Scott W. Myers

Influence of Potassium Fertility on Soybean Aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), Population Dynamics at a Field and Regional Scale

Abstract Soybean aphid populations have been hypothesized to respond to nutrient availability in soybean plants. We examined how soil potassium (K) deficiency affects soybean aphid population at both regional and field level scales. First, we measured soil and leaf nutrient levels and monitored soybean aphid populations in 34 production soybean fields throughout Wisconsin. A principle component analysis (PCA) was used to examine the relationship between soil and leaf nutrients and soybean aphid population growth. Results showed that aphid population growth rate was negatively correlated with soil K and P and leaf K, N, P, and S, whereas peak aphid densities were positively correlated with the same suite of soil and leaf nutrients. In a manipulative field experiment, we established low, medium, and high K fertility soybean plots and determined life table parameters of soybean aphids. Aphids developing within clip-cages showed a significantly greater intrinsic rate of population increase and net reproductive rate in the low K treatments in comparison with the medium and high K treatments. In these same plots, naturally colonizing populations of soybean aphids also had significantly higher peak abundance and rate of population increase in the low K treatment compared with medium and high K treatments. In general, these findings indicate that soil K availability and leaf K levels affect plant quality and may play an important role in soybean aphid population dynamics.

Efficacy of Heat Treatment for the Thousand Cankers Disease Vector and Pathogen in Small Black Walnut Logs

ABSTRACT Thousand cankers disease, caused by the walnut twig beetle (Pityophthorus juglandis Blackman) and an associated fungal pathogen (Geosmithia morbida M. Kolarík, E. Freeland, C. Utley, and N. Tisserat), threatens the health and commercial use of eastern black walnut (Juglans nigra L.), one of the most economically valuable tree species in the United States. Effective phytosanitary measures are needed to reduce the possibility of spreading this insect and pathogen through wood movement. This study evaluated the efficacy of heat treatments and debarking to eliminate P. juglandis and G. morbida in J. nigra logs 4–18 cm in diameter and 30 cm in length. Infested logs were steam heated until various outer sapwood temperatures (60, 65, and 70°C in 2011; 36, 42, 48, 52, and 56°C in 2012) were maintained or exceeded for 30–40 min. In 2011, all heat treatments eliminated G. morbida from the bark, but logs were insufficiently colonized by P. juglandis to draw conclusions about treatment effects on the beetle. Debarking did not ensure elimination of the pathogen from the sapwood surface. In 2012, there was a negative effect of increasing temperature on P. juglandis emergence and G. morbida recovery. G. morbida did not survive in logs exposed to treatments in which minimum temperatures were 48°C or higher, and mean P. juglandis emergence decreased steadily to zero as treatment minimum temperature increased from 36 to 52°C. A minimum outer sapwood temperature of 56°C maintained for 40 min is effective for eliminating the thousand cankers disease vector and pathogen from walnut logs, and the current heat treatment schedule for the emerald ash borer (60°C core temperature for 60 min) is more than adequate for treating P. juglandis and G. morbida in walnut firewood.

Walnut twig beetle (Coleoptera: Curculionidae: Scolytinae) Colonization of eastern black walnut nursery trees

Thousand cankers disease, caused by the invasive bark beetle Pityophthorus juglandis Blackman and an associated fungal pathogen Geosmithia morbida M.Kolařík, E. Freeland, C. Utley, N. Tisserat, currently threatens the health of eastern black walnut (Juglans nigra L.) in North America. Both the beetle and pathogen have expanded beyond their native range via transport of infested walnut wood. Geosmithia morbida can develop in seedlings following inoculation, but the ability of P. juglandis to colonize young, small diameter trees has not been investigated. This study assessed the beetle’s colonization behavior on J. nigra nursery trees. Beetles were caged directly onto the stems of walnut seedlings from five nursery sources representing a range of basal stem diameter classes. Seedlings were also exposed to P. juglandis in a limited choice, field-based experiment comparing pheromone-baited and unbaited stems. When beetles were caged directly onto stems, they probed and attempted to colonize seedlings across the range of diameters and across sources tested, including stems as small as 0.5 cm in diameter. In the field experiment, beetles only attempted to colonize seedlings that were baited with a pheromone lure and appeared to prefer (though not statistically significant) the larger diameter trees. Despite several successful penetrations into the phloem, there was no evidence of successful progeny development within the young trees in either experiment. Further investigation is recommended to better elucidate the risk nursery stock poses as a pathway for thousand cankers disease causal organisms.

