Toxicity of insecticides to the tsetse fly,Glossina palpalis palpalis in Nigeria and comparison of tolerances in 1974–1975 and 1979–1982

Abstract

Toxicities o1 12 chemical insecticides to wild‐caught tsetse flies, Glossina palpalis palpalis in Nigeria were measured by topical application. Median lethal doses (as ng per fly) at 48 h after application for older flies, males (females), were: DDT 331 (700), dieldrin 14 (46), endosulfan 8 (15), malathion 193 (273), fenitrothion 47, pirimiphos methyl 31 (45), tetrachlorvinphos 14 (33), sumicidin 28 (58), neopynamin 12 (15), sumithrin 10 (8), permethrin 4.4 (5.9), deltamethrin 0.45 (0.94). Lethality expressed as dose per whole fly can be termed effective toxicity/tolerance and those expressed as dose per weight unit of fly can be termed intrinsic (or true) toxicity/tolerance. Generally, effective tolerance was greater for females than males, especially for older flies. However, intrinsic tolerance was often about equal for the sexes or greater for males. Regardless of sex, effective tolerance increased with increasing fly age and intrinsic tolerance increased during later ageing but not during early ageing. This suggested that protecting mechanisms developed during ageing. Flies fed a few hours before treatment in 1979–1982 were more tolerant of three organochlorines and three organophosphates than flies fed the day before treatment in 1974–1975, probably due to diversion of poisons from sites of action into inert undigested blood. However, results and statistical analysis suggested a slight increase in true tolerance of males to DDT during the intervening years. Continued monitoring of tolerance in the fly populations is recommended.     

What have we learned from studies of wild plant-pathogen associations?—the dynamic interplay of time,space and life-history

The interplay of host and pathogen life history traits with disease epidemiology and the selective pressures exerted on hosts drives genetic change and the long-term coevolutionary trajectories of host-pathogen associations. Many studies have addressed various aspects of the ways in which hosts and their pathogens interact but have tended to focus on individual populations, on comparisons made at single points in time, or on broader comparisons that confound patterns from different epidemiological and evolutionary units. While such studies provide valuable information, their essentially ‘static’ snap-shot nature limits the ability to interpret the nature of the underpinning coevolutionary processes. An increasing number of long-term studies involving repeat sampling of multiple interaction demes distributed across space are giving insight into the complexity of the numerical and genetic dynamics of host and pathogen interactions. These illustrate: (a) the ephemerality of disease in individual populations in contrast to its predictability at the metapopulation scale; (b) the spatial and temporal dynamics of selection ‘hot-spots’, rates of extinction and recolonization; and (c) differences in coevolutionary dynamics among demes within a metapopulation. Such long-term studies further emphasise the interplay between life history traits, time and space, and the importance of developing a framework to classify the seemingly daunting diversity of host-pathogen associations.     

Susceptibility to neonicotinoids and risk of resistance development in the brown planthopper, Nilaparvata lugens (Stål) (Homoptera: Delphacidae)

BACKGROUND: In recent years, outbreaks of the brown planthopper, Nilaparvata lugens (Stål), have occurred more frequently in China. The objective of this study was to determine the susceptibility of N. lugens to neonicotinoids and other insecticides in major rice production areas in China. RESULTS: Results indicated that substantial variations in the susceptibility to different insecticides existed in N. lugens. Field populations had developed variable resistance levels to neonicotinoids, with a high resistance level to imidacloprid (RR: 135.3–301.3‐fold), a medium resistance level to imidaclothiz (RR: 35–41.2‐fold), a low resistance level to thiamethoxam (up to 9.9‐fold) and no resistance to dinotefuran, nitenpyram and thiacloprid (RR < 3‐fold). Further examinations indicated that a field population had developed medium resistance level to fipronil (up to 10.5‐fold), and some field populations had evolved a low resistance level to buprofezin. In addition, N. lugens had been able to develop 1424‐fold resistance to imidacloprid in the laboratory after the insect was selected with imidacloprid for 26 generations. CONCLUSION: Long‐term use of imidacloprid in a wide range of rice‐growing areas might be associated with high levels of resistance in N. lugens. Therefore, insecticide resistance management strategies must be developed to prevent further increase in resistance. Copyright © 2008 Society of Chemical Industry     

Relative importance of climate factors and human activities in impacting vegetation dynamics during 2000–2015 in the Otindag Sandy Land,northern China

In recent years, there has been increasing research interests in differentiating the relative importance of climate factors and human activities in impacting vegetation dynamics. In this study, based on residual trend method, we used MOD13A3(MODIS vegetation index product), MCD12Q1(MODIS land cover product) and meteorological datasets to differentiate the relative importance of climate factors and human activities in impacting vegetation dynamics during 2000–2015 in the Otindag Sandy Land, northern China. Results show that during the study period(2000–2015), the overall vegetation condition had improved in the Otindag Sandy Land. The driving forces of vegetation dynamics differed spatially in the whole study area over the study period. The area with vegetation degradation solely resulted from human activities accounted for 8.23% of the study area, while the area with vegetation degradation resulted from others(including climate factors and combination of climate factors and human activities) occupied 1.53%. The area with vegetation recovery benefitted from human activities occurred over 26.02% of the study area; the area benefitted from climate factors accounted for 23.69%; and the area benefitted from both climate factors and human activities occupied 37.74%. All in all, impacts of climate factors and human activities on vegetation dynamics varied at the county/city/banner scales and locality-specific measures should be adopted to protect the environments.