Brian A. Nault

Patterns of Insecticide Resistance in Onion Thrips (Thysanoptera: Thripidae) in Onion Fields in New York

To develop an insecticide resistance management program for onion thrips, Thrips tabaci Lindeman (Thysanoptera: Thripidae), on onions (Allium spp.), we surveyed populations in commercial onion fields in New York and evaluated their susceptibility to the two most widely used classes of insecticides plus two new insecticides during 2003-2005. All insecticide evaluations were conducted using the Thrips Insecticide Bioassay System (TIBS). As in our surveys conducted during 2002-2003, there were large temporal and spatial variations in susceptibility to the pyrethroid lambda-cyhalothrin (Warrior) across onion-growing regions in 2003. New data indicate that the field rate of methomyl (Lannate LV) still provides control but that the genes for resistance to methomyl are present in some populations. Tests with the two new insecticides, acetamiprid (Assail 70 WP) and spinosad (SpinTor 2CS), indicated they provided > 85% mortality at the field rate. To determine the spatial variation in insecticide susceptibility within a region, a series of systematic assays were conducted with lambda-cyhalothrin and methomyl. In 2004 and 2005, our data indicated that the within-region spatial variation in susceptibility to lambda-cyhalothrin was not large at the field rate or for the 100 ppm rate of methomyl. In 2005, a year in which T. tabaci densities in most fields were much higher than in 2004, growers were unable to control T. tabaci in particular fields and attributed this lack of control to resistance. Yet, we found similar levels of high susceptibility in all fields when using TIBS. This finding suggests that resistance had not developed and that variation in control may have been due to other factors, such as localized higher populations, poor spray coverage, too much time between spray applications, or different onion varieties.

Onion Thrips (Thysanoptera: Thripidae): A Global Pest of Increasing Concern in Onion

ABSTRACT During the past two decades, onion thrips, Thrips tabaci Lindeman (Thysanoptera: Thripidae), has become a global pest of increasing concern in commercial onion (Allium cepa L.), because of its development of resistance to insecticides, ability to transmit plant pathogens, and frequency of producing more generations at high temperatures. T. tabaci feeds directly on leaves, causing blotches and premature senescence as well as distorted and undersized bulbs. T. tabaci can cause yield loss >50% but can be even more problematic when it transmits Iris yellow spot virus (family Bunyaviridae, genus Tospovirus, IYSV). IYSV was identified in 1981 in Brazil and has spread to many important onion-producing regions of the world, including several U.S. states. IYSV symptoms include straw-colored, dry, tan, spindle- or diamond-shaped lesions on the leaves and scapes of onion plants and can cause yield loss up to 100%. Here, we review the biology and ecology of T. tabaci and discuss current management strategies based on chemical, biological, and cultural control as well as host resistance. Future directions for research in integrated pest management are examined and discussed.

Temperature and Precipitation Affect Seasonal Patterns of Dispersing Tobacco Thrips, Frankliniella fusca, and Onion Thrips, Thrips tabaci (Thysanoptera: Thripidae) Caught on Sticky Traps

Abstract Effects of temperature and precipitation on the temporal patterns of dispersing tobacco thrips, Frankliniella fusca, and onion thrips, Thrips tabaci, caught on yellow sticky traps were estimated in central and eastern North Carolina and eastern Virginia from 1997 through 2001. The impact that these environmental factors had on numbers of F. fusca and T. tabaci caught on sticky traps during April and May was determined using stepwise regression analysis of 43 and 38 site-years of aerial trapping data from 21 and 18 different field locations, respectively. The independent variables used in the regression models included degree-days, total precipitation, and the number of days in which precipitation occurred during January through May. Each variable was significant in explaining variation for both thrips species and, in all models, degree-days was the single best explanatory variable. Precipitation had a comparatively greater effect on T. tabaci than F. fusca. The numbers of F. fusca and T. tabaci captured in flight were positively related to degree-days and the number of days with precipitation but negatively related to total precipitation. Combined in a single model, degree-days, total precipitation, and the number of days with precipitation explained 70 and 55% of the total variation in the number of F. fusca captured from 1 April through 10 May and from 1 April through 31 May, respectively. Regarding T. tabaci flights, degree-days, total precipitation, and the number of days with precipitation collectively explained 57 and 63% of the total variation in the number captured from 1 April through 10 May and from 1 April through 31 May, respectively.

