Location: Crop Protection and Management Research2012 Annual Report
1a. Objectives (from AD-416):
1. Determine biological, ecological, and structural mechanisms driving stink bug population dynamics in the southeastern region of the United States. 1.A. Study the role of landscape make-up on populations of stink bugs. i. Confirm the sequence of habitats used by the stink bugs Nezara viridula and Euschistus servus in southern Georgia prior to colonization of cotton. ii. Estimate the parameters (net reproductive rate and interpatch movement) in our simple patch model that predicts stink bug colonization of cotton, and fit the model using data. iii. Using the parameterized model, predict the effects of landscape structure on the colonization of cotton by these stink bugs and test the model predictions. 1.B. Evaluate semi-field bioassays for the effects of relative crop quality on major crops used simultaneously by stink bugs. 1.C. Determine the role Bt technology and concomitant reduction in insecticide use and both Bt-targeted and non-targeted inter-specific insect pest interactions on pest invasiveness. 1.D. Assess survival of stink bug egg masses in soybean, cotton, and peanut. 1.E. Identify uncultivated host plant sources of stink bugs for cotton. 2. Develop and test bio-based management systems for stink bugs that are widely adaptable to various cropping systems in the southeastern region of the United States. 2.A. Evaluate non-chemical management practices that reduce populations of overwintering stink bugs such as through the use of controlled burns in woodland understory. 2.B. Determine the effectiveness of pheromone traps to capture stink bugs in a trap crop. 2.C. Determine the ability of a habitat of nectar-producing plants to provide food to natural populations of stink bug parasitoids. 2.D. Determine the effectiveness of a multifunctional habitat to serve as a trap crop for stink bugs and a site for conservation and feeding for bees and other insect pollinators and natural enemies of stink bugs. 3. Assess the ability of various southeastern region winter crops (legumes and small grains) to host a diversity and abundance of beneficial and pest species, and to determine the impact that these insects have on crop protection and damage in continuous cropping systems. 3.A. Determine the host plant affinity of the strains of fall armyworm to winter grain species grown in the southeastern U.S. 3.B. Determine the relative benefit of grasses, legumes, and winter weeds as early season habitat for beneficial arthropods and their relay into later planted sorghum. 4. Using knowledge gleaned about insect enemies, evaluate the use of trained parasitoid wasps in detection of aflatoxin concentrations in peanuts at the peanut grading stage.
1b. Approach (from AD-416):
Map and ground-truth aerial photos and collect data on stink bug 5th instar density over time in corn, cotton, soybean and peanut in four landscapes to estimate parameters (habitat colonization and net reproductive rate) of an existing simple patch model and confirm sequence of host use for stink bugs. Conduct a study on stink bug longevity for Bt cotton, RR cotton, peanut and soybean using plant cages. Use data on relative longevity of stink bugs and data from previous studies on relative stink bug preference for crops to further parameterize the model. Conduct studies on competition between stink bugs and heliothines at the cotton boll and branch scales and on stink bug feeding and oviposition preference for heliothine damaged and undamaged cotton plants. Volatiles and plant tissue will be analyzed for herbivore anti-feedants. Stink bug eggs will be placed as sentinels in Bt cotton, RR cotton, peanut and soybean to obtain data on egg mortality. Occurrence and abundance of stink bugs will be assessed for uncultivated host plants of stink bugs adjacent to cotton fields. Data on density of overwintering populations of stink bugs will be collected in agricultural fields with managed low intensity burns under the woodland and in fields with no woodland burns. Data on density of a stink bugs will be collected in soybean trap crops with and without stink bug pheromone capture traps in agricultural farmscapes. Data will be collected on stink farmscapes with and without a habitat of nectar-producing plants. Data will be collected on stink bug density and damage to cotton in agricultural farmscapes with and without a multifunctional habitat with plant species for trapping stink bugs and other plants for providing resources to natural enemies of these pests. Data will be collected on density of specific sorghum pest and beneficial insects and predation and parasitism rates of pests in both the winter cover crops and subsequent summer crops. Volatiles from aflatoxin infested and uninfested peanuts will be collected and analyzed using gas chromatography mass spectrometry (GC-MS) and a strong volatile correlate to aflatoxin infested peanuts will be identified. Data on the ability of wasps to detect aflatoxin infested peanuts at the grading stage will be collected using the portable 'wasp hound'.
3. Progress Report:
The third year of a study of the effects of landscapes on stink bug populations in southern Georgia was conducted (Objective 1). All of the field data in the regional analysis and most of the data for parameterization of the model predicting stink bug populations in cotton have been collected. The stink bug populations were found not to originate from the woodland adjacent in four major crops grown in the region, regardless of the landscape. There were also competitive interactions between heliothine larvae and stink bugs that were species dependent. Stink bugs prefer to oviposit on undamaged cotton over cotton damaged by heliothine larvae, and preferences for these plants for feeding was dependent on the stink bug and heliothine species. The third year of a study of the effects of various legumes on pest and beneficial arthropod species in a sorghum for biofuel and cotton rotation system was conducted (Objective 3). Cahaba white vetch and lupine winter covers were found to increase the beneficial to pest ratios in the covers and this transferred into the subsequent cotton and sorghum crops compared to the other four legume species. Lupine covers were also found to increase both crop yields significantly more than the other legume winter covers. Wasps as biosensors were studied (Objective 4). Learning and reporting of three chemicals by the wasp species, Microplitis croceipes, is both chemical and concentration dependent and results were reported in the provisional patent (Docket # 0025.10). Additional experiments conducted with two other compounds, one of which is associated with strawberry rot from the fungus, Phytpphthora cactorum, have confirmed these results and will be added to the final patent due in August 2012. The second year of a study to determine the ability of a trap cropping system in peanut-cotton plots was conducted (Objective 2). The trap cropping system included a trap crop, soybean, a nectar-producing plant, buckwheat, and stink bug pheromone capture-kill traps. Stink bugs were much lower in cotton with the trap cropping system compared to cotton without this system. A laboratory study was conducted to determine the ability of two IGR (insect growth regulator) insecticides to kill southern green stink bugs and brown stink bugs (Objective 2). Both azadiractin (Neem) and novaluron (Diamond) effectively killed immature stink bugs as they tried to molt into the succeeding stage of maturation.
