Effect of vermiwash-treated plants on the population growth parameters of Diadegma semiclausum (Hellen) (Hymenoptera: Ichneumonidae) on its host Plutella xylostella (Linnaeus) (Lepidoptera: Plutellidae)

The parasitoid wasp Diadegma semiclausum Hellen (Hymenoptera: Ichneumonidae) is an effective endoparasitoid for controlling the larvae of Plutella xylostella (L.) (Lepidoptera: Plutellidae). Fertilizer application can induce resistance mechanisms in plants against herbivores. In bottom-up effects, resistance-related signaling pathways triggered by fertilizers in plants may affect the fitness of natural enemies. This study aimed to investigate the effect of induced resistance by vermiwash on some fitness-related parameters of D. semiclausum, including immature survival, development time, reproduction, and life table parameters. The experiment was conducted in a standard climate chamber set at 25 ± 1 °C, a photoperiod of 16 h light: 8 h dark, and 65 ± 5% RH. The results showed that D. semiclausum developing within P. xylostella larvae reared on vermiwash-treated canola plants had a longer duration and lower survivorship of immature stages than those developing within P. xylostella larvae reared on untreated canola plants (control). Furthermore, the parasitoid females that emerged from the vermiwash treatment deposited fewer eggs compared to those emerging from the control treatment. The R₀ and r values of D. semiclausum were lower on the vermiwash treatment (9.96 offspring/female and 0.150 day⁻¹, respectively) compared to the control population (15.94 offspring/female and 0.198 day⁻¹, respectively). These results suggest that if vermiwash is sprayed on canola and P. xylostella larvae feed on the plant, it has the potential to adversely affect the population growth of D. semiclausum. Therefore, more care should be taken regarding the application of this fertilizer in D. semiclausum-based integrated pest management (IPM) programs.