2010 Annual Report
1a.Objectives (from AD-416)
Develop vegetational designs and therapeutic interventions that foster desirable pest/natural enemy balances. Increase the foraging efficacy of parasitoids and other natural enemies of key pests of row crops. Develop spin-off benefits emerging from an understanding of natural systems, such as use of trained wasps for chemical biosensors in precision agriculture and food safety.
1b.Approach (from AD-416)
Research will focus on better landscape ecology practices for total habitat management, improved knowledge of inherent strengths in crop attributes, and development of biorational, therapeutic products/procedures which complement inherent strengths in the cropping systems and the development of decision-making tools that better utilize natural enemies in agronomic crops in the Southern Coastal Plain. Emphasis will be placed on development of control strategies for insect pests utilizing biological control, conservation tillage practices, cropping sequences, and cultural practices. Efforts will be directed toward conserving and enhancing natural enemies for managing primary pests of agronomic crops.
This project has termed and bridging project #6602-22000-039 was established. Studies were conducted to characterize the population dynamics and ecology of stink bugs and their natural enemies in row crops. Seasonal succession of crop host plants was corn, peanut, and cotton-soybean. The southern green stink bug and brown stink bug were the predominant stink bugs in these crops, but green stink bugs sometimes were found in cotton. In corn-cotton and peanut-cotton farmscapes, stink bugs dispersed from corn or peanut into cotton when cotton bolls became available. Egg predation was high in peanuts and soybeans, and similarly lower in cotton. Egg parasitism was low overall, but higher in cotton than in peanuts and soybeans. The odds of colonization of soybeans were substantially higher than peanut and cotton by both brown and southern green stink bugs. Experiments were conducted to test vegetational designs that could enhance natural enemies of pests and insect pollinators. We investigated whether the benefits of field margins established for conservation of northern bobwhite populations extended to the enhancement of biological pest control in adjacent cotton fields. Second year margins yielded higher densities for most species sampled, yet thrips and their predator were the only species that were also more abundant in cotton. A simple model was developed that will aid in understanding the mechanisms underlying species specific edge effects or the lack thereof. The preliminary results of a field study suggest that lupin, winter pea and possibly faba bean are good candidates as cover crops for reduced insect pest pressure in subsequent sorghum crops. We found that stink bug parasites, bees, and wasps readily fed on milkweed nectar on-farm. Research was conducted to examine pest intervention management strategies for control of key pests and that use of an in-furrow treatment of a starter fertilizer can act as an alternative management strategy to aldicarb application for control of thrips in cotton. We found that aphid numbers increased in conservation tillage but so did the aphid fungus and conclude that conservation tillage does not affect aphid control by fungal pathogens in cotton. Preliminary tests indicate that wheat is capable of hosting both strains of the fall armyworm. Susceptibility of a predatory stink bug to selected insecticides was higher than that of brown stink bug. Selected insecticides were as toxic to a stink bug parasite as they were to the southern green stink bug. We demonstrated that the southern green stink bug can be trapped with its reported pheromone on-farm. Studies were conducted on the foraging efficacy of the wasp M. croceipes. We found that the wasp was equally attracted to cotton plants with both leaf and root damage. Root feeding by M. incognita had little influence on direct defenses of cotton against insect herbivory. We determined that both water stress and nitrogen levels outside the recommended levels decreased attraction of the wasp to cottonand that trained wasps were able to indicate through distinct behaviors the identity of different concentrations of chemical products produced in uncastrated boars.
Spatiotemporal patterns and dispersal of stink bugs in peanut-cotton farmscapes. In cotton, stink bugs are primary pests responsible for millions of dollars in losses and cost of control. Generally, peanut is grown in association with cotton in peanut-cotton farmscapes. The objective of this on-farm study was to examine the spatial and temporal patterns and dispersal of the southern green stink bug and the brown stink bug in these farmscapes. We used GIS mapping, a new spatial analysis technique, and graphs of stink bug development over certain periods of time to examine spatial distribution and abundance of these pests in these farmscapes. Altogether, the analyses for each of the peanut-cotton farmscapes strongly indicated that southern green stink bugs and brown stink bugs dispersed from peanut into cotton at the interface, or common boundary, of peanut-cotton farmscapes, as cotton bolls became available as food. Spatial analysis revealed that stink bugs of both species aggregated at the interface in cotton as they fed on cotton bolls. A marking technique demonstrated that adults and nymphs of the southern green stink bug and brown stink bug dispersed from peanut into cotton at the interface of the farmscape. Understanding the spatial and temporal patterns of stink bugs in peanut-cotton farmscapes will help in developing management strategies for these pests in cotton.
