Effects of landscape composition and rotation distance on Leptinotarsa decemlineata (Coleoptera: Chrysomelidae) abundance in cultivated potato

Knowledge of the Colorado potato beetle's, Leptinotarsa decemlineata (Say), relationship to previous potato crops has contributed to the development of a pest management strategy focused upon crop rotation. Previous investigations revealed that potato rotations exceeding 0.4 km were effective in reducing colonization in current season potato. The current study examines the relationship between beetle abundance in potato (Solanum tuberosum L.) and distance from multiple, previous year potato fields in Wisconsin, and integrates information about the influence of natural habitats adjacent to previous season potato. Colorado potato beetle count data were collected in 1998 and 2008 and distance to previous potato, field areas, and landscape classes were estimated using maps from 1997 and 2007. Poisson regression was used to relate counts to combinations of distance and local landscape characteristics calculated for all fields within 1,500 m of sampled potato. In 1998, beetle counts measured in current season potato declined significantly with increasing distance from previous potato fields and field size did not influence these counts. However, there was no relationship between beetle abundance and distance to prior year potatoes in 2008. In both years, increased proportions of surrounding habitats, previously described as preferred for diapause sites (e.g., wooded field boundaries), did not relate significantly to counts. However, grassland habitat was negatively correlated with counts. Results indicate that distance from previous potato remains an important factor to reduce the magnitude of colonization. This analysis further suggests that certain landscape components (e.g., grassland) may influence infestation, which may be useful for refining future integrated pest management programs.

Long-term retention of ice-nucleating active Pseudomonas fluorescens by overwintering colorado potato beetles

Ice nucleating-active Pseudomonas fluorescens F264C was fed to Colorado potato beetles to determine bacterial retentioin in the beetle gut and its effect on the cold hardiness of this insect pest. The bacrterium was present in beetles recovered after overwintering in the field, seven months after their exposure to P. fluorescens. Retention was evident not only in the detection of the P. fluorescens ice nucleating gene, inaW, in bacterial cultures from beetle guts but also in the elevated supercooling points of some treated beetles.

Polymerase chain reaction detection of viruliferous Bemisia tabaci (Homoptera: Aleyrodidae) with two tomato-infecting geminiviruses

The sweetpotato whitefly, Bemisia tabaci (Gennadius), is an important pest worldwide. A new biotype of sweetpotato whitefly, biotype B, causes damage by direct feeding and by the transmission of plant viruses, such as geminiviruses. In the Mediterranean area, tomato yellow leaf curl geminivirus (TYLCV) is the most serious disease of tomatoes. Another whitefly-transmitted geminivirus, tomato mottle geminivirus (ToMoV), is presently a serious problem in tomato production in west-central and southwestern Florida. Because of the increasing incidence of whitefly-transmitted geminiviruses, it is necessary to develop rapid and simple diagnostic methods for the detection of viruliferous whiteflies. The polymerase chain reaction is a sensitive and specific technique for the detection and identification of plant pathogens. Polymerase chain reaction methods were used successfully to amplify 1.1-kb DNA fragments from individual viruliferous B. tabaci carrying either TYLCV or ToMoV, and no amplified DNA fragments were obtained when nonviruliferous B. tabaci adults were processed similarly. Southern hybridization analysis proved that fragments amplified from viruliferous B. tabaci adults were viral DNA. This polymerase chain reaction-based detection method is sensitive enough to detect TYLCV and ToMoV in individual viruliferous B. tabaci in mixed samples of up to 25 (1 viruliferous: 24 nonviruliferous) and 10 (1 viruliferous: 9 nonviruliferous) individuals, respectively. The potential uses of this polymerase chain reaction-based detection method in epidermiological studies of geminiviruses are discussed.

Laboratory evaluation of three mosquito pathogenic strains of Bacillus sphaericus isolated in Egypt

Three strains of Bacillus sphaericus H-5a5b designated Ghar. 1 & 10, Ghar. 2 & 20, and Ghar. 3 & 30 were tested for growth, virulence, and larvicidal activity against Culex pipiens in the laboratory. Incubation temperature was positively correlated (r = 0.91) to the rate of bacterial growth (strain Ghar. 2 & 20). All three strains retained their virulence through 25 successive transfers on nutrient agar. Acetone powder preparations showed high larvicidal activity against C. pipiens, although second instar larvae were more susceptible than fourth instars to all three strains. The most active strain was Ghar. 2 & 20 with LC50 values of 0.51 mg/liter (second instar) and 1.62 mg/liter (fourth instar) after 48 hr of exposure. Mortality rates in fourth instar larvae exposed to an acetone powder form of strain Ghar. 2 & 20 were significantly greater at higher than at lower temperatures.