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Abstract
Field and Laboratory experiments were carried out to evaluate the effect of certain insecticides on the leafminer L. trifolii attacking the garden bean (Phaseolus vulgaris), the related ectoparasitoid D. isaea and the yield components. The evaluated insecticides were spinosad, Capl-2®, abamectin, lambda-cyhalothrin and thiamethoxam.
Part 1 - Field experiments
The field experiments were carried out during the summer and Neely seasons of 2005 and 2006 at the Agricultural Research Station Farm at El-Sabahia, Alexandria using the garden bean variety Bronco. The survey of the main insect pests attacking green bean was carried out during the growing summer season under field conditions, to show the type of injury and the extent of damage for two successive seasons of 2005 and 2006. During the summer season no insecticides were used due to the low infestation of the leafminer. Treatments were arranged in a complete randomized block design with three replicates for each treatment. Two insecticide applications were done only during the Neely season at 15 days interval. The numbers of the inspected leafminer and its parasitoid were counted to calculate the reduction of the leafminer percentage 2, 5, 7, 10 and 15 daysd post- insecticides application. The obtained results can be summarized as follows:
I. Survey of pests attacking garden (green) bean
A. Summer season of 2005
1. The number of the leafminer individuals (as larvae and / or pupae) was very low during the summer season and the number of those individuals did not exceed 2.33 individuals / 30 leaves by the end of May 2005. The number of the related parasitoid was also very low because the number of the host was very low and therefore, the number of the host individuals reflected on the number of that ecto-parasitoid (Diglyphus isaea). The number of the parasitoid was more or less relevant to that number of the host (leafminer). During the summer season (April- June), the prevailing conditions of temperature and relative humidity are not suitable for both the host and the parasitoid.
2. The number of the white fly Bemisia tabaci individuals started to grow up as the temperature and relative humidity increases. The highest number was found during mid-May (73.33 individuals / 30 leaves). On the other hand, the aphid number was very high during the first week of May (68.66 insects /30 leaves) and then the number started to be decreased as the temperature increased reached the lowest number of 0.66 insect /30 leaves in June the 10th. Same trend as that of the white fly was found with the jassid since its number was 12.66 insects /30 leaves during the last week of April and dropped to 2.66 insects /30 leaves in June the 10 th. Both aphid and jassid number decreased as the temperature increased.
3. There was a negative correlation between the prevailing relative humidity (R.H.) during the cultivation summer season of 2005 and the number of individuals of the white fly, Jassid, leaf miner and the inspected parasitoid. Meanwhile, there was a lower positive correlation ship between R.H. and the aphid, thrips and spider mite.