Long-term captive-rearing affects oviposition behavior and nymphal survival of a weed biological control agent

Abstract

Abstract Adaptation to artificial rearing conditions is a well-documented phenomenon in insects and has been shown to reduce the efficacy of biological control agents. The knotweed psyllid, Aphalara itadori Shinji (Hemiptera: Psyllidae), is a biological control agent for Fallopia japonica (Houtt.) Ronse Decr. (Caryophyllales: Polygonaceae) that has been released in North America and Europe, however, to date successful establishment of the insect over multiple field seasons has not been observed. We conducted a series of experiments to explore the possibility that long-term rearing in laboratory conditions has impaired the psyllid’s ability to survive in the field. We used light intensity to manipulate leaf toughness in F. japonica, and used the resulting plants in laboratory bioassays to assess the effects of foliage toughness on the survival of the psyllids. We conducted laboratory-choice tests to compare the effects of leaf age on oviposition behavior by A. itadori. Finally, we conducted a field experiment, comparing the effects of foliage age on adult oviposition and nymphal survival. All experiments were conducted using a line of psyllids that have been reared in captivity since their collection from Japan, in 2004 (K1 psyllids). The final two experiments also utilized a line of psyllids collected from the same location more recently in 2019 (K2 psyllids). We observed a reduction in K1 A. itadori nymphal survival on tough F. japonica plants compared to soft plants. Aphalara itadori from the K1 line laid significantly more eggs on young versus old leaves, and survived best on young F. japonica regrowth in the field. Conversely, K2 A. itadori showed no oviposition preference between young and old leaves, and no preference between cut and uncut F. japonica foliage in the field. Our results indicate that recently collected psyllids (K2) may be better able to establish on field-conditioned knotweed in North America than older colonies and highlights the possible effects of long-term rearing on biological control agent performance.