Influence of biological control and ant tending on citrus mealybug (Planococcus citri) in California’s Central Valley

Citrus mealybug, Planococcus citri, is a cosmopolitan pest known to damage commercial citrus in Coastal and Southern California. The species has been present in California’s Central Valley since the late 1980’s, but has only caused minor and sporadic harm in the region. It is unclear why citrus mealybug failed to establish as an economic pest, but it is likely due to the action of biological control agents such as lady beetles, lacewings, and Anagyrus and Leptomastix parasitic wasps. Beginning in 2019 Central Valley citrus mealybug populations grew to economically damaging levels, resulting in losses for lemon, navel, and grapefruit growers. This uptick in mealybug activity coincides with an increase in ant activity in citrus orchards as well as the 2020 California ban of chlorpyrifos, the primary ant management tool in the state. Ant tending is known to reduce biological control of citrus pests in Southern California, but there is no data regarding mealybug biological control or tending ant species in the Central Valley. To address this knowledge gap, we sampled citrus mealybug populations in three Central Valley citrus orchards over the 2024 growing season. Here we present findings from this first field season including: 1) the identity of citrus mealybug associated biological control agents and tending ant species. 2) The impact of biological control agents on mealybug populations as measured through colony netting. And 3) quantification of the influence of ants on biological control activity via ant exclusion trials. Work funded by the Agricultural Research Institute and Citrus Research Board.