Mark R. Abney

Rise and Fall of Cotton Aphid (Hemiptera: Aphididae) Populations in Southeastern Cotton Production Systems

Abstract The impact of natural enemies on cotton aphid, Aphis gossypii Glover (Hemiptera: Aphididae), populations in cotton, Gossypium hirsutum L., production systems in the southeastern United States was evaluated over 3 yr in irrigated commercial cotton fields. Fungal epizootics caused by the entomopathogen Neozygites fresenii (Nowakowski) Batko reduced aphid numbers to subthreshold levels in 1999, 2000, and 2001 and occurred consistently in early to mid-July in all 3 yr. Scymnus spp. were the most abundant aphidophagous predators, although other coccinellid species and generalist predators such as spiders, fire ants, heteropterans, and neuropterans also were present. Studies using arthropod exclusion cages demonstrated little impact of predators or parasitoids on aphid populations before fungal epizootics. Arthropod natural enemies were most abundant after epizootics and may have suppressed aphid populations late in the season. Seed cotton yield, and lint quality were not affected by aphicide applications in any year of the study. Implications of these findings for aphid management in the southeastern United States are discussed.

Influence of Preceding Crop on Wireworm (Coleoptera: Elateridae) Abundance in the Coastal Plain of North Carolina

ABSTRACT Three studies were conducted to determine the effect of preceding crop on wireworm (Coleoptera: Elateridae) abundance in the coastal plain of North Carolina. In all three studies, samples of wireworm populations were taken from the soil by using oat, Avena sativa L., baits. Treatments were defined by the previous years crop and were chosen to reflect common crop rotations in the region. Across all three studies, eight wireworm species were recovered from the baits: Conoderus amplicollis (Gyllenhal), Conoderus bellus (Say), Conoderus falli (Lane), Conoderus lividus (Degeer), Conoderus scissus (Schaeffer), Conoderus vespertinus (F.), Glyphonyx bimarginatus (Schaeffer), and Melanotus communis (Gyllenhal). The effect of corn, Zea mays L.; cotton, Gossypium hirsutum L.; fallow; soybean, Glycine max (L.) Merr.; sweet potato, Ipomoea batatas (L.) Lam.; and tobacco (Nicotiana spp.) was evaluated in a small-plot replicated study. M. communis was the most frequently collected species in the small-plot study and was found in significantly higher numbers following soybean and corn. The mean total number of wireworms per bait (all species) was highest following soybean. A second study conducted in late fall and early spring assessed the abundance of overwintering wireworm populations in commercial fields planted to corn, cotton, peanut (Arachis hypogaea L.), soybean, sweet potato, and tobacco in the most recent previous growing season. C. lividus was the most abundant species, and the mean total number of wireworms was highest following corn and soybean. A survey was conducted in commercial sweet potato in late spring and early summer in fields that had been planted to corn, cotton, cucurbit (Cucurbita pepo L.), peanut, soybean, sweet potato, or tobacco in the most recent previous growing season. C. vespertinus was the most abundant species, and the mean total number of wireworms per bait was highest following corn.

Effects of Thrips Density, Mode of Inoculation, and Plant Age on Tomato Spotted Wilt Virus Transmission in Peanut Plants

