Within-tree and temporal distribution of Pezothrips kellyanus (Thysanoptera: Thripidae) nymphs in citrus canopies and their influence on premature fruit abscission.

Abstract

Pezothrips kellyanus (Bagnall) (Thysanoptera: Thripidae) has recently become a pest of citrus whose nymphs feed on the surface of young fruitlets. This feeding habit causes patches or rings of tissue scar around the apex as fruit mature. Currently, little is known about the distribution of P. kellyanus nymphs. Further knowledge would allow the development of an appropriate sampling protocol and targeted pesticide application. In our first experiment, the abundance of first- and second-generation P. kellyanus nymphs was surveyed in a citrus orchard at different times of day to characterize their spatial and temporal distributions. The distribution of damaged fruit was also measured at harvest. Our results showed that P. kellyanus nymphs tended to be present in the upper half of the canopy and mainly damaged the fruit located in this area of the canopy. However, P. kellyanus nymphs were uniformly distributed among the four cardinal directions of the canopy and throughout the day. Consequently, cardinal direction and time of the day seem to be less important when developing a sampling plan or in improving targeting or timing of insecticidal spray applications. In our second experiment, we tracked the presence of P. kellyanus nymphs in labeled fruit daily. These data were used to determine how many days the nymphs occupied a fruit and to relate occupancy and premature fruit abscission. The nymphs of P. kellyanus remained on the same fruit for only 1 d. The rate of fruit abscission in June was significantly higher in fruit occupied by first-generation P. kellyanus nymphs than in nonoccupied fruit.