Project : USDA ARS

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Research Project: Mitigation of Invasive Pest Threats to U.S. Subtropical Agriculture

Location: Subtropical Horticulture Research

2023 Annual Report

Objectives
1. Identify semiochemicals that mediate the behavior and physiology of exotic insect pests and develop semiochemical-based tools that lead to products for pest detection, behavioral disruption, and surveillance. [NP 304, Component 4, Problem Statement 4A] 1.A. Document behavioral responses and olfactory chemoreception to semiochemicals that have potential application in pest monitoring and control systems. 1.B. Identify and quantify insect semiochemicals; develop improved systems to collect, analyze and identify semiochemicals. 1.C. Develop synthetic and natural product lures based on host location and/or feeding cues that are formulated for effective use in IPM programs. 2. Evaluate ‘next generation’ technologies to advance methods for fruit fly detection and eradication, such as lasers, sonic methods, or nano-technologies. [NP 304, Component 4, Problem Statement 4A] 2.A. Compare available remote trapping systems that can automatically count and identify trapped insects; optimize automated detection systems for adult fruit fly pests. 2.B. Evaluate imaging techniques and non-destructive chemical analysis methods for detection of larval infestation within host fruit. 3. Evaluate essential oils for natural insect pest toxicants and elucidate the physiological mechanisms underlying resistance to conventional pesticides. [NP 304, Component 4, Problem Statement 4A] 3.A. Determine the molecular/physiological basis for development of pesticide resistance in adult fruit flies. 3.B. Identify plant essential oils and plant extracts that have insecticidal, repellent, or oviposition deterrent properties against adult fruit flies and other target pests. 3.C. Determine the specific chemical components responsible for the toxic/repellent effects of essential oils and plant extracts. 4. Integrate tools, technologies and management strategies to reduce the threat of pest establishment and mitigate the impact of exotic pest incursions. [NP 304, Component 4, Problem Statement 4A] 4.A. Develop new approaches to assess efficacy of lures, repellents, and control practices based on spatial statistics and contour analysis of trap captures in the field. 4.B. Develop improved IPM protocols for tephritid fruit flies, ambrosia beetles, and other target pests by integrating semiochemical-based technologies with other management options, such as biological control, judicious alternating use of insecticides to manage pesticide resistance, sanitation and other cultural practices.

Approach
Research will consist of field and laboratory experiments to investigate aspects of basic biology, physiology and chemical ecology that can be exploited to develop integrated pest management approaches for invasive insects that impact subtropical agriculture. Target species will include pests that threaten to invade or have recently established in south Florida, including fruit flies in the family Tephritidae (Oriental fruit fly, Medfly, and Anastrepha species) and ambrosia beetles that vector fungal pathogens (redbay ambrosia beetle and Euwallacea shot-hole borers). Strategies will include (1) identifying semiochemicals from natural product sources that can alter insect behavior, such as attractants, repellents, and oviposition deterrents; (2) developing new detection and delimitation tools that will include formulated lures, discrete attract-and-kill bait stations, next generation technologies like smart traps for automated pest surveillance, and non-destructive imaging techniques for detection of hidden infestation in agricultural commodities; (3) improving pesticide resistance management by identification of pesticide modes of action and physiological responses of fruit flies to toxicants; (4) evaluating plant essential oils as sources of natural toxicants (biopesticides) with less environmental impact; and (5) developing new approaches to assess efficacy of lures, repellents, and control practices based on spatial statistics and contour analysis of trap captures in the field.

