Ecological host range of Pseudophilothrips ichini (Thysanoptera: Phlaeothripidae), a biological control agent of Brazilian peppertree, Schinus terebinthifolia

Abstract

Ecological host range testing complements pre-release fundamental host range testing by offering a more realistic picture of insect host plant use in the field, including spillover risk. The biological control program targeting the weed Schinus terebinthifolia Raddi (Anacardiaceae) first released the flush-feeding thrips Pseudophilothrips ichini (Hood) (Thysanoptera: Phlaeothripidae) in Florida in 2019. Pre-release quarantine testing indicated that P. ichini could oviposit and develop on ten host plant species, two of which (Rhus sandwicensis and Dodonaea viscosa) are culturally and ecologically important in Hawaii, where S. terebinthifolia is also a serious weed. We performed two open field experiments, one to simulate temporary spillover and one to simulate continuous spillover and determine if P. ichini could damage non-target plants under natural conditions. In the first experiment, P. ichini thrips dispersed from most non-targets within 24 h, did not move onto non-target plants following the cutting of adjacent S. terebinthifolia plants at soil level, and produced larvae only on R. sandwicensis. In the second experiment, S. terebinthifolia plant quality declined from P. ichini feeding damage, the thrips dispersed more quickly from non-target plants than S. terebinthifolia, produced larvae only on the weed S. terebinthifolia, and did not damage apical meristems of non-target plants. These results indicated that P. ichini has a narrow ecological host range and poses minimal risk to non-target species in Florida and Hawaii.