Currant-lettuce aphid (CLA), Nasonovia ribis-nigri, migrated from New Zealand to Tasmania on low-level jet streams in January 2004 and spread throughout Australia within two years. CLA is primarily a contamination pest which colonises lettuce hearts and rosettes, rendering them unsalable. Like many small winged insects, aphids migrate predominantly via wind and human activity. The timing and distance of their dispersal is influenced by many factors including plant quality, photoperiod, temperature and weather events.
Understanding how such factors interact is critical to determining the size of quarantine zones. To investigate factors critical to aphid dispersal, six, nine-metre fully automated suction traps for sampling winged CLA were built and placed at strategic locations in south eastern Australia. The traps sample 45 cubic metres of air per minute, which is funnelled into a fine mesh cone dropping insects into 70ml jars containing polyethylene glycol. Trap catches are segregated daily, which allows analysis of the effects of temperature, wind direction and run, and rainfall events on aphid numbers. Abiotic factors such as plant water availability, nutrition and ambient temperature can also play a major role in initiating insect dispersal through an increase in the development of alate adults.
Experiments were conducted to determine the effects of varying water availability on alate production. CLA were introduced to caged lettuce plants with low, medium and high levels of water available to them. Ten alates were released onto each plant, and plants were destructively sampled after 10 days at 20° C (one generation of CLA) to determine the numbers of alate and apterous fourth stage nymphs. No significant effect of water availability on the alate development of fourth stage CLA was observed. To discount the breeding predisposition of adult parthenogenetic alate CLA, further split-plot experiments will be undertaken.