TRAP CROPPING FOR BOTTOM-UP AND TOP-DOWN CONTROL OF DIAMONDBACK MOTHS (PLUTELLA XYLOSTELLA) IN HAWAI`I

Abstract

Plutella xylostella, the diamondback moth (DBM), is a detrimental pests of many plants in the family Brassicaceae. Populations of DBM have become resistant to many types of pesticides. My thesis investigated the use of trap crops for the bottom-up and top-down control of DBM. The first research chapter examined the effects of putative dead-end trap crops on Hawaiian DBM. The second research chapter examined the role of the naturalized weed, Virginia pepperweed (Lepidium virginicum) on the behaviors of DBM and their natural enemies.To determine a suitable dead-end trap crop for use against DBM on cabbage (Brassica oleracea cv. K-K Cross) in Hawai`i, a series of larval feeding, oviposition, and survival experiments were conducted. The plants tested were Barbarea verna and two varieties of Lepidium sativum. All three plants have shown dead-end properties against DBM in North America and Europe. However, I found that Hawaiian DBM populations from O`ahu and Kaua`i behaved differently from these previous studies. The DBM populations used in this study only prefered to oviposit on one variety of L. sativum relative to cabbage, and showed no preference for the other two plants. More importantly, both DBM populations survived from egg to adult on all of the “dead-end” trap crops, just as well as they did on cabbage. Next, I examined the effects of L. virginicum on DBM feeding and oviposition behavior as well as the plant’s effects on the behavior of DBM natural enemies. A series of lab and field experiments were conducted to observe predation and parasitization activity on the L. virginicum compared to cabbage. DBM favored L virginicum relative to cabbage for both feeding and ovipostion. The endoparasitoid, Cotesia plutellae, favored L. virginicum for initial prey searching behavior and more DBM were parasitized on L. virginicum than on cabbage. In conclusion, the putative dead-end trap crops were unsuccessful in preventing the two populations in Hawai`i from completing their lifecycle. However, the naturally occuring weed, L. virginicum, may act as a different type of dead-end trap crop by harboring high numbers of natural enemies of DBM, which could help to control the pest.