Location: Crop Production and Protection
2017 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
Water primrose. Native to South America,19 species of specialized insects were found in Argentina. A thrips described as a new species was selected for further studies. In new surveys in the islands of the Parana River delta, a different species of Liothrips was found on Ludwigia peruviana. It has not yet been identified.
Waterhyacinth. Studies were focused on one promising biological control agent, the planthopper Taosa longula, specifically its field reproductive biology, and its relationship with physical and chemical features of the host plant. These studies took two years, and were performed in the insect’s native range in northern Argentina. There was an apparent increase of gravid females during summer associated with plant –leaf toughness and nitrogen content, which is now being investigated in a biological station (CECOAL) in Northeastern Argentina in large field cages. Also, the FUEDEI team is following the development of waterhyacinth populations in two lakes where the plant is invasive. One is in the porvince of La Rioja (150 ha) where the plant was reported as invasive 50 years ago, and biological control was implemented 42 years ago with the release of the waterhyacinth weevil. The weevils reduced plant cover from the full 150 ha to less than 1 ha. In the second lake (30 ha) the BC program was begun recently (less than 3 years ago). The data show a reduction in biomass and density of almost 50 % coincidental with a weevil population increase, suggesting it is probably a consequence of the weevils we added to the system.
Alligator weed. Native to South America its characteristics and natural enemies have been studied at FuEDEI for several years. According to a predictive model for weed distribution, the main environmental variables are temperature, seasonality and precipitation of the warmest quarter. Ploidy levels affect the impact of biocontrol agents and were determined for 20 populations from the whole range of the plant. Sampling for natural enemies on AW populations will continue for another year. Some organisms are pending identification. Specialist insects collected were the known thrips and five flea beetles.
Floating pennywort. This plant grows on slow water bodies preventing light penetration, producing eutrophication, oxygen depletion, local species extinctions and water fouling, affecting water use and quality. Tests show the weevil Listronotus elongatus to be a likely biocontrol agent as it is specialized on floating pennywort, but quarantine tests in UK suggest the European native, marsh pennywort, may be at risk. Lab tests showed that the South American native Hydrocotyle modesta could sustain high adult feeding, but in natural settings this did not occur. We carried out two-way tests between floating pennywort and H. modesta together with similar tests performed at CABI, UK, between floating and marsh pennywort. After two weeks no survival was observed in the H. modesta pots. All the feeding damage occurred within the first 10 days. Ovipositions observed did not prosper because the leaf petioles cannot take the oviposition damage. Also, oviposition was around twenty-fold higher on the weevil’s natural host; larval survival was significant.
Giant salvinia. Invasive in tropical and subtropical areas, it is invading more temperate areas with harsher winters. The aquatic weevil, Cyrtobagous salviniae is an effective natural enemy, but it cannot overwinter in temperate areas. We are searching for cold-hardy strains of the weevil in Argentina and Uruguay, studying its abundance and reproductive stages in the southern range of salvinia. Cold tolerant assessments suggest survival at 0°C was greater in the Lower Paraná-Uruguay Delta population compared to the Louisiana population, so the Lower Paraná-Uruguay Delta provenance should be considered for managing the fern in temperate regions. Population dynamics of the weevil is being studied. A lake near Buenos Aires city, mostly covered with the fern, is used to attempt the introduction and establishment of the weevil for experimental purposes. Dome-floating cages containing weevils were installed on the lake and are checked periodically.
Cabomba. A South American plant, fanwort grows rooted in mud of stagnant to slow-flowing water. It is a severe weed in temperate North America, and other countries. South America and USA were surveyed for natural enemies; herbivores were found feeding on cabomba, all in Argentina, but only one weevil is likely to be specific to this plant. Tests were run on several submerged plants in the fanwort environment in South America as no other species of Cabombaceae was recorded for Argentina. No-choice testing was shifted to other plant species. Results suggest larvae are highly specific, and unable to feed on any of the other aquatic plants. All the larvae died within 4 or 5 days, but a significant proportion of the larvae could re-enter fresh cabomba stems. As for adult feeding, mortality was not considered since adult weevils can go without food for weeks. But some inconsistent feeding was observed on two species of water lilies.