ABSTRACT n Spotted wilt caused by tomato spotted wilt virus (TSWV; family Bunyaviridae; genus Tospovirus) is a serious disease of peanut (Arachis hypogaea L.) in the southeastern United States. Peanut genotypes with field resistance to TSWV are effective in suppressing spotted wilt. All commercially available genotypes with field resistance to TSWV were developed through conventional breeding. As a part of the breeding process, peanut genotypes are regularly screened under field situations. Despite numerous advantages associated with field screening, it is often limited by inconsistent vector (thrips) and TSWV pressure. A greenhouse transmission protocol would aid in thorough screening of selected genotypes and conserve time. In this study, various parameters associated with TSWV transmission, including tobacco thrips, Frankliniella fusca (Hinds) density, mode of inoculation, and plant age, were evaluated. Greater incidences of TSWV infection were obtained with thrips-mediated inoculation when compared with mechanical inoculation. TSWV inoculation with three, five, and 10 thrips resulted in greater incidences of TSWV infection in plants than inoculation with one thrips. However, incidences of TSWV infection did not vary between plants inoculated with three, five, and 10 viruliferous thrips. With both thrips-mediated and mechanical inoculation methods, incidences of TSWV infection in 1-wk-old plants were greater than in 4-wk-old plants. TSWV copy numbers, as determined by qPCR, also decreased with plant age. Results suggest that using at least three thrips per plant and 1- to 2-wk-old plants would maximize TSWV infection in inoculated plants.

Applying insecticides through drip irrigation to reduce wireworm (Coleoptera: Elateridae) feeding damage in sweet potato†

BACKGROUNDnA 2 year field study was conducted at multiple locations to determine whether insecticides or an entomopathogenic nematode, Steinernema carpocapsae Weiser, applied through drip irrigation in sweet potato reduced wireworm damage when compared with the non-treated check and/or insecticides applied conventionally.nnnRESULTSnWireworm damage was low in 2012, and there were no differences in the proportion of roots damaged or the severity of damage between treatments. In 2013, a preplant-incorporated (PPI) application of chlorpyrifos followed by either bifenthrin, imidacloprid, clothianidin, or oxamyl injected through drip irrigation significantly reduced the proportion of wireworm damage as well as the severity of wireworm damage when compared with the non-treated check. The incidence and severity of wireworm damage in these treatments did not differ significantly from those in the conventional management practice. The PPI application of chlorpyrifos followed by either cyantraniliprole or S. carpocapsae injected through drip irrigation was not significantly different from the non-treated check in the proportion of wireworm damage; however, both treatments reduced the severity of wireworm damage compared with the non-treated check.nnnCONCLUSIONnApplying insecticides through drip irrigation provides an alternative to conventionally applied insecticides.

THREE DECADES OF MANAGING TOMATO SPOTTED WILT VIRUS IN PEANUT IN SOUTHEASTERN UNITED STATES

Southeastern states namely Georgia, Florida, and Alabama produce two-thirds of the peanuts in the United States. Thrips-transmitted Tomato spotted wilt virus (TSWV), which causes spotted wilt disease, has been a major impediment to peanut production for the past three decades. The cultivars grown in the 1980s were extremely susceptible to TSWV. Early yield losses extended to tens of millions of dollars each year (up to 100% loss in many fields). This situation led to the creation of an interdisciplinary team known as SWAT: Spotted Wilt Action Team. Initial efforts focused on risk mitigation using a combination of chemical and cultural management practices along with a strong investment in breeding programs. Beginning in the mid 1990s, cultivars with field resistance were developed and integrated with cultural and chemical management options. A Risk Mitigation Index (Peanut Rx) was made available to growers to assess risks, and provide options for mitigating risks such as planting field resistant cultivars with in-furrow insecticides, planting after peak thrips incidence, planting in twin rows, and increasing seeding rates. These efforts helped curtail losses due to spotted wilt. The Peanut Rx continues to be refined every year based on new research findings. Breeding efforts, predominantly in Georgia and Florida, continue to develop cultivars with incremental field resistance. The present-day cultivars (third-generation TSWV-resistant cultivars released after 2010) possess substantially greater field resistance than second-generation (cultivars released from 2000 to 2010) and first-generation (cultivars released from 1994 to 2000) TSWV resistant cultivars. Despite increased field resistance, these cultivars are not immune to TSWV and succumb under high thrips and TSWV pressure. Therefore, field resistant cultivars cannot serve as a stand-alone option and have to be integrated with other management options. The mechanism of resistance is also unknown in field resistant cultivars. Recent research in our laboratory evaluated field resistant cultivars against thrips and TSWV. Results revealed that some resistant cultivars suppressed thrips feeding and development, and they accumulated fewer viral copies than susceptible cultivars. Transcriptomes developed with the aid of Next Generation Sequencing revealed differential gene expression patterns following TSWV infection in susceptible than field resistant cultivars. Results revealed that the upregulation of transcripts pertaining to constitutive and induced plant defense proteins in TSWV resistant cultivars was more robust over susceptible cultivars. On the flipside, the long-term effects of using such resistant cultivars on TSWV were assessed by virus population genetics studies. Initial results suggest lack of positive selection pressure on TSWV, and that the sustainable use of resistant cultivars is not threatened. Follow up research is being conducted. Improvements in TSWV management have enhanced sustainability and contributed to increased yields from <2800kg/ha before 1995 to ∼5000kg/ha in 2015.