Composition and abundance of stink bugs and their natural enemies in corn. Stink bugs have increased in importance as pests of agricultural crops over the past several years, but very little information is available on the abundance of stink bugs in corn. The objectives of this on-farm study were to determine the species of stink bug pests feeding on corn, and the abundance of these pests and their natural enemies in corn fields. The predominant stink bug pests were the southern green stink bug and the brown stink bug, and at least one generation of each of these pests occurred in corn each year. Stink bug adults were parasitized by tachinids. Stink eggs were parasitized by scelionids. Predators, such as Geocoris punctipes, Orius insidiosus, spiders, and lady beetles, preyed on stink bugs on corn. Population dynamics of stink bugs were different on early- and late-planted corn. Density of stink bug adults in early-planted corn was relatively low throughout the growing season. In late-planted corn, females of both stink bug species consistently laid eggs in mid-to-late-July on corn with developing ears. This habitat favored continued nymph development, and the resulting adult population reached high levels. These results indicate that corn management practices play a key role in the ecology of stink bugs in corn agroecosystems and provide information for designing management strategies to suppress stink bugs in farmscapes with corn.
Crop specific predation and parasitism of stink bugs in agricultural farmscapes. Although there are several parasitoid species of eggs, nymphs and adults of stinkbugs, they currently do not sufficiently control populations of this major pest species. There is a need to find additional natural enemies of these species for biological control. We investigated southern green stink bug egg mortality by placing sentinel egg masses in plots of soybean, Bt-cotton, Round up Ready (RR) cotton and peanut plants in the Southeast. Egg masses were photographed at placement and at 12h, 24h and 48h after placement to help evaluate relative predation and parasitism in the crops. After 72h, surviving egg masses were collected and held in the laboratory to assess parasitism. Predation of eggs was high in peanuts (74%) and soybeans (65%), and similarly lower in Bt (26%) and RR cotton (21%). Most egg predation in cotton and peanuts was attributable to fire ants. Parasitism was low overall but higher in the cotton (8%) than the peanuts (0.17%) and soybeans (2%). Both predation and parasitism were higher at plot edges than the centers of all three crops. These results suggest that there are crop specific predator species that are able to cause high mortality of stink bug eggs masses which allows us to further investigate their use as biological control agents in given agricultural landscapes in the region.
Relative crop preference for stink bugs. Stink bugs have become an important pest of many row crops in the region. Because of rotation practices in the region, cotton, peanut and soybean are often planted in close proximity and all three crops are fed upon by stink bugs. To test the effects of landscapes on stink bug populations, relative crop preference for cotton, peanut and soybean are needed. We conducted field plot studies to determine the odds ratios of stink bugs colonizing each crop. We found that the odds of colonization of soybeans are substantially higher than peanut and cotton by both brown and southern green stink bugs. The odds ratios of colonization of these species in Bt cotton and RR cotton did not differ, but the odds of colonizing cotton was higher than for peanuts by southern green stink bugs. This information is critical to allow predictions of stink bug population structure in the agricultural landscape, and would provide information that would aid in the development of management tactics to prevent population build-up.
