Metapopulation approach for landscape level management of western tarnished plant bug, Lygus hesperus, in Texas (Hemiptera, Miridae)

Insect source-sink dynamics are vital to ecologically intensive pest management. Maintaining sink plant hosts, or "trap crops", and destroying alternate hosts or breeding places adjacent to the field crop are effective pest management strategies for some arthropods. However, determining whether a host acts as a source or a sink is challenging, especially when the pest species is highly mobile and polyphagous. The western tarnished plant bug, Lygus hesperus, is highly polyphagous, and can utilize >300 hosts. Its presence has been documented in 26 roadside weed hosts in the Texas High Plains. Previous studies demonstrated that L. hesperus prefer alfalfa over cotton and several alternate weed hosts. A four-year project involved surveying and sampling for L. hesperus in the agricultural landscapes of several sub-regions of the southwestern United States, including the Texas High Plains. In Texas, geographic information of the landscape vegetation complex was compiled from a 150 km radius in the Texas High Plains. In one study, fifty irrigated cotton fields representing the crop diversity within this region were sampled via sweep-net for 10 weeks. This effort also included sampling of up to six non-cotton insect habitats within a 3 km radius of each field. Seasonal average L. hesperus abundance data were regressed with 27 field characteristics (variables), including habitat-specific land cover, distance between focal cotton fields and non-cotton habitats, longitude, latitude, elevation, habitat heterogeneity index, and several environmental/ecological variables. Significant variables were selected using a stepwise regression at 15% probability rate. A 10-parameter linear model explained 93% of the variation in the data. Major parameters contributing significantly to variation in L. hesperus abundance in cotton were corn and sunflower acreages, focal cotton field distances from several non-cotton hosts, and habitat heterogeneity index. In addition, field marking-and-capture studies were conducted using protein markers and enzyme-linked immunosorbent assays to characterize L. hesperus intercrop movement behavior. The field marking-and-capture approach can be used to study the effects of various crop management practices on L. hesperus intercrop movement and can potentially be applied to other pests and cropping systems.     

Regional reversion of insecticide resistance in Helicoverpa armigera (Lepidoptera: Noctuidae) is associated with the use of Bt cotton in northern China

A continuous programme for monitoring resistance of Helicoverpa armigera (Hubner) to commonly used insecticides was undertaken for assessing the impact of Bt cotton planting on the evolution of the pest resistance from 1994 to 2002 in China. The bioassay results showed that the resistance levels per year in field populations of H armigera to lambda-cyhalothrin, phoxim and endosulfan decreased, respectively, to 9-15-fold, 11-14-fold and 6-8-fold in 2001-2002 from 197-262-fold, 52-74-fold and 18-38-fold before the cultivation of Bt cotton in 1997. This significant increase in susceptibility to insecticides is expected to result in a reduction in insecticide application for H armigera control in Bt cotton. It is concluded that Bt cotton is playing an important role in the long-term management of H armigera by increasing the potential for natural and chemical control of the pest.     

红铃虫对Bt棉花抗性治理的研究进展

综述了Bt棉花对红铃虫的抗性效率和红铃虫对Bt棉花的抗性机理、抗性遗传、抗性监测及治理对策的研究进展.研究结果表明,不同种植区Bt棉花对红铃虫的抗性水平有较大差别.红铃虫中肠内Bt毒素结合位点数量减少是产生抗性的主要机制.抗性由具1个主效应的多位点基因控制,高水平抗性的产生与编码钙蛋白基因变异有关.避难所策略是红铃虫抗性治理的主要措施.抗性监测表明,自1997年以来,美国亚历桑那州红铃虫田间种群对Bt棉花的抗性频率无显著性变化.     

Insecticide resistance in field populations of Bemisia tabaci (Hemiptera: Aleyrodidae) in West Africa

BACKGROUND: The tobacco whitefly, Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae), has developed a high degree of resistance to several chemical classes of insecticides throughout the world. To evaluate the resistance status in West Africa, eight insecticides from different chemical families were tested using the leaf‐dip method on four field populations collected from cotton in Benin, Togo and Burkina Faso. RESULTS: Some field populations showed a significant loss of susceptibility to pyrethroids such as deltamethrin [resistance ratio (RR) 3–5] and bifenthrin (RR 4–36), to organophosphates (OPs) such as dimethoate (RR 8–15) and chlorpyrifos (RR 5–7) and to neonicotinoids such as acetamiprid (RR 7–8) and thiamethoxam (RR 3–7). Bemisia tabaci was also resistant to pymetrozine (RR 3–18) and to endosulfan (RR 14–30). CONCLUSION: The resistance of B. tabaci to pyrethroids and OPs is certainly due to their systematic use in cotton treatments for more than 30 years. Acetamiprid has been recently introduced for the control of whiteflies. Unfortunately, B. tabaci populations from Burkina Faso seem to be already resistant. Because cross‐resistance between these compounds has never been observed elsewhere, resistance to neonicotinoids could be due to the presence of an invasive B. tabaci biotype recently detected in the region. Copyright © 2010 Society of Chemical Industry     

