UC Berkeley

With the increase of globalization, the introduction of exotic species into new regions has become a worldwide threat for biodiversity and agricultural production. However, invasiveness of alien species depends on the extent to which abiotic and biotic factors affect the impact of exotic species in a new region. The Light Brown Apple Moth (LBAM), Epiphyas postvittana (Walker) (Lepidoptera: Tortricidae), is a leafroller native to southeastern Australia that was discovered in California in 2006. At the time of its discovery, little was known about how abiotic and biotic factors might limit its distribution and impact in California and North America. I therefore measured high and low temperature tolerance of LBAM in laboratory studies and found that it exhibited only moderate tolerance of extreme temperatures, which may limit its potential distribution in California and North America. I also monitored LBAM populations in the field and measured parasitism rates over a four year study period to determine the influence of of biotic resistance and to provide baseline population data for use in management decisions. I found that LBAM populations were cyclic or decreasing, had strongly overlapping generations and produced three generations annually in San Francisco and and four in Santa Cruz. The parasitoid assemblage of LBAM in California consisted of many species and parasitism rates were unusually high, but provided no evidence of an ability to regulate LBAM populations. I also found that low density LBAM populations did not exhibit demographic Allee effects, but instead populations of all sizes exhibited strong negative density dependence.

I also studied life history parameters of Meteorus ictericus, the most abundant parasitoid of LBAM in California, and found that it has a number of traits that could account for its dominance in the parasitoid assemblage. It was able to attack and develop in a wide range of host larval instars, had a preference for late larval instars, a female only lifestyle, a low generation time ratio in relation to LBAM, and similar temperature maxima and minima for development. However, M. ictericus exhibited an unusually low lifetime fecundity, which could pose an important constraint on its potential to suppress LBAM populations.

Overall, the results of these studies have provided valuable insights that can be used to better understand the potential geographic distribution of LBAM, and to better inform management decisions. In addition, I suggest that the high level of resistance from resident parasitoids on LBAM in California, in combination with other pest management strategies, could prevent the widespread losses from agricultural crops that were originally anticipated in the United States.