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Research Project: Integrated Management of South American Pests and Weeds

Location: Office of International Research Engagement and Cooperation

2022 Annual Report

Objective 1: Conduct research on the systematics, biodiversity, and taxonomy of insects, pathogens and plants that are pests, or potential pests, of the Nation’s crops and natural ecosystems, as well as insects and microbes that are natural enemies of invasive pests. Especially those that show promise to be developed as biological control agents. Objective 2: Develop biological control programs for invasive plants threatening the US environments and agriculture, through the discovery, identification, efficacy testing, and safety testing of new biological control agents. This objective implies conducting faunistic and pathogen inventories to discover natural enemies that may serve as biological control agents for target species. It also involves studying the ecology and population dynamics of targeted weeds and their potential arthropod and pathogen biological control agents, and investigate the impact of weed suppression on community and ecosystem structure and function. Objective 3: Develop biological control programs for invasive arthropods threatening U.S. environments and agriculture, through the discovery, identification, efficacy testing, and safety testing of new biological control agents. Again, this involves conducting faunistic and pathogen inventories, as well as elucidating the biology, ecology and population dynamics of target insects and their potential arthropod and pathogen biological control agents. Objective 4: Conduct risk analyses to determine the environmental safety of new and existing potential biological controls, and investigate the impact of insect and plant suppression on community and ecosystem structure and function. This objective requires identifying the biological and physical parameters that affect the efficacy and safety of potential agents, including climatic conditions, host specificity, effective rearing conditions, and biogeography.

Many of the invasive plants and arthropods in the United States are of South American origin, introduced without natural enemies from their native habitat. These organisms invade natural and agricultural communities, causing the disruption of ecosystem processes necessary for the sustenance of urban, agricultural, and natural areas. The research program at FuEDEI (ex-SABCL) aims at achieving long-term sustainable management of these invaders. Its Project Plan approved by OSQR in 2020 includes target weeds: the water fern (Salvinia molesta) commonly known as giant salvinia, Brazilian peppertree (Schinus terebinthifolius), Brazilian waterweed (Egeria densa), water primrose (Ludwigia hexapetala), water lettuce (Pistia stratiotes) and waterhyacinth (Pontederia crassipes ex-Eichhornia crassipes). Insect targets are cactus moth (Cactoblastis cactorum), little fire ant (Wasmannia auropunctata), Harrisia cactus mealybug (Hypogeococcus pungens), imported fire ants (Solenopsis invicta and S. richteri) and the Tawny crazy ant (Nylanderia fulva). The basic approach consists of the discovery, development, and release of natural enemies, and other biologically-based techniques such as semiochemicals. Research is required to determine the exact identity of both the invaders and their natural enemies, where to search for natural enemies of these invasive species, which of the various natural enemies are safe to import, and what effect such introductions could have on the invaded community. Long-term, sustainable, biological-control-based management of invasive species will result in the reduction of pesticide use, and provide landscape-level suppression of the targets. These research efforts will contribute to the recovery and rehabilitation of natural ecosystems and conservation of native species.

