Assessing efficacy of mating disruption in an apple orchards by release and recapture of males in net-cages

Codling moth Cydia pomonella (L.) is regarded as a major pest of pome fruit worldwide. The implementation of mating disruption for its control has been increasing during the last two decades (Witgall et al., 2008; Angeli et al., 2007). Due to increased regulatory restrictions of conventional insecticides and other environmental issues, in some fruit growing districts mating disruption is now deployed on well over 50% of the pome fruit area and it is considered an integral part of pest management programs for this species (Thomson et al., 2009). The evaluation of the efficacy of the commercial formulation used for mating disruption appears to be a relevant factor for further support the use of this technique. In this work we evaluate the use of net-cages (Doye & Koch, 2005) as a field method for the evaluation of the efficacy of mating disruption. A pheromone treated plot and an untreated area were provided with four 2 mc net-cages each equipped with a trap. No plants were included in the cage. Codling moth males were released in the cages and caught in unbaited or female baited delta trap. In each of the four cages, a fixed number of males (5, 10, 15, and 20) were released with the aim to evaluate the effect of male density on trap catch. Release of males was replicated three times. As a general result, the number of males captured in the female baited traps was dependent on the number of released males in the cage (Linear regression, R2=0.996; ANOVA, P<0.001). A different pattern was, however, observed between the untreated and the pheromone treated plot. While in the control plot the captures could be represented by a linear curve with no apparent saturation (R2=0.959), in the pheromone plot we observed a logarithmic trend with a tendency to saturation (R2=0.968). Although the treatment did not affect the number of males caught in the blank traps (ANOVA, P>0.05), a higher proportion of males was trapped with the lowest male dose in the control plot indicating that this dosage may be strongly biased by accidental captures. The efficacy of the pheromone formulation was calculated as catch inhibition by comparing the fraction of males caught by female baited traps in the treated and control plots. The inhibition of captures due to the treatment was 68% with a release of 20 males and 96% with the dose of 5 males. From these preliminary results it appears that a dose of 20 males per cage is necessary to highlight behavioural differences of searching males due to a pheromone treatment. Further research on factors such as trap architecture, presence of plants in the cage and volume of the cage may be of help for the optimization of this method.