.06 AE 0.01, 7.29 AE 0.03, 7.32 AE 0.05, 7.07 AE 0.08, 7.24 AE 0.11, 7.09 AE 0.13, 7.50 AE 0.06, 7.23 AE 0.01, 7.30 AE 0.02 and 7.19 AE 0.07 days, respectively. The mean time to death of larvae decreased with increasing viral dose, and corrected mortality decreased as the larval mean time to death increased. These findings have significance for understanding the effects of host plants on the infectivity of baculovirus to noctuids.

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

“…Spodoptera exigua multiple nucleopolyhedrovirus ('NPV' hereafter) is an important biocontrol agent of beet armyworm, and is able to cause epizootics in populations of this herbivore . In an earlier study, we measured the effects of 14 species of host plants on the susceptibility of beet armyworm to NPV, and found high susceptibility of caterpillars raised on a diet of soybeans ( Glycine max ), intermediate susceptibility of those fed collards ( Brassica oleracea ) and low susceptibility of those fed water convolvuluses ( Ipomoea aquatica ) . In the current study, we used these three plants together with an artificial diet to examine the mechanisms underlying viral effects on the immune response of beet armyworm to NPV.…”

Phytochemical variation mediates the susceptibility of insect herbivores to entomoviruses

“…Previous studies have reported effects of plant species on the susceptibility of several insects to their entomoviruses, including that of Helicoverpa zea (Ali et al., , ; Farrar & Ridgway, ; Forschler, Young, & Felton, ) and Heliothis virescens (Ali et al., , ; Hoover et al., ). Some cases found higher mortality (Forschler et al., ), shorter mean time to death (Ali et al., ), lower LD 50 (Ali et al., ) and shorter LT 50 (Wan et al., ) after virus‐infected larvae of noctuids fed on soybeans. But these same four susceptibility indices showed the opposite trend when virus‐infected larvae were fed on collards (Farrar & Ridgway, ; Shikano et al., ; Wan et al., ).…”

“…(Ali et al., ; Farrar & Ridgway, ; Shikano et al., ; Wan et al., ), while it is higher on oligophenolic plants (soybeans, corns, tomatoes, etc.) (Ali et al., ; Forschler et al., ; Monobrullah et al., ; Wan et al., ). Phenolics from the foliage can inhibit the infectivity of the entomovirus to tissues in insect guts, thus decreasing the susceptibility of larvae to the entomovirus (Ali et al., ; Felton, Duffey, Vail, Kaya, & Manning, ).…”

“…Some cases found higher mortality (Forschler et al, 1992), shorter mean time to death (Ali et al, 2002), lower LD 50 (Ali et al, 1998) and shorter LT 50 (Wan et al, 2016) after virus-infected larvae of noctuids fed on soybeans. But these same four susceptibility indices showed the opposite trend when virus-infected larvae were fed on collards (Farrar & Ridgway, 2000;Shikano et al, 2010;Wan et al, 2016). These results are consistent with those from our study.…”

“…In crop fields, herbivorous insects often acquire baculoviruses when feeding on specific plants, which in turn may affect the insect's susceptibility to the baculovirus. Indicators of host susceptibility include mortality (Ali, Felton, Meade, & Young, ; Ali, Young, Felton, & McNew, ; Ali, Young, & McNew, ), mean time to death of larvae (Farrar & Ridgway, ; Raymond et al., ), median lethal time (LT 50 ) or median lethal dose (LD 50s ) (Wan, Jiang, & Li, ). Previous studies have indicated that the susceptibility of herbivorous insects to baculoviruses can be affected by some phytochemicals (Cory & Hoover, ; Lindroth, Hwang, & Osier, ), as for example, foliar phenolics, which decrease susceptibility (Farrar & Ridgway, ; Monobrullah, Shankar, Bharti, Gupta, & Kaul, ; Shikano, Ericsson, Cory, & Myers, ; Shikano, Shumaker, Peiffer, Felton, & Hoover, ), likely because aggregates formed by phenols and virus proteins inactivate virus (Felton & Duffey, ; Young, Yang, & Felton, ).…”