Desempenho biológico e reprodutivo de Tetrastichus howardi (Hymenoptera: Eulophidae) criado em hospedeiro alternativo

Abstract

The mass rearing of natural enemies is a strategy that optimizes the use of biological control in agriculture. Tetrastichus howardi (Olliff, 1893) (Hymenoptera: Eulophidae) is a gregarious endoparasitoid that has stood out in the control of lepidopteran pests and can be reared on an alternative host, Tenebrio molitor L. (1758) (Coleoptera: Tenebrionidae). However, successive rearing on the same host may affect the reproductive characteristics of the insect and lead to population degeneration. In addition, reproductive strategies such as superparasitism, host exposure time, and energetic supplementation may ensure greater reproductive success. The objective of this research was to evaluate biological and reproductive parameters of T. howardi reared on T. molitor over successive generations. Five bioassays were conducted: (i) evaluation of the biological and reproductive characteristics of T. howardi on T. molitor across generations; (ii) different exposure times of the parasitoid to the host; (iii) reproductive capacity of T. howardi at low densities; (iv) evaluation of superparasitism strategies; and (v) supplementation of parasitoid females with a honey and water solution. The following parameters were evaluated: parasitism and emergence rates, total progeny number, number of females and males, sex ratio, life cycle, and longevity. For insect counting, a stereomicroscope was used, and sex determination was performed based on antennal morphology. All experiments were analyzed using the R software (R Core Team, 2024), version 4.4.1. Generalized Linear Models (GLM) were applied, with a quasi-Poisson distribution used for count data, a binomial distribution for parasitism and emergence rates, and beta regression for sex ratio, all considering a 5% significance level. The results demonstrated that T. howardi parasitized and emerged in all evaluated generations; however, a reduction in the number of females was observed from the ninth generation onward. Between the fifth and sixth generations, biological and reproductive characteristics showed stabilization. An exposure time of 72 hours of the parasitoid to the host resulted in higher parasitism and emergence rates, as well as a greater number of offspring. No significant differences were observed among the tested parasitoid-to-pupa densities; however, pupal abnormalities were recorded under low parasitoid density conditions. Superparasitism increased parasitism and emergence rates compared with self-superparasitism and reduced the life cycle and longevity. Energetic supplementation increased parasitism and emergence rates and enhanced female longevity. It is concluded that T. howardi can be reared on T. molitor pupae without changes in reproductive characteristics for up to eight generations, that the ideal exposure time for better utilization of host resources and higher offspring production is 72 hours, that low densities should be avoided, that superparasitism strategies are important for the reproduction of this species, and that energetic supplementation of females is essential.