Attractiveness and competitiveness of irradiated light brown apple moths

Abstract

The sterile insect technique (SIT) potentially provides a socially acceptable approach for insect eradication of new pest incursions. The light brown apple moth, Epiphyas postvittana (Walker) (Lepidoptera: Tortricidae), was discovered in Berkeley (CA, USA) in 2006, leading to an incursion response that included this technology. In this study, we assessed factors affecting mating success from a bisex release of irradiated moths: effects of radiation dose on male multiple mating, male flight competition, female sex pheromone titre and attractiveness of irradiated females to males, and identification of successful mating in vineyards of either irradiated or wild males (identified by isotope analysis of spermatophores from sentinel females). There was a significant negative relationship between male radiation dose and mating frequency. In head-to-head flights of irradiated males against non-irradiated males to a pheromone lure in a wind tunnel, irradiated males reached the lure first only 31% of the time. With increasing radiation dose, the production of the major sex pheromone component in females, (E)-11-tetradecenyl acetate, dropped, from 0.7 AE 0.1 ng per female in non-irradiated females to 0.2 AE 0.07 ng per female when irradiated at 300 Gy. Male catch was reduced to 11% of control females in traps containing females irradiated at 300 Gy. Isotope analysis of spermatophores found in the bursa copulatrix of females indicated that mating success of irradiated males inside the live (entry-only) traps containing virgin females was lower (13.1 AE 3.3%) than suggested by male catch (21.2 AE 3.8%) in pheromone traps, the current standard for assessing field competitiveness. Impacts of irradiation on male and female moth fitness should be taken into account to improve estimates of irradiated to wild male E. postvittana overflooding ratios needed for population suppression.

Low-Oxygen Atmospheric Treatment Improves the Performance of Irradiation-Sterilized Male Cactus Moths Used in SIT

“…The relationship of radiation dose and mating frequency of the light brown apple moth was found to be significantly negative (Stringer et al 2013). In addition, the production of the sex pheromone by the females declined significantly with increasing doses of radiation.…”

“…In head-to-head comparisons of flights of irradiated light brown apple moth males and non-irradiated males toward a pheromone lure in a wind tunnel, irradiated males reached the lure first only 31% of the time (Stringer et al 2013). Light brown apple moth males were irradiated as pupae at intervals up to a dose of 300 Gy, and their flight success was assessed in a wind tunnel equipped with flight track recording software.…”

“…Isotope analysis of spermatophores found in the bursae copulatrices of females indicated that mating success of irradiated males inside the live (entry-only) traps containing virgin females was less than suggested by the male catch in pheromone-baited traps. Impacts of irradiation on the quality of male and female moths should be taken into account to improve estimates of irradiated to wild male E. postvittana over-flooding ratios needed for population suppression (Stringer et al 2013). …”

Global range expansion of pest Lepidoptera requires socially acceptable solutions

“…Some of these programs faced issues of stockpiling insects, synchrony, losses during extended storage, and other tradeoffs. Placement of irradiated pupae to emerge in the field has been done experimentally, but requires adequate protection from predation (Stringer et al 2013). The Australian painted apple moth program in New Zealand was an operational example using pupal irradiation ) and this approach was also explored for gypsy moth (Reardon and Mastro 1993).…”

“…Despite attempts to model the effects of bi-sex or male-only releases of moths that suggested little benefit from females (Kean et al 2011), there is evidence for a background contribution of the female moths through communication disruption of males from calling virgin females, despite their irradiationreduced attractiveness and pheromone titre (Stringer et al 2013;Suckling et al 2006). Further, it has been suggested that there may be a benefit from sterile females acting as a ''sperm sink'' for wild males thereby reducing wild male fertility, which could contribute to part of the observed effect of population suppression.…”