Do Locusts seek greener pastures?

English: The image of C. terminifera at "...

The Australian plague locust (APL), Chortoicetes terminifera (Walker), is a native but serious pest in Australia. In order to control locust plagues, managers need to know not only what areas are at risk as the adults disperse but where the highest densities of locusts are. Foraging theory indicates that areas with greener grass (more digestible, with higher protein, carbohydrate and water content) should be where adult locusts would preferentially feed. Anecdotal evidence from farmers and the Australian Plague Locust Commission also supports this, however there is no published field research on this area. This work aimed to investigate the relationship between APL abundance and greenness as derived from satellite remote sensing vegetation indices.

Locust eggbeds in Victoria spring 2010

Locust eggbeds in Victoria spring 2010

In 2010-2011, Victoria suffered from its largest locust plague since 1976. Over a four month period from December to April 2011, 150 sites in 19 localities across central Victoria were monitored weekly and adult APL densities recorded. MODIS satellite Vegetation indices (FPAR, GPP and NDVI) were utilised as an indication of grassland and cereal crop’s “greenness”.

Bayesian hierarchal analysis was utilised to model densities of APL at different sites, localities, type of grassland use, time periods and determine the level of correlation to the Vegetation indices.

No evidence was found for increased locust abundance at greener sites. The most important variables were site and location which indicate two scales of spatial autocorrelation or clustering. The least important variables in determining abundance were any of the Vegetation indices and grassland landuse.

Possible confounding factors are the spatial and temporal resolution of the satellite data and the unusually wet summer contributing to much higher levels of greenness found throughout the study area.

PhD Research

Predicting the dispersal of exotic insect pests is critically important in managing and restricting their impact. Insects disperse to resources or hosts that are often highly patchy and variable in distribution and quality. Host selection involves not only choosing the right species of plant, but also selecting an individual plant within that species that is, or will be, suitable for feeding, survival and development. Insects need to detect their host from a distance usually utilising visual or olfactory cues or both. Many phytophagous insects are attracted by greens and yellows, although other wavelengths can also be attractive.  By using NASA’s Terrestrial Observation Prediction System – Gross Primary Production model (TOPS GPP) to model daily photosynthetic rates of vegetation types for South Eastern Australia we hope to measure their suitability to particular pests.

In theory, by combining the daily environmental and climatic parameters (soil moisture, soil type, temperature, light exposure, aspect, etc) with the host’s biology, one can predict the photosynthetic rate (in terms of gC uptake/m2/day) or suitability to a pest of a vegetation type. By then combining this measure of suitability with a pest’s biology, climate-based simulations can then predict pest outbreaks and help identify feasible and effective containment or management options.

We will compare TOPS predictive pest dispersal model with models run on a static landuse layer to determine which has better predictive power. The Australian plague locust  will be piloted, with the project aiming to produce a more generic template model for other pests.

Aust. Plague Locust records (blue presence, red absence) 08-09 with MODIS SE Australia satellite image