Spatial distribution of Diaphorina citri (Hemiptera: Liviidae), its natural enemies, and biotic mortality in citrus groves

Diphorina citri, Asian citrus psyllid (ACP), is an economically important pest and vector of huanglongbing (HLB) disease. Therefore, its management is critical. ACP adults flying into citrus blocks are likely to colonize the border trees first and use those as a breeding ground before further spreading into the block. These colonization and distribution patterns may have implications for psyllid management. Therefore, four commercial citrus groves were investigated in southwest Florida between 2020 and 2022. Stem tap, suction, and yellow sticky trap methods were employed to sample ACP and natural enemies in the block border and interior. Exclusion techniques were employed to evaluate biotic mortality in the developing colonies of psyllid immatures in the block border and interior. In the border of the blocks, psyllid populations were doubled compared to the interior averaging 0.11 and 0.04 per tap sample, respectively. More psyllids were also observed in the border than interior with sticky traps and suction sampling methods. The common predators were ladybeetles, lacewings, spiders, and ants, which were also high in the border but common throughout the block. The exclusion experiments revealed biotic mortality of 50-90% throughout the block. Findings suggest that block borders can be treated with sprays of insecticides more often than the interior for greater suppression of ACP and to conserve beneficial insects. Spraying the entire citrus block may not be cost-effective and cause more harm to beneficial organisms such as predators and parasitoids, much needed for controlling citrus pest complex including ACP.