Location: Crop Production and Protection
2019 Annual Report
Objectives
Objective 1: Explore for natural enemies of invasive weeds identified as high priority targets by the ARS Office of National Programs, performing collections, importations and exportations in compliance with local and international regulations. High priority invasive weeds include but are not limited to water hyacinth, water lettuce, Brazilian waterweed, Brazilian peppertree, water primrose and giant salvinia.
Objective 2: Explore for natural enemies of invasive insect pests identified as high priority targets by the ARS Office of National Programs, performing collections, importations and exportations in compliance with local and international regulations. High priority pests include but are not limited to black imported fire ant, red imported fire ant, little fire ant, tawny crazy ant, cactus moth, and cactus mealybug.
Objective 3: Perform taxonomic and phylogenetic studies as needed to support the development of biological control agents, such as characterizing undescribed or cryptic parasites and herbivores of the targets.
Objective 4: Identify 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
FuEDEI (ex-SABCL) research program Project Plan approved by OSQR in 2010 includes target weeds: Brazilian peppertree (Schinus terebinthifolius), Brazilian waterweed (Egeria densa), water primrose (Ludwigia hexapetala), water lettuce (Pistia stratiotes) and waterhyacinth (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 water fern (Salvinia molesta) commonly known as giant salvinia.
Prior to the collection of their natural enemies, more in depth studies on the biology, ecology, genetics, and/or taxonomy of water primrose, cactus moth and little fire ant are required. These studies are planned as sub-objectives.
Target priorities are set by Congressional mandates, as a result of stakeholder workshops, or by hierarchical decision with input from ARS National Program Leaders (NPLs), stakeholders, Laboratory director and ARS scientists. Flexibility in this Project is needed to deal with new pest problems in the U.S., with concurrence of PLs and ARS laboratories.
FuEDEI (ex-SABCL) functions as an overseas arm for several U.S.-based biological control programs on invasive pests of South American origin, conducting foreign exploration, collection and evaluation of potential biological control agents to be used in the U.S.
Waterhyacinth, Brazilian peppertree and imported fire ants were also targets in the previous Project Plan and, except for Brazilian peppertree, Obj.1 and Obj.2 have already been accomplished; current work is limited to collecting and shipping of selected agents (Obj.3). Brazilian waterweed, water primrose, water lettuce, cactus moth, little fire ants and Harrisia cactus mealybug were added by NPLs during the implementation of the previous Project Plan and investigations are in different stages of progress; for the most recently- added targets (cactus moth, little fire ant and Harrisia cactus mealybug), specific approach and procedures for Obj.2 will be determined as soon as natural enemies are discovered, collected and identified.
The general impact of work conducted at FuEDEI (ex-SABCL) includes conservation of non-renewable resources by self-perpetuation of natural enemies; cost-effective suppression of target pests; decreased use of hazardous pesticides; improved environment quality; protection of natural ecosystems from invasive species, favoring biodiversity; sustainable production systems and land use; higher quality food and fiber; higher protection of human health; enhanced scientific understanding of successful biocontrol programs and integrated pest management.
Progress Report
Brazilian peppertree: Brazilian peppertree is a sprawling shrub or small tree that has been introduced to California, Texas, Hawaii, Arizona, Nevada, Louisiana and Florida. Planted originally as an ornamental outside of its native range, Brazilian pepper has become widespread and is considered an invasive species in many subtropical regions. The release petition for a sawfly with a restricted host range as a control agent for BP was delayed to assess whether the insect is toxic to wildlife and livestock. Field and laboratory host range studies are being conducted with previously untested species.
Giant salvinia: This aquatic fern, an important fern in the US, has an effective natural enemy in a weevil. However, it is invading areas with harsher winters where the weevil cannot establish. The aim is to find cold-hardy strains of the weevil from Argentina and Uruguay. The southern limits of Salvinia were explored in Argentina, south of Buenos Aires city, where the weevil is not known to thrive.
Floating pennywort: Floating pennywort is an aquatic creeper that blocks the surface of water bodies affecting the health and use of fresh water bodies in its invasive range in Europe and Australia. A species of weevil that impacts native pennywort populations heavily in its native range has been studied quite intensively as a biocontrol candidate and was introduced in quarantine facilities in the UK for specificity and impact tests. Problems with exportation permits from Argentina have made it very difficult to ship enough live material to perform these tests. Export permits were obtained from Paraguay, and a fresh batch of field-collected weevils were hand carried to UK to complete specificity studies on Old World plant species.
