Abstract:
With a rapidly growing population to feed, finding ways to increase crop yields has become
more important than ever. Insect pests contribute hugely to yield losses every year and finding
methods to effectively control pest levels is therefore crucial to reduce these losses. Insecticide
use alone is no longer a viable solution, due to ever increasing levels of resistance developing
amongst crop pests, as well as the environmental concerns associated with their overuse.
Biological control – the use of natural predators to keep pest populations under control – has
proven to be a highly effective method of pest control and generally has less severe
environmental impacts than pesticides (although introducing non-native species can result in
undesirable changes to local biodiversity). Biological control agents are therefore a key
component of Integrated Pest Management (IPM) strategies, which aim to manage pest
populations in a sustainable and economical manner. IPM programs prioritise selective
insecticides which target the pest species and are harmless to the beneficial predators.
However, the numbers of reported insecticide resistance cases are far lower in beneficial
predators as opposed to crop pests. As a result, insecticide application often harms beneficial
predator populations and reduces their biological control capabilities, which may allow
resistant pest populations to surge after application.
Genomic information is readily available for a multitude of crop pest species, however, when
this project began, there was minimal genomic data available for beneficial predators. By
increasing the availability of genomic data for beneficial predators, we can perform
comparative analyses between crop pests and their predators of insecticide target-sites and
genes encoding metabolic enzymes potentially responsible for insecticide resistance. These
analyses may help uncover whether there is any genomic basis for the reduced number of
insecticide resistance cases in beneficial predators compared to crop pests.
The aim of this project was to firstly sequence and assemble the genomes of key beneficial
predators for which no genomic information is currently available. This included Orius
laevigatus (minute pirate bug), Sphaerophoria rueppellii (European hoverfly) and Microctonus
brassicae (parasitoid wasp). Next, these genomes were annotated and manual curation of
resistance-associated detoxification genes was performed. The resultant detoxification gene
sets were then used to perform comparative analyses between beneficial predators and crop
pests.
The results from the comparative analysis suggest a greater degree of detoxification family
gene expansion within crop pests compared to beneficial predators. This difference was
particularly apparent in the families associated with detoxification of plant xenobiotics and
suggests that the plant-based diet of crop pests provided increased selection pressure for
resistance mechanisms prior to the introduction of insecticides. Once insecticides were
introduced, crop pests may therefore have had an advantage over beneficial predators in terms
of developing insecticide resistance. In addition, variation in the levels of resistance between
different beneficial predators correlated to some extent with gene expansion, with several
factors having likely had some influence on this, including diet, migration and length of
commercial use.
The knowledge gained from this project could contribute to our understanding of insecticide
resistance from a genomic perspective and aid in the development of successful IPM strategies.