Phytosanitary Treatments Against Bactrocera dorsalis (Diptera: Tephritidae): Current Situation and Future Prospects

Abstract Bactrocera dorsalis (Hendel) (Diptera: Tephritidae) is arguably the most important tephritid attacking fruits after Ceratitis capitata (Wiedemann) (Diptera: Tephritidae). In 2003 it was found in Africa and quickly spread to most of the sub-Saharan part of the continent, destroying fruits and creating regulatory barriers to their export. The insect is causing new nutritional and economic losses across Africa, as well as the losses it has caused for decades in infested areas of Asia, New Guinea, and Hawaii. This new panorama represents a challenge for fruit exportation from Africa. Phytosanitary treatments are required to export quarantined commodities out of infested areas to areas where the pest does not exist and could become established. This paper describes current phytosanitary treatments against B. dorsalis and their use throughout the world, the development of new treatments based on existing research, and recommendations for further research to provide phytosanitary solutions to the problem.

Postharvest Treatment of Fresh Fruit from California with Methyl Bromide for Control of Light Brown Apple Moth (Lepidoptera: Tortricidae)

ABSTRACT Methyl bromide (MB) chamber fumigations were evaluated for postharvest control of light brown apple moth, Epiphyas postvittana (Walker) (Lepidoptera: Tortricidae), in fresh fruit destined for export from California. To simulate external feeding, larvae were contained in gas-permeable cages and distributed throughout loads of peaches, plums, nectarines (all Prunus spp.), apples (Malus spp.), raspberries (Rubus spp.), or grapes (Vitis spp.). Varying the applied MB dose and the differential sorption of MB by the loads resulted in a range of exposures, expressed as concentration x; time cross products (CTs) that were verified by gas-chromatographic quantification of MB in chamber headspace over the course of each fumigation. CTs ≥60 and ≥72 mg liter-1 h at 10.0 ± 0.5 and 15.6 ± 0.5°C ( ± s, average ±SD), respectively, yielded complete mortality of ≈ 6,200 larvae at each temperature. These confirmatory fumigations corroborate E. postvittana mortality data for the first time in relation to measured MB exposures and collectively comprise the largest number of larval specimens tested to date. In addition, a kinetic model of MB sorption was developed for the quarantine fumigation of fresh fruit based on the measurement of exposures and how they varied across the fumigation trials. The model describes how to manipulate the applied MB dose, the load factor, and the load geometry for different types of packaged fresh fruit so that the resultant exposure is adequate for insect control.

Phytosanitary Cold Treatment for Oranges Infested With Bactrocera zonata (Diptera: Tephritidae)

ABSTRACT The peach fruit fly, Bactrocera zonata (Saunders), attacks a wide range of tree fruits in countries from Egypt to Vietnam and is occasionally trapped in the United States. Phytosanitary treatments may be required to export fruit hosts of this insect from countries where it is endemic to countries where it is absent but could become established. This research describes comparative studies to determine if B. zonata could be phytosanitarily controlled by cold treatment schedules existing for Ceratitis capitata (Wiedemann) and Anastrepha ludens (Loew), and the development of a cold treatment of 18 d at 1.7°C for B. zonata infesting oranges. Fruit were infested by puncturing holes in oranges and allowing tephritids to oviposit in the holes. The treatments were initiated when the larvae reached late third instar because previous research had shown that stage to be the most cold-tolerant. B. zonata was not found to be confidently as or less cold tolerant than C. capitata; therefore, treatment schedules for the latter are not supported by this research for the former. B. zonata was found to be more susceptible to 1.7°C than A. ludens; therefore, the use of treatment schedules for A. ludens is supported by this research for B. zonata. However, the treatment for A. ludens requires 22 d. A shorter treatment was verified for B. zonata when 36,820 third instars reared from the eggs in oranges were stored at 1.7°C for 18 d with no larvae moving on examination 24 h after removal from the cold treatment chamber.

Effects of Phosphine Fumigation on Survivorship of Epiphyas postvittana (Lepidoptera: Tortricidae) Eggs

ABSTRACT Light brown apple moth, Epiphyas postvittana (Walker), eggs were subjected to phosphine fumigations under normal atmospheric and elevated oxygen levels in laboratory-scale chamber experiments to compare their susceptibilities to the two different fumigation methods. In fumigations conducted under atmospheric oxygen at 5 and 10°C, egg survivorship decreased with increase in phosphine concentration but then increased at a concentration of 3,000 ppm; this increase was significant at 10°C. Based on egg survivorship data, phosphine fumigations conducted in a 60% oxygen atmosphere were significantly more effective than those conducted under atmospheric oxygen conditions. Oxygenated phosphine fumigations at 5 and 10°C killed all 1,998 and 2,213 E. postvittana eggs treated, respectively, after 72 h of exposure. These results indicate the great potential of oxygenated phosphine fumigation for the control of E. postvittana eggs.

