Crucifer host plant suitability for bertha armyworm (Mamestra configurata) and diamondback moth (Plutella xylostella)

Crucifer host-plant suitability for bertha armyworm, Mamestra configurata, and diamondback moth, Plutella xylostella, was examined using cultivars and breeding lines of Brassica napus L., B. juncea L., B. rapa L., B. carinata L. and Sinapis alba L. Larval growth, development and survival, as well as feeding and oviposition preferences, were examined on physically and chemically distinct cruciferous plants using choice and no-choice experiments. In larval feeding experiments the high glucosinolate B. juncea and S. alba lines were the poorest host plants in terms of bertha armyworm weight gain, development and feeding preference. The results indicate that specific foliar glucosinolates such as sinigrin and sinalbin may provide crucifer crops with some protection from bertha armyworm larvae.;Bertha armyworm oviposition preferences were also examined. Oviposition was greater on B. napus than on B. juncea in all experiments; however, S. alba received the greatest number of eggs despite being relatively resistant to larval feeding. Bertha armyworm laid most eggs in the upper portion of the crop canopy on the underside of leaves, and flowering plants were preferred for oviposition over plants in the pre-flower or pod stages. Gravid females also preferred plant material with conspecific eggs, and females showed a much stronger preference for plants with a different female's eggs than for plants with their own eggs. Leaves which had been treated with a methanol egg wash were also preferred by gravid females, indicating that the source of attraction may be chemically based.;There were no consistent differences in diamondback moth larval growth, development, survival or fourth-instar feeding preference among the crucifer lines tested. However, there were differences in oviposition and first-instar feeding preferences on glossy and waxy lines of B. rapa. Although females laid more eggs on glossy plants, there was a strong preference among first-instar larvae for waxy plants in a choice situation. The results indicate that B. rapa expressing the glossy leaf wax characteristic shows some resistance to diamondback moth, similar to that observed previously with glossy B. oleracea. The resistance appears to have a behavioural basis and is expressed against early instar larvae.