Brownheaded leafrollers - Dispersal

The dispersal ability of brownheaded leafrollers has very important implications for management.With high levels of control achieved by insecticides or Bacillus thuringiensis, the resident population of brownheaded leafrollers 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. weeds like blackberry and honeysuckle) can contribute to control. There have been no mark-recapture studies of the dispersal of brownheaded leafrollers. Like lightbrown apple moth, brownheaded leafrollers also have numerous alternative host plants in the environment of orchards and immigration of wild moths into orchards can be very high. This can be both a problem for control of brownheaded leafroller 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.

Brownheaded leafrollers are predominantly nocturnal fliers, with maximum activity 2-6 hours after sunset. The lower temperature threshold for flight in Auckland has been estimated at 7-8^oC but further data is required in this and other regions.

Another important aspect of movement is the dispersal ability of larvae, especially 1st stage caterpillars hatching from their egg batches. This has been detected in water traps placed alongside apple trees. 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, such as Acmena sp. and Populus sp..