Functional IPM for Asian citrus psyllid under circumstances of chronic HLB.

Functional IPM for Asian citrus psyllid under circumstances of chronic HLB.

Report Date: 12/15/2020
Project: 18-056C   Year: 2020
Category: ACP Vector
Author: Lukasz Stelinski
Sponsor: Citrus Research and Development Foundation

Objective 1: Survival of sentinel Asian citrus psyllids (ACP) was substantially higher, as compared to sentinels that could be accessed by natural enemies, in organic groves. ACP nymphs are suitable prey for a wide range of generalist predators. Although natural enemies may have occurred at lower densities in organic than conventional groves during our survey, our exclusion cage experiments indicated an overall effect of natural enemies on mortality of ACP in organic than conventional groves. It is also possible that cryptic or nocturnal predators could have contributed to the difference in predation observed between treatments in our exclusion cage experiments. For example, adult syrphid flies are nocturnal and larvae are cryptic as well as active mostly during dusk and dawn (Hagen et al., 1999), which may have been overlooked during our visual observations. In future studies, we could improve the sampling of natural enemies using additional methods such as sticky traps or vacuums, in addition to visual observations in order to better estimate natural enemy populations. Further investigations elucidating the impact of ants and their interaction with generalist predators on biological control of ACP could further improve management practices for this insect vector. The current study suggest that intermittent applications of insecticides sprays for management of ACP could sufficiently disrupt activity of  natural enemy populations to reduce normal population regulation of ACP, even if populaitons of natural enemies are not eliminated entirely populations. In constrast, undesurbed populations of natural enemies in organically managed groves in Florida can maintain populations of ACP at levels lower than observed in nearby conventional groves. Objective 2: Continuous selection imposed on a field-collected population of ACP with fenpropathrin for ten generations caused development of moderate to high levels of resistance (96.67-fold). Our investigation revealed that ACP has the capacity to develop a high level of fenpropathrin resistance as a result of continuous and persistent selection. Given the apparent lack of cross resistance between pyrethroids and other commonly used modes of action against ACP such an organophosphates and neonicotinoids, mode of action rotation should remain an effective model for managing resistance in D. citri as demonstrated in field studies. Expression variability analysis of detoxification related genes indicates that elevated levels of CYP enzymes are associated with fenpropathrin resistance. Furthermore, our results specifically implicate the CYP6A2-1 gene with fenpropathrin resistance. Objective 3: ACP populations develop high levels of resistance to thiamethoxam under continuous selection by label rate applications in cultivated citrus. A high level of resistance occurred following only 3-4 consecutive neonicotinoid sprays and within five egg to adult generations and was associated with subsequent product failure. We also showed that resistance in ACP to thiamethoxam declined significantly in the absence of selection pressure under laboratory conditions and when modes of action rotation was implemented after initially selecting for resistance under field conditions. Recovery to a susceptable state under rotation in the field was more rapid than under no selection in the laboratory population. These results suggest that thiamethoxam resistance is likely unstable under the field conditions. Collectively, our results indicate that rotation of thiamethoxam with insecticides from other chemical classes, including cyantraniliprole, fenpropathrin, dimethoate, spinetoram and diflubenzuron should mitigate neonicotinoid resistance in areas where ACP are managed with insecticides.   


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