Parasitism rate of Plutella xylostella (Lepidoptera: Plutellidae) larvae in greenhouse by Tetrastichus howardi (Hymenoptera: Eulophidae) females at different densities.

Parasitoids control insect pests, but their number per host affects their efficiency. The objective of this work was to evaluate the best density of Tetrastichus howardi (Olliff, 1893) (Hymenoptera: Eulophidae) individuals parasitizing fourth instar Plutella xylostella (Linnaeus, 1758) (Lepidoptera: Plutellidae) larvae in greenhouse conditions. These larvae were exposed to parasitism by T. howardi females with 1:1, 3:1, 6:1, 9:1, 12:1, 15:1 and 18:1 parasitoid/host ratios with 10 replications during 96 hours. After this period the larvae were kept on host plants (Brassica oleracea) until pupa formation. Tetrastichus howardi parasitized and reproduced in P. xylostella larvae at all its densities tested, but with higher values, 84% and 10 ± 2.4 individuals, respectively, with 9:1 parasitoids/host. Nine T. howardi females per P. xylostella larvae are the adequate number to manage this insect pest.

Effects of Methanolic Extracts of Annona Species on the Development and Reproduction of Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae).

Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) causes significant losses in corn crops and necessitates the use of alternative control strategies, such as the application of bioinsecticides. We report the effect of methanolic leaf extracts of Annona dioica, Annona cacans, and Annona coriacea on the development and reproduction of S. frugiperda. A quantitative analysis was carried out to determine the total concentration of phenolics, flavonoids, and condensed tannin (CT) in leaf extracts. Corn leaves were immersed in a 1% methanolic leaf extract solution and fed to second instars of S. frugiperda. Leaf disks dipped in the synthetic insecticide Connect® (Bayer CropScience Ltda) composed of a neonicotinoid (imidacloprid) and a pyrethroid (ß-cyfluthrin), which are harmful to S. frugiperda, was used as positive control. Distilled water was used as a negative control treatment. The leaf extract of A. coriacea decreased larval survivorship, arrested pupal development, and affected the weight gain of S. frugiperda. A. dioica also affected larval survivorship, but its effects were more pronounced for the adult stage, as fecundity, fertility, egg hatchability, and embryonic development were severely affected. Leaf extracts from A. cacans had no effect on S. frugiperda. The leaf extracts of A. dioica and A. coriacea showed a higher content of flavonoids and phenols, respectively. Our results indicated that both A. dioica and A. coriacea have the potential for development as botanical insecticides.