Up to now, the search for an efficient artificial diet to rear the predator Eriopis connexa, native to the Colombian highlands of Cundinamarca and Boyacá has been without success. Therefore, it is necessary to determine which of the available preys supply the best food for its development, survival and fertility. With this purpose, under controlled conditions, three aphid species, accessible within the natural habitat of the predator, were evaluated. The cabbage aphid (Brevicoryne brassicae) does not provide an adequate nutrition for the predator, and apparently, the glucosinolate content of this aphid is transferred and affecting the predator. Based on the demographic parameters such as net reproductive rate, finite reproduction rate, generational time and intrinsic growth rate, for three consecutive generations, it was determined that none of the other two aphid species can be considered either as optimum prey. Macrosiphum euphorbiae, as prey stands out over the alder aphid, Pterocallis sp., supplied as food. The influence that these three prey species had on the growth potential of the larval stages of the predator, under particular ambient conditions, is reported.
As an alternative for pest management, plants were developed to express lethal proteins against target insects, which may develop resistance due to their constant exposure to these proteins. To monitor changes in susceptibility to Cry1Ac protein and determine the effect exerted by the diet composition on the susceptibility of Heliothis virescens, bioassays were carried out in the U.D.C.A´s laboratory of Agricultural Biotechnology with populations collected on Desmodium sp., at Espinal, Tolima. The diets employed were ICRISAT, Greene and Shorey & Hale, incorporating serial concentrations of Cry1Ac, ranging from 0.01 to 100 ppm. Bioassays consisted of six treatments and six replicates; each experimental unit was represented by a plastic cup with diet, in which one or five neonate larvae were placed. With the mortality assessed at day seven the lethal concentration (LC 50 ) was calculated. The diet composition influenced the susceptibility response. The LC 50 obtained for Heliothis in 2011 (0.956 ppm) indicates that this insect lost susceptibility to Cry1Ac expressed by Bollgard®; however, this plant variety still has control over the species. Results also showed that the mortality obtained with five larvae per experimental unit was influenced by cannibalism and not by the consumption of Cry1Ac, indicating that only one larva per container should be used to eliminate the effect of cannibalism on mortality.
since the introduction of genetically-modified (transgenic) crops around the world, an effort to monitor the susceptibility to Cry toxins on targeted insects has been implemented. However, these results are hardly comparable from region to region, not only due to the use in strains from different parts, but also due to methodological differences. Among these discrepancies is the use of meridic diets containing different ingredients. The goal of this study was to evaluate the effect of three meridic diets on the toxicity of crystal proteins from the bacterium B. thuringiensis on three cotton pests from El Espinal and Tolima. In all the tests, the lowest susceptibility was obtained with the ICRIsAT diet, which in turn, it is superior for rearing these pests under our environmental conditions. The results also suggest that there is an increase or dilution of resistance in Heliothis virescens populations due to the fact that these insects were collected from Desmodium sp. Spodoptera frugiperda's susceptibility was not affected, nor acquired resistance, while Helicoverpa zea had a slightly Revista U.D.C.A Actualidad & Divulgación Científica 14 (1): 39-48 2011 40increase in susceptibility. These results suggest that Btsusceptibility should continue using the same methodology to decrease variability as well as tests to be conducted on populations from different areas and host plants.
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