Craig S. Eckel

Variation in thrips species composition in field crops and implications for tomato spotted wilt epidemiology in North Carolina

Thrips were surveyed in tomato spotted wilt‐susceptible crops in five areas across North Carolina. Tomato, pepper, and tobacco plants in commercial fields were sampled and 30 species of thrips were collected over a 3‐year period. The most common species overall was Frankliniella tritici (Fitch). The most common thrips species that are known to vector Tomato Spotted Wilt Virus (TSWV) were F. fusca (Hinds), and F. occidentalis (Pergande). Relatively low numbers of Thrips tabaci Lindeman, another reported vector, were collected. The spatial and temporal occurrence of vectors varied with sampling method, crop species, region of North Carolina, and localized areas within each region. In a laboratory experiment, no difference was detected between the ability of F. fusca and F. occidentalis to acquire and transmit a local isolate of TSWV. Based on vector efficiency and occurrence, F. fusca is considered the most important vector of TSWV in tobacco, whereas both F. fusca and F. occidentalis are important vectors of TSWV in tomato and pepper.

Comparison of Colored Sticky Traps for Monitoring Thrips Populations (Thysanoptera: Thripidae) in Staked Tomato Fields

The response of flower thrips, Frankliniella spp., to various colors and sticky trap designs was evaluated in staked tomato fields in western North Carolina. Yellow sticky traps caught significantl...

Changes in insecticide efficacy against Helicoverpa zea (Boddie) on soybean due to larval size and plant phenology

The within-plant distribution of corn earworm, Helicoverpa zea (Boddie), on soybean, Glycine max (L.) Merrill, changes with larval size and plant phenological stage. Small (instars 1 and 2) larvae on H. zea are often found within rolled leaves and flowers when each plant part is available (vegetative and flowering stages). Medium (instars 3 and 4) and large (instars 5 and 6) larvae at all plant reproductive growth stages, and small larvae when rolled leaves and flowers are not available, are found primarily on open leaves. Because both rolled leaves and flowers may protect small larvae from exposure, insecticide efficacy may be reduced in soybean fields during the vegetative or flowering stages. To ensure that any differences observed in field experiments were not due to differences in susceptibility, the relative mortality of small, medium, and large H. zea larvae fed on soybean foliage treated with insecticides was assessed in the laboratory. No significant difference between small, and medium plus large larvae (combined) was detected in one test, but mortality of small larvae was significantly higher in another test. In the field, the number of H. zea larvae on insecticide-treated and untreated soybeans was compared 1 and 7 days after application, with separate experimental designs. The relative number of small, medium, and large larvae in each treatment varied with soybean growth stage. Differences between insecticide treatments were greater for large larvae than for small larvae when soybeans were flowering. When soybeans were in the pod-forming stages, few larvae of any size were found in the insecticide-treated plots one day after application. One week after application, greater differences in larval numbers were observed for small and medium larvae on soybeans in early reproductive growth stages than for large larvae in early stages or all sizes in later stages. It was concluded that insecticide efficacy for small H. zea larvae is low on soybeans in vegetative or early flowering growth stages. Because mortality of small larvae was higher at later plant growth stages, and as mortality of small larvae fed on insecticide-treated foliage was as high as, or higher than, mortality of larger larvae, the low efficacy may be attributed to lower exposure to insecticides.