Reproductive Modes in Onion Thrips (Thysanoptera: Thripidae) Populations from New York Onion Fields

Abstract Thrips exhibit different reproductive modes including thelytoky (females produced from unfertilized eggs), arrhenotoky (males produced from unfertilized eggs and females produced from fertilized eggs) and deuterotoky (females and males produced from unfertilized eggs). We investigated patterns of reproductive modes in onion thrips, Thrips tabaci Lindeman, populations and potential effects of the bacterium Wolbachia and temperature on these modes. We also examined the possibility that male-producing T. tabaci populations were resistant to the frequently used insecticides, lambda-cyhalothrin and methomyl. In New York during 2002–2004, T. tabaci populations were sampled from 20 onion fields and reproductive mode was determined by identifying sex of progeny from virgins. Half of the populations were thelytokous and half were a mix of thelytokous, arrhenotokous and deuterotokous individuals, which we refer to as a male-producing population. In two of four cases, the reproductive mode of a population from the same onion field changed across years, suggesting that populations either mix or an external factor caused the change. To address the latter, we speculated that Wolbachia or high temperature mediated reproductive modes. Samples of T. tabaci representing each reproductive mode were examined for Wolbachia using diagnostic polymerase chain reaction (PCR), but it was not detected. Cytological examination of ovaries from two additional thelytokous lines also showed no evidence of Wolbachia. Similarly, high temperature did not affect sex allocation ratios in either thelytokous or male-producing populations. Male-producing T. tabaci populations were not positively correlated with resistance to lambda-cyhalothrin, or tolerance to methomyl. The role of the different reproductive modes in T. tabaci populations in onion fields remains unclear.

Performance of Apis mellifera, Bombus impatiens, and Peponapis pruinosa (Hymenoptera: Apidae) as Pollinators of Pumpkin

ABSTRACT Pollination services of pumpkin, Cucurbita pepo L., provided by the European honey bee, Apis mellifera L., were compared with two native bee species, the common eastern bumble bee, Bombus impatiens (Cresson), and Peponapis pruinosa Say, in New York from 2008 to 2010. Performance of each species was determined by comparing single-visit pollen deposition, percentage of visits that contacted the stigma, flower-handling time, fruit and seed set, and fruit weight per number of visits. Fruit yield from small fields (0.6 ha) supplemented with commercial B. impatiens colonies was compared with yield from those not supplemented. A. mellifera spent nearly 2 and 3 times longer foraging on each pistillate flower compared with B. impatiens and P. pruinosa, respectively. A. mellifera also visited pistillate flowers 10–20 times more frequently than B. impatiens and P. pruinosa, respectively. Yet, B. impatiens deposited 3 times more pollen grains per stigma and contacted stigmas significantly more often than either A. mellifera or P. pruinosa. Fruit set and weight from flowers visited four to eight times by B. impatiens were similar to those from open-pollinated flowers, whereas flowers pollinated by A. mellifera and P. pruinosa produced fewer fruit and smaller fruit compared with those from open-pollinated flowers. Fields supplemented with B. impatiens produced significantly more pumpkins per plant than nonsupplemented fields. B. impatiens was a better pollinator of pumpkin than P. pruinosa and should be considered as a promising alternative to A. mellifera for pollinating this crop.

Seasonal and Spatial Dynamics of Alate Aphid Dispersal in Snap Bean Fields in Proximity to Alfalfa and Implications for Virus Management

Abstract Alfalfa is a source for viruses that may be acquired by aphids and transmitted to snap bean, Phaseolus vulgaris L. Snap bean fields in proximity to alfalfa could have an increased risk of virus infection. Knowledge of the abundance and temporal and spatial dispersal patterns of commonly encountered aphids in commercial snap bean fields, varying in distance from alfalfa, could provide insight into this risk. Alate aphids were monitored using water pan traps in snap bean and alfalfa fields that were adjacent to or >1 km away from each other. The pea aphid, Acyrthosiphon pisum (Harris), was the most common aphid species captured in early-planted snap bean fields in 2002 and 2003 (56 and 23% of total, respectively), whereas the corn leaf aphid, Rhopalosiphum maidis (Fitch), also was common in 2003 (15% of total). In contrast, the yellow clover aphid, Therioaphis trifolii (Monell), and soybean aphid, Aphis glycines Matsumura, were the most abundant species trapped in late-planted snap bean fields in 2002 (77% of total) and 2003 (64% of total), respectively. These species were prevalent in traps in alfalfa as well. The abundance and temporal dispersal patterns of these species in snap beans adjacent to and >1 km away from alfalfa were similar, suggesting that the risk for virus infection may not be affected by proximity to alfalfa. A similar number of alate aphids also were captured along snap bean field edges and field centers, regardless of their proximity to alfalfa. This suggests that the aphids dispersed into snap bean randomly rather than directionally from the field edge. The implication of these results is that separating snap bean fields from alfalfa or using crop borders/barriers are not likely to be successful virus management strategies.

Evaluation of Onion Cultivars for Resistance to Onion Thrips (Thysanoptera: Thripidae) and Iris Yellow Spot Virus

