Monitoring the seasonal population density of Pandemis pyrusana (Lepidoptera: Tortricidae) within a diverse fruit crop production area in the Yakima Valley, WA

A. L. Knight


The population dynamics of Pandemis pyrusana (Kearfott) were studied in 60 contiguous orchard blocks (154 hectares) of mixed fruit production situated in the Yakima Valley, Washington. Grids of sex-pheromone-baited and liquid-food-baited traps were placed at a rate of one trap of each type per 2 hectares. Trees within 50 m of each trapping location were sampled for overwintering and summer generation larvae, and fruit injury prior to harvest. Larvae from both generations were found in a low proportion of apple (Malus domestica Borkh.), pear (Pyrus communis L.), and cherry (Prunus avium L.) orchards, but not in the peach/nectarine (Prunus persica (L.)), apricot (Prunus armeniaca L,), or prune (Prunus domestica L.) orchards. Larval densities between generations increased 5-fold in apple and 10-fold in cherry and non-bearing apple. Parasitism of field-collected larvae by tachinid parasitoids averaged 37% and 23% for each generation, respectively. Low levels of fruit injury (<0.5%) by P. pyrusana were detected in only five apple and pear orchards. Cumulative moth catch was 10-fold higher in sex-pheromone than food-baited traps. Moth catch in both types of traps varied significantly among crops, In general, moth catches were highest in apple and cherry. Cumulative moth catch in both trap types in apple and pear during the first flight was weakly correlated with levels of fruit injury. In contrast, moth catch during the second flight was not correlated with fruit injury. The observed low predictive ability of traps was likely due to trap saturation and contamination with non-target moths and a general dispersal of moths among orchards throughout the region. The capture of female moths versus the total of both sexes caught in food bait traps did not improve the prediction of fruit injury in apple or pear.

Key words: Pandemis; leafrollers; sex pheromone traps; food bait traps; fruit crops

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