Microsatellite and mating type markers reveal unexpected patterns of genetic diversity in the pine root‐infecting fungus Grosmannia alacris

Grosmannia alacris is a fungus commonly associated with root‐infesting bark beetles occurring on Pinus spp. The fungus has been recorded in South Africa, the USA, France, Portugal and Spain and importantly, has been associated with pine root diseases in South Africa and the USA. Nothing is known regarding the population genetics or origin of G. alacris, although its association with root‐infesting beetles native to Europe suggests that it is an invasive alien in South Africa. In this study, microsatellite markers together with newly developed mating type markers were used to characterize a total of 170 isolates of G. alacris from South Africa and the USA. The results showed that the genotypic diversity of the South African population of G. alacris was very high when compared to the USA populations. Two mating types were also present in South African isolates and the MAT1‐1/MAT1‐2 ratio did not differ from 1:1 (χ² = 1·39, P = 0·24). This suggests that sexual reproduction most probably occurs in the fungus in South Africa, although a sexual state has never been seen in nature. In contrast, the large collection of USA isolates harboured only a single mating type. The results suggest that multiple introductions, followed by random mating, have influenced the population structure in South Africa. In contrast, limited introductions of probably a single mating type (MAT1‐2) may best explain the clonality of USA populations.     

Cross‐resistance study and biochemical mechanisms of thiamethoxam resistance in B‐biotype Bemisia tabaci (Hemiptera: Aleyrodidae)

BACKGROUND: B‐biotype Bemisia tabaci (Gennadius) has invaded China over the past two decades. To understand the risks and to determine possible mechanisms of resistance to thiamethoxam in B. tabaci, a resistant strain was selected in the laboratory. Cross‐resistance and the biochemical mechanisms of thiamethoxam resistance were investigated in the present study. RESULTS: A 66.3‐fold thiamethoxam‐resistant B. tabaci strain (TH‐R) was established after selection for 36 generations. Compared with the susceptible strain (TH‐S), the selected TH‐R strain showed obvious cross‐resistance to imidacloprid (47.3‐fold), acetamiprid (35.8‐fold), nitenpyram (9.99‐fold), abamectin (5.33‐fold) and carbosulfan (4.43‐fold). No cross‐resistance to fipronil, chlorpyrifos or deltamethrin was seen. Piperonyl butoxide (PBO) and triphenyl phosphate (TPP) exhibited significant synergism on thiamethoxam effects in the TH‐R strain (3.14‐ and 2.37‐fold respectively). However, diethyl maleate (DEM) did not act synergistically with thiamethoxam. Biochemical assays showed that cytochrome P450 monooxygenase activities increased 1.21‐ and 1.68‐fold respectively, and carboxylesterase activity increased 2.96‐fold in the TH‐R strain. However, no difference was observed for glutathione S‐transferase between the two strains. CONCLUSION: B‐biotype B. tabaci develops resistance to thiamethoxam. Cytochrome P450 monooxygenase and carboxylesterase appear to be responsible for the resistance. Reasonable resistance management that avoids the use of cross‐resistance insecticides may delay the development of resistance to thiamethoxam in this species. Copyright © 2009 Society of Chemical Industry     

江西亚洲柑橘木虱的种群遗传结构研究

亚洲柑橘木虱Diaphorina citri Kuwayama是芸香科Rutaceae植物新梢期的重要害虫,也是黄龙病Huanglongbing的主要传播媒介,严重威胁江西柑橘产业的发展。本文利用线粒体基因标记,研究江西10个地点亚洲柑橘木虱的种群遗传结构和多态性。扩增了2个线粒体COⅠ基因片段,长度为1 431 bp。其中多态性位点2个(均为非同义突变,A/G转换),单倍型3个(Hap-1,Hap-2和Hap-3)。最常见的单倍型是Hap-1(占总样本数的91.7%),发生在所有采样点;其次为Hap-3(6.3%),分布在大余和崇义;Hap-2(2.0%)仅在兴国出现。单一直线型的单倍型网络结构模式、小而不显著的HR(Harpending’s raggedness)指数值,以及单峰型错配分布曲线均表明:江西地区的亚洲柑橘木虱是近期入侵并经历了快速的种群动态扩张。