Comparative fitness of invasive and native populations of the potato psyllid (Bactericera cockerelli)

Two genetically distinct potato psyllid populations [Bactericera cockerelli (Sulc) (Homoptera: Psyllidae)] were identified in our previous study: native and invasive. The invasive population, ranging from Baja, Mexico to central California, was the result of a recent invasion, while the native population is endemic to Texas. The native (Texas) and invasive (California) populations were collected from tomato and pepper, respectively, and were examined on both hosts to test the comparative fitness of invasive populations. Our results indicated that on both plant hosts, psyllids from the native range demonstrated higher survivorship, a higher growth index, and shorter development times than the psyllids from invasive populations. The fecundity of the native-range psyllids also was significantly higher than that of invasive psyllids on tomato, but not on pepper. For the native population, host plant differences for all fitness measurements were not significant. However, within the invasive population, psyllids feeding on tomatoes showed consistently better survivorship and a higher growth index than those feeding on pepper, despite the decreased developmental time required on peppers. The LC50 values (concentrations causing 50% mortality) of both populations were determined for three pesticides. Resistance to two of these pesticides was found in the invasive population. Thus, the invasive quality of the California populations may be related to increased pesticide resistance. However, it is impossible to determine if the California population was preadapted to pesticide resistance, or if the resistance developed after the range expansion and is simply a contributing factor to maintaining the expansion.