San Jose scale - male monitoring with pheromone traps

Female San Jose scales produce a pheromone which attracts the winged males for mating. This pheromone has been identified and synthesised for use in pheromone traps. Male activity and flight can be monitored by placing the baited traps in the orchard through the season. The time to place the traps in the field depends on the life cycle but is about early September in the central and northern regions and early to mid-October in the south. Traps are placed at a height of 1.8 - 2.4 m above the ground just within the southern canopy of the trees. The recommended trap density is 1 trap/2 hectares for survey or timing information and 1 trap/1 hectare if catches are to be used as an action threshold. The male scale insects are caught on the sticky trap which can be removed for counting and replaced, usually weekly. The pheromone cap is replaced every four to six weeks.

The timing of the first male caught in the traps can be used as a 'biofix' for the season and the day degrees (DD) above the threshold of 10.6^oC or 10.5^oC can be summed to predict the time of crawler release or other events in the life history. The trap manufacturers recommend spraying for scale control (targeting the crawlers) when 333-389 DD above 10.5^oC have accumulated after the first male catch in the traps. This procedure is not currently part of the apple IFP programme because it has not been shown to fit New Zealand conditions. A variety of other methods have been used to estimate the timing of male flight. The number of males caught in the traps is also being investigated to determine a spray or action threshold.

The pheromone traps of San Jose scale also attract and catch adult wasps which parasitise scale insects. This assists the parasitoids in locating scale populations, and the traps can therefore be used to monitor the numbers and activity of these beneficial insects in the orchard.