ABSTRACT Onion thrips, Thrips tabaci Lindeman (Thysanoptera: Thripidae), a worldwide pest of onion, Allium cepa L., can reduce onion yield by >50% and be even more problematic when it transmits Iris yellow spot virus (family Bunyaviridae, genus Tospovirus, IYSV). Because T. tabaci is difficult to control with insecticides and other strategies, field studies on onion, Allium cepa L., resistance to T. tabaci and IYSV were conducted in 2007 and 2008 in two locations in New York state. Forty-nine cultivars were evaluated for resistance by counting the number of larvae weekly and recording leaf damage. In another experiment, the impact of T. tabaci and IYSV on plant growth and yield was examined by spraying half of the plants with an insecticide. Eleven of the 49 cultivars had very little leaf damage and were considered resistant to T. tabaci. Visual assessment indicated that all resistant cultivars had yellow-green— colored foliage, whereas the other 38 had blue-green—colored foliage. The visual assessment of color agreed with data on color taken with a HunterLab Ultra Scan XE colorimeter. The onions ‘Colorado 6’ and ‘NMSU 03-52-1’ had the lowest numbers of T. tabaci, suggesting strong antibiosis and/or antixenosis. The other nine cultivars had variable numbers of T. tabaci, indicating a possible combination of categories of resistance. In the nonprotected treatments there were significant reductions in plant height and plant weight in most of the resistant cultivars, but there were reductions in bulb weight only in a few of them. The average of plants infected with IYSV was 10% in 2007 and 60% in 2008. Our findings indicate potential for developing onion resistance to T. tabaci as part of an overall integrated pest management strategy but suggest difficulties in identifying resistance to IYSV.

Impact of Insecticide Efficacy on Developing Action Thresholds for Pest Management: A Case Study of Onion Thrips (Thysanoptera: Thripidae) on Onion

ABSTRACT An action threshold (AT) is one of the most important decision-making elements in integrated pest management. Unlike economic thresholds, ATs are not typically derived from an economic injury level model, but they are more commonly used. ATs may be identified from research-based, pest—crop relationships, but they also may be based on experience. ATs may be adjusted depending on, e.g., weather and plant variety, but modifying ATs to accommodate differences in insecticide efficacy has received little attention. To examine this point, several combinations of ATs and insecticides were evaluated against onion thrips, Thrips tabaci Lindeman (Thysanoptera: Thripidae), a major pest of onion (Allium cepa L.). Studies were conducted in New York onion fields from 2006 to 2008 by using registered insecticides for T. tabaci on onions. We hypothesized that the most efficacious insecticides would provide acceptable control of thrips populations regardless of AT (one, three, and five thrips per leaf), whereas less effective products would only control populations using the lowest AT (one thrips per leaf), Results indicated that T. tabaci infestations were managed effectively when spinetoram was applied after a three larvae per leaf threshold, but not when using lambda-cyhalothrin, methomyl or formetanate hydrochloride. However, T. tabaci infestations were managed well when methomyl and formetanate hydrochloride were applied after a one larva per leaf threshold. T. tabaci infestations were never controlled using lambda-cyhalothrin, regardless of the AT used. None of the products reduced T. tabaci populations to an acceptable level when applied at a five larvae per leaf threshold. Implications of adjusting ATs based on efficacy of different insecticides are discussed.

Establishment of multicolored Asian lady beetle in Eastern North Carolina: Seasonal abundance and crop exploitation within an agricultural landscape

Seasonal abundance and cropexploitation of the multicolored Asian ladybeetle, Harmonia axyridis (Pallas)(Coccinellidae: Coleoptera), were identifiedduring its initial establishment in the easternNorth Carolina agroecosystem. Densities ofH. axyridis adults and larvae werecompared with densities of previouslyestablished predaceous coccinellids in wheat,potato, corn and soybean, which are thepredominant crops in this region. One-hundred-fifty whole plant samples werevisually inspected for coccinellid adults andlarvae in each crop on six farms every 7 to 14days. H. axyridis adults colonizedwheat, potato and corn, but reproduced only inwheat and potato. Soybean fields were notcolonized. The presence of H. axyridisin a crop was typically associated with anabundance of aphids, with the exception ofpotato, and no aphids were encountered insoybean. In addition to H. axyridis,four other lady beetle species, Coccinellaseptempunctata L., Coleomegilla maculata(DeGeer), Hippodamia convergens (Guerin)and Cycloneda munda L., were encounteredin the landscape. In wheat, potato and corn,densities of H. axyridis adults averagedthroughout the 1995 and 1996 seasons wereseven, ten and 28 times lower, respectively,than the season average density of the leastabundant species of previously established ladybeetle, whereas these densities averaged 82, 42and 356 times lower, respectively, than theaverage density of the most abundantestablished coccinellid species. H.axyridis is commonly encountered in theeastern North Carolina agricultural landscape,but its impact on the existing coccinellidassemblage cannot yet be determined. Theresults presented provide a baseline againstwhich the results of future studies can becompared to determine if H. axyridis isdisplacing established species.

Colonization of potato fields in eastern North Carolina by Colorado potato beetle

Rotated and non‐rotated commercial potato fields were sampled intensively to follow Colorado potato beetle, Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae), colonization and subsequent oviposition patterns in the spring of 1990 and 1991. Maximum densities of colonizing adults ranged from 0 to 14,891/ha and maximum egg mass densities ranged from 0 to 48,451/ha. Crop rotation generally resulted in lower potato beetle populations. Regardless of crop rotation management practices, colonization of fields planted in potatoes began at field edges and progressed inward in all fields for both years. Management of potato beetles is discussed in light of these findings.