Influence of Two Acyclic Homoterpenes (Tetranorterpenes) on the Foraging Behavior of Anthonomus grandis Boh
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Previous studies have shown that the boll weevil, Anthonomus grandis, is attracted to constitutive and conspecific herbivore-induced cotton volatiles, preferring the blend emitted by cotton at the reproductive over the vegetative stage. Moreover, this preference was paralleled by the release of the acyclic homoterpenes (tetranorterpenes) (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT) and (E,E)-4,8,12-trimethyltrideca-1,3,7,11-tetraene (TMTT) in Delta Opal cotton being higher at the vegetative than at the reproductive stage. Here, we evaluated whether this difference in release of acyclic homoterpenes also occurred in other cotton varieties, and if boll weevils could recognize these compounds as indicators of a specific cotton phenological stage. Results showed that cotton genotypes CNPA TB-90, BRS-293 and Delta Opal all produced higher levels of DMNT and TMTT at the vegetative stage than at the reproductive stage and that these homoterpenes allowed for principal component analysis separation of volatiles produced by the two phenological stages. Electroantennograms confirmed boll weevil antennal responses to DMNT and TMTT. Behavioral assays, using Y-tube olfactometers, showed that adding synthetic homoterpenes to reproductive cotton volatiles (mimicking cotton at the vegetative stage in terms of homoterpene levels) resulted in reduced attraction to boll weevils compared to that to unmodified reproductive cotton. Weevils showed no preference when given a choice between plants at the vegetative stage and the vegetative stage-mimicked plant. Altogether, the results show that DMNT and TMTT are used by boll weevils to distinguish between cotton phenological stages.
KeywordsCotton Homoterpenes Host plant Phenological stages Plant volatiles Ontogenetic Coleoptera Curculionidae
We thank Hélio Moreira dos Santos for helping with laboratory rearing of weevils and Dr. Fabio Aquino de Albuquerque for providing cotton seeds. We also thank the Post-Graduate Zoology Program of the University of Brasília (UnB) for use of their facility. This work received financial support from the Coordination of Superior Level Staff Improving’s (CAPES) through a grant to DMM (no. 99999.014964/2013-09), National Counsel of Technological and Scientific Development (CNPq), Federal District Research Foundation (FAP-DF) and the Brazilian Corporation of Agricultural Research (EMBRAPA). Rothamsted Research received grant-aided support from the Biotechnology and Biological Sciences Research Council (BBSRC) of the United Kingdom.
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