Evaluation of imidacloprid (Confidor OD®) genotoxicity in Chrysoperla externa eggs (Neuroptera: Chrysopidae) through comet assay

The comet assay allows the analysis of DNA damage caused by different genotoxins. This assay has recently gained interest because of its ease of studying the interactions of xenobiotics with different organisms. Chrysoperla externa (Hagen, 1861) is a species of great economic relevance because it is a predator of major agricultural pests during its larval stage. Neonicotinoids are the most important chemical class of insecticides introduced into markets. A previous imidacloprid toxicity assessment on C. externa showed that this neonicotinoid insecticide reduced the egg viability. The objective of this study was to analyze the genotoxicity of Confidor OD® (imidacloprid 20% a.i., LS, Bayer CropScience) on the biological control agent C. externa at DNA level using the comet assay as an ecotoxicological biomarker. A comet assay protocol has been developed for this species at first time. For the bioassays, the commercial product formulated Confidor OD® was used at two concentrations: 100 and 180 mg/l of the active ingredient. Selected eggs were dipped in a Confidor OD® solution for 15 s. Descriptors evaluated in the comet assay were damage index, % DNA damage, and tail length. The damage index did not show any significant differences between the different concentrations evaluated, but differences were observed for tail length, because at higher concentrations of Confidor OD®, there were greater DNA breaks. The DNA of the cells from treated eggs analyzed at 48 h and 96 h of development showed the same % DNA damage; that is, they had no recovery capacity. Application of Confidor OD® to C. externa eggs produced irreparable breaks at the DNA level. The technique adjusted for C. externa can be used in other beneficial insects to study pesticide genotoxicity using a comet assay.

The Peculiarities of Metopolophium dirhodum (Walk.) Population Formation Depending on Its Clonal and Morphotypic Organization during the Summer Period

The ecological plasticity of aphid populations is determined by their clonal and morphotypic diversity. Clones will be successful when the development of their component morphotypes is optimized. The purpose of this work was to reveal the peculiarities of clonal composition and the developmental characteristics of different summer morphotypes for the rose-grass aphid, Metopolophium dirhodum (Walk.), which is an important host-alternating cereal pest and a useful model species. During the experiments, aphids were kept under ambient conditions on wheat seedlings at natural temperatures and humidity levels. An analysis of the reproduction of summer morphotypes and the resulting composition of offspring found that variation among the clones and morphotypes, as well as generational effects and an influence of sexual reproduction (and interactions between all factors) influenced the population structure of M. dirhodum. The reproduction of emigrants was less among the clones than that of the apterous or alate exules. The number of offspring produced by apterous exules differed throughout the growing season (generational effects) and between years, with different clones exhibiting different responses. There were dispersing aphids only among the offspring of apterous exules. These results can contribute to future advances in the forecasting and monitoring of aphid populations.

Generalism in nature: a community ecology perspective

Life on Earth is complex and generally abounds in food webs with other living organisms in terms of an ecological community. Besides such complexity, and the fact that populations of most living organisms have never been studied in terms of their molecular ecology, it is best to tread carefully when describing a given species as a ‘generalist’, more especially in terms of dietary and habitat breadth. We very much doubt that population homogeneity ever exists—because populations are always undergoing molecular-genetic changes, sometimes rapid, in response to various ecological challenges (e.g. climate, intra- and interspecific competition). In any case, a population may already have begun to undergo cryptic speciation. Such entities can occupy different habitats or exhibit different dietary breadths as a result of various ecological interactions formed over different spatial scales. These scales include everything from local (including islands) to geographic. The fossil evidence reveals that specialisations have existed over vast swathes of time. Besides, as is well documented, evolution only occurs as a result of adaptations leading to specialisation, and ultimately, specialist entitles, i.e. species and lower levels of ecological-evolutionary divergence. Here, focusing on diet, we posit that the terms mono-, oligo-and polyphagous are more accurate in relation to the dietary breadth of animals, with omnivory adopted in the case of organisms with very different food items. Thus, we strongly urge that the dubious and unscientific term ‘generalism’ be dropped in favour of these more precise and scientifically accurate terms directly relating to levels of phagy.

Endosymbiotic Bacterial Diversity of Corn Leaf Aphid, Rhopalosiphum maidis Fitch (Hemiptera: Aphididae) Associated with Maize Management Systems

In this study, different maize fields cultivated under different management systems were sampled to test corn leaf aphid, Rhopalosiphum maidis, populations in terms of total and endosymbiotic bacterial diversity. Corn leaf aphid natural populations were collected from traditionally managed maize fields grown under high agricultural and natural landscape diversity as well as conventionally treated high-input agricultural fields grown in monoculture and with fertilizers use, hence with low natural landscape diversity. Total bacterial community assessment by DNA sequencing was performed using the Illumina MiSeq platform. In total, 365 bacterial genera were identified and 6 endosymbiont taxa. A high abundance of the primary endosymbiont Buchnera and secondary symbionts Serratia and Wolbachia were detected in all maize crops. Their frequency was found to be correlated with the maize management system used, probably with fertilizer input. Three other facultative endosymbionts (“Candidatus Hamiltonella”, an uncultured Rickettsiales genus, and Spiroplasma) were also recorded at different frequencies under the two management regimes. Principal components analyses revealed that the relative contribution of the obligate and dominant symbiont Buchnera to the aphid endosymbiotic bacterial community was 72%, whereas for the managed system this was only 16.3%. When facultative symbionts alone were considered, the effect of management system revealed a DNA diversity of 23.3%.

Differentiation in the eastern Asian Periphyllus koelreuteriae (Hemiptera: Aphididae) species complex driven by climate and host plant

Divergent adaptation to different ecological conditions is regarded as important for speciation. For phytophagous insects, there is limited empirical evidence on species differentiation driven by climate and host plant. The recent application of molecular data and integrative taxonomic practice may improve our understanding of population divergence and speciation. Periphyllus koelreuteriae aphids feed exclusively on Koelreuteria (Sapindaceae) in temperate and subtropical regions of eastern Asia, and show morphological and phenological variations in different regions. In this study, phylogenetic and haplotype network analyses based on four genes revealed that P. koelreuteriae populations comprised three distinct genetic clades corresponding to climate and host plants, with the populations from subtropical highland regions and on Koelreuteria bipinnata host plants representing the most basal clade. These genetic lineages also showed distinct characteristics in terms of morphology and life cycle. The results indicate that P. koelreuteriae is a species complex with previously unrevealed lineages, whose differentiation may have been driven by climatic difference and host plant.