1. Pest tradeoffs in technology. Reduced damage by caterpillars in Bt cotton benefits aphids. The rapid adoption of genetically engineered plants that express insecticidal Cry proteins derived from Bacillus thuringiensis (Bt) has raised concerns about their potential impact on non-target organisms. Particular concern lies with the possibility that herbivores insensitive to the Bt toxin might develop pest status in Bt crops, and a number of studies have now reported increased levels of non-target pests in Bt crops which threatens to compromise the sustainable use of the transgenic varieties. We show that, because of effective suppression of Bt sensitive lepidopteran herbivores, Bt cotton contains reduced levels of induced terpenoid aldehydes and changes in the overall level of these defensive secondary metabolites are associated with improved performance of a Bt-insensitive herbivore, the aphid Aphis gossypii, under glasshouse and field conditions. This study helps explain non-target pest outbreaks in Bt crops and will improve management of resistance development in the target pest populations.
2. Release from competition with Bt-susceptible pest species may contribute to increased stink bug populations in Bt cotton. Competitive interactions through differences in growth rates between the two stink bug species, Nezara viridula and Euchistus servus, and the Bt-susceptible pests Heliocoverpa zea and Heliothis virescens caterpillars had equivalent effects on resource availability, but distinctly different effects on stink bug growth rates. Fourth instar H. zea reduced growth rates of both stink bug species by 60% when caged on a single cotton boll and reduced growth rates of only E. servus by 36% when caged on a cotton branch. In contrast, H. virescens had no effect on stink bug growth rates. Resource competition was apparent in the interactions between H. zea and E. servus, but interference competition (i.e. direct aggressive interactions between individuals that interfere with foraging, survival, reproduction or by physical prevention of establishment in a portion of the habitat) may also have contributed to the interactions. Competitive release as a contributing mechanism of stink bug population increases in Bt cotton is possible, and is more likely for E. servus than for N. viridula.
3. Deterrence and facilitation of stink bugs through induced responses in cotton. Herbivory often induces systemic plant responses that affect subsequent herbivores feeding preference. Understanding the mechanisms of feeding preferences provides insight into the potential ecological significance of preference. Preference responses of two fruit-feeding stink bug species, Nezara viridula and Euschistus servus to herbivory by two caterpillar species, Helicoverpa zea and Heliothis virescens was investigated on cotton plants. Prior H. zea feeding inhibited, whereas H. virescens feeding facilitated, E. servus feeding on damaged plants. Caterpillar feeding did not affect N. viridula feeding behavior. Caterpillar herbivory caused an overall reduction in phenolic concentration with a particularly strong reduction in chlorogenic acid in bolls from plants damaged by H. virescens. Euschistus servus preference was strongly influenced by host selection and host edibility but phenolics did not likely influence plant choice.
4. Effects on stink bugs of field edges adjacent to woodland. Stink bug responses to crop edges in fields of corn, peanut, cotton and soybean adjacent to woodland were found most often to be random with respect to the woodland edge of all crops examined. The exception occurred mainly in corn fields, where more stink bugs were found at the crop edge when flowering alternative hosts were present in the woodland edges. In 113 fields of four major crops grown in this area, the woodland edge was not a major source from which stink bugs colonized these crops. These results suggest that edge-specific control measures should not be concentrated at those field edges adjacent to woodlands, thereby reducing insecticide applications and management and environmental costs.
5. Threshold detection of boar taint chemicals using parasitic wasps. The need for threshold chemical detection, rather than simple detection of absence/presence of a chemical applies to many food quality issues, including the detection of spoilage or pest damage in crops or stored foods. Surgical castration has been long used to prevent consumers from experiencing taint in meat from male pigs, which is a large problem in the pig husbandry industry. Due to obvious animal welfare issues, Europe now wants an alternative for castration, suggesting an urgent need for novel methods of boar taint detection. The wasp, Microplitis croceipes showed both compound and concentration specific responses to the boar taint compounds, skatole, androstenone and indole. Also tested was the wasps’ ability to discriminate between known concentrations of indole, skatole and androstenone in real boar fat samples at room temperature. The wasps were also successful in reporting low, medium and high concentrations of indole, skatole and androstenone in boar fat at room temperature. Application of the wasp biosensor for the commercial detection of boar taint at threshold and higher concentrations appears to have high potential.
6. Food provision for natural enemies. Many natural enemies of agricultural insect pests require food, such as nectar or pollen, to live and reproduce. However, in many agricultural systems, food resources for natural enemies are lacking. Stink bug parasites and insect pollinators were observed feeding on nectar of milkweed near cotton. Parasitism of the southern green stink bug and the green stink bug was 3-5 times higher in cotton when this nectar resource was present than in cotton without this resource. In conclusion, providing food for natural enemies of stink bugs can increrase their ability to kill stink bugs in cotton.
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