Dan L. Horton

Temperature-Dependent Development and Prediction of Emergence of the Summer Generation of Plum Curculio (Coleoptera: Curculionidae) in the Southeastern United States

Abstract Timely insecticide application against the summer generation (first field generation) of the plum curculio, Conotrachelus nenuphar Herbst, is critical in the production of peach and other stone fruits in the southeastern United States. In the absence of monitoring tools that are effective during midseason when the adults of this generation emerge, a temperature-based emergence model would be useful as an alternative decision aid. In this study, we determined rates of larval development (from oviposition to peak emergence of larvae) and pupal development (from larval emergence to peak emergence of adults) for two populations of C. nenuphar in constant temperatures ranging from ≈11–37°C, developed linear regression models to describe the relationships between developmental rate and temperature for both stages, and estimated degree-day requirements for completing development from these models. The lower threshold temperature was 11.1 and 8.7°C for larval and pupal development, respectively. The thermal time requirement from oviposition to peak emergence of larvae was 215.5 DD, and peak emergence of adults occurred 442.4 DD later. For model validation, rearing experiments were carried out with both populations in fluctuating temperatures in the greenhouse and outdoors. Observed degree-day requirements were not significantly different from model-predicted values for larval emergence in the greenhouse and for adult emergence in the greenhouse and outdoors. For larval emergence outdoors, the model overestimated time to peak emergence by ≈35 DD (2–3 calendar d), most likely because these trials were carried out during relatively cool conditions in which overestimation by a linear model would not be unexpected. Aspects related to further validation of the model and its use in orchard conditions are discussed.

Trap Capture of Brown and Dusky Stink Bugs (Hemiptera: Pentatomidae) as Affected by Pheromone Dosage in Dispensers and Dispenser Source

Brown, Euschistus servus (Say), and dusky, E. tristigmus (Say), stink bugs (Heteroptera: Pentatomidae) readily respond to traps baited with the Euschistus spp. aggregation pheromone methyl (E, Z) -2,4-decadienoate. Previous studies examining trap capture of these stink bugs have used either laboratory-prepared dispensers or commercial dispensers with various known and unknown pheromone doses. We compared trap captures of E. servus and E. tristigmus using yellow pyramid traps baited with a range of pheromone doses (20 - 120 μL) loaded onto rubber septa and when baited with 2 commercially available pheromone dispensers. These baited traps were located primarily in or alongside pecan orchards with one exception being alongside a peach/plum orchard. Traps were monitored weekly for 4 wk during 2008 and 2009. Dispensers were either replaced weekly or the same dispenser remained in use for the entire study. All pheromone doses tested resulted in a numerical increase of both E. servus and E. tristigmus captured in traps compared with traps using no pheromone. In each experiment for each species, at least one pheromone dose significantly increased trap capture compared with traps using a septa containing no pheromone. In direct comparisons, neither commercial dispenser ever captured significantly more E. servus or E. tristigmus than traps without pheromone. Numerically higher trap captures were observed with a higher pheromone dose in each of 5 month-long studies. However, captures were not always significantly higher for either species suggesting that other factors affected stink bug capture in pheromone-baited traps. Results from this study could facilitate the use of this stink bug trap as a barrier to impede movement of pest Euschistus spp. into orchards or other crop habitats.

Hosts of Plum Curculio, Conotrachelus nenuphar (Coleoptera: Curculionidae), in Central Georgia

Abstract Potential host plants for the larvae of plum curculio, Conotrachelus nenuphar (Herbst) (Coleoptera: Curculionidae), in central Georgia’s peach producing region were surveyed. This fruit-attacking curculionid is reported to have a broad host range, including many plants in the Rosaceae and other families. However, our collections indicated that in this region plum curculio largely is limited to peach (Prunus persica) and plum (P. angustifolia and P. umbellata). Abandoned peach orchards and wild plum thickets are important hosts for the spring generation of plum curculio and are sources of subsequent infestations of managed peach orchards. However, only abandoned peach orchards were available to the summer generation of plum curculio. May haw, Crataegus aestivalis, was also a host, but other species of Crataegus were not used. Although the plum curculio was reported to be a significant pest of blueberries (Vaccinium spp.) in North Carolina, New Jersey, and Delaware, they were only rarely used as a host in central Georgia. Apple (Malus domestica) and Asian pear (Pyrus pyrifolia), when available, were ovipositional hosts of plum curculio in central Georgia; however, no larvae emerged from these hosts. We report the first records of plum curculio developing in Vaccinium stamineum and Vitis rotundifolia. Our results are compared with a previous survey conducted in the northeastern United States, as well as to data reported in the literature.

