Location: Crop Production and Protection
2016 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. A thrips was evaluated by lab and field studies in Argentina as a candidate for biocontrol of water primrose, an invasive plant in California. The thrips was tested following no-choice feeding protocols, testing related plants and species that coexist in the environment. They only developed on two invasive species of water primrose. Damage tests showed that thrips’ nymphs and adults affected the development of the plant. Lab tests were complemented with field searches of the thrips in different potential host plants in Argentina; results showed that the thrips was associated only with the target host. Studies should be completed in quarantine facilities in the US on native species.
Waterhyacinth. Two ongoing studies are a) biocontrol of waterhyacinth in water bodies of Argentina with native insects to evaluate compatibility and impact in the field; b) search for clues to improve rearing methodologies of a potential biological control agent. In the El Ojo Lake, Buenos Aires, a lake isolated from the natural distribution of the plant, only the weevils Neochetina spp established among four species released. Weevil density had increased exponentially18 months after their release, waterhyacinth biomass diminished to almost half of its original weight (from 15 tons to 8 tons/ha). The search for factors that affect the reproductive behavior of a planthopper in northeastern Argentina continues. Efforts concentrate on the apparition of sperm cells and/or eggs in females in relation to physical and chemical plant characteristics and other environmental clues.
Water lettuce. Work on water lettuce is on hold, evaluating effects and interaction of two biocontrol agents on a natural population of Pistia invading a provincial reserve in Buenos Aires.
Brazilian waterweed. Experiment underway involving 10 250-liter tubes connected to pumps imitating a tidal system to compare in the lab the reproductive success of the leaf-mining shore fly Hydrellia egeriae on Brazlian waterweed patches with stable water levels (plants always accessible for ovipositing) to their success on patches subjected to a tidal regime (plants periodically inaccessible).
Brazilian peppertree. During reporting period July 2015-July 2016, testing of prospective agents and the search for new ones in Argentina continue to be priorities for the Brazilian peppertree (BP) biological control project. Surveys in Argentina and Brazil revealed the presence of several defoliating caterpillars: inchworms and two cryptic moth species. During a 6-day fieldtrip in November 2015, a total of 23 inchworms, 19 Paectes sp. moth and 214 Episimus sp. moth larvae were collected by beating on 236 Brazilian peppertree plants at 14 sites. Parasitism rates of collected moth species were: inchworms 0%; Paectes sp. moth 19% and Episimus sp. moth 18%. The defoliating sawfly, Heteroperreyia hubrichi, has been intensively studied as a prospective biocontrol agent for BP. Further studies with this insect are delayed due to the potential toxicity of the larvae of this species. Considering the restricted host range of the sawfly, additional toxicity studies are conducted to determine the existence of toxic peptides in this species. In an 8-day trip in May 2016, a total of 72 larvae of the sawfly and nine larvae of a closely related species were collected, fixed in 100% ethanol and preserved for subsequent toxicity studies.
Giant salvinia. The aquatic salvinia weevil is an effective natural enemy of Giant salvinia in most tropical and subtropical areas of the world. The plant is invading more temperate areas with harsher winters in the US (Texas and Louisiana), so that the weevil populations cannot get established and overwinter. During the reporting period, July 2015- July 2016, 6 field day-trips were made to study the seasonal abundance and population dynamics of cold-hardy ecotypes/strains of the salvinia weevil at a site in the south of Entre Ríos Province, Argentina. A total of 10330 adults of the weevil were collected from 28 kg of dry matter of Salvinia plants in Berlese funnels. The physiological age structure of the salvinia weevil is being studied. A subsample of 20 females from each collection trip is being dissected and their reproductive developmental stage determined. Besides the salvinia weevil, about 30 morphospecies of weevils associated with Giant salvinia have been collected and are being identified.
Cactus moth. Focused on improvement of mating, rearing and colony maintenance of a parasitoid; and the reduction of male biased sex ratio of the colony. Experiments conducted to expand on the knowledge of the parasitoid regarding lifetime fecundity, potential fecundity and parasitoid oviposition behavior. A lab colony of the target insect Cactoblastis cactorum was also maintained to supply hosts for the parasitoid. C. cactorum larvae were exposed to the parasitoid under different environmental conditions to standardize the maintenance of the parasitoid colony under the condition producing the highest proportion of females. Potential and actual lifetime fecundity of single mated females of the parasitoid was determined, and parasitoid learning and stimuli recognition was assessed by experiments. Based on various behavioral traits measured, it was determined that C. cactorum larvae that fed on artificial diet, or in the presence of frass from feeding on artificial diet, were significantly unattractive to the parasitoid females, regardless of the previous stimuli presented. Field collected infested C. cactorum larvae are to be shipped or hand-carried to the quarantine facility in Gainesville.
