Consequences of Asian citrus psyllid intensive insecticide management strategies on phytoseiid mite assemblages
Abstract: The Asian citrus psyllid (ACP), Diaphorina citri, is one of two known vectors of huanglongbing (HLB), the most destructive disease in citrus. Vector control is considered a basic component for management of HLB. Insecticidal control is still the most commonly used and recommended approach. However, intensive insecticide programs often result in important biological control disruptions. Florida citrus was known to harbor a rich and abundant phytoseiid community before HLB detection in 2005. Ours is the first study that aims to assess effects of recent intensive insecticide programs on these assemblages. Two 3-year experiments were conducted in commercial orange blocks. Three different insecticide ACP management regimens were evaluated and compared to an untreated control in a large scale randomized complete block design with 4 treatments and 4 replicates. Phytoseiid mites assemblages were sampled monthly and adult specimens were determined to species. Effects of specific active ingredients on specific phytoseiid species and on the whole assemblage were tested by comparing numbers before and after each application in treated and untreated plots. Insecticide programs had an overall negative impact on these assemblages by affecting abundance (51.1% reduction) and species richness (35.7% reduction). These effects were nevertheless not reflected in important changes on Shannon diversity index (1.04 ± 0.11 and 0.97 ± 0.05 in untreated and plots under an intensive insecticide program, respectively). While most species were negatively affected by insecticides, some increased after the treatments. These results indicate that insecticide impacts under field conditions were partially determined by complex competitive interactions within the assemblage.