Sunday, December 10, 2006 - 9:35 AM

Do gall-inducing insects avoid plant indirect defenses?

John Tooker,, Pennsylvania State University, Department of Entomology, 501 ASI Building, University Park, PA and Consuelo De Moraes,, Pennsylvania State University, Entomology, 501 ASI Building, University Park, PA.

Herbivorous arthropods can induce host plants to release volatile compounds that aid foraging natural enemies. Volatile responses to damage caused by chewing insects have been characterized for several plant species, and these indirect plant defenses are also known to be induced by some non-chewing herbivores, such as piercing-sucking mites. But the responses of plants to gall-inducing insectsówhich are unique in the degree of control they exert over host plantsóremain to be studied. We explored the indirect defenses of the distantly related host plant species Triticum aestivum L. (Poaceae) and Solidago altissima L. (Asteraceae) in response to feeding by larvae of the specialist gall flies Mayetiola destructor (Say) (Cecidomyiidae) and Eurosta solidaginis Fitch (Tephritidae), respectively. In both systems, galled and ungalled plants emitted the same compounds in similar amounts, suggesting that neither host plant species produces an indirect defensive response to feeding by gall fly larvae. In addition, the presence of gall insects significantly reduced the volatile response of both host plant species to attack by the generalist-feeding caterpillar Heliothis virescens (Fabricius) (Lepidoptera: Noctuidae). The absence of a volatile response to gall insect herbivory could be caused by the insect sapping plant resources required for such a response. Alternatively, these galling species may evade detection by host plants or actively suppress host-plant defenses. For M. destructor, the failure of larvae to elicit a volatile response from their host plants may help explain why natural enemies, which often rely on induced volatile cues, fail to inflict significant mortality on Hessian fly populations in the field.

Species 1: Diptera Tephritidae Eurosta solidaginis (goldenrod gall fly)
Species 2: Diptera Cecidomyiidae Mayetiola destructor (Hessian fly)

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