Management of field margins to maximize multiple ecological services. Vegetative buffers in agricultural landscapes can provide a range of important ecological services, including conservation of native flora & fauna, enhancement of biological pest control, or reduction of agrochemical emissions. Typically, studies addressing the impact of such vegetative elements focus on one particular benefit. We investigated whether benefits of field margins that had been established for conservation of northern bobwhite populations extend to the enhancement of biological pest control in adjacent conservation tillage cotton fields. Densities of select insect species and predation and parasitism rates of insect pest species were measured in first and second year field margins established for bobwhite as well as in an adjacent cotton crop. With the exception of staphylinids and cotton aphids, second year margins yielded higher densities of all species sampled, yet thrips species and their predator, Orius insidious, were the only species that were also more abundant in the adjacent cotton field. Tachinids, Trichogramma, and Lygus species appeared to prefer the edge vegetation over the cotton. Overall, the impact of second year margins on the cotton crop did not significantly differ from first year margins with regard to pests or biological control. Analysis of the sugar content in Meteorus autographae, a generalist parasitoid of Lepidoptera larvae, suggested that this species is severely food-limited in the set-asides. This study shows that non-crop structures designed for a particular ecological function may be unsuitable in providing other ecological services. By making small adjustments in the vegetative composition of these structures, we might be able to effectively stack multiple ecological services and thereby optimize benefits.
Patch edge and insect populations. Responses of insect populations may be related to patch size and patch edge responses, but it is not clear how to identify these rapidly. We used a random-walk model to identify three qualitative responses to edges: no edge effect (the null model), reflecting edges and absorbing edges. Interestingly, no edge effect meant that abundance was lower at edges than in the center of patches, and reflecting edges have similar abundance at edges and centers. We then characterized several insect species’ response within maize plots to patch edges and patch size, using a simple, quick, qualitative experiment. Coleomegilla maculata and Trichogramma spp. were the only organisms that responded to patch size and edges as patch theory and the null edge model would predict. Ostrinia nubilalis larvae and possibly Rhopalosiphum maidis and eggs of Chrysopa spp. responded to patch size and edges as predicted by an attracting edge model. Estimation of predation rates suggested that the spatial distribution of these species might be determined by predators. Edge effects or the lack thereof relative to patch size may be rapidly determined for arthropod species, which could lead to understanding the mechanism(s) underlying these effects. This information may be useful in reaction diffusion models through a scaling-up approach to predict population structure of species among patches in a landscape.
Vegetational design to enhance beneficial arthropods. Early season insects samples in cahaba white vetch, cereal rye, winter pea, fallow with no fertilizer, fallow with fertilizer, lupin, faba bean and an organic control cover crop plots indicated that the density of beneficial arthropods was much higher than pest species in lupin and winter pea than the other cover crops and this trend carried over to the adjacent sorghum plots. Faba bean also showed this trend but not as strongly. Rye insect density and diversity was very low overall. There were equal or higher densities of pest insects than beneficial insects in both fallow plots and adjacent sorghum. These preliminary results suggest that lupin and winter pea and possibly faba bean are good candidates as cover crops for reduced insect pest pressure in subsequent sorghum crops. The choice of winter cover crops is also influenced by other desired characteristics such as weed control and bio-mass production.
Milkweed providing nectar to natural enemies. Insect pollinators are essential for the reproduction of more than two-thirds of the world’s crop species, and beneficial insects play an important role in reducing or controlling populations of pest insects in agricultural farmscapes. These insects depend on nectar for their survival in these farmscapes. Because the flowers of milkweed provide a rich supply of nectar, establishing a habitat of tropical milkweed could possibly enhance beneficial insects and insect pollinators on-farm. The purpose of this study was to monitor feeding activity of these insects on tropical milkweed in corn. Eight flowering potted plants of tropical milkweed were placed next to a corn field, and then insects feeding on nectar of these milkweed plants were observed and recorded throughout the day on weekly basis for the growing season. It was determined that many species of beneficial insects and insect pollinators fed on the nectar of topical milkweed, and for the first time scelionids and other small parasitoids were observed feeding on nectar of a milkweed species. Corn plants do not produce nectar, and so an addition of a habitat of nectar-producing milkweed plants in this environment could possibly enhance beneficial insects and insect pollinators.