Progress Report
Mediterranean fruit fly, or medfly Ceratitis capitata, is a worldwide pest of fruit crops. Trimedlure is currently the only commercialized attractant used by regulatory agencies world-wide to monitor medfly populations. To develop alternative attractants, ARS scientist in Miami, Florida, developed a thin-layer chromatography assay for separating and assaying fractions of tea tree oil, a known medfly attractant, to develop alternatives. Using gas chromatography coupled with electroantennographic detection and gas chromatography coupled with mass spectrometry, five distinct fractions from tea tree oils were identified and four monoterpenes from fraction 1, and two alcohols from fraction 3 have been identified as attractive to male medflies. Behavioral assays indicated that the two alcohols were more attractive than tea tree oils, and the addition of one monoterpene to the alcohols increased attraction compared to either alcohol alone. These studies are useful for the development of low-cost alternative attractants for medfly management. Caribbean fruit fly, or caribfly, Anastrepha suspensa, is a production pest of guava and other specialty fruits in Florida. Traps baited with food-based lures are used to monitor caribfly populations in fruit fly free zones. As one of the effective means for fruit fly management, oviposition repellents may offer growers alternative control tools with lower cost for control of this pest. ARS scientists in Miami, Florida, in collaboration with ARS scientists in Hilo, Hawaii, are investigating the use of coconut oil derived free fatty acids as caribfly oviposition repellents. Preliminary behavioral assays in the laboratory indicate that the complete fatty acid blend reduces caribfly oviposition for 14 days, and ongoing work is investigating the deterrent effects of six individual fatty acid constituents. This is an ongoing study. The invasive lychee erinose mite, Aceria litchi, is a microscopic and serious pest of lychee fruit trees in Florida. Currently, little is known about the chemical ecology of lychee mites. In collaboration with the University of Florida, ARS scientists in Miami, Florida investigated potential host-based attractants or host defensive compounds induced by mite infestation. Qualitative comparison of the headspace profiles of uninfested and infested lychee plants revealed that six volatile organic compounds nonanal, decanal, limonene, sabinene, ß-caryophyllene, and ar-curcumene were present in samples of infested lychee plants, and the amounts varied from infested plants. Behavioral bioassays showed that the chemical concentration significantly influenced mite attraction, and provide useful information on developing attractive lures for lychee mite management. The hibiscus bud weevil, Anthonomus testaceosquamosus, is an invasive pest attacking flower buds of hibiscus (Hibiscus rosa-sinensis) in South Florida. The volatile organic compounds released by hibiscus plants are responsible for the attraction of the hibiscus bud weevil, and different color cultivars show variation in attraction to this weevil. In collaboration with the University of Florida, ARS scientists in Miami, Florida, investigated volatile compounds from the leaves, buds, and open flowers of different cultivars. In red-flowering cultivars, saturated and unsaturated fatty alcohols and aldehydes were the primary compounds identified in open flower and bud mixtures of alkanes, primary alcohols, aldehydes, and fatty acids were typically highest in leaves. Identification of volatiles from cultivars with pink and yellow flowers are ongoing. The giant African snail, Achatina fulica, is native to Africa and a quarantine pest in southern Florida. The snail has posed significant threat to agricultural production as well as transmitting diseases to human. In collaboration with APHIS, ARS scientists in Miami, Florida, developed a methodology to determine the key components that are emitted by snail for detection by dogs. To identify biomarkers of giant African snail, volatile emissions from four invasive gastropods species (Macrochlamys indica, Bulimulus guadalupensis, Zachrysia provisoria, and Parmarion martensi) were analyzed and the methodology was developed for African snail biomarker analysis. Using this methodology, odor profiles among African snail, Z. provisoria, and M. indica, was varied but shared similarity. This study is currently ongoing. Current surveillance networks for pest fruit flies rely on many static traps baited with synthetic lures that require regular servicing to sort, count, and identify insect captures. Development of automated ‘smart traps’ could reduce program costs and optimize detection systems. Scientists at ARS in Miami, Florida, have developed a prototype automated trap for tephritid flies that photographs the captures and transmits images using Wi-Fi technology to the cloud for processing. However, the