Disruption of Darna pallivitta (Lepidoptera: Limacodidae) by Conventional and Mobile Pheromone Deployment.

The nettle caterpillar moth, Darna pallivitta (Moore) (Lepidoptera: Limacodidae), is an important invasive pest in the Hawaiian Islands with impacts on both agriculture and public health. Nettle caterpillars defoliate ornamental nursery stock, damage a number of agricultural crops (including coffee and macadamia), and have been reported to feed on over 45 plant species in 22 families (Conant et al. 2002). As suggested by their common name, D. pallivitta caterpillars have urticating hairs that can cause painful stings and skin inflammations. While the nettle moth is a problem for homeowners because of the direct plant damage and the injuries that occur during yard work, nursery producers must also comply with regulations on plant movement due to the quarantine status of D. pallivitta. To help mitigate the negative impacts of D. pallivitta, the Hawai’i Department of Agriculture began releasing a Eulophid parasite, Aroplectrus dimerus Lin, in mid-2010 (Bautista et al. 2014). The results of these releases have been encouraging, and it is hoped that the parasite will help to reduce the moth populations. Monitoring of moth populations has been aided by the identification of a sex pheromone lure, n-butyl (E)-7,9-decadienoate (E7,9-10:COOnBu), for D. pallivitta (Siderhurst et al. 2007). The pheromone lure has been used in trapping grids on several islands to monitor and delimit moth populations and to help document declines in D. pallivitta associated with releases of A. dimerus (N. Reimer, personal communication). Although moth sex pheromone lures can be used as monitoring tools, they also have potential to directly reduce pest moth populations when used in pheromone-based control strategies, such as mass trapping or mating disruption. Mass trapping involves deploying a large number of pheromone traps in an area to capture male moths before they can mate with females. If enough mates are removed in this way, the pest population will decline to a point where economic damage is reduced (El-Sayed et al. 2006). Mating disruption uses synthetic sex pheromones to interfere with the ability of an insect to locate a mate (Sarfraz et al. 2006). With lepidopteran pests, the most commonly used strategy is to release the female sex pheromone which masks the pheromone plumes produced by females or causes false trail following in male moths or both (Suckling 2000). Either mechanism can potentially lead to reductions in the moth population due to the reduced probability of male moths successfully locating and mating with females (Bartell 1982). A more recently proposed control method involving pheromones, termed mobile mating disruption (MMD), involves the use of a carrier species to disrupt normal mating communication in a target pest species. The first investigation of this cross species disruption was studied with melon fly, [Bactrocera cucurbitae (Coquillett)] and oriental fruit fly, [B. dorsalis (Hendel)] using the male specific lures for both species (Suckling et al. 2007). Although a reduction in mating was observed in large field cages, mating in neither species was completely inhibited. Sex pheromones are often more powerful behavioral triggers than other semiochemicals and were therefore the subject of a more recent MMD study using Mediterranean fruit fly, Ceratitis capitata (Wiedemann), as carriers for the light brown apple moth, Epiphyas postvittana (Walker), pheromones (E)-11-tetradecenyl acetate and (E,E)-9,11-tetradecadien-1-yl acetate (Suckling et al. 2011). Pheromone-treated C. capitata flies used in this MMD field study were prepared by spraying flies with an aqueous suspension of microencapsulated pheromone. Results showed percent disruptions of ≥90% during the first 24 h, which fell off during the following several days. Suckling et al. (2011) suggest that this novel method of pheromone dispersal may provide advantages over conventional dispersal methods such as offering a more socially acceptable approach to spreading an active agent to control invasive insects in urban environments and other areas that are geographically inaccessible for conventional pheromone mating disruption applications (Suckling et al. 2011). Apart from establishing a proof-of-concept for MMD, Suckling et al. (2011) provided a framework for continued study of the control technique. In particular, they suggest the following stages be addressed when experimenting with new carrier/pest systems: 1) “do no harm” to the carrier organism; 2) sustained attraction and a scalable application method and 3) orientation disruption in the field. In addition to the three areas of this framework, we were also interested to assess the amount and longevity of pheromone carried by treated “carrier” insects. In this study, we return to using B. cucurbitae as used by Suckling et al. (2007). In addition to having been used in a previous MMD study, melon flies have the advantage of being a large tephritid, and they were easily obtained from stocks mass-reared at the USDA ARS Pacific Basin Agricultural Research Center. The objectives of the presented research were to evaluate the use of communication disruption techniques to control D. pallivitta using both conventional disruptors (rubber septa or plastic spiral matrix releasing E7,9-10:COOnBu) and mobile disruption (E7,9-10:COOnBu carried and released by B. cucurbitae). Conventional disruption techniques were tested in separate experiments with septa and spiral disruptors in easily accessible fields dominated by tall grasses. Mobile disruption experiments were conducted to assess mortality induced by application of E7,9-10:COOnBu to adult B. cucurbitae, to assess strength and longevity of attraction of D. pallivitta to E7,9-10:COOnBu-treated B. cucurbitae, and to assess mobile disruption under field conditions.