Cover crop, rye residue, and in-furrow treatment effects on thrips. Thrips feeding damage on seedling cotton and peanuts can have deleterious effects on growth and yield. Most growers use an in-furrow treatment of aldicarb which has lethal and sub-lethal effects on a diversity of non-target species. Thus, an alternative thrips control option would be desirable. Thrips, and thrips damage to cotton and peanut plants were compared in plots with in-furrow treatments of aldicarb, phorate, and diammonium phosphate (DAP) fertilizer under two tillage regimes with a winter cover of crimson clover and under different levels of rye residue ground cover. Thrips numbers were significantly lower in cotton plots following winter crimson clover compared with no cover plots in all three years. Thrips numbers did not differ with respect to the in-furrow treatments within the clover plots, but within the no cover plots, they were significantly higher in the untreated control and DAP treatments compared with the aldicarb treatment. Thrips damage was higher in the no cover than the clover plots except in the aldicarb treatments. Within the cover crop plots, thrips damage was highest in the control and phorate treatments and similar in the DAP and aldicarb treatments. There was an inverse relationship between amount of rye residue ground cover and thrips density and damage in cotton and peanuts. There was also an inverse relationship between density of rye residue and damage to peanuts from Bunyaviridae tospovirus. These results suggest that ground cover alone decreases thrips numbers and damage in both cotton and peanuts and that a winter crimson clover cover and an in-furrow treatment of DAP added additional plant protection from thrips in cotton. Thus, the use of conservation tillage and cover crops with an in-furrow treatment of a fertilizer can act as an alternative thrips management strategy than the use of a toxic and water soluble, aldicarb to control thrips in cotton production.
Effect of field tillage on cotton aphids. In the Southeast US, fungi are effective natural control agents of the cotton aphid, reducing their numbers dramatically and eliminating the need for chemical control. With the increase in the use of conservation tillage in the region, we investigated the potential for this management strategy to negatively affect the natural control by the fungus in cotton. We found that aphid numbers increased in conservation tillage but so did the fungus, and conclude that conservation tillage does not affect aphid control by fungal pathogens in cotton crops.
Host plant affinity of fall armyworm strains in wheat. The fall armyworm is a polyphagous crop pest with an unusually wide host range, and is represented by two strains in the southeastern U.S., including the “C-strain” with primary affinity for corn and sorghum and the “R-strain” with primary affinity for rice and turf. Presently, small grain crops are an integral part of southeastern agriculture, but have not yet been “typed” for their strain affinity. In winter wheat, fall armyworm infestations require that about 2% of the regional production receive insecticidal control. Unknown in this management process is the predominate strain that infests wheat and the potential of this strain to more aggressively infest subsequent summer grain crops such as corn or sorghum. The purpose of this research is to first determine the preference that each strain of fall armyworm has for wheat and other small grains grown in the region, and secondly determine the influence that these winter crops may have on insect damage in the following summer grain crops. Initial results indicate that wheat is capable of hosting both races of fall armyworm.
Impact of insecticides on stink bugs and their natural enemies. Stink bugs have continued to increase in importance as key pests in cotton, and thus, understanding the impact of insecticides on these pests and their natural enemies has high priority. Studies were conducted to compare the susceptibility of stink bug pests and their natural enemies to insecticides. Generally, susceptibility of the predatory stink bug Podisus maculiventris to selected insecticides was higher than that of the brown stink bug pest. Selected insecticides also were as toxic, or more toxic, to the stink bug parasite Trichopoda pennipes as they were to the southern green stink bug. A laboratory study was conducted to determine the impact of two biopesticides, azadirachtin (neem) and spinosad (Entrust), on T. pennipes when walking on, being sprayed with, and feeding on the insecticides. Azadirachtin was the only insecticide in which T. pennipes adults survived in each of the experiments suggesting that this biopesticide would probably be the safer than the other biopesticide to this parasitoid in organically grown crops.
