Influence of weather and nocturnal illumination on the activity and abundance of populations of Noctuids (Lepidoptera) in south coastal Queensland

Abstract

AbstractA light-trap separating hourly catches was operated on a pasture research station in south coastal Queensland for 18 months in 1972 and 1973. A total of 339 000 Noctuid moths was captured. Half of the catch comprised pest species. Weather and nocturnal illumination were recorded on the trapping site. Multiple regression analyses were performed on the raw data, and, for comparison, some pest species were reared under semi-field conditions for a year. Night temperature, night wind and nocturnal illumination, in that order, were the most important factors influencing catch. Temperature and wind were each responsible for about one-fifth of the variance in catch, nocturnal illumination for about one-tenth. Twenty per cent of the variance in catch cannot be ascribed to changes in local weather or illumination. Wind had a significantly stronger influence on males than on females all year round, temperature a significantly stronger one on females than on males in summer. This was probably due to differences in the vertical distribution of flight in the two sexes, females flying lower than males. Nocturnal illumination had a significantly stronger influence on females than on males; on females its influence was almost as strong as that of wind, increasing with rising temperature to be twice as strong in summer as in winter. Females were most abundant in the first part of the night, males in the second. Temperature, wind and moonlight maintain this nocturnal distribution which is probably endogenously controlled. Female flight is probably linked to oviposition, male flight to response to pheromone release from calling females. Heavy out-of-season rainfall had a negative effect on Noctuid populations in the area and strongly increased both larval and adult mortality. Temperatures and rainfall during the larval and adult periods equal to the corresponding long-term averages and totals create optimal conditions for the development of Noctuid populations. Strong indications of migration were found in autumn and spring of 1973. Many moths of different species probably entered the area during nights with wind convergence caused by the passage of cold fronts. Separate analyses on the most abundant pest species confirmed the results of the analyses on the total catch of Noctuids.