Rogério Fernando Pires da Silva

Effectiveness of Bacillus thuringiensis strains against Spodoptera frugiperda (lepidoptera: noctuidae)

The fall armyworm (Spodoptera frugiperda) is one of the most important pests of maize, causing up to 20% production losses when defoliation occurs near to flowering, or even complete destruction of plants. Among the alternatives to control this pest, the use of Bacillus thuringiensis (Bt) has gained attention due to its efficiency and low impact on natural enemies. Strains Bt dendrolimus HD 37, Bt aizawai HD 68, Bt kurstaki HD 73, Bt darmstadiensis HD 146, and Bt thuringiensis 4412 were tested against second instar larvae in in vivo assays. Suspensions of Bt aizawai HD 68 and Bt thuringiensis 4412, containing 3 x 10 8 cells/ml, induced mortality of 100% and 80.4%, respectively. To test virulence, cell concentrations of 8 x 10 5 to 3 x 10 8 cells/ml of strains Bt aizawai HD 68 and Bt thuringiensis 4412 were applied on the second instar larvae: LC 50 were 6.7 x 10 6 and 8.6 x 10 6 cells/ml, respectively.

Olfactory reception of conspecific aggregation pheromone and plant odors by nymphs of the predator, Podisus maculiventris

Olfactory reception of 23 odorants, including plant volatiles and male-produced aggregation pheromone, by third and fifth instars of the spined soldier bug (SSB) Podisus maculiventris was investigated by using electroantennograms (EAGs). Both nymphal stages were sensitive to male-produced aggregation pheromone components (E)-2-hexenal, benzyl alcohol, and α-terpineol. The plant volatile, (E)-2-hexen-1-ol (a chemical known to be released by plants in response to prey feeding over the short-term), elicited the largest EAGs of all volatiles tested. While third instars were sensitive to nonanal, only fifth instars responded to both nonanal and (±)-linalool, both compounds released systemically by plants in response to feeding by potential prey. Antennal extirpation experiments showed that sensilla responsive to hexan-1-ol, (E)-2-hexenal, and α-terpineol are situated mainly on the terminal antennal segment. The results support the hypothesis that P. maculiventris nymphs use both plant volatiles and pheromone components in locating potential prey and other behaviors.

Interação entre Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), Campoletis flavicincta (Ashmead) (Hymenoptera: Ichneumonidae) e Bacillus thuringiensis aizawai, em laboratório

Larvae of healthy Spodoptera frugiperda (J.E. Smith), parasitized by Campoletis flavicincta (Ashmead), infected by Bacillus thuringiensis aizawai, and both parasitized and infected, were obtained in the laboratory and fed with corn leaves. Parasitized and infected larvae showed less leaf consumption (in average 2.3 cm2) than the others, but did not differ from only parasitized larvae. Mean mortality of larvae both parasitized and infected was higher (96.5%) than the only parasitized (78.4%) and only infected ones (44.3%). The feeding period of the infected larvae (in average 29.6 days) did not differ from that of the healthy ones, in spite of having a longer larval period. Offsprings from pairs of parasitoids that had emerged from infected larvae did not have the biological characteristics modified. Therefore, the combined use of the parasitoid and the bacterium results in higher mortality and less foliar consumption and does not result in damage to the parasitoid.

Ocorrência de parasitóides de Spodoptera frugiperda (J. E. Smith) (Lep., Noctuidae) em lavouras de milho em Cachoeirinha, RS

Rio Grande do Sul State is one of the greatest maize producers of the country, however, little is known in terms of the main natural enemies associated to insect pests in this crop. The objective of this work was to survey parasitoids of fall-armyworm, Spodoptera frugiperda. Samplings in maize areas of the Instituto Riograndense do Arroz (IRGA) were conducted in Cachoeirinha, RS, during the growth seasons of 1999/2000 and 2000/2001. Insect larvae were collected weekly, during the crop cycle. Larvae were individualized and kept in laboratory until emergence of adults or

Receptors and Lethal Effect of Bacillus thuringiensis Insecticidal Crystal Proteins to the Anticarsia gemmatalis (Lepidoptera, Noctuidae).

Bioassays with insecticidal crystal proteins (ICPs) from Bacillus thuringiensis have demonstrated that Cry1Aa, Cry1Ac, and Cry1Ba are the most active toxins on larvae of the Anticarsia gemmatalis. The toxins Cry1Da and Cry1Ea are less toxic, and toxins Cry2Aa are not active. Binding of these ICPs to midgut sections of the A. gemmatalis larvae was studied using streptavidin-mediated detection. The observed staining patterns showed that Cry1Aa and Cry1Ac bound to the brush border throughout the whole length of the midgut. However, the binding sites of Cry1Ba were not evenly distributed in the midgut microvilli. The in vivo assays against larvae of 2nd instar A. gemmatalis confirmed the results from the in vitro binding studies. These binding data correspond well with the bioassay results, demonstrating a correlation between receptors binding and toxicity of the tested ICPs in this insect.