Pheromone attraction of stink bugs in the field. Detecting infestations of stink bugs using pheromones remains problematic, particularly so in the U.S. for the exotic stink bug, the southern green stink bug, and our native stink bug, the green stink bug. An on-farm study was conducted to examine the attractiveness and possible cross-attraction of the reported pheromones for the southern green stink bug and the green stink and those previously discovered for the brown stink bug and the brown-winged green stink bug to the southern green stink bug, the green stink bug, and the brown stink bug. The attractiveness of selected pentatomid pheromones to tachinid parasitoids of stink bugs was also examined. We demonstrated for the first time under field conditions that the southern green stink bug can be trapped with its reported pheromone. The green stink bug was significantly cross-attracted to the brown-winged green stink bug pheromone. The brown stink bug pheromone was more attractive to the brown stink bug than to any other pheromone tested. In general, tachinid parasitoids were found responsive to the pheromones of their known hosts, including the attractiveness of Trichopoda pennipes to the pheromones of the green stink bug and the southern green stink bug. A tachinid parasitoid of the brown stink bug, Cylindromyia spp., appeared to be attracted to the brown stink bug pheromone. In conclusion, our results indicate that stink bug traps baited with lures containing the southern green stink bug pheromone blend, the brown-winged green stink bug pheromone, and the brown stink bug pheromone have the greatest potential for detecting populations of the southern green stink bug, the green stink bug, and the brown stink bug, respectively, in diversified agroecosystems.
Pest insects and natural enemies in transitional organic cotton. The demand for organically grown crops has increased over the last 10 yrs due to consumer concern over food safety and the environment. However, there is a 3-yr period under the USDA National Organic Program Standard for farmers to transition their land to organic production from conventional production, and throughout this period, only compounds certified for use in organic production can be used for management of insects. The goal for this research was to determine the prospects for transitioning to a totally organic management system for cotton and peanut in Georgia. Heliothine larvae and stink bugs were the two major groups of insect pests in both cotton and peanut. Geocoris punctipes, red imported fire ants, and spiders were the most abundant predators of pest insects. The biopesticide neem oil was used for effective control of heliothine larvae. Currently, a biopesticide is not available for control of stink bugs so the main insect management problem in organic production of these crops is stink bugs. Other strategies, or combination of strategies, will need to be developed for management of these stink bug pest in organically-produced crops.
Plant-herbivore-carnivore interactions in cotton: linking belowground and aboveground. Most studies on plant-herbivore interactions focus on either root or shoot herbivory in isolation, but above- and belowground herbivores may interact on a shared host plant. Cotton produces a variety of terpenoids that exhibit toxicity to a wide range of herbivores and pathogens. Cotton plants also can emit herbivore-induced volatile compounds systemically on all tissues above the site of damage, and as these volatile compounds attract natural enemy species of the herbivore, they are thought to represent an indirect plant defense. Our study evaluated terpenoids and systemically induced volatile production by cotton plants in response to foliage feeding (Heliocoverpa zea), root feeding (Meloidogyne incognita) or their combination as well as the attraction of the parasitic wasp Microplitis croceipes to those plants. We also evaluated whether foliage or root feeding affected foliar nitrogen levels in cotton. After 48 hours of leaf feeding and 5 weeks of root feeding, systemic induction of volatiles (known to attract parasitoids such as M. croceipes) occurred with herbivore damage to leaves and increased in levels when root herbivory was added. Microplits croceipes were equally attracted to plants with both leaf and root damage and leaf damage only. In contrast to previous studies in cotton, terpenoids were not induced in leaf and root tissue following foliage or root herbivory, or their combination. We conclude that root feeding by M. incognita has little influence on direct defenses of cotton against insect herbivory.
Nitrogen and water affects on direct and indirect plant defense in cotton. Plants have direct and indirect constitutively produced and inducible defenses against herbivores and pathogens, which can substantially aid in their ability to defend themselves. However, very little is known about the influence of agronomic factors on such defenses. Here, we tested the effects of nitrogen levels and water availability on the ability of cotton plants to deter feeding by Spodoptera exigua through induction of anti-feedants, and to attract Micropitis croceipes through systemic induction of volatile emission. Cotton plants were grown with various nitrogen levels and were either exposed to water stress or normal water, before being exposed to S. exigua for 48 hours for induction of defenses. Dual choices of various nitrogen and water treatments were provided to M. croceipes in flight tunnel bio-assays. Dual choices of leaf tissue from the various nitrogen and water treatments were provided to S. exigua larvae. Both water stress and nitrogen levels under and over the recommended levels increased leaf tissue consumption and decreased attraction of M. croceipes to the plants. Analyses of induced volatiles released from herbivore damaged plants indicate that their concentrations differ among the nitrogen levels tested, plants receiving no nitrogen or twice the recommended dose having amounts much lower than plants receiving the recommended dose. Because both direct and indirect plant defense mechanisms are negatively affected by improper nitrogen and insufficient water, suggesting that these factors should be considered for a better natural control of pests in cotton and most probably in other crops.