Influence of Prunus spp., Peach Cultivars, and Bark Damage on Oviposition Choices by the Lesser Peachtree Borer (Lepidoptera: Sesiidae)

Abstract An examination of oviposition choices by the lesser peachtree borer, Synanthedon pictipes (Grote and Robinson) (Lepidoptera: Sesiidae), showed that wounded peach, Prunus persica (L.) Batsch, bark was attractive to females for oviposition. Females responded to bark that was injured mechanically (e.g., hammer blows, knife cuts, pruning wounds), infested by lesser peachtree borer larvae or injured by disease. In fact, there was no difference in female oviposition response to knife cut wounds and knife cut wounds infested with lesser peachtree borer larvae. Oviposition on wounded bark from three different high chill peach cultivars was similar and strongly suggests that the narrow genetic base of high chill peach cultivars grown in the southeastern United States has little inherent resistance to the lesser peachtree borer. In stark contrast, when provided different Prunus spp., i.e., exotic peach and the native species P. angustifolia and P. serotina, the exotic peach was highly preferred for oviposition by the native lesser peachtree borer.

INVERTEBRATE PREDATORS AND PARASITOIDS OF PLUM CURCULIO, CONOTRACHELUS NENUPHAR (COLEOPTERA: CURCULIONIDAE) IN GEORGIA AND FLORIDA

Abstract The extent of predation and parasitism on larvae of the plum curculio, Conotrachelus nenuphar (Herbst) (Coleoptera: Curculionidae), was measured independently with several different experimental designs at sites in northern Florida and central Georgia. Experimental manipulation in Monticello, FL, and in Byron, GA, demonstrated equivocal impacts by predation. However, direct observations in Byron, GA, revealed that ants are the dominant invertebrate predators of plum curculio larvae, causing up to 62% mortality. Primary ant predators included Solenopsis invicta (Buren) (Hymenoptera: Formicidae) and Dorymyrmex bureni (Trager) (Hymenoptera: Formicidae). Predation may be more important later in the season when infested fruit does not abscise and plum curculio larvae must drop to the ground from the trees and spend a considerable time burrowing into the soil. This contrasts with the early season when infested fruit abscise and larvae crawl from the fruit directly into the soil, reducing their exposure to predators. Recorded parasites included Nealiolus curculionis (Fitch) (Hymenoptera: Braconidae) and Cholomyia inaequipes Bigot (Diptera: Tachinidae). Parasitism, particularly by N. curculionis, was common in northern Florida but rare in middle Georgia.

Management of Plum Curculio and Catfacing Insects on Peaches in Central Alabama: Standard Crop Stage–Based vs. Integrated Pest Management–Based Approaches

ABSTRACT Plum curculio, tarnished plant bug, brown stink bug, and green stink bug are the major insect pests causing fruit damage on peaches grown in the southeastern United States. Insect management aids, monitoring techniques, predictive models, and action thresholds for southeastern peaches are either lacking or they are not robust enough to facilitate industry acceptance of as-needed insecticide applications during the growing season (Horton et al., 2003). In this 3-year study, we compared two approaches to scheduling insecticide applications for control of these pests on three peach cultivars in an established central Alabama orchard: 1) an industry standard, representative of prevailing practice in the southeastern United States, which consisted of scheduled insecticide applications timed to coincide with crop stage; and 2) an integrated pest management (IPM) treatment, which employed limited prescheduled insecticide applications timed to coincide with the crops developmental stage, supplemented with as-needed insecticide applications when preestablished action thresholds were reached. Percentage of insect-damaged fruit from trees under the IPM treatment was similar to, or in some cases greater or less than, that of fruit from trees receiving the standard treatment. Depending on the year, the same or fewer insecticide applications were made under the IPM treatment compared with the standard treatment. The IPM treatment came close to providing acceptable levels of plum curculio control with the early-season cultivar Correll but not with the mid- and late-season cultivars Sunland and Biscoe.