Evaluation of Alternatives to Carbamate and Organophosphate Insecticides Against Thrips and Tomato Spotted Wilt Virus in Peanut Production

Abstract Thrips are important pests of peanut. They cause severe feeding injuries on peanut foliage in the early season. They also transmit Tomato spotted wilt virus (TSWV), which causes spotted wilt disease. At-plant insecticides and cultivars that exhibit field resistance to TSWV are often used to manage thrips and spotted wilt disease. Historically, peanut growers used the broad-spectrum insecticides aldicarb (IRAC class 1A; Temik) and phorate (IRAC class 1B; Thimet) for managing thrips and thereby reducing TSWV transmission. Aldicarb has not been produced since 2011 and its usage in peanut will be legally phased out in 2018; therefore, identification of alternative chemistries is critical for thrips and spotted wilt management. Here, eight alternative insecticides, with known thrips activity, were evaluated in field trials conducted from 2011 through 2013. In addition, different application methods of alternatives were also evaluated. Imidacloprid (Admire Pro), thiamethoxam (Actara), spinetoram (Radiant), and cyantraniliprole (Exirel) were as effective as aldicarb and phorate in suppressing thrips, but none of the insecticides significantly suppressed spotted wilt incidence. Nevertheless, greenhouse assays demonstrated that the same alternative insecticides were effective in suppressing thrips feeding and reducing TSWV transmission. Spotted wilt incidence in the greenhouse was more severe (∼80%) than in the field (5–25%). In general, field resistance to TSWV in cultivars only marginally influenced spotted wilt incidence. Results suggest that effective management of thrips using alternative insecticides and subsequent feeding reduction could improve yields under low to moderate virus pressure.

A Spatial Ecology Study on the Effects of Field Conditions and Crop Rotation on the Incidence of Plectris aliena (Coleoptera: Scarabaeidae) Grub Damage to Sweetpotato Roots

A farmscape study was conducted in commercial sweetpotato (Ipomoea batatas (L.) Lam) fields in Columbus County, NC, in 2010 and 2011 to investigate the effects of the following field conditions: soil drainage class, soil texture, field size, border habitat, land elevation, and the previous years crop rotation on the incidence of damage caused by Plectris aliena Chapman (Coleoptera:Scarabaeidae) larval feeding. Soil drainage and crop rotation significantly affected the incidence of damage to roots, with well drained soils having a low estimated incidence of damaged roots (0.004) compared with all other drainage classes (0.009-0.011 incidence of damaged roots). Fields with soybeans [Glycine max (L.) Merr] planted the preceding year had the highest incidence of root damage (0.15) compared with all other crops. The effects of border habitats, which were adjacent to grower fields where roots were sampled, showed that as the location of the roots was closer to borders of soybean (planted the year before) or grass fields, the chance of damage to roots decreased. Results indicate that growers can use crop rotation as a management technique and avoid planting sweetpotatoes the year after soybeans to reduce the incidence of P. aliena larval feeding on sweetpotato roots. Environmental conditions such as fields with poor drainage and certain border habitats may be avoided, or selected, by growers to reduce risk of damage to roots by P. aliena.

