Repellent Effects of Volatile Extracts from Herb Plants against Larvae of Pieris rapae crucivora Boisduval

Abstract

Environmental pollution and intensive use of toxic chemicals, as well as resistance to pesticides, has forced scientists to find new ways of controlling pests. Numerous substances that repel insects and inhibit eating and egg-laying have been discovered in a variety of plants. The cabbage white butterfly, Pieris rapae crucivora Boisduval, is a serious pest to Brassicaca species such as cabbage, cauliflower and broccoli, and its larvae damage the host plant leaves when feeding. In this study, to develop a botanical insecticide against P. rapae larvae, we assessed the effect of 7 kinds of herb (rosemary, spearmint, eucalyptus, sage, chili pepper, chives and tansy) extracts as feeding repellents against P. rapae larvae. Feeding repellent tests were conducted by placing two cabbage leaf disks on filter paper treated with herb extract or diethyl ether in a box; then a larva was placed between the disks and its preference was observed. The repellent rate of rosemary, spearmint, eucalyptus, sage, chili pepper, chives and tansy was 75%, 72%, 64%, 59%, 40%, 40% and 36%, respectively. These results clarified that of the tested herbs, rosemary and spearmint volatile extracts have a notable feeding repellent effect against P. rapae larvae.