Interactions between Acetoin, a Plant Volatile, and Pheromone In Rhynchophorus palmarum: Behavioral and Olfactory Neuron Responses

Abstract

Aggregation of Rhynchophorus palmarum weevils on host plants is mediated by a male pheromone (rhynchophorol: R) and host-plant volatiles (PVs) acting in synergy. Synthetic PV blends synergizing pheromone contain acetoin (A) and ethyl acetate (EtAc). R, A, and EtAc are detected by specialized olfactory receptor neurons (ORNs). In addition, particular types of ORNs are tuned to both A and R. To specify the role played by acetoin in pheromone perception, we recorded the responses of ORNs to 100 ng of A or R presented either separately or mixed. Behavioral responses to R, A, and EtAc were studied in a four-armed olfactometer and by field trapping. We screened 59 R-, A-, and AR-tuned ORNs by recording specific responses to odors presented either separately or mixed. Stimulations by blends elicited complex response profiles from the three ORN types: some gave synergistic responses, others were inhibited, and the remainder responded as though both odors were detected independently. Several gave either a weak or no response to a first stimulation by R, but responded clearly to a second stimulation after an intercalary stimulation by A. In the olfactometer, both sexes were more attracted to a blend of A + R (1 + 0.01 ng/sec) than to pure compounds, whereas EtAc did not enhance response to R. Pheromone-baited traps (1 mg/day) containing PV blends (650 mg/day) based on an ethanol/EtAc blend (1:1), plus either 5 or 10% A, or a more complex reference blend, or sugarcane (natural pheromone synergist), caught similar numbers of weevils and about twice as many insects as a control ethanol/EtAc blend. Traps with only pheromone caught about 10 times fewer insects. Behavioral results support the role of acetoin as a pheromone synergist for R. palmarum, and electrophysiological data provide evidence of modulation of peripheral sensory responses to pheromone by acetoin. Sexual dimorphism was observed neither at the ORN nor at the behavioral levels.

Behavioral responses of Drosophila to biogenic levels of carbon dioxide depend on life-stage, sex and olfactory context

“…The four-field olfactometer has been used in chemical ecology studies on several insect species (Vet et al, 1983;Quiroz and Niemeyer, 1998;Hilker et al, 2002;Saïd et al, 2005), but not to investigate Drosophila olfactory behavior (Devaud, 2003). This assay has distinct advantages.…”

Sex Pheromones and Their Impact on Pest Management

“…Captures with pure rhynchophorol increase considerably with the addition of plant material, leading to the development of an efficient control method based on mass trapping (Oehlschlager et al 1993). Laboratory studies corroborate that aggregation is mediated by a male-produced pheromone and host-plant volatiles that include acetoin and ethyl acetate (Said et al 2005). The American palm weevil is an important pest of several palm species in tropical America.…”

The Relevance of Background Odor in Resource Location by Insects: A Behavioral Approach

“…For example, the attraction of the palm weevil Rhynchophorus palmarum to its aggregation pheromone (rynchopherol, a RIO) is enhanced when plant odor emitted from sugarcane (a multiple background odor) is simultaneously present (Said et al 2005). The odor blend emitted by sugarcane (Saccharum officinarum) was attractive to the palm weevil when presented alone (Rochat et al 2000).…”