Managing Plutella xylostella in Crucifers: Field Application of Diadegma semiclausum in Cameron Highlands

Abstract

Diadegma semiclausum is one of the promising biological control agents used to control the pest of cruciferous crops, Plutella xylostella. Its mechanism of action is by injecting its egg into the second and third instar larva of P. xylostella. The egg will develop inside the larva, causing the larva to weaken and reducing the population of P. xylostella in the field. This tiny parasitoid was introduced from Australia in the late 1970’s and has since been utilized as a biological control agent in cruciferous vegetable farms across the Cameron Highlands. As a key component of Integrated Pest Management (IPM), the use of biological control agents promotes the reduction of synthetic pesticide applications, aligning with sustainable agricultural practices. In 2019, MARDI reintroduced D. semiclausum to the Cameron Highlands, where the parasitoids were mass-reared at the insect rearing laboratory and subsequently released into selected vegetable farms to evaluate their effectiveness and field population stability. Six farmers representing different zones; Habu and Batu 33 (southern zone), Sg. Palas and Sg. Menson (central zone), and Ulu Telom and Kg. Raja (northern zone) was selected for scheduled D. semiclausum releases. Each farm was visited three times within three months. During each visit, both D. semiclausum and P. xylostella populations were monitored, and pupa samples were collected for laboratory assessment of parasitism rates. Additionally, 100 to 200 adults of D. semiclausum were released per visit at each farm. Throughout the program, farmers received training to identify biological control agents and other beneficial insects, along with guidance on safe pesticide usage and the adoption of environmentally friendly alternatives. Field observations demonstrated a consistent increase in D. semiclausum populations, accompanied by a corresponding decline in P. xylostella populations over the three visits, indicating the parasitoid’s potential as an effective biological control agent. Laboratory assessments recorded an average D. semiclausum parasitism rate of 83.33%, whereas field parasitism rates ranged from 43% to 73.33%. The comparatively lower field parasitism rates suggest that D. semiclausum populations were still establishing stability under field conditions. From the economic study, the biological control was costing RM57,491/ha with a net profit of RM32,989/ha and a Benefit-Cost Ratio (BCR) of 1.57. In contrast, conventional farming had lower costs (RM53,603/ha), higher profit (RM40,897/ha), and a better BCR of 1.76. While conventional methods currently yield better returns, long-term pesticide use may lead to insect resistance and rising costs. Thus, biological control offers a safer and more sustainable alternative for the long-term effects.