Desempenho biológico de Ooencyrtus submetallicus (HYM.: Encyrtidae) para manejo de Euschistus heros (HEM.: Pentatomidae) na cultura da soja

Abstract

The successful use of parasitoids in biological control programs depends on knowledge of several factors, including the natural and alternative host, the ideal density for large scale rearing, and field release strategies. This study aimed to evaluate the biological performance of Ooencyrtus submetallicus (Howard, 1897) (Hymenoptera: Encyrtidae) for the control of Euschistus heros (Fabricius, 1798) (Hemiptera: Pentatomidae) in soybean crops, integrating studies on the influence of rearing on an alternative host, optimization of mass production, and the effectiveness of different densities and releases of the parasitoid under semi-field and field conditions. The experiments were conducted at the Insect Biological Control Laboratory (LECOBIOL) at the Faculty of Biological and Environmental Sciences (FCBA) of the Federal University of Grande Dourados (UFGD), in Dourados, Mato Grosso do Sul, Brazil, and at the Rincão Borevi Farm, located in the city of Ponta Porã, Mato Grosso do Sul, Brazil. For the study of reproductive performance after prior rearing on an alternative host, O. submetallicus was multiplied for three generations on two hosts: the alternative host Bombyx mori (Linnaeus, 1758) (Lepidoptera: Bombycidae) and the natural host E. heros. Life cycle, percentage of parasitism, sex ratio, and longevity with food were similar between the hosts. However, the emergence rate and the number of individuals per egg were significantly higher in E. heros eggs. In the study of different densities, a completely randomized design with five parasitoid:host ratios was used. The duration of the egg-to-adult cycle remained stable (17.7 ± 0.15 to 18.0 ± 0.26 days) across treatments. The parasitism rate (%) ranged from 79.99 ± 3.33 to 88.68 ± 1.11, with higher values at higher densities (T4 and T5). Similar results were observed for emergence (%), which reached up to 94.23 ± 0.83. The number of individuals per egg (1.85 ± 0.03) and adult longevity (23.80 ± 0.47 days) did not differ between treatments. For the semi-field trials, increasing female density resulted in a significant increase in parasitism and emergence (R² > 0.90), as well as in the individual production index. In the field, releases of O. submetallicus at different densities showed a positive relationship between the released density, parasitism, and soybean productivity, which also increased with increasing release densities. Treatment 4 (20,000 eggs/ha = 800 eggs/400 m²) showed the best economic return (R$ 7,771.55/ha), while intermediate densities (treatments 1, 2, and 3) also showed a good cost-benefit ratio. Ooencyrtus submetallicus can be reared for up to three generations on the alternative host B. mori without compromising its biological performance when subsequently maintained on the natural host E. heros. The increase in the number of O. submetallicus and the availability of eggs favored parasitism and emergence rates, mainly at higher densities, without affecting biological characteristics. The combination of 30 O. submetallicus females to 300 E. heros eggs showed the best results for large-scale rearing of this parasitoid. Under semi-field and field conditions, a significant increase in parasitism, in the production of O. submetallicus offspring, and in soybean productivity was observed, resulting in a greater economic return. Thus, the strategic use of this parasitoid represents an efficient, sustainable, and economically viable alternative in the biological management of E. heros, which can contribute to reducing the use of synthetic insecticides and to the adoption of more balanced and environmentally safe agricultural practices.