ABSTRACT: While the cultivation of conventional Bt corn has been widely adopted in Brazil, the production of Bt sweet corn is still incipient. The main lepidopteran pests found attacking conventional and sweet corn in Brazil are Spodoptera frugiperda (J.E. Smith) and Helicoverpa zea (Boddie). Additionally, a new harmful Lepidoptera species has recently appeared in Brazil, Helicoverpa armigera (Hübner). Since Bt sweet corn in Brazil is as yet cultivated on a limited scale there is no scientific information available about the performance of Bt sweet corn against lepidopterans out in the field. Thus, we conducted two field experiments to evaluate the efficacy of Bt sweet corn (event MON89034), alone and in conjunction with insecticides, against major lepidopteran pests found in midwestern Brazil (in the state of Goias). Both experiments followed a completely randomized block design (2 × 2 factorial) with two levels of sweet corn (Bt or conventional) crossed with two levels of insecticide (insecticide or no insecticide). The experimental treatments were replicated six times in each experiment. The results showed a slower advancing of defoliation caused by S. frugiperda in treatments with Bt corn. Likewise, less severe injury was observed on the corn ears (especially on the kernels) of Bt plants. The number of larvae (S. frugiperda and Helicoverpa spp.) sampled was also lower in the treatments with Bt corn. Overall, the application of insecticide did not increase the protection of Bt sweet corn and there was no significant difference in corn ear size and weight, nor in kernel yield, when comparing Bt and insecticide-sprayed plants.

Conduziu-se este trabalho visando a estudar as intensidades de perdas, densidades de insetos-praga e inimigos naturais em 49 cultivares de milho (Zea mays L.) em cultivo de safrinha em Coimbra, MG, Brasil. A produtividade média das cultivares foi de 3438,74 kg/ha, sendo as cultivares Traktor, CDX98D06, CO9621, OC705 e 97TR61 as mais produtivas. Ocorreram 29,62% de perdas na produtividade das cultivares, devido principalmente ao ataque de Sitophilus zeamais (Motsch., 1865) (Coleoptera: Curculionidae) aos grãos. O inseto-praga mais abundante foi Dalbulus maidis (DeLong & Wolcott, 1923) (Homoptera: Cicadellidae), seguido por adultos de Diabrotica speciosa (Germ., 1824) (Coleoptera: Chrysomelidae) e lagartas de Spodoptera frugiperda (Smith, 1797) (Lepidoptera: Noctuidae). O inimigo natural mais abundante foi o predador Doru luteipes (Scudder, 1876) (Dermaptera: Forficulidae). As densidades desses insetos foram semelhantes nas cultivares, com exceção de D. maidis. As cultivares menos atacadas por D. maidis foram: SHS5060, COE9994, HT8A97, NB6077, Z8550, CD3351, Maister, AG122, HS12L1133, HT47C, 97TR61, CDX98D04 e A975.

This work aimed at to study the intensities of losses and densities of insect pests and natural enemies to 49 cultivars on the late maize (Zea mays L.) cultivation in Coimbra, Minas Gerais State, Brazil. The medium productivity of the maize cultivars was of 3438.74 kg/ha. The most productive cultivars were Traktor, CDX98D06, CO9621, OC705 and 97TR61. It happened 29,62% of losses in the productivity of the cultivars and the critical component of losses was the grain. The key factor of losses was the attack of Sitophilus zeamais (Motsch., 1865) (Coleoptera: Curculionidae) to grain. The insect pests with highest densities on the plants were Dalbulus maidis (DeLong & Wolcott, 1923) (Homoptera: Cicadellidae), adults of Diabrotica speciosa (Germ., 1824) (Coleoptera: Chrysomelidae) and larves of Spodoptera frugiperda (Smith, 1797) (Lepidoptera: Noctuidae). The most abundant natural enemy was the predator Doru luteipes (Scudder, 1876) (Dermaptera: Forficulidae). The densities of those insects were similar to cultivars except for D. maidis. SHS5060, COE9994, HT8A97, NB6077, Z8550, CD3351, Maister, AG122, HS12L1133, HT47C, 97TR61, CDX98D04 and A975 were the cultivars less attacked by D. maidis.

Este trabalho objetivou estudar a seletividade dos inseticidas carbaril, deltametrina, paratiom metílico, permetrina e triclorfom em favor do predador Doru luteipes (Scudder) (Dermaptera: Forficulidae) e do parasitóide Cotesia sp. (Hymenoptera: Braconidae), em relação ao controle do curuquerê Ascia monuste orseis (Godart) (Lepidoptera: Pieridae). Foram determinadas as CL90 para A. monuste orseis e estas foram utilizadas como doses discriminatórias para se avaliar o grau de seletividade dos inseticidas. Deltametrina e permetrina foram altamente seletivos em favor de D. luteipes. Deltametrina foi medianamente seletiva em favor de Cotesia sp. e a permetrina não apresentou seletividade em favor deste parasitóide. Triclorfom foi altamente seletivo em favor de ninfas de quarto estádio e adultos de D. luteipes e mediamente seletivo em favor de Cotesia sp. e de ninfas de primeiro estádio do predador. Carbaril foi medianamente seletivo em favor de Cotesia sp. mas não apresentou seletividade em favor de D. luteipes. Paratiom metílico não foi seletivo em favor de Cotesia sp. e D. luteipes. Adultos de D. luteipes foram menos sensíveis a deltametrina, permetrina e triclorfom do que adultos de Cotesia sp., sendo que o inverso ocorreu com o carbaril. Esses inimigos naturais apresentaram alta sensibilidade ao paratiom metílico. Ninfas de quarto estádio e adultos de D. luteipes foram mais sensíveis ao paratiom metílico e triclorfom que ninfas de primeiro estádio. Ninfas e adultos de D. luteipes apresentaram semelhante sensibilidade ao carbaril, deltametrina e permetrina.

This work aimed to study the selectivity of the insecticides carbaryl, deltamethrin, methyl parathion, permethrin and trichlorfon in favor of the predator Doru luteipes (Scudder) (Dermaptera: Forficulidae) and of the parasitoid Cotesia sp. (Hymenoptera; Braconidae) in relation to the control of the kale leafworm Ascia monuste orseis (Godart) (Lepidoptera: Pieridae). LC90 were determined for A. monuste orseis, and these were used as discriminatory doses to evaluate the degree of selectivity of the insecticides. Deltamethrin and permethrin were highly selective in favor of D. luteipes. Deltamethrin was intermediate selectivity in favor of Cotesia sp., while permethrin was not selective in favor of this parasitoid. Trichlorfon was highly selective in favor of fourth instar nymphs and adults of D. luteipes, and it was intermediate selectivity in favor of Cotesia sp. and first instar nymphs of the predator. Carbaryl was intermediate selectivity in favor of Cotesia sp., but it did not show selectivity in favor of D. luteipes. Methyl parathion did not show selectivity in favor of D. luteipes and Cotesia sp. Adults of D. luteipes were less sensitive to deltamethrin, permethrin and trichlorfon than adults of Cotesia sp. and the inverse happened with carbaryl. Both natural enemies presented high sensibility to methyl parathion. Fourth instar nymphs of and adults of D. luteipes were more sensitive to methyl parathion and trichlorfon than first instar nymphs. Both nymphs and adults of D. luteipes presented similar sensibility to the carbaryl, deltamethrin and permethrin.