Evaluating Bottom‐Up Effects of Cruciferous Cultivars to Optimise Mass‐Rearing and Fitness of the Parasitoid Diadegma insulare

The diamondback moth, Plutella xylostella (L.) (Plutellidae: Lepidoptera), is one of the major pests of cruciferous vegetables. To control this notorious pest, the caterpillar parasitoid Diadegma insulare (Cresson) (Ichneumonidae: Hymenoptera) is the most used biocontrol agent. Efficient mass‐rearing of D. insulare is therefore essential to produce high‐quality parasitoids. In the present study, we examined the bottom‐up indirect effects of ten cruciferous cultivars, mediated through P. xylostella , on the parasitism efficiency, developmental performance and body fitness of D. insulare . The results revealed that ‘White Marble’ (cauliflower) and ‘Asha’ (cabbage), characterised by higher nitrogen and phosphorus levels and lower potassium levels than the other cultivars, had positive effects on the bioecological parameters and fitness of D. insulare . The durations of the egg‐larval, pupal and preadult stages of D. insulare were found to be optimal in association with these cultivars. Moreover, higher adult longevity, increased hind tibia length and greater adult body weight of the parasitoid were also observed in relation to these two cultivars. These findings suggest that cruciferous cultivars with higher nitrogen and phosphorus and lower potassium content exert favourable effects on D. insulare through P. xylostella . Such cultivars may be strategically used to enhance parasitoid activity in the field, to optimise mass‐rearing in the laboratory, and to support biological control programs in organic farming and as a part of integrated pest management programs.