Biology and temperature requirements of the invasive seed bug Leptoglossus occidentalis (Heteroptera: Coreidae) in Europe

Leptoglossus occidentalis, a species native to North America, has been expanding through European conifer forests. The fast spread across the European continent demonstrates its great invasive potential and poses a threat to conifer seed orchards. To better understand its potential distribution and population growth in infested regions, the temperature-dependent development in laboratory as well as life history, phenology, and winter survival were investigated in southern Slovakia during 2009-2011. The lower temperature thresholds to complete embryonic and postembryonic development estimated with the linear model were 13.38 and 14.37 °C, respectively. The number of degree-days required for completion of development from egg to adult estimated by the linear model was 533 °C. Overwintered adults or late nymphal instars became active in mid-March, oviposition was not observed before mid-April, and nymphs passing through five stages reached adulthood after mid-July. Individual females laid on average 31 eggs (max 78). The second generation started in August but did not complete its development till winter, although part of the 5th instar nymphs did survive until spring. Using temperature data of 41 localities across Europe and cumulative degree-days for complete life cycle, a prediction of the potential number of generations per year was made. In conditions of southern Slovakia L. occidentalis was univoltine, but up to four generations per year were estimated depending on the locality in Europe.