Using ultra-violet light traps to monitor autumn gum moth, Mnesampela privata (Lepidoptera: Geometridae), in south-eastern Australia

Abstract

Summary Autumn gum moth (Mnesampela privata (Guenée)) is one of the most significant insect defoliators of plantation eucalypts in temperate Australia. Two 8 W ultra-violet light traps, able to sequentially sub-sample through time, were installed in a Eucalyptus plantation on the outskirts of Canberra, south-eastern Australia. Populations of M. privata were monitored from late November (end of spring) to the start of May (late autumn) in 1999/2000 and 2000/2001. Moth catches peaked during March of both trapping periods. The total number of moths trapped in each period was low (165 and 54, respectively). Female moths were rarely trapped (e.g. only 20 and 6 individuals in 1999/2000 and 2000/2001, respectively), but all had eggs. Most moths were caught between 0100 to 0430 h. Few moths were caught during the period up to 2130 h. At the time when most moths were trapped the minimum temperature was 10–18°C. More than 60% of moths were caught when the average wind speed was less than 1.0 ms−1. There was a tendency for moths to be caught on dates a few days after the new or crescent moon, but before the first quarter. Trap catches a couple of days either side of the last quarter were also likely to be higher. The lowest temperature at which a male moth was trapped was 4.5 °C; males were often caught when there was no wind. No females were trapped at temperatures lower than 15.2°C, and the lowest average wind speed at which female moths were caught was 0.8 m s−1. To enhance the attractiveness to industry of light trapping for population surveillance of M. privata in plantations, concentrating trap deployment to nights in March and timing trapping to coincide with post-crescent but pre-first or pre-last quarter moon phases is recommended.