Research Project: Integrated Management of South American Pests and Weeds

Location: Office of International Research Engagement and Cooperation

2023 Annual Report

Objectives
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.

Approach
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
The aggressive water invaders Ludwigia grandiflora and L. peploides are native from southern South America where they show a great variability and adaptability to colonize different environments. Efforts are currently concentrated on a planthopper, Pissonotus paraguayensis, and a flea beetle, Lysathia flavipes, for biological control. Molecular analyses indicate that L. flavipes has greater morphological variability but is still grouped in one species. However, a small population that separates from L. flavipes is probably a new undescribed species. Comparisons were also made with a North American Lysathia species, and a Brazilian species utilized to control M. aquaticum in South Africa. A combination of genome-wide SNP data and mtDNA of a planthopper, (Megamelus scutellaris), used as a biological control agent of water hyacinth (Pontederia crassipes) in the U.S., were used to evaluate genetic diversity and phylogeographic patterns in Argentina and Paraguay. Mitochondrial data shows two main haplogroups among sampled populations. Genome-wide SNP data support the presence of three main lineages that are congruent with the mitochondrial haplogroups. These results would indicate that the M. scutellaris populations introduced in South Africa and the U.S most likely belong to different lineages, which is useful to choose the most suitable populations for release. Surveys conducted in central-western Argentina on Pampa’s grass revealed the presence of an unidentified flower-feeding moth (Gelechiidae). Surveys also revealed the presence of a seed-feeding midge, Spanolepis selloane (Diptera: Cecidomyiidae). This midge has been observed to cause a lot of seed mortality in Spain and Portugal. Future efforts will focus on conducting additional surveys to find additional potential biocontrol agents. The cactus moth, Cactoblastis cactorum (CM), is native to South America and invasive in North America, where it threatens wild and cultivated native Opuntia cacti. Cactus moth and related species are being studied to understand the evolutionary processes involved in diet changes in these phytophagous insect species with different trophic ranges. Harrisia Cactus Mealybug (HCM) is a scale insect that has been causing extreme damage to endemic threatened cacti in Puerto Rico. The geographical distribution of HCM as well as the composition of primary and secondary parasitoids in Puerto Rico were studied. Quarantine colonies of the potential biological control agents A. cachamai and A. lapachosus were mass reared at the University of Puerto Rico. Results so far indicate the parasitoids would only attack the target pest. The tawny crazy ant (TCA) is a damaging South American ant that has invaded the U.S. from Texas to Florida. The distribution and abundance of the three species of Nylanderia found in Argentina have been clarified. One of the species was recorded for the first time in Argentina. Only one of the three native lineages of N. fulva was introduced in the U.S. Imported fire ants (IFA) have a parasitic ant in the same genus known as Solenopsis daguerrei. However, recent research determined this species to be several cryptic species with variable host specificity. This may explain why previous attempts to transfer this parasitic ant to colonies of S. invicta failed. In 2020, collaboration with the USDA-ARS lab in Stillwater, Oklahoma began to study peanut smut strain variability and distribution in Argentina. This pathogen is a grave risk for peanut production in the U.S. Peanut smut samples from 76 sites were collected from Argentina to compare their DNA sequence. In order to obtain large quantities of DNA, a laboratory culture technique was developed in plates and liquid media to produce large numbers of fungal spores. Cultures obtained through these methods are undergoing morphological studies in cooperation with the USDA-ARS in Ft. Detrick, Maryland. Citrus greening (HLB) is a disease produced by a bacteria transmitted by an Asian psyllid, Diaphorina citri. The parasitoid, Tamarixia radiata, used to control the vector has several genetic variants (haplotypes) that show ecological and behavioral differences in their capacity to attack the Asian psyllid. The analyses of 54 sequences of D. citri from 52 samples in 10 northern Argentine provinces confirmed there is a single population (haplotype) of the vector in Argentina. On the other hand, a diversity study from over 40 sequences of this parasitoid from Argentina and the U.S., indicate a highly diverse, but unclear, variety of parasitoid populations. Insect populations of M. scutellaris from Paraguay and Argentina have been introduced into the U.S. Differences in their performance have been reported across seasonal temperatures. The water hyacinth petiole miner fly, Thrypticus truncatus, is being reconsidered as a biocontrol agent. Petioles with mines were sampled every two weeks in delta Buenos Aires