Studies Of A Wild Crucifer Barbarea Vulgaris G-type As A Dead-end Trap Crop For The Diamondback Moth

(1) The term "dead-end trap cropping" has been proposed to identify a plant that is highly attractive for oviposition by an insect pest but on which offspring of the pest cannot survive. In laboratory and greenhouse experiments, we evaluated the potential of a wild crucifer, Barbarea vulgaris G-type, to allure and serve as a dead-end trap crop for the diamondback moth (DBM), Plutella xylostella. We also investigated the behavioural and chemical mechanisms responsible for the attractiveness of the plant to DBM.(2) Barbarea vulgaris plants showed very strong attractiveness to ovipositing females of DBM and allowed little or no survival of their offspring. When DBM adults were provided with a dual-choice of plants of B. vulgaris and Chinese cabbage in one arena, the moths laid over 72% of their eggs on B. vulgaris plants; when DBM adults were provided with a dual-choice of plants of B vulgaris and common cabbage in one arena, the moths laid virtually all their eggs on B. vulgaris plants. The rosette plants and flowering plants of B. vulgaris showed similar attractiveness to DBM moths. In a comparative experiment in which DBM females were provided with either B. vulgaris plants or common cabbage plants throughout their adult life, the females laid significantly more eggs on B. vulgaris than on common cabbage, indicating that B. vulgaris had a stimulating effect on the egg production of DBM. Nearly all DBM eggs laid on each of the three species of plants hatched successfully, but the survival of DBM larvae differed dramatically between the three plants. Nearly all larvae on rosette plants of B. vulgaris died as neonates or early instar larvae, over 90% of the larvae on flowering plants of 5. vulgaris died as neonates or early instar larvae, and less than 10% of the larvae survived to successfully pupate, while 87-100% of the larvae on Chinese cabbage and common cabbage plants survived to pupation. The few survivors on flowering plants of B. vulgaris were approximately 1 day slower to reach pupation compared to those feeding on Chinese cabbage, and their pupal weight was lighter, their adult body size was smaller and the fecundity of the ensuing adults was lower.(3) Experiences by DBM had little or limited effect on the attractiveness of B. vulgaris to this insect. When DBM moths were reared from Chinese cabbage or common cabbage plants, or exposed to an experience of the leaf odor of Chinese cabbage or common cabbage, their preference for oviposition on the experienced host plant was slightly increased. However, DBM females still laid most or nearly all of their eggs on B. vulgaris plants when provided with a dual choice, indicating that the increased oviposition preference through various experiences had no marked effect on the attractiveness of B. vulgaris plants.(4) In various plant arrangements with both B. vulgaris and common cabbage, B. vulgaris always showed much stronger attractiveness to ovipositing DBM females, meanwhile application of an repellent exhibited significant effects of repellency to this insect. When the two species ofplants were intercropped with each other, or B. vulgaris were planted around edges of common cabbage plants in greenhouses, the number of eggs deposited by DBM moths B. vulgaris plants was always significantly higher than that on common cabbage. Repellent applied on the common cabbage plants could effectively deter the female moths from laying eggs on them, but did not significantly enhance the attractiveness of B. vulgaris plants to DBM moths.(5) The color and shape of B. vulgaris plants were unimportant factors for its attractiveness to DBM. Behavioural tests with plant models showed that shape of B. vulgaris was slightly more attractive to DBM than that of common cabbage. However, when the female moths were provided with B. vulgaris and common cabbage plants wrapped in transparent polyethylene film respectively, they laid slightly less eggs on the former than on the latter, indicating that the entire physical features of B. vulgaris, includ...