Twenty counties in China’s Jiangsu and Zhejiang Provinces are planting vetiver as an ecological engineering method (trap crop) for the control of two stem borer species – Chilo suppressalis (striped stem borer) and Sesamia inferens (pink stem borer). The results are very encouraging and it appears that rice farmers are excited with the significant increase in protection (70%) against stem borer damage and as a result a reduction in pesticide use and cost. Stem borer populations on rice decreased by up to 84% when vetiver rows were planted 50 meters apart and 3-5 meter apart in the row (in most cases hedgerows on the paddy field boundaries). A number of research papers have been published in China that describe why vetiver is such an effective trap crop. First, there are indications that some of the unique oils in vetiver when acting together act as a pheromone – volatiles – that attract the stem borer moths. Secondly vetiver contains toxic substances, which have lethal effect on the larvae that inhibit the esterase and cytochrome P450 enzyme activities, leading to the function loss of larvae in detoxification and metabolism. Additionally, compared to rice, reduced nutrients in vetiver cannot meet the demand of the larvae, and led to digestive function and physiological activity disorder and ultimately death. For newcomers to this topic you should be aware that the maize stem borer moth also is attracted by vetiver where it lays its eggs, thus reducing damage to the adjacent maize crop. Copies of the Chinese research papers relating to this topic (all with English abstracts) are:

Rice Pest Management by Ecological Engineering: A Pioneering Attempt in China
Optimal planting pattern of trap plant vetiver grass, Vetiveria zizanioides, for controlling rice striped stem borer, Chilo suppressalis
Effects of Vetiver Grass, Vetiveria zizanioides, on the Activities of detoxification of enzymes and acetylcholinesterase in the pink stem borer Sesamia inferens larvae
The Lethal Mechanism of Trap Plant, Vetiveria zizianioides, Against the Larvae of Chilo suppressalis (Striped Rice Stem Borer)
The effects of spraying on host plants on the oviposition preference of Asia Pink stem borer Sesamia inferens
Effects of Trap Plant, Vetiver Grass (Vetiveria zizanioides) on Nutritional and Digestive Enzyme Activities of Pink Stem Borer (Sesamia inferens) Larvae

Electrophysiological responses of the rice striped stem borer Chilo suppressalis to volatiles of the trap plant vetiver grass (Vetiveria
zizanioides L.)