Nicholas J. Seiter

Reduction of Soybean Yield Components by Megacopta cribraria (Hemiptera: Plataspidae)

ABSTRACT Since its discovery in the United States, the invasive plataspid Megacopta cribraria (F.) (Hemiptera: Plataspidae) has infested soybean [Glycine max (L.) Merrill] fields in often alarming numbers in parts of the southeastern United States. Although a known feeder on soybean, reports of its pest status in its native Asian range are conflicting, and little information exists documenting its impact on soybean yields. Our objective was to examine the relationship between M. cribraria density and soybean yield loss. M. cribraria adults and nymphs were confined to small soybean plots by using walk-in field cages from late vegetative stage to harvest in 2011 and 2012. Adults (0, 5, or 25 per plant) were added at late vegetative stages, and their progeny were allowed to complete a full generation within the caged plots. Densities reached as high as 182.5 ± 23.1 (SEM) nymphs and adults per plant, and soybean yield was reduced by as much as 59.6% at the highest density treatment. The yield components seeds per pod and individual seed weight were reduced as M. cribraria densities increased, but pods per plant and protein and oil content were not affected. Preliminary economic injury level curves for a range of grain prices and management costs were calculated based on 2012 yield loss data combined with population monitoring. M. cribraria is capable of causing severe reductions in soybean yields at densities that are relevant within its invasive U.S. range.

Within-Field Spatial Distribution of Megacopta cribraria (Hemiptera: Plataspidae) in Soybean (Fabales: Fabaceae)

ABSTRACT The recently introduced plataspid Megacopta cribraria (F.) can infest fields of soybean (Glycine max (L.) Merrill) in the southeastern United States. Grid sampling in four soybean fields was conducted in 2011 and 2012 to study the spatial distribution of M. cribraria adults, nymphs, and egg masses. Peak oviposition typically occurred in early August, while peak levels of adults occurred in mid-late September. The overall sex ratio was slightly biased at 53.1 ± 0.2% (SEM) male. Sweep samples of nymphs were biased toward late instars. All three life stages exhibited a generally aggregated spatial distribution based on Taylors power law, Iwaos patchiness regression, and spatial analysis by distance indices (SADIE). Interpolation maps of local SADIE aggregation indices showed clusters of adults and nymphs located at field edges, and mean densities of adults were higher in samples taken from field edges than in those taken from field interiors. Adults and nymphs were often spatially associated based on SADIE, indicating spatial stability across life stages.

Insecticidal Control of Megacopta cribraria (Hemiptera: Plataspidae) in Soybean

Abstract  The invasive kudzu bug, Megacopta cribraria (F.) (Hemiptera: Plataspidae), has become an economic pest of soybean, Glycine max (L.) Merrill, in the southeastern United States since its initial discovery in Georgia. Information on management practices, including insecticides, is limited due to its uncertain pest status in its native range and recent introduction to the United States. We evaluated the efficacy in controlling M. cribraria and economic benefits of a variety of insecticides labeled for use in soybean from different chemical classes in field trials in South Carolina and Georgia from 2010 through 2012. Several pyrethroids were among the most effective insecticides for control of M. cribraria. The pyrethroid bifenthrin had an immediate (2–6 d after treatment application) percentage of control of 97.5 ± 0.2% (SEM), which was the highest of the active ingredients tested. Likewise, net marginal benefits were typically greatest for pyrethroids, either alone or tank-mixed with other materials. Our results confirm that chemical control of M. cribraria in commercial soybean production is economically viable, but the number of effective chemical classes is limited.

Beauveria bassiana is a Pathogen of Megacopta cribraria (Hemiptera: Plataspidae)in South Carolina

Megacopta cribraria (F.) (Hemiptera: Plataspidae), a native of eastern Asia, has rapidly dispersed across the southeastern U.S. since its discovery in Georgia in 2009 (Suiter et al. 2010, J. Integr. Pest Manag. 1: F1-F4). Known as the kudzu bug or bean plataspid, this insect is a threat to soybean, Glycine max(L.) Merrill, production (Seiter et al. 2013, J. Econ. Entomol. 106: 1676-1683) and a nuisance pest (Suiter et al. 2010). Few natural enemies have been observed in the U.S. range of M. cribraria, likely contributing to its rapid expansion (Ruberson et al. 2013, Appl. Entomol. Zool. 48: 3-13). The entomopathogenic fungus Beauveria bassiana (Balsamo) Vuillemin infects M. cribraria in Asia (Borah and Dutta 2002, Insect Environ. 8:7-8). However, no data on B. bassiana pathogenicity and subsequent mortality are available from its U.S. range. In Georgia, two B. bass/ana-infected individuals were reported by Ruberson et al. (2013), with additional infected adults and an epizootic observed in soybean in 2013 (W. A. Gardner, University of Georgia, pers. comm.). Adults and nymphs of M. cribraria with visual signs of infection by a Beauveria sp. pathogen were observed on soybean plants at the Clemson University Edisto Research and Education Center in Blackville, SC, on 19 September 2012. Cadavers covered in white mycelia and conidia were found in caged plots of soybean with high densities of M. cribraria (installed to measure the effects of M. cribraria on soybean production; Seiter et al. 2013), as well as in nearby soybean fields. Our objectives were to (1) isolate and identify the fungus

Action thresholds for managing Megacopta cribraria (Hemiptera: Plataspidae) in soybean based on sweep-net sampling.

