Transcriptomic responses of the Cabbage Moth (Mamestra brassicae) to sub-lethal exposures of the pesticides Azoxystrobin and Cypermethrin.

The Cabbage Moth (Mamestra brassicae) is a polyphagous species found in almost all Palearctic regions. The M.brassicae for this study is kept at the UK Centre for Ecology & Hydrology (UKCEH) and has been cultured for over 40 years. Using information from the literature, we determined the M. brassicae 96-hour EC50 value for growth for Azoxystrobin as 53.3 mg/kg-1. We also conducted a series of exposure experiments to determine the Cypermethrin exposure level that generates a broadly equivalent sub-lethal effect, identifying the value of 0.4 mg/kg-1. Using the above concentrations, we exposed M. brassicae larvae (12 days after hatching from an egg) to either Azoxystrobin, Cypermethrin or Acetone. Acetone was used as a carrier (i.e., no pesticide exposure) control in these experiments. Each chemical was mixed into the media while the diet was liquid (at approximately 50C) to ensure an even pesticide distribution. The spiked diet was pipetted into each well of a 12-well plate to give a 1 ml volume. Each plate was left to set and cool at room temperature for 15 minutes before adding the larvae. Individual M. brassicae larva were weighed (mg) and added to the diet surface in each well (time 0 hours). Each larva was exposed at a constant 20C under constant darkness. Larvae were then harvested (6 biological repeats each containing 5 larvae) for each chemical and time point (4hr, 24hr and 48hr) - generating 54 libraries in total. To generate the transcriptomes, RNA was isolated from the whole-body of individuals and cDNA libraries generated from approximately 400 ng of RNA for each sample (KAPA mRNA HyperPrep kit, Roche Ltd, UK). Sequencing was performed on the Illumina NovaSeq platform (100 bp single-ended).