development and application of automatic identification algorithms will require large-scale data collection. Collaborations are being sought with scientist in ARS Hilo, Hawaii, researchers in China (NFCA), and a company to facilitate development of automated traps. The current inspection of incoming fruit at US ports of entry for quarantine fruit fly pests is achieved by manually cutting open a small sample (= 2%) of fruit and searching for larvae. Consequently, there is a need for more sensitive, high-throughput screening methods. Scientists at ARS in Miami, Fl, are evaluating imaging techniques and non-destructive chemical analysis methods for detection of larval infestation. Initial experiments using the Cyranose Electronic Nose (eNose) on infested guava identified four VOCs. Further experiments will be conducted to optimize the testing system.Progress was made on Objective 3 as follows: Development of insecticide resistance in tephritid flies is an ongoing challenge. ARS scientists in Miami, Florida, continues to detect and document resistance levels of caribfly in Miami-Dade County, FL. From March to May 2023, wild caribflies were collected and assayed as done in 2022 to determine the median lethal dosage of methomyl to detect the insecticide resistance level. This was then compared to baseline susceptibility to determine the resistance ratio, which was <8 for both males and females. Results indicated that caribfly populations are beginning to develop low levels of resistance to carbamate insecticides. ARS will continue to monitor changes in caribfly resistance levels over time; however, to prevent further resistance development, alternative control strategies will be required. To improve the isolation of plant extracted EO components, high-performance thin-layer chromatography, an efficient, rapid, and convenient tool with low costs, were used for isolation of tea tree oil components that attract male medflies. ARS scientists in Miami, Florida, explored the utilization of high-performance thin-layer chromatography fingerprinting in identifying components in tea tree oils and four other Melaleuca spp. essential oils. Variations were observed in the profile of bands and peak intensity of tea tree oils and Melaleuca spp. The results showed that high-performance thin-layer chromatography can be used as a stand-alone fingerprinting platform for tea tree oils and other Melaleuca essential oils, which facilitated the isolation process. Current management of tephritid fruit flies typically relies on bait systems that incorporate attractants with insecticides. Extensive use of synthetic insecticides has led to an increase of pesticide resistance of these pests. To develop alternative biopesticide, ARS researchers in Miami, Florida, identified plant EO, from three chamomile species, German chamomile (Matricaria chamomilla), Roman chamomile (Chamaemelum nobile), and Chinese chamomile (Chrysanthemum x morifolium) and evaluated their toxicity against caribflies. Results showed that all essential oils showed some mortality against caribfly adults, with the highest toxicity from C. x morifolium oil. The monoterpene compounds (borneol and bornyl acetate) are high in C. x morifolium oil which may contribute to their toxicity. Research is currently ongoing to further identify the active components of C. x morifolium oil against caribflies. Alternative environmentally safe products for control of tephritid fruit flies are urgently needed. Phthalimides are found in both natural and synthetic products with a myriad of biological activities, including toxicity against insects. In collaboration with Marmara University, Turkey, ARS scientists in Miami, Florida, investigated a series of 13 phthalimide derivatives to determine the toxicities against female caribflies. Bioassays showed that three phthalimide derivatives (4a, 4c, and 4d) exhibited potent insecticidal activity against caribflies with median lethal dose values ranging from 0.70 to 1.91 µg/fly. The physicochemical properties of these phthalimides demonstrated that higher lipophilicity tended to show stronger insecticidal activity. This study showed that phthalimides demonstrated potential for development of new biopesticides for control of caribflies. To evaluate efficacy of cultural practices, scientists from University of Florida, in collaboration with ARS, investigated the effect of avocado canopy cover on ambrosia beetle abundance. Monitoring for 12 months indicated that groves with full canopy cover exhibited the highest number of beetles and the lowest light intensity. The opposite was found for topworked and newly planted groves. In addition, solar radiation had a significant effect on beetle dispersal flight. The results indicate that thinning canopy cover, which increases light intensity, suppresses ambrosia beetle abundance in commercial groves, thereby reducing the spread of laurel wilt disease.