Waterhyacinth (WH): WH is an aquatic floating plant that invades and covers entire water bodies, changing both structure and diversity of macrophyte communities, increasing fish mortality, degrading wetlands and water bodies. This invasive species is currently spreading to higher latitudes than historically recorded, probably as a result of global warming. WH sites in South Africa and Argentina were sampled for morphological and demographic plant features to compare invaded sites in the exotic range and invaded and natural sites in the native range. Data is used to calibrate different climate change models for the weed. A Community Engagement Biocontrol Program was devised in which students from an agricultural school are now mass rearing a weevil and a planthopper to control WH in the local lake.
Water primrose: WP is an aggressive invader that reproduces by seed and vegetatively, and is a serious threat to the stability of aquatic ecosystems in the USA and Europe. Neither chemical nor mechanical control provide long term results. In their native range these species tend to grow in small patches and are usually mixed with other native plants. Promising biocontrol agents are being evaluated from among the 19 insect species found in association with the plant in its native range in Argentina. Morphological and molecular studies as well as biological and host specificity studies of a very damaging flea beetle are being carried out.
Little fire ant: We evaluated interference competition of LFA with 3 invasive species: red fire ant (RFA), Argentine ant and tawny crazy ant, to determine their hierarchy in the southernmost limit where all coexist. Species supremacy varied according to daily and seasonal temperature in each region. RFA was dominant over the 3 species. LFA was less cold-tolerant showing it cannot continue invading further south in Argentina.
Leaf-cutting ants (LCA): LCA are important forestry pests. Willow and poplar plantations were studied for 5 years to determine preference and defoliation damage in new forestations. Coexistence of both LCA species in this region was analyzed. For the first time, the level of economic damage and threshold of action were determined for LCA.
Tawny crazy ant (TCA): TCA is an ant species from southern South America introduced in Central and North America. It affects native ant biodiversity and hinders urban environments and agriculture. A phorid fly that attacks TCA was found in Buenos Aires and Misiones provinces, and confirmed by a phylogenetic study to be a single species. Samples in the native range showed four distinct groups of haplotypes. The sympatric distribution of two of these groups that represent TCA populations suggest that the species is going through a speciation process. Studies show that there is a mixed reproductive system: sexual and clonal reproduction as well as diploid males in populations of Argentina. Population analysis showed that TCA has a super colonial structure in the US with colonies up to 2000 km wide, while in the native range, super-colonies seem to be much smaller (5 km). In the introduced range, hundreds of reproductive queens were found, each mated by a single male, but only a maximum of nine queens and dozens of males were found in native nests.
Harrisia cactus mealybug (HCM): This mealybug from South America is a serious threat to native and endemic cacti from Puerto Rico and continental U.S. Laboratory host range testing is being conducted to predict post-release impacts on the two parasitoids shipped from South America to Puerto Rico. We tested five populations of mealybugs closely related to the Puerto Rico cacti pest, plus two non-target mealybug species. The results of this study continue to be promising; both parasitoids, as occurs in the field in the native range, are specific to the cacti pest genera. Specificity tests are soon to be completed in Argentina and Puerto Rico after which we will apply for the release of these biological control organisms. Identity of the mealybug species that invaded Puerto Rico is also under study. Evidence suggests that HCM is not a single species, rather a species complex. Preliminary results indicate that the complex could comprise the cacti pest of Puerto Rico plus 4-5 different species. These results were supported by genetics and biological studies. We also found that the Puerto Rican cacti pest is the result of only one invasive event.
Cactus moth: This moth is native to Southern South America, and it threatens several crop and vulnerable cacti from North America. Research continues on the mass rearing of a parasitoid that is a potential biocontrol agent for cactus moth. The fluctuations in field parasitism rates of the parasitoid were evaluated, as well as the effect of the cactus moth on fruit production of prickly pears in the native range. Genetic analyses have started to shed light on population structures of the cactus moth and related species regarding their host plants.
