Comparative behavioral and EAG responses of female obliquebanded and redbanded leafroller moths (Lepidoptera: Tortricidae) to their sex pheromone components

Studies were conducted investigating the responses of female obliquebanded leafrollers, Choristoneura rosaceana (Harris) and redbanded leafrollers, Argyrotaenia velutinana (Walker) (Lepidoptera: Tortricidae), to components of their sex pheromone. Electroantennogram (EAG) recordings revealed significant responses from antennae of female moths of both species to the major pheromone component, (Z)-11-tetradecenyl acetate, at dosages ranging from 2 μg – 2 mg. However, tested individually, the minor pheromone components of the obliquebanded leafroller, (E)-11-tetradecenyl acetate and (Z)-11-tetradecenol, elicited little or no antennal response from conspecific females. This result was consistent for redbanded leafroller females, which showed only weak responses to the minor component (E)-11-tetradecenyl acetate at a 2 mg dosage. For both species, species-specific blend ratios of the Z and E isomers of tetradecenyl acetate did not elicit a greater antennal response than the Z isomer alone. Virgin females of each species (2–4 d old) were placed into 1-liter plastic assay chambers with constant throughput of carbon-filtered air passed through 1-liter flasks containing rubber septa loaded with (Z)and (E)-11-tetradecenyl acetates and (Z)-11-tetradecenol for trials with female obliquebanded leafrollers or with (Z)and (E)-11-tetradecenyl acetates and dodecyl acetate for trials with female redbanded leafrollers. Exposure to pheromone-permeated air delayed the onset of calling by 1 h and terminated the calling period 1 h earlier for both species compared with solvent-control exposed females. Furthermore, the total proportion of calling females was reduced by half in chambers receiving constant throughput of pheromone-permeated air compared with solvent controls. Exposure to pheromonepermeated air also significantly reduced egg-laying in both species compared with clean-air controls. Furthermore, application of the major pheromone component, (Z)-11-tetradecenyl acetate, at dosages ranging from 2 μg–2 mg to wax-paper ovipositional substrates, deterred oviposition by females of both species. Our data suggest that application of synthetic sex-attractant pheromones for mating disruption of leafroller species may have deleterious effects on female moth behavior, which may contribute to pest control. Field investigations will need to be conducted to test this hypothesis. 187 * Corresponding author; current address: Entomology and Nematology Department, Citrus Research and Education Center, University of Florida, 700 Experiment Station Road, Lake Alfred, FL 33850, USA; e-mail: [email protected] et al., 1975). Control of redbanded leafroller by mating disruption using synthetic pheromones has been judged successful (Cardé et al., 1975; Novak et al., 1978; Novak & Roelofs, 1985; Cardé & Minks, 1995); however, results have been inconsistent for the obliquebanded leafroller (Reissig et al., 1978; Agnello et al., 1996; Lawson et al., 1996). Greater success has been recorded with a Western population of obliquebanded leafroller in British Columbia, Canada (Evenden et al., 1999a,b). The females of this Western population contain different amounts and ratios of the four-component pheromone and the males are characterized by different behavioral and antennal responsiveness to blends of these four components as compared with Eastern U.S. populations of this species (Vakenti et al., 1988, Thomson et al., 1991; El-Sayed et al., 2003). Despite numerous studies on mating disruption of these two species, the mechanisms behind its effectiveness are still poorly understood. Specifically, little is known about the effect of synthetic pheromone applications on female behavior and how that may contribute to the effectiveness of mating disruption. Many studies have been conducted examining male moth antennal and behavioral responses to pheromone for both the redbanded leafroller (Bartell & Roelofs, 1973, 1976; Cardé & Roelofs, 1977; Novak & Roelofs, 1985; El-Sayed et al., 2003; Stelinski et al., 2003a, b, 2004a) and obliquebanded leafroller moths (Evenden et al., 2000; Stelinski et al., 2003a, b, 2004a). Some of these investigations have suggested that high-dosage exposure of male moths to their pheromone blend components decreases subsequent responses of male moths due to adaptation, habituation, or a combination of both. This decreased responsiveness following previous exposure has been implicated as a potential contributing factor to mating disruption (Bartell & Roelofs, 1973; Evenden et al., 2000; Stelinski et al., 2004a). Despite great attention to the effects of pheromone exposure on male moth behavior, similar effects on the responses of conspecific female moths have not been investigated in depth. It is known that females of many tortricid species are capable of detecting their sex pheromone (Palanaswamy & Seabrook, 1978; Barnes et al., 1992; Stelinski at el., 2003c, 2006; DeLury et al., 2005; Gökçe et al., 2006). In addition to tortricid moths, noctuid (Mitchell et al., 1972; Birch, 1977; Light & Birch, 1979; Ljungberg et al., 1993; Groot et al., 2005), yponomeutid (van der Pers & den Otter, 1978), and arctiid (Schneider et al., 1998) females are reported to be capable of detecting their sex pheromone. Furthermore, exposure to pheromone is known to either advance or delay the onset of calling periodicity and/or increase the total proportion of calling female moths (Palanaswamy & Seabrook, 1978, 1985; Noguchi & Tamaki, 1985; Weissling & Knight, 1996; Stelinski et al., 2006). Despite extensive evidence among a wide variety of species that female moths are capable of detecting their sex pheromone and that this modifies their behavior as compared with moths in clean air, little is known about how this may contribute to mating disruption. Stelinski et al. (2003c) provided initial evidence that female obliquebanded and redbanded leafroller moths are sensitive to their major sex pheromone component as measured by electroantennograms (EAGs). The objectives of the current study were to (1) describe EAG dose-response relationships of obliquebanded and redbanded leafroller females to their major and selected minor pheromone components and species-specific blends of the major component and its geometric isomer, (2) determine whether exposure to a blend of synthetic pheromone components that is highly attractive to males affects calling behavior and/or oviposition of female moths, and (3) determine whether pheromone applied to ovipositional substrates affects egg laying. Our hypotheses were that females of both species are capable of detecting their sex pheromone components and that exposure to these chemicals affects calling and oviposition behavior. MATERIAL AND METHODS