Chemical and Behavioral Ecology of Palm Weevils (Curculionidae: Rhynchophorinae)

Abstract

Palm weevils in the subfamily Rhynchophorinae (Curculionidae) (Rhynchophorus spp., Dynamis borassi, Metamasius hemipterus, Rhabdoscelus obscurus, and Paramasius distortus) use male-produced aggregation pheromones for intraspecific chemical communication. Pheromones comprise 8, 9, or 10 carbon, methyl-branched, secondary alcohols. (4S,5S)-4-Methyl-5-nonanol (ferrugineol) is the major aggregation pheromone for R. ferrugineus, R. vulneratus, R. bilineatus, M. hemipterus, and D. borassi and a minor component for R. palmarum. (5S,4S)-5-Methyl-4-octanol (cruentol), (3S,4S)-3-methyl-4-octanol (phoenicol), and (4S,2E)-6-methyl-2-hepten-4-ol (rhynchophorol) are the main aggregation pheromones for R. cruentatus, R. phoenicis, and R. palmarum, respectively. Plant kairomones strongly enhance pheromone attractiveness but none of the identified volatiles, such as ethyl acetate, ethyl propionate, or ethyl butyrate are as synergistic as fermenting plant (palm or sugarcane) tissue. Studying orientation behavior of foraging weevils to semiochemical devices helped to design and test traps for weevil capture. Generally, 3 mg per day of synthetic pheromone (with non-natural stereoisomers being benign) plus insecticide-treated plant tissue constitute highly attractive trap baits. Potential exists for pheromone-based mass-trapping of weevils to reduce their populations and the spread of the weevil-vectored red ring disease, for monitoring their population dynamics to facilitate pest management decisions, and for detection and possible interception of non-native weevils at ports of entry.