Deterrent effect of carboxylic acids on cabbage root fly oviposition

In laboratory experiments, 11 selected carboxylic acids were tested to determine which part of the sinapic acid molecule is responsible for deterring cabbage root fly from laying its eggs on otherwise-acceptable cauliflower host-plants. The deterrent effect was only obtained with compounds containing at least one carboxylic group in the molecule. Hence, the aliphatic acids were as deterrent as the aromatic acids to the fly and all the carboxylic acids were as deterrent as sinapic acid, reducing oviposition by > 50%. The inclusion of two carboxylic groups in the molecule, (e.g. phthalic acid and oxalic acid) did not increase the deterrent effect observed with sinapic acid. Some of the long chain fatty acids, with low volatility, low water solubility and thus greater persistence, offer practical opportunities for deterring Delia radicurn from laying its eggs on plants in the field.