The effect of host plant on the development and larval midgut protease activity of Plutella xylostella (Lepidoptera: Plutellidae)

Plutella xylostella L. (diamondback moth) is a pest of cruciferous plants and has devastating effects on the yield and quality of cruciferous vegetables. Insect midgut protease plays an important role in the digestion of host plant nutrients and the detoxification of defensive compounds. The effects of host plants on the larval midgut protease activity and the performance of P. xylostella larvae were examined on six different host plants, including qingan 70, lvqiu 66, qingan 80, Brassica chinensis, broccoli and oilseed rape The results showed that P. xylostella larvae ingested all hosts, and the protease activities were significantly different at different instars. In the 3rd instar and early 4th instar, which were the important periods for digestion, 4 proteases activities of P. xylostella were greater than activity in other instars. Meanwhile, the activities of the high-alkaline trypsin and low-alkaline trypsin (important proteases in the insect midgut) were greatest when P. xylostella larvae ingested qingan 80. The relative host suitability, ranked from highest to lowest was: broccoli > oilseed rape = Brassica chinensis > qingan 70 > qingan 80 > lvqiu66. The intrinsic rate of increase indicated that P. xylostella had the best adaptability and food receptivity to the oilseed rape, whereas when P. xylostella larvae ingested Brassica chinensis, the activities of the trypsin were highest. This suggests Brassica chinensis in an appropriate host for P. xylostella that highly elevates the activities of trypsin that subsequently helps the insect to digest nutrients obtained from host plants. In practical application, we can reduce the harm to target plants by adjusting the plantation structure by optimally planting different hosts limit growth and reproduction to minimize pest outbreaks.