Multitrophic interactions of the silverleaf whitefly, host plants, competing herbivores, and phytopathogens

Abstract

Our laboratory found that silverleaf whitefly (SLW; Bemisia argentifolii Bellows & Perring) feeding alters host plant physiology and chemistry. The SLW induces a number of host plant defenses, including pathogenesis-related (PR) protein accumulation (e.g., chitinases, beta-1,3-glucanases, peroxidases, chitosanases, etc.). Induction of the PR proteins by SLW feeding occurs in various plant species and varieties. The extent and type of induction is dependent on a number of factors that include host plant growing conditions, the length of time the host plant is exposed to SLW feeding, the plant variety, and SLW population densities. The appearance of PR proteins correlates well with reduced infestations of conspecific insect herbivore competitors. Greenhouse and field experiments in which herbivore competitors (cabbage looper, Trichoplusia ni; leaf miner, Liromyza trifolii) were placed on plants previously exposed to SLW feeding demonstrated behavioral differences (oviposition, feeding preferences) and reduced survival rates and development times of these insects. The interaction was asymmetrical, i.e., SLW infestations of plants previously exposed to leaf miners had little or no effect on SLW behavior (oviposition). Induction of plant-defensive proteins by SLW feeding was both local (at the feeding site) and systemic (uninfested leaves distant to the feeding site). There are interactions between diseases such as tomato mottle virus (ToMoV; a geminivirus) and the host plant and SLW. PR proteins were induced in tomato plants infected with ToMoV much as they were via non-viruliferous SLW feeding. The presence of ToMoV in tomato plants significantly increased the number of eggs produced by SLW females. Experiments using tomato plants, powdery mildew (PM), and tobacco mosaic virus (TMV) show that whitefly infestations can affect plant pathogen relationships but the effects vary among pathogen types. Enzyme analyses prior to pathogen inoculation showed that whitefly treatment significantly increased the activities of foliar chitinase and peroxidase. Evaluation of pathogen growth 3 weeks after inoculation showed that whitefly feeding significantly reduced the incidence of PM. However, TMV levels evaluated by ELISA were not significantly affected by whitefly feeding. Six weeks after inoculation with pathogens, the chitinase and peroxidase activities were still elevated in plants initially fed on by whiteflies but continuing pathogen infection had no effect on these enzymes. The possibility that geminivirus infection and/or SLW infestations isolate the host plant for the selected reproduction of the virus and the insect is discussed. Multitrophic cascade effects may contribute to the successful eruptive appearance of SLW on various crops, ranking them as a major pest. They may explain the general observation that when SLW infest a host plant there are few if any competing insect herbivores and pathogens found in the host. However, the results indicate that certain SLW-virus relationships could be mutualistic.

Differential Activity of Peroxidase Isozymes in Response to Wounding, Gypsy Moth, and Plant Hormones in Northern Red Oak (Quercus rubra L.)

“…Like the differential greenhouse responses to GM, wounding, and JA, this also suggests that red oak POD responses may be unique to the attacking insect. While studies of POD in the context of herbivory have focused on total POD activity (e.g., Cipollini and Redman, 1999;Mayer et al, 2002;Roitto et al, 2003;Traw et al, 2003), the plant pathology literature provides many examples of pathogen-specific POD isoform activity or profiles (Kristensen et al, 1999;Kandan et al, 2002;Tognolli et al, 2002;Maksimov et al, 2003). In some cases, POD isoform function is based on hostplant substrate specificity and the production of specific defenses (Calderón et al, 1990).…”

Local and systemic responses induced by aphids in Solanum tuberosum plants

“…Wool & Hales (1996) reported that a previous infestation of cotton plants by Aphis gossypii decreased subsequent colonization by conspecific aphids. Another phloem-feeding insect, the silverleaf whitefly, Bemisia argentifolii , induced PR protein accumulation in collard and tomato plants, which negatively affected the colonization process of conspecific and heterospecific competitors (Mayer et al, 2002). Conversely, previous infestation by Myzus persicae (Sulzer) (Homoptera: Aphididae) carried out on three different peach cultivars led to an improvement of conspecific performance (Sauge et al, 2002(Sauge et al, , 2006.…”

Pathogenicity of Beauveria bassiana to fall webworm (Hyphan­tria cunea) (Lepidoptera: Arctiidae) on different host plants

“…Host plants of phytophagous insects can significantly influence host susceptibility to entomopathogenic microorganisms in at least three different ways: (1) by affecting growth rates (SantiagoÁlvarez & Ortiz-Garcia 1992), (2) through dietary stress (Mayer et al 2002) or (3) through direct antimicrobial activity of the plant (Costa & Gaugler 1989b;Vega et al 1997;Lacey & Mercadier 1998;Inyang et al 1999a,b;Poprawski et al 2000a,b;Klingen et al 2002). In order to maximise the potentiality of B. bassiana as a component of integrated pest management of H. cunea, it is necessary to understand the effects of different environmental factors and agricultural practices on fungal efficacy.…”