Thomas C. BAKER. Agenor MAFRA-NETO, Henry FADAMIRO, Marlin E. RICE
Department of Entomology, Iowa State University, Ames, Iowa, USA
A controlled release system for long term storage and intemmittent delivery of pheromone over long periods of time, at specified release rates, was developed and tested for use in the field as a mating disruption system for the stored products pest, Cadra cautella (Walker) (Lepidoptera: Pyralidae). Field tests were also commenced against the European comborer, Ostrinia nubilalis, in grassy aggregation sites adjacent to Iowa cornfields, and against the cranberry blackheaded fireworm, Rhopobota naevana (Hubner) in commercial cranberry bogs in Wisconsin. The MSTRS system (Metered Semiochemical Timed Release System) consists of aerosol canisters loaded with gram amounts of pheromone that are timed to discharge their aerosol spray-burst onto a cloth pad every 15 minutes, with the pad serving as a high-emission-rate point source that is rejuvenated with fresh pheromone every 15 minutes (Mafra-Neto and Baker, 1996). The system can be set to release pheromone only during specific periods of the day or night when the moths are active, thus avoiding wasteful emission of pheromone during periods of the day when moths will not be affected by it. The pheromone is protected from oxidation from atmospheric oxygen since it is housed inside the pressurized propellant-filled canister, as well as from UV exposure in the canister's dark interior.
Against C. cautella, there were no signs of degradation or reduction of biological activity of pheromone stored in the canisters that were kept at ambient temperatures in the fiel'd throughout the summer. Pheromone discharged at a rate of 50µg/spray upon demand from those cans disrupted all mating of freely flying virgin C. cautella males and females present in the rooms at moderate to high densities of a 2:1 male/female ratio for 24 hours in 3 X 3 X 2.5m storage rooms. Up to 92% mating suppression was achieved at high moth densities over a 72 hour period. Disruption was measured directly by recapturing females and examining their bursa copulatrices for spermatophores, which are indicators of successful mating encounters with males. MSTRS devices emitting only 5µg/spray caused greater than 60 percent mating disruption. One MSTRS device per room was as good as two per room at high moth densities and the 50µg/spray rate.
Observations of C. cautella moths in the field and in complementary laboratory experiments indicates that the elevation of pheromone response thresholds of males that were pre-exposed to pheromone from the MSTRS devices likely played a major part in the observed disruption. Both the lower (activation) and the higher (arrestment) thresholds were elevated, resulting effectively in an upward shift of the response spectrum of males to a higher optimal range.
MSTRS devices emitting either O. nubilalis or R. naevana pheromone were deployed at a density of either 1, 5, or 8 per acre in both the grassy divisions between cornfields that serve as mating "activity" sites, and along the borders of cranberry bogs. Disruption of males' ability to locate traps containing calling virgin females, as well as their ability to mate with tethered virgin females was greater than 90% in some plots, even at low canister densities.
LiteratureThis research was supported by grant No. 9202914 from the USDA NRI competitive grants program (to TCB), and by grants to TCB and MER from the Leopold Center for Sustainable Agriculture, Ocean Spray Cranberries, Inc., and the Wisconsin Cranberry Board.