Effects of contemporary agricultural land cover on Colorado potato beetle genetic differentiation in the Columbia Basin and Central Sands

Landscape structure, which can be manipulated in agricultural landscapes through crop rotation and modification of field edge habitats, can have important effects on connectivity among local populations of insects. Though crop rotation is known to influence the abundance of Colorado potato beetle (CPB; Leptinotarsa decemlineata Say) in potato (Solanum tuberosum L.) fields each year, whether crop rotation and intervening edge habitat also affect genetic variation among populations is unknown. We investigated the role of landscape configuration and composition in shaping patterns of genetic variation in CPB populations in the Columbia Basin of Oregon and Washington, and the Central Sands of Wisconsin, USA. We compared landscape structure and its potential suitability for dispersal, tested for effects of specific land cover types on genetic differentiation among CPB populations, and examined the relationship between crop rotation distances and genetic diversity. We found higher genetic differentiation between populations separated by low potato land cover, and lower genetic diversity in populations occupying areas with greater crop rotation distances. Importantly, these relationships were only observed in the Columbia Basin, and no other land cover types influenced CPB genetic variation. The lack of signal in Wisconsin may arise as a consequence of greater effective population size and less pronounced genetic drift. Our results suggest that the degree to which host plant land cover connectivity affects CPB genetic variation depends on population size and that power to detect landscape effects on genetic differentiation might be reduced in agricultural insect pest systems.     

七角星蜡蚧在云南省的分布与危害

[目的]七角星蜡蚧(半翅目:蚧次目:蚧科:蜡蚧属)是一种外来入侵害虫,自2013年在云南省西双版纳州勐仑镇发现以来,中国大陆再无系统性的调查。近年来作者在云南省收集蚧虫期间,在多地发现七角星蜡蚧为害,现对其在云南省的发生情况进行报道,以期为其监测和防治提供参考。[方法]2016年10月—2021年9月,对云南省15州(市)的64个县(区市)进行了系统调查,详细研究了七角星蜡蚧的分布、寄主及一些生物学习性。[结果]七角星蜡蚧在云南省西双版纳州的景洪市、勐腊县(勐仑镇和磨憨镇)、勐海县(打洛镇),普洱市的宁洱县,德宏州的盈江县(那邦镇),红河州的河口县、金平县(勐拉乡和者米乡)4州(市)7县(市)9地有分布,新增8个分布点。除宁洱县外,其余发生地均位于边境线上,表明其可能为境外多点入侵。在云南该虫危害寄主植物共4科4属5种,包括杧果和莲雾2种经济树种。七角星蜡蚧多寄生在叶片背面,沿叶脉分布,1年发生多代。在河口县的龙船花上,该虫每雌产卵38~50粒,虫口密度达185~250头·叶^-1。[结论]七角星蜡蚧在云南省零星分布,尚未造成严重损害,但有向内扩散的趋势,应加以警惕。     

A spatial model of the development of pest resistance to a transgenic insecticidal crop: European corn borer on Bt maize

A mathematical model was constructed to describe the evolution of resistance to the Bacillus thuringiensis toxin (Bt) in an insect pest (European corn borer) population on a transgenic crop (Bt corn). The model comprises a set of partial differential equations of the reaction-diffusion type; local interactions of three competing pest genotypes formed by alleles of Bt resistance and susceptibility are described as in the Kostitzin model, and the spread of insects is modeled as diffusion. The model was used to evaluate the influence of pest characteristics on the efficacy of the high-dose/refuge strategy aiming to prevent or delay the spread of Bt resistance in pest populations. It was shown, by contrast, that a model based on Fisher-Haldane-Wright equations and formally incorporating a diffusion term cannot adequately describe the evolution of Bt resistance in a spatially inhomogeneous pest population. Further development of the proposed demo-genetic model is discussed.     

冬小麦粒叶比杂种优势及遗传效应分析

用9个冬小麦品种按5×4不完全双列杂交设计组配20个杂交组合,对小麦粒叶比的杂种优势和遗传效应进行分析。结果表明,小麦粒叶比表现出一定的杂种优势;一般配合力和特殊配合力方差均达极显著水平,说明亲本的粒叶比差异及杂交互作均对F1代产生遗传差异,该试验中石6021、农大99260080等的一般配合力较大,石6021×农大99260080、鲁麦14×济南17等组合的特殊配合力较大,产生了较强的杂种优势;粒叶比遗传符合加性-显性遗传模型,但以加性效应为主,其遗传决定度达87.65%,狭义遗传力为64.71%;在高粒叶比品种选育上应重视高粒叶比亲本筛选利用和杂交后代的早代选择。     

First report of the invasive crop pest Stenocranus pacificus (Hemiptera: Delphacidae) in temperate Asia

Numerous delphacid planthopper species are major pests of economically important and widely cultivated crops (i.e. rice, corn, and sugarcane). These insects have the potential to become serious crop pests in areas where they have either naturally migrated or been newly introduced. The white-bellied planthopper, Stenocranus pacificus Kirkaldy, 1907, originally known from tropical South Pacific islands, appeared in tropical and subtropical Asia in the early years of the 21st century. Since then, S. pacificus has become a serious pest of corn in some Southeast Asian countries, although it also feeds on rice, sugarcane, sorghum, and other grasses. Here, we report the presence of S. pacificus in mainland Japan, representing the first record of this species in temperate Asia. Seven male and 17 female adult individuals collected in Kumamoto Prefecture in 2019 and 2020 were identified as S. pacificus based on their morphological characteristics and mitochondrial COI sequences. In addition, molecular phylogenetic analysis showed that S. pacificus formed a distinct clade from other Stenocranus species, indicating uncertainty in its generic assignment. Although crop damage by S. pacificus has not yet been reported from temperate regions, given its wide range of plant hosts and the potential for future range expansions, damaged crops in Asia, including in temperate regions, should be monitored for the presence of this species.     

