A short-term divergent selection for resistance to Teladorsagia circumcincta in Romanov sheep using natural or artificial challenge

This experiment was conducted to assess the efficiency of selection on the basis of response to artificial challenges in order to breed sheep resistant to natural infection. A short-term divergent selection process was designed to estimate the genetic parameters of these two traits. Two flocks, including 100 Romanov ram lambs each, were challenged in 1990 when they were 6 months old. One flock received three artificial infections with 20 000 third-stage Teladorsagia circumcincta larvae, at intervals of 7 weeks. Faecal egg counts (FEC) were performed on Days 22, 25 and 28 post infection (p.i.) and the animals were drenched on Day 28 p.i. The other flock was grazed for 5 months on a pasture contaminated with the same species. Faecal samples were taken from the lambs at similar ages. About 5 rams with the lowest FEC and 5 with the highest FEC were selected in each flock and mated with unselected ewes. Their offspring (200 animals) were challenged in 1992, half in the same way as their sires, and the other half by the other method. Because of a drought in the summer of 1990, it was necessary to repeat part of the experiment, and in 1992 the 5 and 8 rams with the lowest and highest FEC, respectively, were selected from the offspring challenged on the pasture in 1992 and were mated with unselected ewes. Their progeny (about 80 animals) were challenged in 1994, half by natural infection, half by artificial infection. The mean FEC of the flock increased from the first to the third artificial infection. The natural infection was highly variable in different years, reflecting the difficulty of assessing resistance using this mode of challenge. Genetic parameters were estimated using animal models and REML solutions. The repeatabilities of the FEC following artificial and natural infection were 0.49 and 0.70 respectively within a period of one week, and 0.22 and 0.41 respectively for periods separated by intervals of 7 weeks; the heritabilities of the single egg count were 0.22 and 0.38 respectively. The genetic correlation was 0.87: the FEC recorded under natural or artificial infection appear to depend on the same genetic potential

Changes in Parasitoid Communities Over Time and Space: A Historical Case Study of the Maize Pest Ostrinia nubilalis

Understanding the ways in which human environmental modifications affect biodiversity is a key challenge in conservation planning, pest control and evolutionary ecology. Parasitoid communities, particularly those associated with agricultural pests, may be susceptible to such modifications. We document here changes in the larval parasitoid communities of Ostrinia nubilalis — the main pest of maize — and its sibling species O. scapulalis, based on two historical datasets, one collected from 1921–1928 and the other from 2001–2005. Each of these datasets encompasses several years and large geographical areas and was based on several thousands/millions of host larvae. The 80-year interval between the two datasets was marked by a decrease in O. nubilalis parasitism to about two thirds its initial level, mostly due to a decrease in the rate of parasitism by hymenopterans. However, a well balanced loss and gain of species ensured that species richness remained stable. Conversely, O. scapulalis displayed stable rates of parasitism over this period, with a decline in the species richness of its parasitoid community. Rates of parasitism and species richness in regions colonized by O. nubilalis during the 1950s were one half to one third those in regions displaying long-term colonisation by this pest. During the recent human activity-driven expansion of its range, O. nubilalis has neither captured native parasitoids nor triggered parasite spill back or spill over

Withdrawal of maize protection by herbicides and insecticides increases mycotoxins contamination near maximum thresholds

Environmental and economic issues affect decision-making for whether or not to control small infestations of pests and pathogens in crops. Even where no crop yield loss is expected, other risks may be evident, such as the slow accumulation of pathogen inocula. The prevalence of toxins, arising from biotic interactions with fungal diseases, can alter crop quality rather than quantity. Thus, farmer decisions for whether to tolerate pest infestation must take into account several direct and immediate and/or delayed potential risks. Published scientific evidence on the co-occurrence of risk factors resulting from the presence of different pests and pathogens are largely absent, and this has stifled the adoption of integrated pest management. Here, we tested how the withdrawal of herbicide and insecticide protection in maize, alone and in combination, might induce higher prevalence of up to 23 mycotoxins in the crop at harvest. The experiment was conducted over 4 years in 29 fields in the south west of France. The test involved a comparison of paired samples collected from treated and untreated plots. All nine major mycotoxins that were observed in more than 4 % of the samples showed highly variable concentrations both between fields and years. The overall trend following the cessation of pesticide protection, however, is for higher levels of mycotoxins and up to a six-fold increased in nivalenol mean concentration (to 202.3 mu g kg(-1) of maize seeds) compared to its treated control. Overall mycotoxin concentrations approached 55-67 % of their maximum acceptable rate, a situation of reduced security margin that could lead to economic penalties and market restrictions. We found that the removal of herbicides had a greater impact than that of insecticides on the prevalence of mycotoxins, which differs from the expectation stated in the literature. This finding is further reinforced by the observation that certain species of weeds harbor several species of Fusarium. This means that weeds not only play a role as crop competitors but also as reservoirs of inoculum in the field. Our findings illustrate the importance of sanitary evaluation when the implementation of new cropping systems will alter the distribution and occurrence of pests and pathogens

Biocontrol of Ostrinia nubilalis and Sesamia nonagrioides by Bt maize in South Western France : search of biological indicators by a model-based approach for managing mycotoxin risks

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Ostrinia nubilalis parasitism and the field abundance of non-target insects in transgenic Bacillus thuringiensis corn ( Zea mays )

International audienceIn this study, we evaluated in field trials the effects on non-target species, of transgenic corn producing the Cry1Ab toxin of Bacillus thuringiensis (Bt). In 1998, we collected Ostrinia nubilalis (Hübner) larvae from transgenic Bt corn (Novartis Hybrid 176) and non-Bt corn at four geographical sites. We found a significant variation in parasitism by the tachinids Lydella thompsoni (Herting) and Pseudoperichaeta nigrolineata (Walker) among sites, and more parasitism in non-Bt than in Bt fields. The Bt effect did not vary significantly among fields. In 1999, we performed a field experiment at two sites, comparing the temporal abundance of non-target arthropods in Bt corn (Monsanto Hybrid MON810) and non-Bt corn. The non-target insects studied included the aphids Metopolophium dirhodum (Walker), Rhopalosiphum padi (L.) and Sitobion avenae (F.), the bug Orius insidiosus (Say), the syrphid Syrphus corollae (Meigen), the ladybird Coccinella septempunctata (L.), the lacewing Chrysoperla carnea (Stephens), thrips and hymenopteran parasitoids. For all species but one, the number of individuals varied greatly over the season but did not differ between the types of corn. The only exception was thrips which, at one site, was significantly more abundant in Bt corn than in non-Bt corn. However this difference did not remain significant when we took the multiple tests into account. Implications for pest resistance management, population dynamics and risk assessment are discussed

A short-term divergent selection for resistance to Teladorsagia circumcincta in Romanov sheep using natural or artificial challenge

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