Population Fluctuations of Diaphorina citri and Its Natural Enemies in Response to Various Management Practices in Florida

Abstract

The Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae), is a serious threat to citrus production because it transmits the bacterium, Candidatus Liberibacter asiaticus Jagoueix (Hyphomicrobiales: Rhizobiaceae), that causes huanglongbing. Currently, there is no cure for huanglongbing, and vector management is implemented to reduce the spread of pathogen. In Florida, calendar-based insecticide application had been used widely for D. citri management, but the evolution of insecticide resistance in D. citri and associated reductions of natural enemy populations mandate more sustainable approaches. The objective of our study was to compare the effects of organic management versus intermittent use of conventional insecticides on population suppression of D. citri by natural enemies in Florida. We conducted a survey of natural enemies in citrus groves that were managed organically versus intermittently treated with conventional insecticides from Mar to Dec 2019. We also compared mortality of D. citri in those groves by deploying sentinel psyllids on leaf flush with or without exclusion cages. The abundance of natural enemies was recorded by visual observations made on tree branches for 2 min intervals. Finally, we estimated tree flush density and monitored adult D. citri populations. Survival of sentinel D. citri was significantly lower on uncaged flush when natural enemies had access to eggs and nymphs during spring, summer, and fall in organic groves; however, such a difference was not observed between caged and uncaged D. citri in intermittently sprayed groves, particularly during summer and fall. Similarly, organic sites had lower numbers of adult D. citri compared to intermittently sprayed sites throughout most of the sampling period, suggesting that natural enemies contributed to regulation of D. citri populations in organic groves more so than in the intermittently treated conventional groves. The most common natural enemies found were Coccinellidae, Chrysopidae, Formicidae, Eulophidae, Syrphidae, Dolichopodidae, and Arachnida. Among these groups, formicids were most abundant in organic groves, whereas dolichopodids and coccinellids were most abundant in intermittently managed groves. Our results suggest that intermittent spraying for D. citri with conventional insecticides could affect activity of natural enemies even though such practices did not entirely eliminate their populations.