Using Odor-Baited Trap Trees as Sentinels to Monitor Plum Curculio (Coleoptera: Curculionidae) in Apple Orchards

Abstract

In commercial orchards in Massachusetts in 2003, we conducted experiments aimed at developing guidelines for use of perimeter-row trap trees baited with grandisoic acid plus benzaldehyde as sentinels in a practical approach to determining need and timing of insecticide applications against overwintered plum curculios, Conotrachelus nenuphar (Herbst). Evaluations were based on percentages of sampled fruit injured by plum curculio. Trap trees baited with grandisoic acid released at approximately 1 mg/d plus benzaldehyde released at approximately 40 mg/d performed as well as or better than trap trees baited with greater or lesser amounts of these attractants in combination. The distance over which a trap tree baited with such odor was effective in aggregating damage to fruit extended to at least 31-33 m (maximum evaluated) along a perimeter row. Trap trees at corners of orchard blocks were as effective as perimeter-row trap trees midway between corner trees. Within the canopy of a trap tree, damage did not tend significantly to be localized in the vicinity of the odor source but tended to be rather evenly distributed among various sectors of the canopy. Finally, among three candidate thresholds evaluated as a trigger for insecticide application, a threshold of one freshly injured fruit proved better than thresholds of two or four freshly injured fruit out of 50 fruit sampled on a trap tree in assuring that orchard-wide damage would remain below a preset economic injury level of 1%. Our findings lead us to suggest that after a whole-orchard application of insecticide to apple trees in Massachusetts orchards shortly after petal fall, subsequent applications of insecticide against plum curculio can be confined to peripheral-row trees and be driven by a provisional threshold of one freshly injured fruit out of 50 fruit sampled on a perimeter-row trap tree baited with the above-mentioned odor.

Temporal Dynamics of Plum Curculio,Conotrachelus nenuphar(Herbst.) (Coleoptera: Curculionidae), Immigration into an Apple Orchard in Massachusetts

“…Therefore, a weak correlation between extent of trap captures and extent of injury to fruit by plum curculio occurring after petal fall can be expected. To overcome this problem, an efÞcient way of monitoring plum curculio activity after petal fall is the trap-tree approach developed by Prokopy et al (2003Prokopy et al ( , 2004. This approach consists in alluring adult plum curculios to a selected perimeter-row tree that is baited with the attractive synthetic odor benzaldehyde ϩ grandisoic acid (Piñ ero and Prokopy 2003) so that it can be used as an indicator of incidence of fresh ovipositional injury by plum curculio to fruit in all orchard trees, thereby determining need to spray insecticide against plum curculio.…”

“…Most of the analyses conducted take into consideration data obtained before and after petal fall because this is the stage of tree phenology at which plum curculios exhibit the highest activity and dispersal (Laßeur and Hill 1987), and also the time at which the Þrst insecticide is applied against plum curculio in Massachusetts orchards (Prokopy et al , 2004. A Kolmogorov-Smirnov test was used to determine nonparametrically, using pairwise comparisons, whether the cumulative distributions of captures varied across years.…”

Evaluating Electrophysiological and Behavioral Responses to Volatiles for Improvement of Odor-Baited Trap Tree Management ofConotrachelus nenuphar(Coleoptera: Curculionidae)

“…Moreover, we saw no signiÞcant difference in the amount of injury in trap trees and laterally located nearest neighbor trees, suggesting a potential decrease in overall aggregation in trap trees. Similarly, Prokopy et al (2004) evaluated increasing the amount of grandisoic acid by 2ϫ to improve trap trees for monitoring purposes and observed no increase in overall activity within baited trap trees. Perhaps the higher release rate of grandisoic acid actually increased the active space of the pheromone leading to increased activity in nearest neighbor trees as well, thereby reducing the overall efÞcacy of the approach.…”

“…Pheromone dispensers contained 35 mg of grandisoic acid (ChemTica, San Jose, Costa Rica); recent studies by Leskey and Zhang (2007) predicted that the release rate was Ϸ0.14 mg/d per trap tree at 25ЊC. The four benzaldehyde dispensers were deployed equidistantly throughout the outer third of the canopy and left for the entire season while the pheromone dispenser was deployed near the center of the tree (Prokopy et al , 2004 and replaced after Ϸ5 wk. Within control plots, unbaited control trees were established using the same spacing criteria ( Fig.…”

“…After petal fall, however, the question as to the need for and timing of subsequent insecticide applications made against plum curculio has been difÞcult for growers to pinpoint because of lack of a reliable monitoring technique. Over the past decade, a trap tree monitoring strategy for plum curculio oviposition has been developed (Prokopy et al , 2004. While captures in baited traps failed to correlate with injury levels in trees , the trap tree approach provided an enhanced method for monitoring oviposition activity and was validated as a threshold-based monitoring tool in seven northeastern states in apple orchards (Piñ ero et al 2011).…”