2019-11_18-056C – Functional IPM for Asian citrus psyllid under circumstances of chronic HLB.

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

Report Date: 12/15/2019
Project: 18-056C   Year: 2019
Category: ACP Vector
Author: Lukasz Stelinski
Sponsor: Citrus Research and Development Foundation, Inc.

Objective 1: Compare the effectiveness of biological control in commercial orchards in FL and determine if abiotic factors or management practices influence effectiveness. Use this knowledge to improve the effect of biological control.
The goal of this research is to better understand the contribution of natural enemies on ACP population regulation among citrus groves characterized by differing management inputs in Florida. Two ACP management practices were compared: i) Organic and ii) Low input (2-4 annual sprays) conventional insecticide treatment. Trees were 10-12 year old sweet orange ‘Valencia’. The study was conducted in 2019 form March to June (Spring) and July to September (Summer). We released two pairs of ACP sentinels with and without exclusion cages to measure mortality of ACP cuased by natural enemies. The number of living and dead ACP were counted for three weeks after deployment. We also monitored abundance of ACP and natural enemy abundance in all groves. Natural enemies were recorded during 2-minute visual inspections. Sixteen trees were sampled at each site per sampling date. Tap samples were used to monitor the abundance of ACP. Numbers of ACP adults were monitored weekly by sampling twenty trees per replicate block per week. Mortality of uncaged sentinel ACP was higher than that of psyllids within exclusion cages indicating that natural enemies were killing ACP. Mortality of uncaged ACP was significantly higher than caged ACP during summer in organically managed groves, but not so in conventionally treated groves. Among the natural enemies collected, spiders were most prevalent followed by Dolichopodid flies and coccinellids (lady beetles). Adult ACP populations were significantly higher at sites that were intermittently sprayed with conventional insecticides than in organically managed groves throughout the season. Populations of natural enemies were similar in groves sprayed intermittently with conventional insecticides vs. groves managed organically and without use of toxicants for ACP. However, populations of ACP adults were higher in conventionally treated than organic groves. These results suggest that the level of insecticide input was insufficient to reduce ACP populations, but may have negatively impacted the effect of biological control even though we could not document this directly by survey of natural enemy densities. Our results also suggest that ACP populations can be regulated more effectively by the action of natural enemies than by intermittent spraying under conditions of endemic HLB where curtailing spread of disease is not intended.

Objective 2. Revise insecticide resistance management for psyllid IPM in new plantings
In order to effectively implement resitance management, we have to understand the mechanisms causing it. We therefore initiated a global transcriptome-based analysis of Asian citrus psyllid (ACP) involved in the neonicotinoid resistance using bioinformatics techniques coupled with high throughput RNA-sequencing. First, we conducted insecticide toxicity bioassays on ACP collected from two field populations where neonicotinoid insecticides were used considerably. We used the leaf dipping bioassay technique to determine the level of existing resistance to thiamethoxam at these two sites. We determined that the populations of ACP were 1,394 and 1,266 times less sensitive to thiamethoxam at these two locations as compared with our laboratory susceptable control population. Therefore, we collected adult ACP samples from these to locations for analysis and also from the laboratory susceptible population as a comparison. These sample were immediately frozen and stored at -80°C. Then the total RNA was extracted from these samples using Trizol according to the manufacture’s protocol. RNA samples of acceptable quality were used to construt non-strand-specfic sequening libraries with the TruSeq RNA sample prep kit. These libraries were sequenced using the PE150 mode on an Illumina HiSeq 3000 platform at GENEWIZ. We are in the process of analyzing and interpreting these data. We believe that this transcriptomic profiles will contribute to a comprehensive understanding of the mechnisms of neonicotinoid resistance in ACP. In the future, we will analyze data by mapping to the ACP referrence genome and compare differential gene and transcription factor expression between susceptable and resistant ACP populations. To date, our results indicate that increased cytochrome P450 metabolic detoxification is the mechanism responsible for ACP resistance to neonicotonoids. However, some of our recent findings also suggest that target site insensitivity should be re-investigated; it is possible that over 12 years of selection pressure (continued insecticide application), the mechanism by which ACP are developing resistance could have changed. Understanding this possible shift will allow us to continue to develop the best possible rotation schedules for mitigating resistance.

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