Effect of strip-intercropping of spring canola with clover in improvement of natural biological control of Plutella xylostella (L.)

The diamondback moth, Plutella xylostella (L.), is an important pest of canola in Iran. In this study, the effect of four treatments including strip-intercropping of two, four and six rows of canola with two rows of clover (2Ca: 2Cl, 4Ca: 2Cl, and 6Ca: 2Cl) and canola monoculture were studied on the population density of P. xylostella, species diversity of its predators, parasitism on eggs, larvae and pupae, and associated yield of canola under the field conditions in Ardabil region during 2015 and 2016. The density of eggs, larvae and pupae were significantly higher in monoculture than in intercrops. Moreover, the density of larvae and pupae was lower in 2Ca: 2Cl than in 6Ca: 2Cl. Shannon diversity index (H') for predator's species composition of moth was higher in intercrops than in monoculture. The values of Morisita–Horn index (CMH) for predators species composition of moth between canola monoculture and each of the three intercrops (CMH ≤ 0.897) were lower in comparision with the values of this index among the three intercrops (CMH ≥ 0.957). The percent parasitism for eggs, larvae and pupae was significantly higher in intercrops than in monoculture. Moreover, the percent parasitism for eggs and larvae was higher in 2Ca: 2Cl than in 6Ca: 2Cl. The dry seed weight loss was also lower in 2Ca: 2Cl and 4Ca: 2Cl in comparison with other two treatments. Thsese results indicated that intercropping 2Ca: 2Cl and 4Ca: 2C could be useful in integrated management of P. xylostella in canola fields.