Quantitative Relationship Between Sticky Trap Catch and Beat Tray Counts of Pear Psylla (Homoptera: Psyllidae): Seasonal, Sex, and Morphotypic Effects

Abstract

Adult pear psylla, Cacopsylla pyricola (Foerster), were monitored with beat trays, yellow sticky traps, and clear sticky traps for 2 yr at 3 orchards to determine whether a general relationship exists between tray counts and sticky trap catch. Samples were also categorized according to morphotype of the insect (summerform versus winterform), diapause status of winterforms (diapausing versus postdiapause and reproductive), and sex of the insect. Most (42 of 48) of the samples indicated that trap catch varied significantly with tray count (by linear regression analysis). However, aside from the fall winterform generation, no general relationship between trap catch and tray count was noted. Results suggest that sticky trap counts often had a large behavioral or activity component that obscured density effects. These effects were especially noticeable in the spring winterform generation and the summerform generation. Factors affecting sticky trap catch included sex of the insect, reproductive status, trap color, insect age, and leaf fall. We suggest that these factors, as well as others not explored here (e.g., weather), contributed to the lack of a general relationship between tray and trap counts. Previous work indicates that either method predicts damage to the tree; thus, for pest-management decisions, both sampling methods are useful. However, for more precise questions about absolute densities of adults, we suggest that beat trays should be preferred.