Four years of light-trap and crop survey data from the Namoi Valley of New South Wales are presented for Heliothis armigera (Hb.) and H. punctigera Wllgr. These suggest there are four generations a year. The associated seasonal sequence of major host-plants supporting successive generations, appeared to be: H. armigera-wheat; pre-flowering cotton; flowering cotton and sorghum; sorghum, flowering cotton and sunflowers; and H. punctigera-lucerne, linseed and medics; pre-flowering cotton; flowering cotton, sunflowers and soyabeans; lucerne and flowering cotton. On host-plants common to both species, a change in dominance from H. punctigera to H. armigera occurred as each summer progressed. Suggested causes are: seasonal changes in the availability of host-plants, favouring H. armigera over H. punctigera; insecticide resistance in H. armigera; and the competitive superiority of H. armigera. Large numbers of H. armigera in cotton appeared to be related to: warm springs, which favoured moth emergence during the period of wheat anthesis; the incomplete control of infestations within cotton itself, leading to the development of resident populations; and the influx of moths from other host-plants, especially sorghum, during the latter half of the season.

No abstract

The sequence and relative injuriousness of insect pests was studied for three successive years in unsprayed cotton of the Namoi Valley. Heliothis punctigera Wallengren, the native budworm, and to a lesser extent H. armigera (Hiibner), the cotton bollworm, prevented the setting of full crops by destroying buds and bolls. After setting, high proportions of bolls were injured by Earias huegeli Rogenhofer, the rough bollworm. Incidental damage was caused to seedlings by Thrips imaginis Bagnall, the plague thrips, and lo leaves by Anomis flava Fabricius, the cotton looper, and by Austracris guttulosa (Walker), the spur-throated locust. In commercial crops, pest control must rely on the use of broad-spectrum insecticides: H. armigera is currently resistant to several of these, and has become the principal species in the local population of cotton pests.A number of enviromncntal features impede the natural control of pests in the southerly areas where cotton is now produced. In comparison to the older dryland cropping practised in central Queensland, a higher yield is necessary to cover the production costs of irrigated cotton; a shorter growing season prevents the plants from compensating effectively for insect damage and the natural enemies of cotton pests are less abundantand less active.

No abstract