ABSTRACT The kudzu bug, Megacopta cribraria (F.), first discovered in the United States in 2009, has rapidly become a pest of commercial soybean, Glycine max (L.) Merrill, throughout much of the southeast. Because of its recent arrival, management practices and recommendations are not well established. To develop action thresholds, we evaluated insecticide applications targeted at different densities of adults and nymphs determined using the standard 38-cm diameter sweep net sampling method in 12 soybean field trials conducted in Georgia, North Carolina, and South Carolina from 2011 to 2013. Average peak densities of M. cribraria in the untreated controls reached as high as 63.5 ± 11.0 adults per sweep and 34.7 ± 8.0 nymphs per sweep. Insecticide applications triggered at densities of one adult or nymph of M. cribraria per sweep, two adults or nymphs per sweep, and one adult or nymph per sweep, with nymphs present, resulted in no yield reductions in most cases compared with plots that were aggressively protected with multiple insecticide applications. A single insecticide application timed at the R3 or R4 soybean growth stages also resulted in yields that were equivalent to the aggressively protected plots. Typically, treatments (excluding the untreated control) that resulted in fewer applications were more cost-effective. These results suggest that a single insecticide application targeting nymphs was sufficient to prevent soybean yield reduction at the densities of M. cribraria that we observed.

The impact of Bt maize as a natal host on adult head capsule width in field populations of western corn rootworm

The success of the current resistance management plan for transgenic maize, Zea mays L. (Poaceae), targeting the rootworm complex hinges upon high rates of mating between resistant and susceptible beetles. However, differences in the fitness of adult beetles could result in assortative mating, which could, in turn, change the rate of resistance evolution. Adult head capsule widths of naturally occurring populations of western corn rootworm, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), were examined in a variety of refuge configurations. Beetles were classified into treatments based on the hybrid – non‐Bt refuge or Bt maize targeting larval rootworms (hereafter Bt‐RW maize) – and location – proximity to other Bt‐RW or refuge plants – of the natal host plant. Treatments included the following: a refuge plant surrounded by other refuge plants, a refuge plant located near a Bt‐RW plant, a Bt‐RW plant surrounded by Bt‐RW plants, and a Bt‐RW plant located near a refuge plant. The mean head capsule width of males emerging from Bt‐RW plants was significantly smaller than the mean head capsule width of males emerging from refuge plants. These results indicate that males emerging from Bt‐RW maize plants may be exposed to sublethal doses of the Bt toxin as larvae. No differences were detected between females emerging from refuge plants compared with Bt‐RW plants. Overall mean head capsule width decreased as the season progressed, regardless of treatment. The diminished head capsule width of western corn rootworm males emerging from Bt‐RW maize may act to enhance resistance management, particularly in a seed mix refuge system.

Developing Sampling Plans for the Invasive Megacopta cribraria (Hemiptera: Plataspidae) in Soybean.

ABSTRACT Since its discovery in the southeastern United States, the invasive plataspid Megacopta cribraria (F.) (Hemiptera: Plataspidae) has infested soybean (Glycine max (L.) Merrill) fields in often very high numbers. To optimize sampling plans, sweep-net and beat-cloth sampling was conducted in soybean fields in South Carolina during 2012 and 2013. Across all fields, densities averaged 7.2 ± 0.5 (SEM) adults and 4.5 ± 0.4 nymphs per 20 sweeps and 5.5 ± 0.3 adults and 4.5 ± 0.3 nymphs per 1.83mof row. Coefficients of Taylors power law were used to generate sampling plans for population estimates and sequential sampling plans for pest management decision making. At an economic threshold of one nymph per sweep, optimum sample sizes were 184, 48, and 22 within 10, 20, and 30% of the mean with the sweep-net method. At the corresponding threshold for the beat cloth (24.7 nymphs per 1.83 m of row), optimum sample sizes were 239, 62, and 29 within 10, 20 and 30% of the mean, respectively. At all adult and nymph densities, fewer sweep-net samples were required for population estimations compared with the number of beat-cloth samples. Sequential sampling reduced the sample size required to reach a management decision for the sweep net and beat cloth compared with a fixed sampling plan. The sweep-net method was more cost reliable for population estimation at low densities of both life stages, with the beat cloth becoming more cost reliable as populations increased. The beat-cloth method was more cost reliable than sweep-net sampling across all densities and life stages for pest management practices. These results may be used by researchers, county Extension agents, consultants, and farm managers to both facilitate sampling and improve reliability of M. cribraria estimates for research purposes and for pest management.

