Arthur R. Richter

Quantification of Soil-to-Plant Transport of Recombinant Nucleopolyhedrovirus: Effects of Soil Type and Moisture, Air Currents, and Precipitation

ABSTRACT Significantly more occlusion bodies (OB) of DuPont viral construct HzSNPV-LqhIT2, expressing a scorpion toxin, were transported by artificial rainfall to cotton plants from sandy soil (70:15:15 sand-silt-clay) than from silt (15:70:15) and significantly more from silt than from clay (15:15:70). The amounts transported by 5 versus 50 mm of precipitation were the same, and transport was zero when there was no precipitation. In treatments that included precipitation, the mean number of viable OB transported to entire, 25- to 35-cm-tall cotton plants ranged from 56 (clay soil, 5 mm of rain) to 226 (sandy soil, 50 mm of rain) OB/plant. In a second experiment, viral transport increased with increasing wind velocity (0, 16, and 31 km/h) and was greater in dry (−1.0 bar of matric potential) than in moist (−0.5 bar) soil. Wind transport was greater for virus in a clay soil than in silt or sand. Only 3.3 × 10−7 (clay soil, 5 mm rain) to 1.3 × 10−6 (sandy soil, 50 mm rain) of the OB in surrounding soil in experiment 1 or 1.1 × 10−7(−0.5 bar sandy soil, 16-km/h wind) to 1.3 × 10−6(−1.0 bar clay soil, 31-km/h wind) in experiment 2 were transported by rainfall or wind to cotton plants. This reduces the risk of environmental release of a recombinant nucleopolyhedrovirus (NPV), because only a very small proportion of recombinant virus in the soil reservoir is transported to vegetation, where it can be ingested by and replicate in new host insects.

Detection of Anticarsia gemmatalis Nuclear Polyhedrosis Virus in Predatory Arthropods and Parasitoids After Viral Release in Louisiana Soybean

Anticarsia gemmatalis Hubner nuclear polyhedrosis virus (AgNPV) was released into field plots; samples were then collected weekly to determine the complex of predatory arthropods and parasitoids contaminated with the virus due to attacks on the infected hosts. No contamination was detected on day 1 after the release or at any time in control samples. In the treated plots, the percentage of contaminated predatory arthropods and parasitoids declined from 79% on day 8 to 20% on day 41. In samples averaging 16 m distance from treated plots, contamination increased from 32% on day 8 to 69% on day 27, then decreased to 21% on day 41. The AgNPV was detected in at least six species of Hemiptera, one Coleoptera, nine species of spiders, one species of hymenopteran parasitoid, and two dipteran parasitoids.

Prevalence, Spread, and Effects of the Microsporidium Thelohania solenopsae Released into Populations with Different Social Forms of the Red Imported Fire Ant (Hymenoptera: Formicidae)

Abstract The microsporidium Thelohania solenopsae Knell, Allen, and Hazard was released into colonies of red imported fire ants, Solenopsis invicta Buren, at four field sites in Louisiana. Social form of the ant affected the establishment of the microsporidium; long-term epizootics developed at two sites with predominantly polygyne populations, whereas the pathogen produced a low disease prevalence before it disappeared or did not infect ants at all at two monogyne sites. This study is the first report of artificial infection of monogyne S. invicta field colonies. When the microsporidium became established in mixed monogyne/polygyne ant populations, prevalence rates peaked at >75% in both social forms. In mixed ant populations, the social form suffering higher prevalence of the disease decreased proportionally to the other form, possibly indicating a competitive disadvantage. Host population density or site characteristics may have influenced spread of the disease; the rate of spread was 0.9 m/mo at one epizootic site and reached 9.4 m/mo at the other. There was little seasonal variation in prevalence, which averaged 47% in February, 51% in April/May, and 57% in October/November at the two epizootic sites. The strongest evidence of microsporidian impact on S. invicta populations was a negative correlation between colony numbers versus percentage infection and a sporadic decrease in the number of foragers. There was some evidence of a decrease in the size and number of colonies at one epizootic site and a decrease in brood at the other. This sporadic weakening of the S. invicta populations did not lead to significant immigration of other ant species.

Interactions of Metarhizium anisoplae and Tree-based Mulches in Repellence and Mycoses Against Coptotermes formosanus (Isoptera: Rhinotermitidae)

Abstract The use of mulch in urban landscapes has increased in the United States for the past decade. Tree-based organic mulches can supply Coptotermes formosanus Shiraki with food, moisture, and shelter. The current research contributes to mulch management technology in termite control. A choice test arena was designed to determine the repellence and mortality caused by commercial mulches treated with different concentrations of the fungus Metarhizium anisopliae (Metschnikoff) against C. formosanus. Each of six tree-based mulches (pine bark, pine straw, bald cypress, eucalyptus, water oak, and melaleuca) was coated with six conidial concentrations ranging from 1 × 103 to 1 × 108 conidia/ml. The foragers of C. formosanus were repelled significantly by the fungal-treated mulch substrates; the proportion of termites on fungal-treated mulch was usually <20% during the 28-d test. By day 28, >99% of the termites were killed in test arenas containing a chamber with mulch treated with 107 or 108 conidia/ml. M. anisopliae significantly reduced mulch consumption by 34–71%. Mulch consumption by the termites was negatively correlated with fungal concentration, and the type of mulch also affected consumption. The differences in termite foraging activities, mortality, and food consumption among mulches were usually confounded by differences in fungal concentrations of M. anisopliae. The results indicate that repellence and virulence of M. anisopliae conidia should significantly reduce the suitability of these six mulches as a habitat for C. formosanus.

EFFICACY OF FOLIAR INSECTICIDES ON EGGS OF NEZARA VIRIDULA (HEMIPTERA: PENTATOMIDAE)

ABSTRACT Stink bugs (Hemiptera: Pentatomidae) are important insect pests of crops. Stink bug feeding reduces yields, lowers crop quality, induces delayed maturity, and wounds tissues allowing for pathogen entry. Historically, effective adult and nymph control of stink bugs has been with insecticides. However, little insecticide efficacy against stink bug eggs is known. The objective of this study was to determine how foliar insecticides currently recommend for southern green stink bug, Nezara viridula (L.), control in soybean impact pre-emergence nymphal mortality using an egg dip bioassay. Eight formulate insecticides were tested. Differences in nymphal stink bug pre-emergence mortality were recorded. The lowest instances of stink bug emergence (and highest mortality) were observed in egg masses treated with bifenthrin (78.7%) followed by beta-cyfluthrin + acephate (42.5%) and acephate (40.9%). The highest emergence (and lowest mortality) occurred in egg masses treated with spinosad (10.4%). Results indicate that insecticides used to control stink bug nymphs and adults can impact nymphal pre-emergence mortality and control southern green stink bugs before emergence.