BACKGROUND The use of chemical insecticides to control Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae) is widespread, although it might exert a sublethal effect on its dominant parasitoid, Encarsia formosa Gahan (Hymenoptera: Aphelinidae). To investigate the sublethal effect of spirotetramat on E. formosa, we observed the ability of E. formosa to locate and handle the host, oviposit and preen after exposure to sublethal concentrations of spirotetramat. RESULTS After exposure to spirotetramat at LC50, the response time of E. formosa to the volatile reached 223.40 s and was significantly prolonged. Only 56.44% of the wasps were attracted by the volatile and the insect crawled the slowest among all of the treatments. The averages of oviposition posture adopted and host handled by each E. formosa in 1 h decreased significantly to 1.79 and 1.27, respectively. At the sublethal concentration of LC10, 94.59% of the wasps were attracted by the volatile and the insect crawled the fastest. The average of host handled by each E. formosa was 3.92, and the frequency of drumming while walking and drumming the host was 12.34 times per second and 12.30 times per second, respectively, demonstrating a significant acceleration in these abilities. CONCLUSION These findings demonstrate that spirotetramat induced hormesis in E. formosa on exposure to its LC10 concentration and accelerated its host locating, host handling and frequency of antennae drumming. These findings could assist in balancing the chemical and biological control of B. tabaci and enhancing the efficacy of E. formosa as a biocontrol agent. © 2021 Society of Chemical Industry.

Agricultural landscape patterns can affect the population dynamics of pest insects. We selected four landscapes (flower field, mountain, river and urban) based on principal components analysis in Yunnan Province, south China. Through systematic investigation carried out in tomato fields, we intended to clarify the population dynamics and densities of Bemisia tabaci under different landscape types. During the main activity period of B. tabaci , the population densities of B. tabaci nymphs in tomato fields in the river and the urban landscape types were the highest compared to the other landscape types; the population densities of female adults in tomato fields in the river landscape type were also the highest. While the population densities of B. tabaci nymphs and female adults in the flower landscape type, no more than five individuals (ind.) 100 cm −2 leaf in both years, were the lowest. The density of B. tabaci nymphs in the middle position of tomato plants was higher than those in the other positions, while the density of adults in the upper position of tomato plants was higher, regardless of landscape types. Our findings showed that the population growth of B. tabaci can be easily controlled by the flower landscape type.

This study aimed to investigate the growth and development parameters of Phthorimaea absoluta (Meyrick) population at each stage when feeding on 4 host plants: Lycopersicon esculentum, Solanum tuberosum, Solanum melongena, and Nicotiana tabacum. The objective was to predict population dynamics and develop appropriate control strategies. The age-stage sex-life table was used to evaluate survival rate, fecundity, life expectancy, reproductive value, population parameters, and population growth prediction of P. absoluta after feeding on the 4 Solanaceae plants. The results showed significant variations in the fecundity parameters of P. absoluta among the different host plants. The L. esculentum population exhibited the highest average egg-laying period (13.17 ± 0.61 days) and average egg production (219.31 ± 21.02 eggs), while N. tabacum had the lowest values (4.56 ± 0.26 days and 26.08 ± 2.53 eggs, respectively). The gross reproduction rate of P. absoluta feeding on L. esculentum was 146.43 ± 21.00, which was 1.80, 3.77, and 6.39 times higher compared to S. tuberosum, S. melongena, and N. tabacum, respectively. The average age period and population doubling time of P. absoluta feeding on L. esculentum were lower than those of the other 3 host plants. These results indicated that while P. absoluta can complete a generation on L. esculentum, S. tuberosum, S. melongena, and N. tabacum, L. esculentum is the most suitable host for its growth and development. Therefore, in the occurrence and adjacent areas of P. absoluta, relevant authorities should promptly monitor and control its population in the planting areas of Solanaceae plants to prevent further spread.