A DNA Marker to Track Conotrachelus nenuphar (Coleoptera: Curculionidae) Dispersal

Plum curculio, Conotrachelus nenuphar (Herbst), is indigenous east of the Rocky Mountains and north of latitude 50°N in the United States (Amis and Snow. 1985, Handbook of Insect Rearing, Vol. 1) with a population in Utah (Hallman 1998, USDA-ARS Report, Weslaco, TX, USA). It is a phytophagous, true weevil and a pest of pome and stone fruit, i.e., apples, plums, cherries, and peaches (Shapiro-llan et al. 2002, J. Nematology 34: 246-349). In Georgia and South Carolina, the peach (Prunus persica [L.]) is a major stone fruit commodity. Plum curculio is the most destructive pest of the commodity (Brannon 1927, J. Elisha Mitchell Scientific Soc. 43: 79-83; Leskey and Wright. 2004, Environ. Entomol. 33: 389-396) on which they feed and into which they oviposit. Commercial fruit orchards also have historically been unable to rely on trap monitoring systems to accurately time insecticide applications (Prokopy et al. 2000, J. Entomol. Sci. 35: 411-420; Leskey et al. 2012, http://digitalcommons.unl.edu/usdaarsfacpub/1108). Thus, in 1994 Mexico halted importation of peaches from Georgia and South Carolina due to concerns of importing plum curculio with the peaches. But, in 2008 the U.S. Department of Agriculture Animal and Plant Health Inspection Service (APHIS) revisited the plum curculio issue on behalf of the peach growers in Georgia and South Carolina. An agreement was reached in 2011 between the U. S. and Mexico which required that specific procedures be in place to insure that peaches shipped to Mexico from Georgia and South Carolina are free of plum curculio. These procedures included field surveys, trapping, packinghouse inspections, fruit-cutting, and post-entry inspections. A DNA verification system designed specifically to track dispersal of plum curculio from Georgia is also needed to track and/or verify infestations, particularly if post-entry

Dermal Efficacy Evaluation of New Insecticides for Control of Plum Curculio in Peaches

Abstract Labeled rates of bifenthrin (Capture® 4EC, 112 mg a.i. ha-1), fipronil (Regent® 4SC, 280 mg a.i.-ha-1), malathion (Bonide® 50% Malathion, 560 mg a.i.-ha-1), thiacloprid (Calypso® 4EC, 288 mg a.i.-ha-1), thiamethoxam (Actara® 25WG, 87 mg a.i.-ha-1), and twice the labeled rates of these same insecticides, were examined (along with an untreated control) for dermal efficacy against plum curculio, Conotrachelus nenuphar (Herbst) (Coleoptera: Curculionidae). Plum curculios treated with labeled rates of fipronil, bifenthrin, and malathion exhibited higher mortality (by no later than 96 hours post-application) than plum curculios left untreated or treated with labeled rates of thiamethoxam and thiacloprid. At 24 h post-application, malathion at the labeled rate, malathion at twice the labeled rate, and bifenthrin at twice the labeled rate resulted in > 90% efficacy. Fipronil at twice the labeled rate produced an acceptable level of control (≤90% mortality) by 48 h post-application. This rapid laboratory method of assaying new insecticides shows promise for selecting insecticides capable of producing dermal toxicity for subsequent field evaluation.

Emergence of Root-feeding Weevils (Coleoptera: Curculionidae) in Central Georgia Peach Orchards

Abstract Injury to peach, Prunus persicae (L.) Batsch, roots is common by several plant pathogen species and by larvae of the peachtree borer, Synanthedon exitiosa Say (Lepidoptera: Sesiidae). External feeding injury to peach roots was observed that was not consistent with S. exitiosa injury but was suspected to be caused by the larvae of root-feeding weevil species (Coleoptera: Curculionidae). Thus, we used conical emergence traps for 3 yr to sample in unsprayed peach orchards (within the dripline of trees and at missing tree sites) to monitor for root-feeding weevils. Fuller rose beetle, Naupactus cervinus (Boheman), whitefringed beetles, Naupactus spp., and the twobanded Japanese weevil, Callirhopalus bifasciatus (Roelofs), (Coleoptera: Curculionidae) were captured at significantly higher numbers within the dripline of the tree than at missing tree sites. Adult N. cervinus emerged from soil year around; whereas, the other 2 species had seasonal emergence. In commercial peach orchards comprised of cultivars with early, mid, and late-season fruit ripening dates, N. cervinus was more abundant than other species. The later a cultivar ripens, the higher the number of insecticide applications it receives; however, we did not detect a difference in N. cervinus emergence between the cultivars. In another sprayed orchard, N. cervinus was again more common than other curculionid species captured. Damage ratings (0 - 5; none to heavy, respectively) on roots revealed a mean rating of 2.79 ± 0.12. Year-long emergence of N. cervinus is likely why it persisted in sprayed orchards. Modification of existing pest management programs will be needed to manage N. cervinus attacking peach roots.