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.

Parasitism rate of Plutella xylostella (Lepidoptera: Plutellidae) larvae in greenhouse by Tetrastichus howardi (Hymenoptera: Eulophidae) females at different densities / Taxa de parasitismo de lagartas Plutella xylostella (Lepidoptera: Plutellidae) em estufa por fêmeas de Tetrastichus howardi (Hymenoptera: Eulophidae) em diferentes densidades

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.

Os parasitoides controlam os insetos pragas, mas o seu número por hospedeiro afeta a sua eficiência. O objetivo deste trabalho foi avaliar a melhor densidade de Tetrastichus howardi (Olliff, 1893) (Hymenoptera: Eulophidae) parasitando o quarto instar de larvas de Plutella xylostella (Linnaeus, 1758) (Lepidoptera: Plutellidae) em condições de estufa. Estas lagartas foram expostas ao parasitismo por fêmeas T. howardi com densidades 1:1, 3:1, 6:1, 9:1, 12:1, 15:1 e 18:1 de parasitoide/hospedeiro com 10 repetições durante 96 horas. Após este período, as lagartas foram mantidas em plantas hospedeiras (Brassica oleracea) até à formação de pupas. Tetrastichus howardi parasitaram e reproduziram em lagartas P. xylostella em todas as suas densidades testadas, mas com valores mais elevados de 84% e 10 ± 2.4 indivíduos, respectivamente, com 9:1 parasitoides/hospedeiro. Nove fêmeas de T. howardi por lagarta de P. xylostella são o número adequado para controlar está praga de inseto.