No abstract

Regression analyses of a long series of light-trap catches at Narrabri, Australia, were used to describe the seasonal dynamics of Helicoverpa armigera (Hübner). The size of the second generation was significantly related to the size of the first generation, to winter rainfall, which had a positive effect, and to spring rainfall which had a negative effect. These variables accounted for up to 96% of the variation in size of the second generation from year to year. Rainfall and crop hosts were also important for the size of the third generation. The area and tonnage of many potential host crops were significantly correlated with winter rain. When winter rain was omitted from the analysis, the sizes of both the second and third generations could be expressed as a function of the size of the previous generation and of the areas planted to lucerne, sorghum and maize. Lucerne and maize always had positive coefficients and sorghum a negative one. We extended our analysis to catches of H. punctigera (Wallengren), which declines in abundance after the second generation. Winter rain had a positive effect on the sizes of the second and third generations, and rain in spring or early summer had a negative effect. Only the area grown to lucerne had a positive effect on abundance. Forecasts of pest levels from a few months to a few weeks in advance are discussed, along with the improved understanding of the seasonal dynamics of both species and the significance of crops in the management of insecticide resistance for H. armigera.

In South Australia, M. rosae is anholocyclic on Rosa, reproducing parthenogentically and viviparously all year round. It feeds mainly on the young leaves and developing flower-buds of hybrid tea roses. The fate of a colony of aphids on a single bud is a function of temperature, rainfall, predation, the time for which the bud remains favourable for the aphids, and the influence of crowding on alatiform production and on dispersal of apterae by walking or dropping off. The numbers of aphids on cultivated hybrid tea roses in a rose garden had three peaks in spring-summer which coincided with three flushes of growth of the rose. The first peak, in spring, was the highest; thereafter numbers of aphids were relatively low, mainly because of predation by three species of native predators, namely the hemerobiid Micromus tasmaniae, the syrphid Melangyna viridiceps and the ladybird Leis conformis. The study was a prelude to computer simulation of the population dynamics of the aphid which will be used to investigate the problem of the regulation of density in natural populations of aphids.

Bactrocera tryoni is a polyphagous fruit fly, originally endemic to tropical and subtropical coastal eastern Australia, but now also widely distributed in temperate eastern Australia. In temperate parts of its range, B. tryoni populations show distinct seasonal peaks driven by changing seasonal climates, especially changing temperature. In contrast to temperate areas, the seasonal phenology of B. tryoni in subtropical and tropical parts of its range is poorly documented and the role of climate unknown. Using a large, historical (1940s and 1950s) fruit fly trapping dataset, we present the seasonal phenology of B. tryoni at nine sites across Queensland for multiple (two to seven) years per site. We correlate monthly trap data for each site with monthly weather averages (temperature, rainfall and relative humidity) to investigate climatic influences. We also correlate observed population data with predicted population data generated by an existing B. tryoni population model. Supporting predictions from climate driven models, B. tryoni did show year-round breeding at most Queensland sites. However, contrary to predictions, there was a common pattern of a significant population decline in autumn and winter, followed by a rapid population increase in August and then one or more distinct peaks of abundance in spring and summer. Mean monthly fly abundance was significantly different across sites, but was not correlated with altitudinal, latitudinal or longitudinal gradients. There were very few significant correlations between monthly fly population size and weather variables (either for the corresponding month or for up to 3 months previously) for eight of the nine sites. For the southern site of Gatton fly population abundance was correlated with temperature. Results suggest that although climate factors may be influencing patterns of B. tryoni population abundance in southern subtropical Queensland, they are not explaining patterns of abundance in northern subtropical and tropical Queensland. In the discussion we focus on the role of other factors, particularly larval host plant availability, as likely drivers of B. tryoni abundance in tropical and subtropical parts of its range.

Serious infestations of Helicoverpa punctigera are experienced yearly in the eastern cropping regions of Australia. Regression analysis was used to determine whether the size of the first generation in spring (G1), which is comprised mostly of immigrants from inland Australia, was related to monthly rainfall in inland winter breeding areas. Data from two long series of light‐trap catches at Narrabri in New South Wales (NSW) and Turretfield in South Australia (SA) were used in the analyses. The size of G1 at Narrabri in each year was significantly regressed on the amount of rainfall in western Queensland and NSW in May and June. The size of G1 at Turretfield each year was significantly regressed on the amount of rain in May, June and July in western Queensland and NSW and also in the desert of central Western Australia. Low r2 values of the regressions suggest that rainfall data for more sites, as well as biological and other physical factors, such as temperature, evaporation, and prevailing wind systems, may need to be included to improve forecasts of the potential magnitude of the infestations in coastal cropping regions.