Effects of transgenic Bacillus thuringiensis corn on insect diversity, guild structure and population dynamics of selected insect pests and beneficial insects: data from the Philippines

anglais. Insect diversity and population abundance of the predatory beetles and lacewings and the parasitoid Trichgramma sp. on yieldgord (bt corn) were assessed for six sites in the Philippines: Alinguigan, Ilagan, Isabela, Carulay, Echague, Villaluna, Cauayan City, Isabela, Namagbagab, Sta. Maria, Pangasinan, panagan, Tigaon, Camarines Sur and Poblacion, Dangcagan, Bukidnon. The study had four treatments comparing the transgenic yieldgard C-818 (bt) corn hybrid with its isohybrid (ISO 818), treated and untreated with insecticide, and a reference hybrid, P30D44. Species richness was measured using the Margaleff index and the indices among treatments were not significantly different for all the samples from all the site except for Tigaon site at silking stage that registered lower insect diversity. The low diversity index for Tigaon at silking stage is due to the dominance of the corn silk beetle , Menolepta bifasciata (Burm.). Yieldgard showed lesss in festation of beetles on average compared with its isohybrid and the commercial hybrid. Different guilds such as phytophagores, neutrals, predators andf parasitoids were also not significantly different among treatments for each sampling dates and sites. Species diversity and guild structures from all sites are density independent. Likewise, the Asian corn borer (ACB) feeding damage for YG C818 was very low and moderately foliage damage for the isohybrids. It appears that very low ACB population on YG C818 does not have detrimental effect on community structure and diversity. Moreover, there was an abundance of the predatory beetles such as Micraspic bicolor (Fabr.), Cheilomenes sexmaculatus Fabr. Symmnus sp. and lacewings, Pseudomicromus igorotus. Banks and Chrysopa sp. in Luzon sites but not in Mindanao. Based on corn crop phenology, natural enemies were generally significantly higher at tasseling, silking and maturity. Although those results showed higher densities of som e important natural enemies of insect pests on bt-corn, long-term studies are necessary to further characterize subtle population differences in the field.

anglais. [Professorial Chair Lecture] 11 Mar 2005 College, Laguna (Philippines)