Progress Report
3a. Under Objective 1, Subobjectives 1.1 and 1.2: Currently, there are three candidates under study to control water primrose: a planthopper called Pissonotus paraguayensis -recently re-described-, for which biology and rearing methodology have been developed. Flea beetles of water primroses described as one species, appear to be a complex in the genus Lysathia. They are being studied morphologically and with molecular tools to discriminate what seem to be several cryptic species. Genetic analysis through mitochondrial DNA sequencing of the cactus moth (Cactoblastis cactorum) showed patterns of genomic variation across its native distribution. We integrated a demographic modeling approach for inferring gene flow and divergence time between cactus moth populations. Results revealed significant population genetic structuring across the native range, suggesting non-random mating populations related to a combination of persistently suitable environmental conditions and host plants during both interglacial and glacial periods. In order to develop an integrated management plan for the vector of Huanglongbing (HLB or Citrus Greening, the genetic variation of the Asian psyllid Diaphorina citri and its ectoparasitoid, Tamarixia radiata (Hymenoptera: Eulophidae) were investigated; 54 samples of D. citri and 40 of T. radiata were collected during 2021 and 2022. These samples are being sequenced in order to characterize the haplotypes present in the country, and establish genealogical relationships and correlations between the vector and the parasitoid. The population structure of D. citri and T. radiata could be associated with ecological, behavioral, geographic and climatic differences. In addition, for the vector it could indicate plasticity to colonize new regions, while for T. radiata it could have differential parasitism capabilities. With these results, a powerful selection criterion could be recognized to massively breed a certain haplotype to release it and control the HLB vector. A new species of Megamelus was found on a plant related to water hyacinth, which is probably a new species for science and is being described. 3c. Under Objective 2, Subobjectives 2.1: The effect of genetic structure on the success of Megamelus scutellaris are being assessed on native populations. We collected adults from 50 sites in different wetlands of Argentina and Paraguay to extract DNA. Preliminary results suggest different haplotypes show differing reproductive success. The relationship between genetics, endosymbionts responsible for efficient feeding, and climate, are also being analyzed. Three new candidate biocontrol agents against water primroses (Ludwigia spp.) are under study: a planthopper called Pissonotus paraguayensis -recently re-described-, for which biology and rearing methodology have been developed; a flea beetle complex in the genus Lysathia, and the fruit-feeding weevil Tyloderma nigromaculatum, for which a rearing protocol is in the works. The host ranges and distribution of these herbivorous species are being assessed through field surveys throughout southern and central Argentina, through the inspection of related plants in the field, and laboratory experiments. Under Objective 2, Subobjectives 2.2: In 2020 FuEDEI started working in cooperation with the USDA-ARS Wheat, Peanut, and Other Field Crops Research lab in Stillwater, OK, to study if there are different peanut smut strains, and their distribution in Argentina. This pathogen is a grave risk for peanut production in the US, and this information is critical to devise a disease management strategy and for the development of resistant peanut cultivars. Molecular techniques relying on DNA extraction require amounts of pathogen biomass which cannot always be found in the field. This led us to develop a process to cultivate the pathogen in vitro, allowing us to a) obtain enough pathogen biomass for DNA extraction and sequencing b) obtain pure cultures of the fungus to study its life cycle and c) keep lab cultures independent from field samples. A first batch of DNA samples from different fields in the peanut-producing region in Argentina has already been shipped to our collaborators in the US, and more will be sent when fresh peanut samples are obtained in harvest season. Furthermore, FuEDEI is conducting field surveys to study pathogen incidence on wild species of peanuts, since southern South America is considered the center of radiation of this plant, and of its pathogens. In addition, this could provide a valuable resource to develop smut-resistant commercial peanut varieties. 3d. Under Objective 3: Harrisia Cactus Mealybug (HCM) is a biocontrol target aimed at protecting native Puerto Rican cacti. Two parasitoid species from Argentina and Paraguay, Anagyrus cachamai and Anagyrus lapachosus have been found in Argentina and Paraguay. They have been introduced in quarantine facilities in Puerto Rico to establish laboratory colonies. Under Objective 3, Subobjective 3.1: The two parasitoid species of HCM from Argentina and Paraguay have been tested on native mealybugs native host range, and experimental host range tests performed in Argentina showed that both parasitoids were restricted to species of Hypogeococcus. A native parasitoid of cactus moth, Goniozus legneri, is under evaluation, assessing attack rates under semi-field conditions, exposing different densities of larvae to female parasitoids. These studies may provide evidence of the ideal release rates for best moth control. G. legneri does not establish in nature, and will thus likely be used in inundative biocontrol programs.

1. Peanut smut cultivation. Peanut smut is a grave disease of peanuts that threatens peanut production worldwide. In order to develop resistant peanut cultivars, we must assess the variation of smut strains. For this, large quantities of the pathogen need to be lab cultured. Until now there were no published papers on peanut smut cultivation, and the reports that exist proved to be incomplete and unreliable. A reliable cultivation method was developed using standard culture media supplemented with peanut peg extracts. This is a major step toward getting to know the pathogen, and managing its impact and spread.

2. Social acceptance for biocontrol. Working the complicated permitting and qualification processes of South American administrations requires building trust with local authorities. Involvement with education and community politics is crucial to these objectives. FuEDEI was awarded a United Nations Development Programme (UNDP) grant together with the National University of Hurlingham (Province of Buenos Aires, Argentina), to support education in biological control and IAS (invasive alien species) in secondary schools. This implies official recognition for FuEDEI as a nationwide leader in biological control.

3. Water primrose. Invasive water primroses (Ludwigia spp.) threaten fresh water waterways in western US and their fauna and flora by covering whole stretches of rivers and lakes. Biological control is probably the only efficient and definitive way of controlling this weed. A rearing method for the planthopper Pissonotus paraguayensis, a promising potential biocontrol agent, was developed. Several agents tested in Argentina for water primroses have been in the shipped to the USA in the last four years, but they were all found to be not specific enough, as they fed on several closely related water primrose species native in the USA. So far this planthopper shows promise and seems to be more specific than previous insects, but a reliable rearing method needed to be cleared first.

4. Insect shipments. In the last year we sent a total of nine insect shipments to collaborators abroad.