Effects of a mustard trypsin inhibitor expressed in different plants on three lepidopteran pests

The effects of mustard trypsin inhibitor MTI-2 expressed at different level s in transgenic tobacco, arabidopsis and oilseed rape lines have been evalu ated against three different lepidopteran insect pests. 1. Plutella xylostella (L,) larvae were the most sensitive to the ingestion of MTI-2. The inhibitor expressed at high levels in arabidopsis plants cau sed rapid and complete mortality. High mortality and significantly delayed larval development were also detectable in oilseed rape expressing MTI-2 at lower levels. 2. Mamesrra brassicae (L.) larvae were sensitive only at high MTI-2 express ion level, as obtained in transgenic tobacco and arabidopsis, whereas no ef fects were observed for larvae fed on plants showing relatively low express ion levels such as those of oilseed rape lines. 3. Feeding bioassays with Spodoptera littoralis (Boisduval) larvae were car ried out using the same oilseed rape lines, showing that at these low expre ssion levels no mortality was observed although a delay in larval developme nt did occur. The levels of insect gut proteolytic activities of the larvae still alive a t the end of a 7 day feeding bioassay were usually higher than in the contr ols, but no new proteinases were expressed in any case. The combined result s described in this paper demonstrate altogether the relevance of a case-by -case analysis [target insects and proteinase inhibitor (PI) level of expre ssion in planta] in a Pi-based strategy for plant protection. (C) 2001 Else vier Science Ltd. All rights reserved.