Jeff Gore

Potential exposure of pollinators to neonicotinoid insecticides from the use of insecticide seed treatments in the mid-southern United States.

Research was done during 2012 to evaluate the potential exposure of pollinators to neonicotinoid insecticides used as seed treatments on corn, cotton, and soybean. Samples were collected from small plot evaluations of seed treatments and from commercial fields in agricultural production areas in Arkansas, Mississippi, and Tennessee. In total, 560 samples were analyzed for concentrations of clothianidin, imidacloprid, thiamethoxam, and their metabolites. These included pollen from corn and cotton, nectar from cotton, flowers from soybean, honey bees, Apis mellifera L., and pollen carried by foragers returning to hives, preplanting and in-season soil samples, and wild flowers adjacent to recently planted fields. Neonicotinoid insecticides were detected at a level of 1 ng/g or above in 23% of wild flower samples around recently planted fields, with an average detection level of about 10 ng/g. We detected neonicotinoid insecticides in the soil of production fields prior to planting at an average concentration of about 10 ng/g, and over 80% of the samples having some insecticide present. Only 5% of foraging honey bees tested positive for the presence of neonicotinoid insecticides, and there was only one trace detection (< 1 ng/g) in pollen being carried by those bees. Soybean flowers, cotton pollen, and cotton nectar contained little or no neonicotinoids resulting from insecticide seed treatments. Average levels of neonicotinoid insecticides in corn pollen ranged from less than 1 to 6 ng/g. The highest neonicotinoid concentrations were found in soil collected during early flowering from insecticide seed treatment trials. However, these levels were generally not well correlated with neonicotinoid concentrations in flowers, pollen, or nectar. Concentrations in flowering structures were well below defined levels of concern thought to cause acute mortality in honey bees. The potential implications of our findings are discussed.

Regional assessment of Helicoverpa zea populations on cotton and non-cotton crop hosts

Selection pressure on bollworm, Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae), by cotton, Gossypium hirsutum (L.) (Malvaceae), that produces one or more Bacillus thuringiensis Berliner (Bt) proteins is reduced by plantings of non‐Bt refuge cotton that produce non‐selected individuals. However, the contributions of non‐Bt, non‐cotton crop hosts to the overall effective refuge for H. zea on Bt cotton have not been estimated. A 2‐year, season‐long study was conducted in five US cotton‐producing states to assess the spatial and temporal population dynamics and host use of H. zea. Helicoverpa zea larval estimates in commercial crop fields demonstrated that non‐cotton crop hosts, such as maize, Zea mays L. (Poaceae), grain sorghum, Sorghum bicolor (L.) Moench (Poaceae), peanut, Arachis hypogaea L. (Fabaceae), and soybean, Glycine max (L.) Merrill (Fabaceae), collectively support much larger larval populations than cotton throughout the season. Larval populations were almost entirely restricted to maize in the middle part of the season (June and portions of July), and were observed in non‐cotton crop hosts more frequently and typically in larger numbers than in cotton during the period when production would be expected in cotton (July and August). Numbers of H. zea larvae produced in replicated strip trials containing various crop hosts paralleled production estimates from commercial fields. In contrast, the number of H. zea adults captured in pheromone traps at interfaces of fields of Bt cotton and various crop hosts rarely varied among interfaces, except in instances where maize was highly attractive. With the exception of this early season influence of maize, moth numbers were not related to local larval production. These data demonstrate that H. zea adults move extensively from their natal host origins. Therefore, non‐cotton crop hosts, and even relatively distant hosts, contribute significantly to effective refuge for H. zea on Bt cotton. The results presented here demonstrate that substantial natural refuge is present for Bt‐resistance management of H. zea throughout the mid‐South and Southeast portions of the US cotton belt.

FIELD AND LABORATORY PERFORMANCE OF NOVEL INSECTICIDES AGAINST ARMYWORMS (LEPIDOPTERA: NOCTUIDAE)

Abstract Beet armyworm, Spodoptera exigua (Hübner), and fall armyworm, Spodoptera frugiperda (J. E. Smith), are occasional pests of cotton, Gossypium hirsutum (L.), and soybean, Glycine max (L.) Merrill. These insects can be difficult to control due to insecticide resistance and larval behavior on plants. The objectives of these studies were to determine the efficacy of selected insecticides against native infestations of beet armyworm in cotton and soybean and to generate baseline dose-mortality responses for beet armyworm and fall armyworm adults to indoxacarb and pyridalyl in the adult vial test. Indoxacarb, pyridalyl, spinosad, methoxyfenozide, and emamectin benzoate controlled beet armyworm infestations up to 10 d after treatment compared to the non-treated control. Thiodicarb reduced beet armyworm densities up to three d after treatment. The LC50 values of indoxacarb and pyridalyl for beet armyworm and fall armyworm exceeded the highest concentrations tested (100-200 μg/vial) in the adult vial test. Dose-mortality values of indoxacarb and pyridalyl were higher than discriminating concentrations of cypermethrin, methomyl, profenofos, and endosulfan used in the adult vial test for monitoring tobacco budworm, Heliothis virescens (F.), and bollworm, Helicoverpa zea (Boddie), susceptibility in Louisiana and Texas. These results indicate that the adult vial test may not be the most efficient test method for indoxacarb and pyridalyl in insecticide susceptibility monitoring programs.