Freeze Susceptibility and Supercooling Temperature of Plectris aliena (Coleoptera: Scarabaeidae) Third Instars

Temperature is a density-independent abiotic mortality factor, although the response of insects to cold temperature varies between and within species (Bale 1989, Agric. Zool. Rev. 3: 157–192). The abundance of the overwintering stage of an insect depends in part on its cold hardiness, or ability to survive lowtemperature exposure aboveground or in subterranean habitats (Bale 1989). Freeze-tolerant insects can survive the freezing of tissues at temperatures below 08C, while freezesusceptible insects perish when their tissues freeze (Chapman 1998, Pp. 509–528, In The Insects: Structure and Function, 4th ed., Cambridge Univ. Press, New York). Insects that are freeze susceptible avoid freeze mortality by supercooling, or maintaining liquid water below the freezing point (Chapman 1998). For many freeze-susceptible insects native to tropical or temperate regions, the supercooling point (the sub-08C temperature at which the tissue water spontaneously freezes) is very low, often below 208C, but this can be influenced (increased or decreased) by life stage, acclimatization, feeding, water content, and cuticular surface moisture (Bale 1989, Chapman 1998). Freezing of freeze-susceptible insects can be induced at a temperature above the supercooling point through ice inoculation by internal or external factors, such as food in the gut or surface contact with an ice-nucleating agent (Bale 1989). Plectris aliena Chapman (Coleoptera: Scarabaeidae) is native to South America and, although it has been in the United States since the early 1900s (Chapin 1934, Proc. Biol. Soc. Wash. 47: 33–36), the insect only became a severe problem for sweetpotato growers in Columbus Co. in southeastern North Carolina beginning in 2006. Sweetpotato Ipomoea batatas (L.) Lamarck roots are rendered unmarketable

Evaluation of Alternatives to an Organophosphate Insecticide with Selected Cultural Practices: Effects on Thrips, Frankliniella fusca, and Incidence of Spotted Wilt in Peanut Farmscapes

Abstract Peanut growers use a combination of tactics to manage spotted wilt disease caused by thrips-transmitted Tomato spotted wilt virus (TSWV). They include planting TSWV-resistant cultivars, application of insecticides, and various cultural practices. Two commonly used insecticides against thrips are aldicarb and phorate. Both insecticides exhibit broad-spectrum toxicity. Recent research has led to the identification of potential alternatives to aldicarb and phorate. In this study, along with reduced-risk, alternative insecticides, we evaluated the effect of conventional versus strip tillage; single versus twin row seeding pattern; and 13 seed/m versus 20 seed/m on thips density, feeding injury, and spotted wilt incidence. Three field trials were conducted in Georgia in 2012 and 2013. Thrips counts, thrips feeding injuriy, and incidence of spotted wilt were less under strip tillage than under conventional tillage. Reduced feeding injury from thrips was observed on twin-row plots compared with single-row plots. Thrips counts, thrips feeding injury, and incidence of spotted wilt did not vary by seeding rate. Yield from twin-row plots was greater than yield from single-row plots only in 2012. Yield was not affected by other cultural practices. Alternative insecticides, including imidacloprid and spinetoram, were as effective as phorate in suppressing thrips and reducing incidence of spotted wilt in conjunction with cultural practices. Results suggest that cultural practices and reduced-risk insecticides (alternatives to aldicarb and phorate) can effectively suppress thrips and incidence of spotted wilt in peanut.

Effect of Soil Moisture on Plectris aliena (Coleoptera: Scarabaeidae) Oviposition

Summary The effect of 3 soil moisture regimes (dry, normal, and wet) on oviposition was studied for the invasive soil pest Plectris aliena Chapin (Coleoptera: Scarabaeidae) in North Carolina agroecosystems. In laboratory cages, there was a significant increase of 20 more eggs deposited by females in wet soil compared with the dry soil (2% moisture) treatment. When the beetles were tested under field conditions, there were no significant differences in oviposition.