Understanding biological invasions: assessing the biosecurity threat of the pink bollworm to Northern Australia

Ignition Grant Round 7 (July 2017)

Biological invasions are rapid evolutionary events that dramatically affect global ecosystems and often result in high economic and environmental costs. From a genetics perspective, invading populations are often subjected to a founder effect during the original colonisation, which results in a readable signature in the invading populations' genetic structure.

Insects are often successful pests due to their ability to quickly invade and spread through new habitat. For example, the pink bollworm (Pectinophora gossypiella) is one of the most destructive global pests of cotton and its spread has largely resulted from human activities around cotton production.

From its original detection in India in 1843, the pink bollworm is now established throughout nearly all cotton-growing countries, with the exception of Russia, Central America, parts of South America, and Northern Australia. In America alone, it costs cotton producers more than US$32 million each year in control and yield losses. In its adult stage, the moth lays its eggs on cotton bolls and the resulting larvae eat cotton seeds, ultimately damaging the cotton fibre.

Because the larvae develop inside the cotton boll, the pink bollworm cannot be controlled with pesticides; instead, transgenic cotton-containing genes from the bacteria, Bacillus thuringiensis (Bt), which produce proteins toxic to most caterpillars following ingestion, has been used to control this pest. However, in some parts of the world (e.g., India), the pink bollworm has become resistant to Bt-cotton crops. 

A limited amount of genetic work (mitochondrial and microsatellite) has focused on Indian, Chinese, and American populations of the pink bollworm and results have indicated that genetic diversity within populations is very low, and indicative of invasions occurring from multiple source populations. Thus, the pink bollworm represents a serious biosecurity threat in Australia and the application of genetic techniques to investigate this species would be invaluable for management strategies moving forward.

Using samples collected from North-West Australia, our project will aim to identify the source population of these Australian individuals, and in particular, assess whether the Australian population has connectivity to the Indian (Bt-resistant) population. 

We have access to ~40 samples of pink bollworm collected from an established native (currently non-resistant) population in North-West Australia. We will process these samples from two angles: (1) genomic sequencing with Illumina technology; and (2) genomic sequencing with MinION technology.

For (1), we will produce short (~150 bp) reads for all samples and extract mitochondrial sequences to generate cytochrome c oxidase (COI) gene data. We will combine data from our samples into an existing COI dataset of 79 samples and 19 geographic locations in India (Sridhar et al., 2016), and perform population genetic analyses (network analyses, diversity statistics, gene flow) to examine the degree of genetic connectivity between Indian and Australian pink bollworm.

For (2), we will use the newly emerged MinION technology to produce long (10kb - ~500 kb) genomic reads for a single individual, in conjunction with the Illumina short reads from (1) to assemble a draft genome of the pink bollworm, which we will then mine for genes related to pest management.

This project will provide vital information about the extent of genetic connectivity between Indian and Australian populations of the pink bollworm, enabling assessment of the biodiversity threat posed to Australia at large. In addition, a genomic resource will be created for this important pest species and this will be used to inform future projects related to pest evolution.