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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.
Selectivity is an important aspect of modern insecticides to be able to target pests whilst maintaining beneficial entomofauna in the crop. The present objective was to assess the selectivity of different insecticides for the pupal parasitoid of soybean caterpillars, i.e., Trichospilus diatraeae Cherian & Margabandhu, 1942 (Hymenoptera: Eulophidae). Acephate, azadirachtin, Bacillus thuringiensis (Bt), deltamethrin, lufenuron, teflubenzuron and thiamethoxam + lambda-cyhalothrin at the highest recommended concentrations for the soybean looper Chrysodeixis includens (Walker, [1858]) (Lepidoptera: Noctuidae), as well as water in the control, were used against the pupal parasitoid T. diatraeae. The insecticides and the control were sprayed on the soybean leaves, which were left to dry naturally and placed in cages with T. diatraeae females in each one. Survival data were submitted to analysis of variance (ANOVA) and the means were compared using Tukey’s HSD test (α = 0.05). Survival curves were plotted according to the Kaplan–Meier method, and the pairs of curves were compared using the log-rank test at 5% probability. The insecticides azadirachtin, Bt, lufenuron and teflubenzuron did not affect T. diatraeae survival, while deltamethrin and thiamethoxam + lambda-cyhalothrin presented low toxicity and acephate was highly toxic, causing 100% mortality in the parasitoid. Azadirachtin, Bt, lufenuron and teflubenzuron are selective for T. diatraeae and could be used in IPM programs.
Tetrastichus howardi (Olliff, 1893) (Hymenoptera: Eulophidae) is an endoparasitoid mainly of Lepidoptera. Its potential as a biological control agent has been investigated for several agricultural and forestry species in different countries. The objective of our study was to evaluate the biological characteristics of T. howardi in larvae, prepupae and pupae of Spodoptera frugiperda (Smith, 1797) (Lepidoptera: Noctuidae), under laboratory conditions. The first bioassay was performed with S. frugiperda larvae in the fifth and sixth instar and prepupal phases, which were exposed to the parasitism of 7 female T. howardi for 24 h. The second bioassay was conducted with S. frugiperda pupae, with parasitism allowed for 24 h, at six parasitoid of T. howardi densities, for one host pupa of S. frugiperda (1, 7, 14, 21, 28 or 35 parasitoids: 1 host). The parasitism of T. howardi in S. frugiperda larvae was confirmed by larval mortality and the emergence of parasitoid descendants. Female T. howardi parasitized and emerged from S. frugiperda larvae of fifth and sixth instars, prepupae, and pupae under laboratory conditions, which is the first record of such in the literature.
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