Pest management practices and environmental factors affect natural regulation of the codling moth
Abstract: Numerous arthropod predators and parasitoids species attack codling moth eggs and larvae, but these antagonists do not efficiently control the pest in commercial orchards. Parasitism of diapausing larvae was assessed in 79 apple and pear orchards from South-eastern France (2007-2008). The predation and parasitism of egg masses was investigated on a sub-sample of 13 orchards in 2008. Diapausing larvae were observed to be parasitize in only 21.0% and 16.4% of orchards in 2007 and 2008, respectively. The mean parasitism rate over the two years was 3.7 %, 2.3% and 0.8% in the organic and conventional with or without mating disruption orchards, respectively. It was higher in apple than in pear orchards, for high than low densities of windbreak hedgerows and for low than for high densities of orchards surrounding the analysed fields. Six parasitoid species were identified, among which Ascogaster quadridentata, Pristomerus vulnerator and Perilampus tristis were the most frequent whatever the management practices. The composition of the parasitoid community was explained by both local (27%) and landscape factors (16%). On average 12.5% and 54.1% of egg masses exposed to natural antagonists were consumed by predators in July and August 2008, respectively. The highest predation rates were also recorded in the organic orchards and close to hedgerows. Egg parasitism was negligible (0.1%). It appears from this analysis that of egg and larval parasitism, the most frequently described in the literature, has lower impact on codling moth populations than the predation of eggs. Comparing with previous analyses in the same area, it appeared that larval or egg parasitism was much more affected by the protection practices than egg predation.