Positive Interactions between Aceria pallida and Bactericera gobica on Goji Berry Plants

Simple Summary The gall mite Aceria pallida can be phoretic on the psyllid Bactericera gobica to overwinter. Phoresy is often considered as a pattern of phoront-vector mutualism. The phoront A. pallida benefits from phoresy during the overwintering season, but no advantages to the vector B. gobica were found during this period. Therefore, this mutualism may occur during the growing season. Because both species share the same host plant and habitat after detachment, interspecific interactions are very likely to occur. To determine whether such interactions were positive or negative, we studied relationships between A. pallida and B. gobica egg abundances on leaves. Our study suggests positive interactions between two pests during the growing season. Outcomes of positive relationships between gall diameter and mite abundance in the gall provided a way to rapidly estimate mite abundances in the field by measuring gall diameters. The gall mite Aceria pallida and the psyllid Bactericera gobica are serious Goji berry pests. The mite can be phoretic on the psyllid to overwinter, but it is unclear whether the vector can obtain benefits from the phoront during the growing season. After detachment, the mite shares the same habitat with its vector, so there are very likely to be interspecific interactions. To better understand whether the interactions are positive or negative, information on relationships between abundances of A. pallida and B. gobica on leaves is needed. Here, B. gobica abundance was represented by the egg abundance because the inactive nymphs develop on the same sites after hatching. (1) We found a positive linear relationship between the gall diameter and the mite abundance in the gall (one more millimeter on gall diameter for every 30 mites increase), which provided a way to rapidly estimate mite abundances in the field by measuring gall diameters. (2) There was a positive relationship between the abundance of mites and psyllid eggs on leaves. (3) Both species had positive effects on each other's habitat selections. More importantly, the interactions of the two species prevented leaf abscission induced by B. gobica (leaf lifespan increased by 62.9%), increasing the continuation of the psyllid population. Our study suggests positive interactions between two pests during the growing season. The positive relationship between A. pallida and B. gobica egg abundances highlights the increasing need for novel methods for Goji berry pest management. In practice, A. pallida control can be efficient by eliminating its vector B. gobica. Both pests can be controlled together, which reduces chemical usage.