Abstract
The Asian citrus psyllid, Diaphorina citri Kuwayama, is the insect vector of the pathogen causing huanglongbing. We selected three botanical oils to evaluate behavioral activity against D. citri. In laboratory olfactometer assays, fir oil was repellent to D. citri females, while litsea and citronella oils elicited no response from D. citri females. In choice settling experiments, D. citri settled almost completely on control plants rather than on plants treated with fir oil at a 9.5 mg/day release rate. Therefore, we conducted field trials to determine if fir oil reduced D. citri densities in citrus groves. We found no repellency of D. citri from sweet orange resets that were treated with fir oil dispensers releasing 10.4 g/day/tree as compared with control plots. However, we found a two-week decrease in populations of D. citri as compared with controls when the deployment rate of these dispensers was doubled. Our results suggest that treatment of citrus with fir oil may have limited activity as a stand-alone management tool for D. citri and would require integration with other management practices.
Highlights
The Asian citrus psyllid, Diaphorina citri Kuwayama, is the vector of the causal agent of the pathogens causing huanglongbing (HLB)
D. citri females were significantly repelled by fir oil at both the 5 and 15 mg doses; their behavior was not affected by litsea oil or citronella oil vs. ethylene glycol (Table 1)
After modifying the assay to use intact, undamaged citrus seedlings in place of crushed citrus, we found that fir oil repelled D. citri at the 15 mg dose, but not at the 1 or 5 mg doses, as compared with undamaged citrus odor (Table 2)
Summary
The Asian citrus psyllid, Diaphorina citri Kuwayama, is the vector of the causal agent of the pathogens causing huanglongbing (HLB). HLB is the most damaging disease of citrus worldwide. HLB, known as citrus greening disease, causes yellowing of shoots, stem dieback, sour fruit, crop losses and eventually tree death [1,2]. The causal agent of this disease in the USA is presumed to be the bacterium, Candidatus Liberibacter asiaticus (CLas) [3], and is transmitted from plant to plant through the movement and feeding of adult D. citri [4]. The impacts of HLB on the Florida economy are dramatic. 80% of citrus is infected with the pathogen [6] and the 2015–2016 citrus yield in Florida decreased by approximately 30% compared to the previous year, and is the worst season for this citrus industry in 50 years
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