Location: Crop Production and Protection
2020 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 (BP). A defoliating sawfly has been studied as a promising biological control agent for BP in Brazil, Hawaii and Florida since late 1990s. Like other members of the sawfly family, this species is known to produce toxic proteins with potential for poisoning wild and domesticated animals that may ingest the insect larvae. However, recent studies revealed that these proteins occurred at low concentrations, so the utilization of this species as a biological control agent for BP is being reconsidered. While conducting BP surveys in southern Brazil, a new species of sawfly larvae was collected feeding on BP. Should outcomes of toxicity and host range testing result positive, it may become a new biological control agent for Brazilian peppertree in the USA.
Giant Salvinia (GS). GS is an aquatic fern that is invasive in most tropical and subtropical areas of the world. An aquatic weevil has been used as an effective natural enemy of GS for decades, however, the plant is invading more temperate areas with harsher winters in the US where the weevil is unable to overwinter. FuEDEI has been trying to find cold-hardy weevil strains in the southern range of Salvinia in South America and to explore the southern limits of Salvinia in Argentina, under the assumption that these weevils might survive Louisiana winters and control the plant. During exploration trips another species of weevil was found on a small patch of Salvinia located ca. 250 Km South of Buenos Aires city. Further field and laboratory host range studies are needed to determine the potential of this new species as a biocontrol agent for Salvinia in the USA.
Salt Cedar (SC). The invasion of saltcedar in the USA and Argentina, constitutes an opportunity for collaboration on this invasive weed. Biological control of this shrub has been highly successful in the USA after the introduction of four Old World leaf beetles. Piggybacking on the biocontrol program undertaken in the USA constitutes an opportunity for Argentina to reduce costs associated with the exploratory surveys, risk assessments and rearing procedures to implement biological control of SC in the country. We have created a consortium with researchers from the ARS, FuEDEI and other local institutions to develop a classical biological control program against the plant in Argentina. The first objective of the project is to sample local populations of SC and related native plants to obtain a checklist of native and exotic insects that feed on these species. Very few herbivores have been found so far, which are in the process of being identified by specialists. Future efforts will be focused on completing the surveys along the SC invaded area in Argentina and on getting permits to import the leaf beetles form the USA with the help of the USDA-ARS-ISPH lab in Albany, CA.
Little fire ant (LFA). Surveys were conducted in central and northern Argentina to collect samples of the invasive LFA. Since there are no known macroscopic effective natural enemies of LFA that can be used in a biological control program, we are exploring for useful microorganisms, such as viruses. Samples from 39 colonies were collected, preserved in ARN/DNA shield and later sent to CMAVE, ARS-USDA. Metagenomics and next generation sequencing will be employed to discover natural enemies (virus) of the LFA in its native (Argentina) and introduced (US and Australia) ranges. RNA quantity was satisfactory to conduct the analyses. Experiments were also conducted to analyze if the thermal and desiccation tolerance of LFA can explain its current and potential geographical distribution. As expected, colonies from regions with colder climates had higher cold tolerance and recovered faster from chill coma (recovery time) than colonies from warmer regions. Unexpectedly, colonies from drier regions showed a slightly higher cuticular permeability (higher loss of water) than colonies from wetter sites, suggesting that susceptibility to desiccation could be a more limiting factor than vulnerability to temperature and competition for this species.
Cactus moth (CM). This species, native to South America, gregariously feeds, damages and threatens prickly pear crops and native cacti from North America. CM physically damages the plants by eating its inner tissues during larval development, causing decreased plant longevity and fruit production. However, losses in the fruit production have not been quantified. Estimation of the effect of CM on prickly pear production was evaluated in a commercial plantation for the first time, resulting in drastic fruit loss as pest density increased. This information supports the need to continue with the biological control program of this pest in North America and advance in the studies for the release of a small wasp that is the most specific and potential biocontrol agent known to date. This wasp is being mass reared at quarantine at DPI-FDACS, FL. Research and specificity tests continue, as well as mass rearing of the parasitoid. Additionally, the evaluation of a second parasitoid and potential biocontrol agent has started with laboratory and semi-field experiments. This parasitoid is used in inundative biocontrol programs against several pests of pome fruits with great success in Argentina. The effectiveness of a pheromone monitoring trap as an estimator of moth abundance in naturally attacked plantations continues to be evaluated. Population structures of native populations of the cactus moth, as well as of related species, are being assessed with next-generation DNA sequencing.