Aggregation and Oviposition Preferences of Megacopta cribraria (Hemiptera: Plataspidae) in Laboratory Bioassays

In its native range, Megacopta cribraria (F.) (Hemiptera: Plataspidae) is reported to have a variety of legume (Fabales: Fabaceae) and non-legume hosts (Eger et al. 2010, Insecta Mundi 0121:1-11). In the southeastern U.S., where M. cribraria was first discovered in 2009 and has quickly spread (Suiter et al. 2010, J. Integr. Pest Manage. 1: F1-F4), 33 plant species were reported as collection sources, of which 17 were legumes (Gardner et al. 2013, J. Entomol. Sci. 48:118-127). Despite the large number of collection sources reported, only legumes have been confirmed to support development of M. cribraria in the southeastern U.S. (Zhang et al. 2012, Environ. Entomol. 41: 40-50; Del Pozo-Valdivia and Reisig 2013, J. Econ. Entomol. 106: 533535; Medal et al. 2013, Florida Entomol. 96: 631-633). Of these developmental hosts, kudzu, Puereria montana (Loureiro) Merrill variety lobata (Montandon), and soybean, Glycine max (L.) Merrill, are the most important (Zhang et al. 2012). In India, M. cribraria was reported to complete development on cotton, Gossypium hirsutum L. (Malvales: Malvaceae), in a no-choice laboratory assay and infested the crop sporadically in the field (Srinivasaperumal et al. 1992, Proc. Indian Natl. Sci. Acad. B Biol. Sci. 58: 333-340). However, there is no evidence of M. cribraria using cotton as a developmental host in the U.S., and adults are rarely encountered in cotton. In South Carolina, adults of M. cribraria are commonly encountered on several species from the genus Wisteria (Fabales: Fabaceae) in addition to soybean and kudzu. Oviposition by M. cribraria was observed on Wisteria frutescens (L.) Poiret in a field-choice trial in Georgia, although no adults developed from these eggs (Zhang et al. 2012). In the same study, a separate choice trial with fewer plant species resulted in no oviposition on Wisteria sinensis (Sims) de Candolle. Both of these choice trials included kudzu, but neither trial included soybean or cotton. The objective of our study was to evaluate the adult resting and ovipositional preferences of M. cribraria among soybean, kudzu, W. sinensis, and cotton in a controlled laboratory setting.

Residual Efficacy of Insecticides Applied to Exterior Building Material Surfaces for Control of Nuisance Infestations of Megacopta cribraria (Hemiptera: Plataspidae)

ABSTRACT The plataspid Megacopta cribraria (F.), which was recently introduced to the United States, forms nuisance aggregations on the exteriors of homes when it seeks overwintering sites in the fall. Little to no published information is available on the efficacy of insecticides labeled for professional use and exterior applications on homes and other structures against this insect. In a series of three experiments, we evaluated the residual efficacy of nine insecticides incorporating pyrethroid, neonicotinoid, and oxadiazine active ingredients on surfaces composed of five exterior building materials (vinyl soffit, brick, painted and unfinished plywood, and metal) at rates labeled for use in structural perimeter applications. Pyrethroids and pyrethroid-neonicotinoid mixes were broadly effective, resulting in 100% mortality or knockdown within 24 h in most cases. The neonicotinoid dinotefuran performed similarly on metal and vinyl surfaces, but its residual efficacy was reduced on more porous brick and wood surfaces. The oxadiazine indoxacarb acted more slowly than the other materials, but its performance was maintained on porous surfaces. Overwintering adults of M. cribraria were generally susceptible to the broad-spectrum insecticides most commonly used for exterior applications to homes and other structures.

A Novel Method for Estimating Soybean Herbivory in Western Corn Rootworm (Coleoptera: Chrysomelidae)

ABSTRACT The western corn rootworm, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), is the key pest of corn, Zea mays L., in North America. The western corn rootworm variant is a strain found in some parts of the United States that oviposits in soybean, Glycine max (L.) Merr., thereby circumventing crop rotation. Soybean herbivory is closely associated with oviposition; therefore, evidence of herbivory could serve as a proxy for rotation resistance. A digital image analysis method based on the characteristic green abdominal coloration of rootworm adults with soybean foliage in their guts was developed to estimate soybean herbivory rates of adult females. Image analysis software was used to develop and apply threshold limits that allowed only colors within the range that is characteristic of soybean herbivory to be displayed. When this method was applied to adult females swept from soybean fields in an area with high levels of rotation resistance, 54.3 ± 2.1% were estimated to have fed on soybean. This is similar to a previously reported estimate of 54.8%. Results when laboratory-generated negative controls were analyzed showed an acceptably low frequency of false positives. This method could be developed into a management tool if user-friendly software were developed for its implementation. In addition, researchers may find the method useful as a rapid, standardized screen for measuring frequencies of soybean herbivory.