Phytosanitation Methods Influence Posttreatment Colonization of Juglans nigra Logs by Pityophthorus juglandis (Coleoptera: Curculionidae: Scolytinae)

Abstract Several North American walnut species (Juglans spp.) are threatened by thousand cankers disease which is caused by the walnut twig beetle (Pityophthorus juglandis Blackman) and its associated fungal plant pathogen, Geosmithia morbida M. Kolarík, E. Freeland, C. Utley and N. Tisserat sp. nov. Spread of this disease may occur via movement of infested black walnut (Juglans nigra L.) wood. This study evaluated the ability of P. juglandis to colonize J. nigra wood previously treated with various phytosanitation methods. Steam-heated and methyl bromide-fumigated J. nigra logs, as well as kiln-dried natural wane J. nigra lumber (with and without bark) were subsequently exposed to P. juglandis colonization pressure in two exposure scenarios. Following a pheromone-mediated, high-pressure scenario in the canopy of infested trees, beetles readily colonized the bark of steam-heated and methyl bromide-fumigated logs, and were also recovered from kiln-dried lumber on which a thin strip of bark was retained. In the simulated lumberyard exposure experiment, during which samples were exposed to lower P. juglandis populations, beetles were again recovered from bark-on steam-heated logs, but were not recovered from kiln-dried bark-on lumber. These data suggest logs and bark-on lumber treated with phytosanitation methods should not be subsequently exposed to P. juglandis populations. Further beetle exclusion efforts for phytosanitized, bark-on walnut wood products transported out of quarantined areas may be necessary to ensure that these products do not serve as a pathway for the spread of P. juglandis and thousand cankers disease.

Phenology and flight periodicity of Sirex noctilio (Hymenoptera: Siricidae) in central New York, U.S.A.

Field and laboratory studies were performed to determine the phenology of flight activity and the thermal requirements for adult emergence of Sirex noctilio. Degree‐day (DD) accumulation from egg to adult was measured in bolts of Pinus sylvestris infested with eggs from laboratory‐reared adults. Adult emergence was similarly monitored in bolts from trees that were naturally infested in the field by wild populations of S. noctilio reared at constant temperature. Laboratory‐infested bolts produced mostly males, whereas field‐collected material produced a 2.7 : 1 male‐biased sex ratio. Mean DDs to emergence was 1477.0 ± 13.4 (males) in laboratory‐infested bolts, as well as 1455.2 ± 11.2 (males) and 1577.8 ± 19.5 (females) in field‐collected material. Field‐trapping studies were conducted to compare flight activity with rearing data. Trap captures showed first flight activity and peak catch occurred at 709 and 1145 DDs. The resulting degree‐day model predicts early flight activity in early to mid‐April for pine stands in southeastern U.S.A., early to mid‐May in the Mid‐Atlantic region, and late June to early July in the northeast.

Relative Tolerance of Six Bactrocera (Diptera: Tephritidae) Species to Phytosanitary Cold Treatment

To compare relative cold treatment tolerance across the economically important tephritid fruit flies (Diptera: Tephritidae), Bactrocera carambolae Drew & Hancock, Bactrocera correcta (Bezzi), Bactrocera cucurbitae (Coquillett), four populations of Bactrocera dorsalis (Hendel), Bactrocera zonata (Saunders), and Bactrocera tryoni (Froggatt), eggs (in vitro), and larvae (in infested fruit or on carrot diet) were cold treated at 2.0 ± 0.2 °C for selected durations. The study was performed to assess whether a single (i.e., generic) cold treatment could be developed that would control the entire group of fruit flies that were tested. Probit regression models showed that the hierarchy of cold resistance was third-instar larvae reared on carrot diet > third-instar larvae reared on orange > eggs test in vitro. Differences in mortality responses of third-instar larvae reared in oranges across populations of B. dorsalis were observed only at subefficacious levels of control. The majority of Bactrocera species responded the same at the high levels of control demanded of phytosanitary treatments, which indicated that cold treatments would be similarly effective across the species and populations tested. B. cucurbitae was found to be the most cold tolerant of all the species tested.