Understanding the diamondback moth (Plutella xylostella) performance in plant alternative cropping systems
The diamondback moth (DBM) (Plutella xylostella) (L.) (Lepidoptera: Plutellidae) is one of the most widespread and harmful insect pests almost exclusively targeting plants belonging to the Brassicaceae family. Understanding of DBM’s behaviour and ecology is therefore crucial to develop novel, economically and environmentally friendly methods of control. One of the main objectives of this study was to determine whether the amount of time (# of generations) spent on a particular host plant by the DBM 4th instar larvae influences their preference, when exposed to and reared on alternative host plants. Experiments included rearing three lineages of DBM on three different plant species for three generations and exposing 4th instar larvae from each generation to the test plant species in a choice experiment. Results indicated that the amount of time spent on a particular host plant had no effect on food selection. The 4th instar larvae prefer turnip (Brassica rapa subsp. rapa) the most and kale (Brassica oleracea var. acephala) is the least preferred plant. Another major objective of this is to examine the response of DBM to intercropping as an integrated pest management strategy and whether intercropping changes the sinigrin concentration in kale leaves. Two DBM males and females were exposed to either kale or kale grown with onions (Allium cepa) in controlled conditions to assess their performance and kale damage. Results indicated that fewer 4th instars and pupae were present in the intercropping. There was no change in the sinigrin content between the two treatments. Results suggested that the physical presence of onions may be necessary for the decreased larval numbers observed in the intercropping system. It is hypothesized that onions may release repellent volatiles rendering the environment less suitable for DBM. Our study shows the complexity of DBM’s interaction with its host plants and adds to the mounting amount of evidence towards the effectiveness of an intercropping system in controlling pest infestation.