Skip to main content
ARS Home » Southeast Area » Gainesville, Florida » Center for Medical, Agricultural and Veterinary Entomology » Chemistry Research » Research » Publications at this Location » Publication #313195
Title: Plant volatiles influence the African weaver ant-cashew tree mutualism

Author
item WANJILU, CAROLINE - International Centre Of Insect Physiology And Ecology
item KHAMIS, FATHIYA - Kenyatta University
item Teal, Peter
item TORTO, BALDWYN - International Centre Of Insect Physiology And Ecology

Submitted to: Journal of Chemical Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/27/2014
Publication Date: 12/1/2014
Citation: Wanjilu, C., Khamis, F.M., Teal, P.E., Torto, B. 2014. Plant volatiles influence the African weaver ant-cashew tree mutualism. Journal of Chemical Ecology. 40:1167-1175.

Interpretive Summary: African weaver ants are well known to have developed highly effective mutualistic interactions between themselves and other insects like aphids and mealy bugs, which they farm like cows to obtain honeydew and in return provide protection against predators. Interestingly, scientists the International Center for Insect Physiology and Ecology (Nairobi, Kneya), Kenyatta University (Nairobi, Kenya) and Center for Medical, Agricultural and Veterinary Entomology, USDA-ARS (Gainesville, Florida) have discovered that these ants have formed a similar mutualistic relationship with the cashew tree. Their research showed that the ants obtain food in the form of nectar from the plants and in return the ants protect the plant against attack by the cashew bug, a stink bug that sucks the juice out of the plant. The research determined that the ants associate food rewards (nectar) with the presence of a set of chemicals naturally produced by the plant, chiefly the perfume chemicals called ocimenes. These chemicals are clearly attractive to the ant, which must protect the cashew plant against attack by the stink bug in order to obtain food. This win-win arrangement may be useful in developing pest control strategies using the weaver ant to clear crops of pest insects by adding these chemicals to the plants.

Technical Abstract: Plant volatiles influence virtually all forms of ant plant symbioses. However, little is known about their role in the mutualistic relationship between the African weaver ant and the cashew tree. In this study, we tested the hypothesis that cashew tree volatiles from plant parts most vulnerable to herbivory viz. inflorescence, leaves, and fruits, are attractive to weaver ants. Using behavioral assays, we show that these volatiles attract weaver ants but without significant difference in preference for any of the odors. These same plant parts are associated with extra floral nectaries (EFNs’) and therefore we evaluated the possibility that the ants associate the volatiles with food rewards. We found that perception of the odors was followed by a searching response that led the ants to nonvolatile sugar rewards. More importantly, we observed that weaver ants spent significantly more time around the odor when it was paired to a reward. Chemical analysis of volatiles showed that the plant parts shared similarities in chemical composition, dominated by monoterpenes and sesquiterpenes. Additionally, we evaluated the attractiveness of a synthetic blend of three ocimene isomers ((E)-ß-ocimene, (Z)-ß-ocimene and allo-ocimene) identified in cashew leaf odor and shown to constitute a candidate kairomone for the cashew pest Pseudotheraptus wayi. We found that the attractiveness of the blend was dose dependent, and the response of the ants was not significantly different to that established with the crude volatiles from plant tissues. These results present new and interesting possibilities for improving weaver ant performance in cashew pest management.