The complete mitochondrial genome of Tuta absoluta (Lepidoptera: Gelechiidae) and genetic variation in two newly invaded populations in China

Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) is a devastating invasive pest worldwide, causing severe damage to tomatoes. Recently, it has been recorded in the northwestern and southwestern parts of China. Here, the mitogenomes and genetic variation of two newly invaded T. absoluta populations in Xinjiang and Yunnan, were determined. The results showed that the complete mitogenome size of T. absoluta is 15298 bp for the individual from Xinjiang and 15296 bp for the individual from Yunnan, which were both longer than the reported mitogenome from Spain (15290 bp). The mitogenome sequences of individuals collected from three locations showed high levels of sequence similarity, except for 8 polymorphic sites, which were in genes cox2 (1 site), cox3 (2 sites), cob (1 site), atp6 (1 site), nad1 (2 sites) and nad5 (1 site). Tuta absoluta mitogenomes share many features with other 6 Gelechiidae mitogenomes, except for several differences in the start and stop codons of protein-coding genes and the length of intergenic spacers. Seven partial mitochondrial genes (cox1, cox2, cox3, atp6, cob, nad1, and nad5) were used for genetic variation analysis, and significant population differentiation was found between the two populations based on cox2, atp6, nad1, and nad5. The complete mitogenomes and sensitive mitochondrial gene markers reported here provide useful data for further population genetics study of this pest.     

Genetics and selective breeding of variation in wing truncation in a flightless aphid control agent

Augmentative biological control by predaceous ladybird beetles can be improved by using flightless morphs, which have longer residence times on the host plants. The two‐spot ladybird beetle, Adalia bipunctata (L.) (Coleoptera: Coccinellidae), is used for the biological control of aphids in greenhouses and on urban trees. Flightlessness due to truncated wings occurs at very low frequency in some natural populations of A. bipunctata. Pure‐breeding strains of this 'wingless' genotype of A. bipunctata can easily be obtained in the laboratory. Such strains have not been commercialized yet due to concerns about their reduced fitness compared to wild‐type strains, which renders mass production more expensive. Wingless strains exhibit, however, wide intra‐population phenotypic variation in the extent of wing truncation which is related to fitness traits. We here use classical quantitative genetic techniques to study the heritability and genetic architecture of variation in wing truncation in a wingless strain of A. bipunctata. Split‐families reared at one of two temperatures revealed strong family‐by‐temperature interaction: heritability was estimated as 0.64 ± 0.09 at 19 °C and 0.29 ± 0.06 at 29 °C. Artificial selection in opposite directions at 21 °C demonstrated that the degree of wing truncation can be altered within a few generations resulting in wingless phenotypes without any wing tissue (realized h² = 0.72), as well as those with minimal truncations (realized h² = 0.61) in two replicates. The latter lines produced more than twice as many individuals. This indicates that selective breeding of wing truncation may be exploited to improve mass rearing of flightless strains of A. bipunctata for commercial biological control. Our work illustrates that cryptic variation can also be a source for the selective breeding of natural enemies.     

Does experimental evolution produce better biological control agents? A critical review of the evidence

Biological control of crop pests is considered a good alternative or complement to the use of pesticides. However, legislation restricts the importation of natural enemies of pests. A potential way to circumvent this limitation is by using experimental evolution and/or artificial selection to improve native biological control agents. Here, we review studies that have used these methodologies and evaluate their success. Experimental evolution or artificial selection has been used on a wide range of traits, with most focusing on improving the performance of natural enemies in ecologically relevant environments, such as in the presence of pesticides or at different temperatures. Although most studies were poorly replicated, the selected traits generally improved following the selection process. However, correlated responses (often in the form of trade‐offs) with other traits of interest were common. We suggest that the selection procedure can be improved by increasing replication and performing experimental evolution under more semi‐natural environments, to ensure that the most useful traits are being selected.     

Comparison of pheromone trap design and lures for Spodoptera frugiperda in Togo and genetic characterization of moths caught

Fall armyworm, Spodoptera frugiperda (JE Smith) (Lepidoptera: Noctuidae), is a pest of grain and vegetable crops endemic to the Western Hemisphere that has recently become widespread in sub‐Saharan Africa and has appeared in India. An important tool for monitoring S. frugiperda in the USA is pheromone trapping, which would be of value for use with African populations. Field experiments were conducted in Togo (West Africa) to compare capture of male fall armyworm using three commercially available pheromone lures and three trap designs. The objectives were to identify optimum trap × lure combinations with respect to sensitivity, specificity, and cost. Almost 400 moths were captured during the experiment. Differences were found in the number of S. frugiperda moths captured in the various trap designs and with the three pheromone lures, and in the number of non‐target moths captured with each lure. The merits of each trap × lure combination are discussed with respect to use in Africa. A nearly equal number of COI‐CS (161) and COI‐RS (158) moths was captured with no differences found in COI marker proportions among traps or lures. However, the diagnostic rice strain marker Tpi was rarely found. Overall, the genetic characterization of the pheromone trap collections indicated a consistent distribution of genetic markers from 2016 to 2017, suggesting a population at or near equilibrium.