LAUSR

The diamondback moth, Plutella xylostella (L.), has become the most destructive insect pest of Brassica crop plants, such as B. napus throughout the world including Iran. In this study, nutritional indices, digestive enzyme activity and cold hardiness of P. xylostella on seven canola cultivars including Delgan, H19, Modena, Okapi, Opera, RGS003, and SLM046 were studied under laboratory conditions (25 ± 1 °C, 65 ± 5% RH, 16:8 L:D). Fourth instar larvae fed on cultivar SLM046 had the highest efficiency of conversion of ingested and digested food (4.35 ± 0.24% and 4.99 ± 0.31%, respectively). Relative consumption rate (RCR) of P. xylostella 4th instar was higher when fed on Opera cultivar (5.62 ± 0.15 mg/mg/day) while it was lower on Okapi (3.33 ± 0.15 mg/mg/day). The larvae fed on cultivars SLM046 and Okapi had the highest (0.194 ± 0.007 mg/mg/day) and the lowest (0.088 ± 0.003 mg/mg/day) relative growth rate (RGR), respectively. We found a significantly higher amylolytic and proteolytic activity in the midgut of the larvae fed cultivar SLM046. Our findings showed that the activity of enzyme inhibitors and polyphenol oxidase, as antidigestive compounds, are major reasons for the low nutritional efficiency of P. xylostella larvae on some cultivars. The results of the present study indicate that cultivar Okapi is an unsuitable host for the feeding of P. xylostella. These results develop our knowledge of the negative effects of plant defenses on P. xylostella.