Bellyache bush: Bellyache bush is a major weed of rangelands and riparian zones in dry tropical Australia. Biological control is considered the most economically viable and long-term management solution for this widespread invader. Native range surveys have come up with two undescribed leaf-feeding gall midges that cause shoot-tip dieback and terminal galls. Host specificity tests were performed on species of economic significance, and to date the results of these no choice trials are promising.
Silverleaf nightshade: Silverleaf nightshade is one of the worst invasive plants worldwide. New explorations in the native range are ongoing to study and develop a biological control program against this invasive weed in Australia. The main objective is to explore the native range of the weed in Argentina and look for potential biocontrol agents. Several natural enemies are being evaluated, including a mite, a leaf beetle, a rust and a lace bug.
Cabomba: Cabomba is a submerged plant native to the Americas, common in the acidic, clear waters of the Iberá wetlands in northeastern Argentina. It is invasive in Australia, southeast Asia, China, India, and parts of Europe and North America. It affects water use in all its forms, as well as native aquatic flora and fauna. Efforts are devoted to the collection, study and rearing of an aquatic weevil which develops on cabomba during its larval stage inside stem mines and as an adult by feeding on the tips and laying its eggs on the leaves. Specificity tests indicate this weevil is probably specific enough to be used as a biocontrol agent where the plant is invasive.
Accomplishments
1. Brazilian pepper tree. In July, the ARS lab in Florida released the first biological control agent of the invasive weed Brazilian peppertree: a leaf-feeding thrips that reduces the growth and reproduction of this noxious weed. A lab in Argentina has been cooperating on the BP project since 2005, conducting extensive exploratory surveys and host range studies of this thrips in South America.
2. Little Fire Ant. Competitive interactions among four highly invasive ant species were studied in connection with ambient temperature. This could allow to predict their hierarchy of dominance depending on the daily and seasonal temperatures of the region in the world where they are able to coexist.
3. Leaf cutting ants. Results related to the natural history of two sympatric species of LCA provide relevant information for their management and control in forest plantations. Economic damage and action thresholds were estimated for the first time in Argentina and for an Acromyrmex species. These values are important for management and a fundamental requirement to obtain a forestry certification (FSC- Forest Stewardship Council) in the Lower Delta of the Paraná River, and other forestry regions of South America
4. Tawny crazy ants. We are beginning to understand which Nylanderia species are present in southern South America, the distribution of the invasive ant N. fulva, and its parasitoid fly, a potential biocontrol agent. Evidence of clonal reproduction and diploid males were found in populations from Argentina.
5. Harrisia Cactus Mealybug. In May 2019, mealybug parasitoids and their hosts were collected in Paraguay. Exportation permits were obtained to ship two mealybug parasitoids to the quarantine facilities in Puerto Rico. Field host range studies and preliminary laboratory host specificity tests with the two parasitoids indicate that both species are restricted to the mealybug. We found the Brazilian origin of the HCM population pest present in Puerto Rico. The cacti pest of Puerto Rico was also found as a pest on Cactaceae in California, U.S. It is a new species restricted to cacti.
6. Bellyache bush. The gall midge collected on this plant was originally identified as the pest species Prodiplosis longifila, yet after testing several crops known to host this gall midge, results show that the Paraguay species is different from the pest species. The rejection of crop species as hosts makes this gall midge a promising candidate for biological control of bellyache bush.
7. Giant Salvinia. A new population of Salvinia weevil was located in temperate, southern areas, opening possibilities for new, cold-resistant, agents for this floating weed.
8. Water hyacinth. The biological control program carried out at the Agricultural School in San Vicente was declared of Scientific and Cultural Interest by the Municipality of San Vicente and by the Congress of the Province of Buenos Aires. The Municipality of San Vicente, the Ministry of Education of the Province of Buenos Aires and FuEDEI signed a cooperation agreement in November 2018. "Biological Control Environment" is now part of the curriculum of the school.
9. Water primrose. A colony of a thrips as biocontrol of water primrose was exported and established at the ARS lab in Albany, California.
10. Cabomba. We managed to complete the life cycle of the cabomba weevil (a probable biocontrol agent) in small tanks under controlled conditions. This is the first time this goal was achieved. Although a mass rearing colony is not established yet, recent results are promising.