Harrisia cactus mealy bug (HCM). Harrisia cactus mealybug, until recently identified as Hypogeococcus pungens and now an unknown species of the genus Hypogeococcus, is a serious pest of native and endemic columnar cacti in the dry districts of southern Puerto Rico. Puerto Rico started a biological control program to search for natural enemies of HCM in its putative native range, South America. The natural enemy selected to manage the Puerto Rico HCM pest depends on the correct identification of the pest. FuEDEI carried out studies on biology, reproductive compatibility of different clades, taxonomy, and molecular genetics in the putative native range of H. pungens to sort out the HCM complex. The species that is a pest of cacti in Puerto Rico is closely related to the Argentine mealybug H. pungens sensu stricto. Genetic studies were insufficient to sort out the identity of this species.
Imported fire ants (IFA). 160 IFA colony samples (workers, alate males and females, and queens) were collected in Mendoza, Tucumán, Misiones and Entre Ríos and sent to the Gainesville quarantine. Molecular data generated was included in the fire ant phylogeny, the fire ant species delimitation, and the Gp-9 supergene/genome projects conducted in cooperation with ARS Gainesville. Molecular phylogenies of fire ants and their South American parasitoid flies were obtained. These data allow to establish species relationships and to delimit populations of each known fly species and putative new fly species.
Little fire ants (LFA). Life history and biology of LFA within their native range was studied to understand their invasion scenario. LFA was widespread at the southernmost limit of its native distribution range, with higher abundances recorded mainly in anthropic habitats. The social organization was mainly supercolonial in all habitat types. The reproductive system was mainly clonal in anthropic habitats, mixed in partially disturbed sites and floodplains, and sexual in natural sites. LFA had a lower competitive ability than expected, indicating that interspecific competition is not the most important factor associated with its success. The natural expansion to high latitudes, to the south of South America, would have allowed it to adapt to colder climates and seasonality, key to its later establishment in the Mediterranean region. Naturally disturbed environments may have played an important role in the appearance of features such as clonality, supercoloniality (widespread colonies), better competitive abilities, and tolerance to cold, all of which would have favored the dispersal of LFA mainly in anthropic habitats, the key to its dispersal outside its native range. A local grant was obtained to begin physiological and genetic (genomic) studies of this invasive ant.
Leaf-cutter ants (LCA). LCA are one of the most important pests in forest plantations and most crops in the Neotropical region. LCA species surveys were conducted in new areas of Argentina. Samples were included in the phylogenetic, delimitation species, and phylogeographical analyses. A species distribution modeling (Maxent) was conducted with occurrence data of some of the most detrimental leaf-cutter ant species. Results showed that two of these species, Acromyrmex lobicornis and A. striatus, were found in two disjunct areas, the Monte ecoregion and the Atlantic Forest ecoregion. Their fragmented distribution could indicate that they are going through a process of genetic differentiation by distance, a typical mechanism of speciation. A. lundi and A. ambiguus were distributed in between these disjunct areas, mainly in the lower basin of the La Plata River slightly overlapping the aforementioned areas. Damage produced by the A. lobicornis and A. striatus in vineyards in San Juan, and by A. lundi and A. ambiguus on willow forestations in the lower basin of La Plata River was quantified. Damage on four commercial clones of poplar forestations is being assessed. Nest density, foraging activity, and diets of the four LCA species are being studied in the field to estimate the magnitude of their impact on vegetation, especially on cultures. Preference studies will be conducted in the lab. An estimation of the loss level was obtained for four commercial clones of willow trees and vineyards in Argentina.
Accomplishments
1. Harrisia cactus mealybug (HCM). Biological and taxonomic comparisons of H. pungens sensu stricto and material from Puerto Rico indicate that they are different species. Although we disentangled the H. pungens complex in at least 4-6 species, we were not able to identify HCM from Puerto Rico. We found a match between Brazil and Puerto Rico mealybug populations, both samples collected on cacti. Recently, we found populations of HCM in Argentina which produce the same damage as HCM in Puerto Rico and in Brazil. From the survey of natural enemies conducted in unexplored areas of Argentina, one species of a primary parasitoid was collected. The biology and taxonomy of two species were studied. Colonies of the three species of Anagyrus were successfully established at the FuEDEI facilities. In addition, the survey of natural enemies continues in Argentina, focusing on unexplored areas.
2. Cactus moth (CM). Significant improvement of rearing conditions of A. opuntiarum allowed the establishment of a lab colony for experimental purposes.