Huanglongbing (HLB): Xylella fastidiosa, the bacterium that causes HLB also causes several plant diseases of economic importance: grapevine Pierce's disease; citrus variegated chlorosis; peach phony disease; plum leaf scald, olive scorch; as well as leaf scorch diseases on almond, coffee, oleander, pecan, and several berry species. This bacterium is vectored by a leafhopper known as Asian citrus psyllid. Our objective is to genetically characterize the populations of the vector’s main parasitoid in Argentina through the study of their population structure and correlation with the known population structure of the disease vector. We are also screening other native leafhopper species that might vector the disease. Several molecular and preservation techniques were compared to find the best technique to achieve this knowledge. Next step is to acquire more samples for another combination of primers to improve the sequencing techniques.
Tawny crazy ant (TCA). TCA is an invasive ant in Central and North America, both in natural and urban areas. Our research has revealed the existence of species complexes within the genus (Nylanderia). In addition, the two invasive species in the U.S. have cryptic workers. Due to these difficulties to determine which species is which, we are carrying out a species delimitation study in the native range, through which we found that invasive TCA populations belong to a single lineage. New explorations in the native range are aimed at collecting TCA decapitating phorid flies to carry out phylogenetic analyses that will confirm if there is only one or more species parasitizing both lineages. Finally, studies of a bacterium, Wolbachia, which infects all lineages, suggests these bacteria are not driving speciation within the TCA species complex.
Harrisia cactus mealybug (HCM): this mealybug is devastating native cacti in Puerto Rico and threatening cactus diversity in the Caribbean and North America. In fact, the California Department of Food and Agriculture has detected and eradicated six times the Puerto Rican pest from nurseries and gardens in California. The cacti pest is an undescribed species of the HCM species complex, constituted by at least 5 species. FuEDEI discovered and reared two parasitoid species that attack HCM populations. Laboratory host range testing was conducted in Argentina to predict post-release impacts on the pest in Puerto Rico. We tested five populations of mealybugs of the same genus as the Puerto Rico cacti pest, plus two species from other genera, and the results of this study indicate that both parasitoids are specific to the pest genus, such that other, non-pestiferous, mealybugs would not be at risk. When travel from South America to Puerto Rico is resumed, a shipment will be made to restart colonies of both parasitoid species and specificity tests on 10 non-target Puerto Rican mealybugs. This shipment was ready by early 2020, but due to the CoV shutdown, the shipment is estimated to be sent toward the end of 2020. Genetic studies indicate that the origin of the Puerto Rican cactus pest is in Brazil, and that the mealybug detected on cacti in California belongs to the same species. The mealybug collected on Amaranthaceae and/or Portulacaceae in Puerto Rico and the continental United States is another member of the HCM complex. These findings suggested two independent invasion events of two different mealybug species in Puerto Rico and the continental United States.
Accomplishments
1. Brazilian peppertree - BP. The discovery of a new phytophagous insect associated with S. terebinthifolia that resulted in the description of a new sawfly species, Heteroperreyia kava Smith.
2. Water hyacinth - WH. A documentary about biological control of the plant and community engagement in a nearby lake is now online. This documentary explains the invasion of the plant, the operation of the biological control program, and the role of the community, particularly the educational sector, in the project.
3. Giant salvinia - GS. A population of the weevil T. parvulus was found in temperate, southern areas, opening possibilities for a new, cold-resistant, biocontrol agent for this aquatic weed.
4. Little fire ant - LFA. The thermal and desiccation tolerance of population of W. auropunctata distributed along temperature and rainfall gradients were characterized which could allow predicting its current and potential spread in the Americas.