from December 22 to June 23, concentrating on developing efficient laboratory rearing techniques. Larval mines were obtained in garden pools with water hyacinth, but it is still not possible to rear it in controlled conditions, as oviposition was not achieved. To investigate the potential impact of natural enemies on water primrose, differences between the morphology and damage of the plants in their native and invaded range are being quantified. After additional surveys, the distribution of water primrose in Argentina is being analyzed in niche modeling to assess potential areas of distribution and climatic matching for future control agents. The effect of genetic structure on the success of Megamelus scutellaris is being assessed on native populations. Preliminary results from collected adults from 50 sites in different wetlands of Argentina and Paraguay suggest different haplotypes with differing reproductive success. The relationship between genetics, endosymbionts, and climate, are also being analyzed. Three new candidate biocontrol agents against water primroses (Ludwigia spp.) are under study: a planthopper (Pissonotus paraguayensis); a flea beetle complex in the genus Lysathia; and a fruit-feeding weevil (Tyloderma nigromaculatum). The host ranges and distribution of these herbivorous species are being assessed through field surveys. Host range tests on the plant hopper Pissonotus paraguayensis are in progress. So far, the plant hopper has been tested on several species in the genus Ludwigia and showed to be restricted to four species of water primrose. It is not certain at this point if this level of specificity would be adequate in the U.S. Giant salvinia is an aquatic fern native to South America that is invasive in most tropical and subtropical areas of the world. The aquatic weevil Cyrtobagous salviniae is an effective natural enemy of giant salvinia in several U.S. states. However, the plant is invading more temperate areas with harsher winters where weevil populations cannot establish and overwinter. Cold-hardy strains of the weevil from southern South America shipped to facilities at LSU proved they could survive Louisiana winters and serve to attain biological control in colder regions. Approval for field release has been granted by APHIS, and a laboratory colony is being maintained at FuEDEI, waiting to be shipped to quarantine facilities in August 2023. 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. A specific parasitoid wasp of CM (Apanteles opuntiarum) is being mass reared in quarantine at Gainesville, Florida. Annual parasitoid shipments from Argentina are added to the colony to increase genetic diversity of the colony. The petition to release this wasp in the U.S. has been completed and is under evaluation. Colonies of two HCM parasitoids, A. cachamai and A. lapachosus, were mass reared at FuEDEI and delivered to the quarantine facility at the University of Puerto Rico in July 2022 and June 2023 to complete the host specificity studies. Currently, the host range studies on two non-target mealybugs were completed and tests on three other non-target species are on-going. So far, the parasitoids have not been able to complete their development and produce viable offspring on non-target hosts. A petition requesting the release of the biological control agents into the Puerto Rican environment will be prepared for submission to APHIS and the Puerto Rico Department of Agriculture for review. The little fire ant (LFA) is a South American ant species is invasive in a great part of the continental U.S., as well as Hawaii and Puerto Rico. A metagenomic study carried out at USDA-ARS in Gainesville, Florida, with samples provided by FuEDEI determined the existence of seven viruses found exclusively in native populations, but not in invasive populations in the U.S. and Australia. At least four of these viruses could be effective biological control agents. These viruses were not found in LFA samples from other parts of the world. Specificity studies need to be replicated on mealybug species from Puerto Rico with A. cachamai and A. lapachosus. A specific parasitoid wasp of the cactus moth CM, Apanteles opuntiarum, is being mass reared in quarantine at Gainesville (FL) from field-collected parasitoids exported in April to increase genetic diversity. The petition to release this wasp in the U.S. is under process, and likely to be submitted this year.

Accomplishments
1. Insight into performance of biological control agent on Water hyacinth. Water hyacinth (WH) threatens freshwater waterways throughout great part of the US by covering whole stretches of rivers and lakes. Biological control is probably the only efficient and definitive way of controlling this weed. A planthopper, native to Argentina and known only as Megamelus scutellaris, was released in the U.S. and other countries, with uneven success. Scientists from FuEDEI, an ARS-associated lab in Argentina, confirmed there are three main lineages of M. scutellaris in the plant hopper’s native range that could be associated to differences of performance in different release sites. This should help reinforce and improve the biological control of WH in the U.S.