Heliothis subflexa is a Lepidopteran caterpillar that feeds exclusively on Physalis spp. fruits. These fruits are encased in the inflated calyces—a characteristic that all plants in the genus Physalis share. Abscission of the fruits on which H. subflexa is feeding is a mechanism employed by members of the Physalis genus to avoid further herbivory. The factor that causes fruit abscission is unknown, and abscission rates in Physalis species vary dramatically; some Physalis species are extremely sensitive to herbivory and fruit drop occurs only hours after initiation of herbivory, while other species require severe damage for abscission to occur.
[...] In addition, some fruits were ‘mock injected,' and only received piercing with the syringe in order to ensure that mechanical damage from the syringe did not elicit fruit abscission (preliminary experiments have confirmed this). In addition to these treatments, caterpillars were placed on several fruits of all plants and enclosed in nylon bags to ensure that the normal response (fruit abscission) occurred. Nylon bags lacking caterpillars were placed on six fruits to ensure that mechanical manipulation resulting from placement of the bags did not influence fruit abscission. [...]
[...] Future experiments with other Physalis species will also provide more information about the effect of elicitors fruit drop, in addition to why there is such variation in sensitivity to herbivory with respect to fruit abscission. The information gained from this experiment and future experiments will add to the body of knowledge that exists on the role of chemical signals in plant-herbivore interactions, which “remains largely unexplored” (DeMoraes, 2001). In addition, data generated from this study paves the path for future studies, which will provide information on the reproductive biology of Physalis species and induced plant defenses in the genus. [...]
[...] In addition, the questions of why this differential response in fruit abscission in Physalis species exists and what evolutionary advantages this may incur for species in this genus have never been examined. This experiment is one step in answering these broad questions. Plant responses to herbivory can be quite complex and often involve the immediate induction of defense- and wound-response pathways (Walling, 2000) which can be activated by a number of stimuli. These stimuli include mechanical damage by insect mouthparts and the act of chewing (Baldwin et al., 2001; Walling, 2000; Korth & Dixon, 1997), mechanical damage by insect ovipositors (Marr & Pellmyr, 2003), elicitors in oviposition fluid (Doss et al., 2000), and elicitors in insect saliva (Alborn et al., 1997; Felton & Eichenseer, 1999; Funk, 2001; Halitschke et al., 2001; Mattiacci et al., 1995; Miles, 1999). [...]
[...] Hartmond Yuan Burns J Citrus fruit abscission induced by methyl-jasmonate. Journal of the American Society for Horticultural Science 547-552. Kessler Baldwin T Plant responses to insect herbivory: the emerging molecular analysis. Annual Review of Plant Biology, 53: 299- 328. Klee, H Control of ethylene-mediated processes in tomato at the level of receptors. Journal of Experimental Botany 2057- 2063. Kostenyuk Burns J Mechanical wounding and abscission in citrus. Physiologia Plantarium 354-361. Laster, M Interspecific hybridization of Heliothis subflexa and H. virescens. [...]
[...] Marr Pellmyr O Effect of pollinator-inflicted ovule damage on floral abscission in the yucca-yucca moth mutualism: the role of mechanical and chemical factors. Oecologia 236-243. Mattiacci Dicke Posthumus M Induction of parasitoid attracting synomone in Brussels sprouts plants by feeding of Pieris brassicae larvae: role of mechanical damage and herbivore elicitor. Journal of Chemical Ecology, 2229-2247. Mattiacci Dicke Posthumus M Beta-glucosidase—an elicitor of herbivore-induced plant odor that attracts host-searching parasitic wasps. Proceedings of the National Academy of Science, 92: 2036-2040. [...]
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