Sublethal Doses of Insecticides Affect the Fecundity and Fertility of the <i>Chrysodeixis includens</i>?

The objective was to determine lethal concentrations and to evaluate the effects of sublethal doses of insecticides on Chrysodeixis includens under laboratory conditions. The standard population of C. includens was kept on artificial diet under controlled conditions (25°C ± 5°C, 60% ± 10 RU, 12:12 h). The active principles used were B. thuringiensis, Indoxacarb and Teflubenzuron. The CL25 and LC50 obtained from dose response curve (estimated from eight concentrations of each active principle) were diluted in water and applied to the back of third instar caterpillars and compared to the control (water). The insecticides used showed lethal and sublethal effects in C. includens. Bacillus thuringiensis was 6.21 and 2.79 times more toxic to soybean looper when compared to the products Indoxacarb and Teflubenzuron, respectively. Insecticides applied to the caterpillars reduced survival and affected the biomass gain with increased larvae and pupae longevity, with a significant reduction in fertility (40%) and fecundity (94.97%) in adults. In the present study it was observed that both survival and larval biomass gain have a direct effect on fecundity and fertility, respectively. Therefore the active ingredients Indoxacarb, Teflubenzuron and B. thuringiensis can be used in rotation as a tool in the C. includens.

Comparative Study of <i>Helicoverpa armigera</i>(Hubner) (Lepidoptera: Noctuidae) Preference for Bt and Non-Bt Soybean Cultivars

Studies on the behavior of Helicoverpa armigera in relation to soybean cultivars expressing Bt proteins are fundamentally important for IPM. We determine the no-choice and feeding choice of H. armigera, the no-choice and oviposition choice in different Bt and non-Bt soybeans cultivars. In the first step it was carried out the experiment to determine the no-choice and food choice in test for 12 Bt and non-Bt soybean cultivars. Simultaneously the consumption was determined. In a second step it was evaluated the no-choice and oviposition choice in different soybean cultivars. Helicoverpa armigera caterpillars showed neither attractiveness and preference for food nor attractiveness and oviposition preference for Bt and non-Bt soybean leaves when simultaneously contrasting the tested cultivars. This study showed that Bt toxin did not influence the oviposition preference, and H. armigera adults did not differentiate Bt and non-Bt soybean cultivars for oviposition indicating no behavioral preference. Third instar caterpillars showed no discrimination between Bt and non-Bt soybean leaves. Research in this area must focus on the possibility of widespread planting of genetically modified soybeans containing the Bt protein, which is associated with selection pressure and the behavior of pest species in relation to their hosts, as well as on the adequacy of management tactics that is able to prevent the loss of technology efficiency.

Resistance of Two Maize Landraces in Breeding Stage to the Attack of <i>Sitophilus zeamais</i>

This study aimed to assess the resistance of grain from two varieties of maize landraces in initial breeding in Bom Jesus-PI, with respect to S. zeamais attack. Seeds of two maize landraces were used: purple straw maize from two different origins (S&atildeo Paulo (SP) and Espírito Santo (ES)) and Peruvian purple maize. The experimental design was completely randomized with four replications. The data for each response variable were subjected to analysis of variance, applying the F-test (p ≤ 0.05), and when significant differences were found, there was a comparison of means by Tukey test (p ≤ 0.05). The statistical analyses were performed using the software SAS&reg. In a free-choice test and bioassay for evaluating the nutritional index (no choice test), maize varieties differed significantly by Tukey test and the cultivar SP was considered resistant, while the cultivars purple and ES were considered susceptible.

Evaluation of Insecticides Targeting Control of Helicoverpa armigera(Hubner)(Lepidoptera:Noctuidae)

Insecticides from different chemical groups were tested by laboratory bioassay to verify the percentage mortality of Helicoverpa armigera (Hubner 1808) (Lepidoptera: Noctuidae). The experiment was conducted in the Crop Science laboratory—Prof. CinobelinaElvas Campus—UFPI, Bom Jesus, PI, from January to June, 2013. The populations utilized came from the University’s own insect breeding laboratories. Third instar larvae of H. armigera were used to conduct the bioassay. The experimental design was fully randomized, with 13 treatments and four replications. Five larvae were used per replication, with 12 insecticides from 9 different chemical groups and a control. Each treatment consisted of three doses. The methods of application used were topical contact and ingestion in artificial diet. According to the results the percentage mortality of H. armigera larvae varied among the treatments. The results demonstrated that chlorpyrifos and spinosad were effective against third instar H. armigera larvae both on contact and by ingestion. Flubendiamide, acephate, methomyl, Bacillus thuringiensis, dimethoate, chlorantraniliprole and fipronil had good responses to control of H. armigera.