Accomplishments
1. Repellents for pest ambrosia beetles. Redbay ambrosia beetle and tea shot-hole borer are vectors of laurel wilt and Fusarium dieback, respectively, two fungal diseases of avocado, woody ornamentals, and native forest trees. Incorporating a repellent into pest management programs may reduce the incidence of these diseases. ARS scientists from Miami, Florida, identified piperitone as a new beetle repellent and compared its efficacy to two other repellents, verbenone and a-farnesene. Beetle captures in traps baited with lures were compared to those containing lures plus a repellent (a push-pull design). Results showed that farnesene was ineffective; however, piperitone and verbenone were equally effective, reducing captures by 50-70% for 10-12 weeks. Since piperitone is less expensive than verbenone, the standard beetle repellent. This study identifies an economical alternative for management of the two beetles with push-pull design in commercial avocado groves.

2. Identification of host kairomones for lychee erinose mite. The invasive lychee erinose mite (LEM, Aceria litchii) is a serious pest of lychee fruit trees in Florida. This tiny mite lives mainly on the underside of the leaves, preventing flowering and fruit production. Currently, little is known about the chemical ecology of LEM and no known attractants or repellents exist. In collaboration with the University of Florida, ARS scientists in Miami, Florida, investigated potential host-based attractants or host defensive compounds induced by LEM infestation. Qualitative comparison of the headspace profiles of uninfested and infested lychee plants revealed that six volatile organic compounds (VOCs) nonanal, decanal, limonene, sabinene, ß-caryophyllene and ar-curcumene were present in almost all samples of uninfested and infested lychee plants. Behavioral (olfactometer) bioassays with these six VOCs demonstrated that with these six VOCs, the chemical concentration significantly influenced LEM attraction, which was typically the most attractive at lower concentrations. The findings of this study provide useful information on the development of a field lure that can be used in pest management programs for LEM.

3. Effect of entomopathogenic fungus Metarhizium anisopliae on morphological changes of insect. Biological control using the entomopathogenic fungus M. anisopliae has shown potential for management of various insect pests, including tephritid fruit flies. Destruxin A (DA) is a mycotoxin isolated from M. anisopliae, but the mechanism of toxicity against insects remains unknown. To better understand the mode of action of DA, scientists from Guangdong Academy of Agricultural Science (China) and USDA-ARS in Miami, Florida, used histopathological methods to investigate the effect of DA on target cells and tissues of the silkworm Bombyx mori. At low doses (i.e., 0.01µg/g), the hemocytes were the most sensitive to DA. At higher doses (i.e., > 0.1µg/g), the muscle cells, fat body, and Malpighian tubules showed morphological changes 24 h after treatment. This study elucidated the target sites in B. mori that responded to DA treatment, indicating that the defensive hemocytes were the first cells damaged. The results of this study will help develop mycopesticides and novel immunosuppressants for improved management of tephritid fruit fly pupae.

4. Identified new plant based toxicants against the Caribbean fruit fly. Tephritid fruit flies are among the most serious agricultural pests worldwide. Current management typically relies on bait sprays or bait stations that incorporate insecticides, but concerns have been raised regarding the adverse effects on the environment and increased insecticide resistance of the pest. To develop environmentally friendly alternative biopesticides, ARS researchers in Miami, Florida, evaluated plant EOs extracted from three species of chamomile plants, commonly used in therapeutic applications, German chamomile (GC, Matricaria chamomilla), Roman chamomile (RC, Chamaemelum nobile) and Chinese chamomile (CC, Chrysanthemum x morifolium). Results showed that CCEO demonstrated the most significant insecticidal activity against caribfly female adults. This study discovered that CCEO is a promising source of potential alternative pesticides for CFF.

5. Discovered novel toxicants against the Caribbean fruit fly. Natural products with insecticidal effects against insect pest have the potential as alternatives to synthetic insecticides for pest control. Phthalimides (isoindoline-1,3-diones, and their N-substituted analogs), are found in natural products, can be synthesized in the laboratory, and have demonstrated biological activities including insecticidal attributes. In collaboration with Marmara University, Turkey, ARS scientists in Miami, Florida, investigated 13 phthalimide derivatives for their toxicities against female caribflies. Results showed that three phthalimide derivatives (4a, 4c, and 4d) exhibited potent insecticidal activity against caribflies with LD50 values ranging from 0.70 to 1.91 µg/fly. The physicochemical properties of these phthalimides demonstrated that higher lipophilicity tended to show good insecticidal activity. This study revealed key structural features responsible for the insecticidal activity and can be promising for the development of new biopesticides.

6. Vibrational communication identified in the spotted lanternfly. The spotted lanternfly Lycorma delicatula, is a polyphagous insect pest that invaded the United States in 2014, in Berks County, Pennsylvania, and has since spread to several northeastern states threatening the agriculture production of many crops. ARS scientists from Miami, Florida, in collaboration with scientists from USDA-APHIS, demonstrated that adult and fourth-instar L. delicatula are attracted to broadcasts of 60-Hz acoustic/vibrational stimuli in the laboratory. This finding expanded the current knowledge on a wider frequency that is attractive to L. delicatula. This study suggests that a vibroacoustic trap may be developed for management of L. delicatula in the field.

U.S. DEPARTMENT OF AGRICULTURE

Subtropical Horticulture Research: Miami, FL