Jasmonate Application to Broccoli Plants Reduce Growth and Survival of the Insect Herbivore, Trichoplusia ni

Lepidoptera species are some of the most serious insect pests to brassica vegetables. Larvae of many Lepidopteran insect pests typically stay on the host plant on which they hatched on due to limited dispersal capacity. For this reason, there has been interest in how jasmonate (JA) treatments to host plants affect the development of lepidoptera larvae. Four weeks old broccoli ‘Green Magic' and ‘VI-158’ seedlings were placed in cages (72 x 50 x 50 cm) in a greenhouse to evaluate the effect of JA plant spray treatments on the growth and development of the cabbage looper (Trichoplusia ni). Eight neonate cabbage looper larvae were infested on each of three different plants of each cultivar sprayed three days previously with different JA treatments (0, 100, 200, 400 µM with 0.1% Triton X-100). After five days of feeding, survival and weight of cabbage looper larvae decreased with increasing JA plant treatment applications. Significant correlations were observed between JA concentrations and the number of days to pupation in both ‘Green Magic’ (r²=0.96) and ‘VI-158’ (r²=0.99). JA glucosinolates accumulation in both broccoli cultivars was measured by high performance liquid chromatography. Gluconasturtiin  (r²=0.85) and neoglucobrassicin (r²=0.99) were increased by JA in a dose dependent manner in ‘Green Magic’ leaves whereas glucobrassicin (r²=0.94) was increased by JA in ‘VI-158’. These glucosinolate concentrations had significant negative correlations with weight after 5 days, survival rate at 5^th days, pupa weight, and were positively correlated with days to pupation. Field application of JA to broccoli plants could induce enhanced resistance to Tricoplusia ni and possibly other insect pests.