Detection of predators within Brassica crops: A search for predators of diamondback moth (Plutella xylostella) and other important pests

Abstract

Techniques based on the Polymerase Chain Reaction (PCR) have been shown to be powerful tools for ecological studies of predator-prey interactions. By using developed species-specific primers from the cytochrome oxidase subunit I (COI) gene for six insect pests of Brassica crops (Plutella xylostella, Pieris rapae, Hellula hydralis, Helicoverpa punctigera, Brevicoryne brassicae, and Myzus persicae) trophic relationships of selected predators and their prey in Brassica fields demonstrated the potential of DNA-based techniques to screen predator communities and to identify their prey. In this investigation, all examined predators including Nabis kinbergii (Heimptera: Nabidae), Oechalia schellenbergii (Hemiptera: Pentatomidae),Micromus tasmaniae (Neuroptera: Hemerobiidae), Hippodamia variegata, Coccinella transversalis(Coleoptera: Coccinellidae) and four wolf spider species including Trochosa expolita, Venatrix pseudospeciosa, Venator spenceri and Hogna kuyani (Araneae: Lycosidae) showed polyphagy to some extent. All tested positive for P. xylostella, hence can be considered as predators of this pest. Although, the records of DNA from the guts of predators probably represent instances of real predation, but interpretation of predation data because of some errors is very difficult. There are limitations for this type of interpretation which has been comprehensively discussed in this paper. Key words: Molecular markers, predator, gut contents, Brassica crop, biological control.