Pear psylla and natural enemy thresholds for successful integrated pest management in pears

Abstract

Pear psylla, Cacopsylla pyricola (Förster), is the most economically challenging pest of commercial pears in Washington and Oregon, the top producers of pears in the United States. The objective of this study was to quantify economic injury levels and thresholds for pear psylla. We used the relationship between pear psylla adult and nymph densities, and fruit downgraded due to psylla honeydew marking to identify injury levels. We calculated economic injury levels using the cost of downgraded fruit and average management costs (spray materials and labor). Using economic injury levels, we determined economic thresholds for pear psylla, which include predicted pest population growth, natural enemy predation, and anticipated delays between when pest populations are measured and when managers apply interventions. Economic thresholds generated by this study were 0.1–0.3 second-generation nymphs per leaf and 0.2–0.8 third-generation nymphs per leaf depending on predicted price and yield for insecticide applications at 1,300 pear psylla degree days in the second generation and 2,600 pear psylla degree days in the third generation. Natural enemy inaction thresholds identified by this study were 6 Deraeocoris brevis or 3 Campylomma verbasci immatures per 30 trays or 2 earwigs per trap for third-generation optional insecticide applications.

Turning a Pest into a Natural Enemy: Removing Earwigs from Stone Fruit and Releasing Them in Pome Fruit Enhances Pest Control

“…Therefore, as is typical for density-independent control [45], it is expected that they are more likely to prevent increases in pest populations, rather than decrease the abundance of already problematic pest populations [46]. This partially explains why earwigs, as an important part of the natural enemy complex of pear psylla in the Pacific Northwest, assist mostly in controlling a pest during their second and third generations [19].…”

“…Overall numbers in the OR orchard were still very low even after two years of releases (seasonal average of one per trap at most), suggesting that yearly releases might still be needed to achieve thresholds for pest control. It has been suggested that greater than two earwigs per trap is correlated with the suppression of second-and third-generation pear psylla [19]. Another argument in favor of yearly releases in orchards with low earwig abundance is that due to their poor dispersal behavior-moving only up to 30 m per month [34]-earwigs are thought to slowly recolonize areas where they have been absent [9].…”

“…This is likely due to earwigs helping prevent pest population increases, rather than controlling already abundant pests. Meanwhile, thresholds for pest control by earwigs have been developed for woolly apple aphids and pear psylla, e.g., [10,19,43], which, alongside earwig monitoring, can provide growers with insights on the need for earwig augmentation. Timing for the proper trapping of earwigs in stone fruit is also a key part of earwig augmentation programs.…”

“…When earwigs are added to apple orchards, aphid populations decrease [10,12]. Earwigs also show potential for controlling pear psylla (Cacopsylla pyri L.) in Europe [17,18] and C. pyricola in the United States [19]. European earwigs can also consume other apple and pear pests, including codling moth, Cydia pomonella L., the most important pest of apples worldwide [20].…”

Diversity, biology, and management of the pear psyllids: a global look

“…Dislodged insects cling to the cloth and are counted. The threshold counts of psyllids on trays which indicate that treatment is necessary to manage russet are discussed in Nottingham et al (2022b) and DuPont et al (2023). A second method for monitoring the adult psyllid is with use of sticky cards.…”