One possibility is that different strains of bacteria living in leaves can exert an influence on insect herbivory. Bacterial infections can lower levels of jasmonic acid, a hormone that acts to increase defenses against insects. Specific bacterial strains may affect the regulation of jasmonic acid in various ways. Some may lower it a little. Others might lower it a lot. Others can even increase it by producing a phytotoxin that mimics jasmonic acid. It will be interesting to see is if Scaptomyza flies can notice these differences. It is possible the flies can taste the levels of isothiocyanates released and decide which plants to lay their eggs on. If a plant is producing less toxins, then the larvae can feed more freely on the plant tissue. Growth and survival of Scaptomyza larvae may depend on adult females making the right choice.