The present studies were carried out to evaluate resistance in the populations of Spodoptera litura Fab. (Lepidoptera, Noctuidae) from five districts of Hunan Province in China to various insecticides from 2010 to 2012 using a standard leaf dip bioassay method. For organophosphates and pyrethroids, resistance ratios compared with a susceptible Lab-BJ strain were in the range of 14–229-fold for organophosphates and 12–227-fold for pyrethroids. Similarly, relative low levels of resistance to emamectin, indoxacarb, and chlorfenapyr were observed in all five populations. In contrast, the resistance to carbamates (thiodicarb or methomyl) was significantly higher than that of organophosphates, pyrethroids and newer chemistry insecticides. The pairwise correlation coefficients of LC50 values indicated that the newer chemistry insecticides and old generation insecticides were not significant except abamectin, which was negatively significantly correlated with methomyl. A significant correlation was observed between thiodicarb, methomyl, and deltamethrin, whereas resistance to bifenthrin showed no correlations with resistance to other insecticides except deltamethrin. The results are discussed in relation to integrated pest management for S. litura with special reference to management of field evolved resistance to insecticides.

The whitefly Bemisia tabaci is an important pest of worldwide agriculture. Previous work has shown that B. tabaci actively suppresses host plant defenses, but our knowledge of the specific mechanisms involved remains limited. Here we describe a B. tabaci salivary protein, the ferritin BtFer1, and its role in facilitating exploitation of host plants. We show that BtFer1 exhibits Fe2+ binding ability and ferroxidase activity, and that secretion of BtFer1 during B. tabaci feeding suppresses H2O2-generated oxidative signals in tomato (Solanum lycopersicum). Silencing BtFer1 enhanced the induction of the jasmonic acid (JA)-mediated defense signaling pathway in response to whitefly feeding, and led to increased callose deposition and the production of proteinase inhibitors that prevent whiteflies from continuously ingesting and digesting phloem sap. Consistent with these effects, silencing BtFer1 reduced whitefly survival on tomato but not on artificial diet. Using a JA-deficient spr2 mutant plant further showed that suppression of JA defenses by BtFer1 is sufficient to increase B. tabaci survival. Taken together, these results demonstrate that BtFer1 acts as an effector protein that mediates whitefly–tomato interactions. These findings represent an important step forward in understanding the molecular mechanisms by which whiteflies and other insect herbivores suppress host plant defenses.

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Tomato yellow leaf curl virus (TYLCV), a begomovirus (genus Begomovirus) is the causal agent of tomato yellow leaf curl disease (TYLCD), which causes severe damage to tomato (Solanum lycopersicum) crops throughout tropical and subtropical regions of the world. TYLCV is transmitted by the whitefly Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) in a circulative and persistent manner. Our previous studies showed that tomato flavonoids deter B. tabaci oviposition, but the effects of tomato flavonoids on the settling and feeding behavior of B. tabaci and on its transmission of TYLCV are unknown. Using two near-isogenic tomato lines that differ greatly in flavonoid levels, we found that high flavonoid production in tomato deterred the landing and settling of B. tabaci. Moreover, electrical penetration graph studies indicated that high flavonoid levels in tomato reduced B. tabaci probing and phloem-feeding efficiency. As a consequence, high flavonoid levels in tomato reduced the primary and secondary spread of TYLCV. The results indicate that tomato flavonoids provide antixenosis resistance against B. tabaci and that the breeding of such resistance in new varieties could enhance TYLCD management.

Green leaf volatiles (GLVs) can induce defence priming, that is, can enable plants to respond faster or more strongly to future stress. The effects of priming by GLVs on defence against insect herbivores and pathogens have been investigated, but little is known about the potential of GLVs to prime crops against virus transmission by vector insects. Here, we tested the hypothesis that exposure to the GLV Z-3-hexenol (Z-3-HOL) can prime tomato (Solanum lycopersicum) for an enhanced defence against subsequent Tomato yellow leaf curl virus (TYLCV) transmission by the whitefly Bemisia tabaci. Bioassays showed that Z-3-HOL priming reduced subsequent plant susceptibility to TYLCV transmission by whiteflies. Z-3-HOL treatment increased transcripts of jasmonic acid (JA) biosynthetic genes and increased whitefly-induced transcripts of salicylic acid (SA) biosynthetic genes in plants. Using chemical inducers, transgenics and mutants, we demonstrated that induction of JA reduced whitefly settling and successful whitefly inoculation, while induction of SA reduced TYLCV transmission by whiteflies. Defence gene transcripts and flavonoid levels were enhanced when whiteflies fed on Z-3-HOL-treated plants. Moreover, Z-3-HOL treatment reduced the negative impact of whitefly infestation on tomato growth. These findings suggest that Z-3-HOL priming may be a valuable tool for improving management of insecttransmitted plant viruses.