Bioassay for Determining Resistance Levels in Tarnished Plant Bug1 Populations to Neonicotinoid Insecticides

A laboratory bioassay was developed and used to test field populations of the tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), for development of resistance to the neonicotinoid insecticides imidacloprid (Trimax®) and thiamethoxam (Centric®). The bioassay determined LC50 values by feeding adult tarnished plant bugs known doses of the insecticides in a 10% solution (by weight) of honey in water. Field populations from 19 (imidacloprid) and nine (thiamethoxam) locations in the mid-South were tested in 2006 and their LC50s were compared to LC50 values determined in tarnished plant bug populations at the same locations in 2007. The LC50 values were also compared to LC50 values determined using imidacloprid and thiamethoxam on a susceptible population from Crossett, AR. Results of the comparisons showed that no resistance to thiamethoxam had developed in the nine populations tested. Some resistance to imidacloprid was found in most of the test populations, because their LC50 values were significantly greater than the LC50 value for the susceptible population from Crossett. Resistance to imidacloprid did not increase in populations at 10 locations from 2006 to 2007, and the LC50 values were not significantly different between the two years. The LC50 for imidacloprid in 2007 was significantly greater than the LC50 in 2006 in populations at only four of the 19 test locations. These results showed that while some resistance to imidacloprid was present, the overall tendency was for the resistance to remain the same or decrease during the two years it was studied. The bioassay developed and used in the study is the only rapid method available for monitoring resistance in tarnished plant bug populations to neonicotinoid insecticides. The baseline data for both imidicloprid and thiamethoxam provide a basis for comparison to determine changes in resistance in future monitoring studies.

Predicting Field Control of Tarnished Plant Bug (Hemiptera: Miridae) Populations with Pyrethroid Insecticides by Use of Glass-Vial Bioassays

Tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), populations from 21 locations in the Mississippi River Delta of Arkansas and Mississippi were tested for resistance to permethrin in 2004 and 2005. Each population was tested using permethrin in a discriminating-dose bioassay to determine percent mortality, and with a glass-vial bioassay that used dose-response regression lines to determine LC50 values for permethrin. Results from the two bioassays were compared by regression of percent mortalities with LC50 values. The regression was significant with an R2 value of 0.90 which showed that the two methods of determining resistance were closely correlated. The regression equation had a slope of −0.74 and an intercept of 72.06, which showed that the LC50 value decreased by 7.4 μg/vial for every 10% increase in mortality in the discriminating-dose bioassay. Percent mortality in the discriminating-dose bioassay and LC50 values were related to control of plant bugs in the field using four spray chamber and one field cage test. Plant bug populations in these tests were not controlled with four different pyrethroids applied at recommended field rates. Results indicated that either a LC50 value of 24 μg/vial or greater of permethrin, or 60% or less mortality in the discriminating-dose bioassay with permethrin, could be used to predict field control problems with plant bugs and pyrethroid insecticides in cotton, Gossypium hirsutum L. The discriminating-dose bioassay is a much easier bioassay to use as compared to determining LC50 values using dose-mortality curves. It could be easily used by researchers, consultants, or Cooperative Extension personnel in an insecticide resistance monitoring program for tarnished plant bugs.

Susceptibility of Chrysodeixis includens (Lepidoptera: Noctuidae) to Reduced-Risk Insecticides

ABSTRACT Field populations of soybean looper, Chrysodeixis includens (Walker) (Noctuidae), were collected from soybean, Glycine max (L.) Merr., fields in Mississippi and Louisiana during 2010 and 2011 to determine their susceptibility to novel insecticides. Flubendiamide and chloran-traniliprole are diamide insecticides that have recently been registered for use in field crops. Baseline data were collected for each of these insecticides as well as for methoxyfenozide, which has been the recommended insecticide for soybean looper in Mississippi soybeans prior to the introduction of these new novel insecticides. Mean LC50 values for flubendiamide and chlorantraniliprole were similar among the populations tested, and susceptibility was higher for methoxyfenozide compared to flubendiamide and chlorantraniliprole. Diet incorporated assays determined a 9.4-fold variation in susceptibility to flubendiamide among the 7 soybean looper populations tested. Variation to chlorantraniliprole was 6.25-fold and variation for methoxyfenozide was 5.37-fold. Variation in the diamide insecticides was higher than methoxyfenozide with less exposure to soybean looper populations. Documenting variability along with baseline data will be useful in the future for resistance monitoring of soybean loopers to diamide insecticides.

Influence of Maize and Pigweed on Tarnished Plant Bug (Hemiptera: Miridae) Populations Infesting Cotton

Abstract. The influence of maize, Zea mays L., and pigweed, Amaranthus spp., on the abundance of tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), adults infesting cotton, Gossypium hirsutum L., in the Mississippi Delta was studied using stable-isotope analyses. Cotton fields adjacent to maize and those farther than 1.6 km from maize were identified in four counties of the Mississippi Delta. Tarnished plant bug adults were collected from the cotton fields weekly throughout the growing season and analyzed with stable-carbon and nitrogen isotopes to determine the natal host. The proportion of tarnished plant bug adults collected from cotton that developed as nymphs on plants that used the C4 photosynthetic pathway, primarily maize and pigweed, peaked from 79–92% during 2008–2009. Distance of cotton fields from maize did not influence the peak proportion of tarnished plant bug adults with a C4 signature from cotton fields, the peak time, or peak duration. Time of the C4 peaks occurred from 28 June to 8 July, and the duration was between 13 and 19 days. Stable-nitrogen isotope analyses indicated maize was the major contributor of C4 tarnished plant bugs infesting cotton compared to pigweed. Nevertheless, pigweed produced a significant proportion of tarnished plant bug adults infesting cotton. Improved control of these weed species could potentially reduce abundance of tarnished plant bugs in cotton. Because maize makes up a significant amount of the crop acreage in the Mississippi Delta, this information can be used to estimate the time of mass movement, thus allowing more efficient use of insecticide to control tarnished plant bugs in cotton. It may also allow future targeting of tarnished plant bugs in field corn before movement to cotton.