Lightbrown apple moth - Dispersal

The dispersal ability of lightbrown apple moth has very important implications for management.With high levels of control achieved by insecticides or Bacillus thuringiensis, the resident population of lightbrown apple moth in most orchards is extremely low. As a result, the immigration of adult moths into orchards is often greater than the resident population, and the removal of outside sources (e.g. gorse, broom) can make a major contribution to control. Mark-recapture studies indicate that while 80% of males have been captured within 100 m of their point of release, some individuals have been recovered up to 600 m away. Similarly, 99% of marked females have been captured within 100m of their release point but maximum dispersal was only 275 m. The low proportion of marked to unmarked moths in these mark-recapture studies has shown the very high density of wild populations of lightbrown apple moths in New Zealand; the research has also shown that immigration of feral lightbrown apple moths into orchards can be very high. This can be both a problem for control of the lightbrown apple moth damage and a benefit for resistance management by diluting the effects of insecticidal selection. Immigrant moths from wild host plants normally contain a high proportion of insecticide-susceptible individuals.

Lightbrown apple moth is predominantly a nocturnal flier, with maximum activity 1-4 hours after sunset. Australian and New Zealand studies indicate a lower temperature threshold for flight of 8-11^oC and, in Australia, an upper limit of 20-28^oC depending on time of year. There is also a lower wind threshold of 0.5-0.8 m/s and an upper limit of about 2.8 m/s. The frequency of flight decreases sharply with increasing wind speed. Rainfall also reduces flight activity and no flights could be expected with a daily precipitation of 39 mm.
Another important aspect of movement is the dispersal ability of larvae, especially 1st stage caterpillars hatching from their egg batches. Major mortality occurs during this process but the caterpillars are able to spread out and reduce competition for food, as well as move to new host plants. Caterpillars may disperse into apple crops from surrounding shelter.