|Shatters, Robert - Bob|
Submitted to: Archives of Insect Biochemistry and Physiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/10/2002
Publication Date: 12/1/2002
Citation: Mayer, R.T., Inbar, M., McKenzie, C.L., Shatters, R.G., Borowicz, V., Albrecht, U., Powell, C., Doostdar, H. 2002. Multitrophic interactions of the silverleaf whitefly, host plants, competing herbivores, and phytopathogens. Archives of Insect Biochemistry and Physiology.51(4):151-169. Interpretive Summary: The silverleaf whitefly is an economic pest of many different commercial crops worldwide. The host range of the insect includes over 500 different varieties of plants. Damage to plants results from feeding and includes squash silverleaf, irregular ripening of tomatoes, chlorosis, and stunting. The insect also vectors over 60 different viruses that are serious problems to farmers. When the silverleaf whitefly appears on crops it often displaces other insect herbivores. We have tried to discover the reasons for the success of the silverleaf whitefly. What we have found is that this whitefly has a great ability to induce defensive mechanisms in the host plant that raise resistance to insects and diseases. Apparently the silverleaf whitefly is unaffected by the resistance that results. Geminiviruses, e.g., tomato mottle virus, also are capable of inducing many of the same defensive mechanisms that the silverleaf whitefly vector does. Both the whitefly and the geminivirus utilize the plants defenses for a competitive advantage against other herbivores and diseases. It is possible that the diseases and the vector have co-evolved so that their presence on/in a host plant isolates the plant for their own reproduction ensuring their survival.
Technical Abstract: Our laboratory confirmed that silverleaf whitefly (SLW; Bemisia argentifolii, Bellows & Perring) feeding alters host plant anatomy, physiology and chemistry. The SLW induces a number host plant defenses, including pathogenesis-related (PR) protein accumulation e.g., chitinases, B-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 where herbivore competitors (cabbage looper, Trichoplusia ni; leaf miner, Liromyza trifolii) were placed on plants previously exposed to SLW feeding showed behavioral differences (oviposition, feeding preferences) and reduced survival rates and development times. 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 also apparent interactions with diseases such as tomato mottle virus (ToMoV; a geminivirus) and the host plant and SLW. PR proteins are induced in tomato plants infected with ToMoV much as they are via non-viruliferous SLW feeding. The presence of ToMoV in tomato plants significantly increases 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 had significantly increased the activities of foliar chitinase and peroxidase. Evaluation of pathogen growth 3 weeks after inoculation showed that whitefly feeding significantly reduced 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 of gemini virus infection and/or SLW infestations operates to isolate the host plant for the selected reproduction of the virus and the insect is discussed. These multitrophic cascade effects may contribute to the successful eruptive appearance of SLW on various crops, ranking them as a major pest. It may explain the general observation that when SLW infest a host plant is that there are few if any competing insect herbivores found in the host. Furthermore, these results indicate that SLW-virus relationships could be mutualistic.