Methyl jasmonate affects population densities of phytophagous and entomophagous insects in wheat

Methyl jasmonate (MEJA), a well-known herbivore-induced plant volatile, promotes plant defences against various stress factors. The aim of this study was to investigate the effects of different doses of exogenously applied MEJA on the population densities of wheat insect pests and their natural enemies by employing three sampling methods (direct visual sampling, sweep net, sticky traps) in 2012 and 2013 under semi-arid conditions. MEJA treatments had repellent effects on aphids (Hemiptera: Aphididae), phytophagous thrips species (Thysanoptera: Phlaeothripidae and Thripidae) and hoverfly species (Diptera: Syrphidae), whereas it was attractive to wheat stem sawflies (Hymenoptera: Cephidae), lady beetle species (Coleoptera: Coccinellidae) and Collyria coxator (Hymenoptera: Ichneumonidae). MEJA treatments had no effect on aphid parasitoids abundances (Hymenoptera: Braconidae). The experimental outcomes varied, depending on plant phenology and sampling method. MEJA treatment also led to reductions in wheat yield and plant height. MEJA treatment could be beneficial as a natural pest control tool when certain species are targeted.