Nitrogen affects beet armyworm performance, feeding, and oviposition preference. Nitrogen (N) is one of the most critical chemical elements for plant and animal growth, exerting a variety of bottom-up effects. Development and oviposition of the insect pest beet armyworm (BAW) were studied in relation to varying N fertilization in cotton. Low N in cotton plants led to reduced plant biomass and a lower percentage of N in leaf blades and petioles. Development of BAW fed low N plant tissue was prolonged relative to plants with higher N. Larvae distinguished between cotton plants with various N and fed preferentially on high N plants. Female moths preferred to oviposit on high N plants. These effects can have important implications for population dynamics and pest status of BAW in
Chemical detection and learning for parasitoid. Many insect species are able to detect chemical compounds at levels that are substantially lower than any technology currently available. We have recently determined that the learning ability of Microplitis croceipes is concentration dependent, and that a single wasp is able to learn and report two different concentrations of a compound using two specific behaviors. This ability is currently being exploited to determine their use in areas such as detection of aflatoxin presence and concentration in peanuts as well as levels of infestation of herbivores and other diseases of crops in the region. Total time and cost will be substantially reduced at the peanut grading process as well as for early detection of crop herbivory and disease in the field.
Peanut as a newly recognized host plant for stink bugs. Even though stink bugs have increased in importance as pests of cotton over the past several years, no information is available on the abundance of stink bugs in adjacent agricultural crops including peanut. The objective of this on-farm study was to determine if peanut harbors populations of stink bugs and their natural enemies. The predominant stink bug pests in peanut were the southern green stink bug and the brown stink bug. All development stages of both of these stink bugs were collected at various times in the study indicating that they were developing on this crop. Seasonal abundance of stink bugs showed that at least two generations of the southern green stink bug occurred in peanut each year, and one to two generations of the brown stink bug occurred in peanut. Adult stink bugs were parasitized by two species of flies. Stink bug eggs were parasitized by five different species of wasps. Stink bug predators also were present in peanut. Percent predation of stink bug eggs was higher than percent parasitization. In conclusion, peanut harbors populations of stink bug pests and their natural enemies, and so the role peanut plays in the distribution and abundance of stink bugs throughout the agricultural ecosystem needs to be ascertained to better understand how to manage stink bugs.
Tillman, P.G. 2009. Beneficial insects and insect pollinators on milkweed in south Georgia. J. Entomol. Sci. 44(4):402-409.
Chen, Y., Olson, D.M., Ruberson, J. 2010. Effects of nitrogen fertilization on tritrophic interactions. Arthropod-Plant Interactions. 4:81-94. DOI:10.1007/s11829-010-9092-5.
Rains, G., Kulasiri, D., Zhou, Z., Samarasinghe, S., Tomberlin, J.K., Olson, D.M. 2009. Synthesizing neurophysiology, genetics, behaviour and learning to produce whole-insect programmable sensors to detect volatile chemicals. Biotechnology and Genetic Engineering Reviews. 36:191-216. DOI:10.1603/EC09301.
Tillman, P.G., Aldrich, J.R., Khrimian, A., Cottrell, T.E. 2010. Pheromone attraction and cross-attraction of Nezara, Acrosternum, and Euschistus spp. stink bugs (Heteroptera: Pentatomidae) in the field. Environmental Entomology. 39(2):610-617.
Scully, B.T., Krakowsky, M.D., Ni, X., Wilson, J.P., Lee, R.D., Guo, B.Z. 2009. Preharvest aflatoxin contamination of corn and other grain crops grown on the U.S. southeastern coastal plain. Toxin Reviews. 28(2-3):169-179.
Tillman, P.G. 2010. Parasitism and predation for stink bug (Heteroptera: Pentatomidae) eggs in Georgia corn fields. Environmental Entomology. 39(4):1184-1194.