Leaf-cutter ants . LCA are pests in forest plantations and crops in the Neotropics. Much of the original coverage of the Parana River lower Delta was replaced by willow and poplar plantations, the habitat of 2 sympatric species of leafcutter ants. Damage produced by LCA on willow forestations was quantified for 3 years. Daily and annual foraging activity and diet of LCA were studied, and nest density in different habitats is under study to estimate impact on vegetation. Critical temperatures were measured for each species in the lab and these parameters of thermal tolerance compared to field foraging temperature for each LCA species. Foraging preference was studied by offering leaves of willows, poplars, and native plants. Field surveys for LCA were extended to new regions of Argentina. Potential areas of distribution and niche overlap analysis for the most widespread and detrimental LCA were estimated. Preliminary phylogenetic analyses were carried out using sequence fragments of nuclear gene and mitochondrial genes.
Tawny crazy ant. A major pest introduced in the US in 2002 from an unknown site in its native range. Nest surveys focused on northeastern Argentina. As in populations introduced in the US, native populations did not show evidence of aggressive behavior between nests. Comparison of sequences from a mitochondrial gene (COI) between the native range and the US showed that the number of mitochondrial haplotypes in the native range was higher and more diverse than in the US. A neighbor joining distance tree recovered three haplogroups: all introduced populations grouped in a single haplogroup containing a haplotype from Misiones (Argentina), Paraguay and Brazil similar to a haplotype in Texas and Louisiana, and a haplotype from Entre Rios (Argentina) which is similar to a haplotype in Florida and Texas and related to the haplotype in Virgin Islands. This suggests that they originated in northeastern Argentina and nearby areas of Paraguay and Brazil, in the Atlantic Forest ecoregion. Population genetic analysis from Argentina revealed that queens were homozygous in more loci than workers, which were mostly heterozygotes. These unusual genotype frequencies could have resulted from a combination of sexual and asexual reproduction, as in other invasive ants.
Harrisia cactus mealybug. Until recently identified as Hypogeococcus pungens and now an unknown species of the genus Hypogeococcus, it is a pest of native and endemic columnar cacti in dry districts of Puerto Rico. Molecular identification of the components of the HCM complex, the description of new species, and the re-description of previously studied valid species of all components of the HCM species complex found in Puerto Rico, Brazil, Paraguay and Argentina, continued. HCM and its parasitoids were collected on different host plants in Brazil, Paraguay and Argentina. Two shipments of parasitoids were successfully sent from South America to a quarantine facility in Puerto Rico.
Cactus moth. Focus continued on improving mating and rearing of the parasitoid wasp colony and reducing the male biased sex ratio. Newly emerged wasps placed in large cages with larvae feeding on whole cacti pads lead to the wasps’ immediate flight and mating of adults in the roof of polyester gauze cages: mating was observed for the first time in laboratory conditions. Field experiments were conducted to compare growth and fruit production in healthy and attacked plants. Attacked cacti produced half the fruit of healthy plants and cladodes decreased with the presence of CM.
Brazilian peppertree. A defoliating sawfly was studied as a probable biocontrol agent for BP. Further studies with this insect were delayed due to potential toxicity of the larvae. Given the restricted field and lab host range of the sawfly and its potential as a BP biocontrol agent, additional toxicity studies were carried out to determine the existence of toxic peptides in the larvae. Host plant use in the native range and host specificity studies with untested cashew family species are being conducted. Sawfly larvae from South America were sent to the Royal Belgian Natural Sciences Institute for toxicity studies.The sawfly laid eggs on all tested species including native South American cashew family and economically important pistachio tree. More tests will be carried out in laboratory and natural scenarios. Parasitoid adults were sent to Fundación Lillo for identification. In Brazil, natural enemies were collected and shipped to US quarantine facilities for further studies.
Accomplishments
1. We can confirm that the pest in Puerto Rico is not Hypogeococcus pungens sensu stricto, given that this species is restricted to host plants of the family Amaranthaceae.
2. A new species of parasitoids was described from Salta province, Argentina, Anagyrus lapachosus Triapitsyn, Aguirre & Logarzo (Encyrtidae).
3. Waterhyacinth: one of the most stunning results of this work was the discovery, looking for different maturity grades of females, of a mating orifice in Taosa longula, which is open and only visible only in mated females. Females dissected that had the orifice visible were found to be full of eggs, or they had elongated ovariols. In females wihout a visible mating orifice, the ovaries were hard to find, because they were very small and immature.
