INSECTICIDE SUSCEPTIBILITY OF, AND METABOLISM OF DDT BY DACUS TRYONI (FROGGATT) AND DACUS CUCUMIS FRENCH (DIPTERA: TEPHRITIDAE)

The susceptibility of a strain of Dacus tryoni (Froggatt) from New South Wales and a strain of Dacus cucumis French from south‐east Queensland to the insecticides DDT, DDD, malathion, azinphos methyl and carbaryl was investigated. The available evidence suggests that these strains were susceptible to the above insecticides and therefore the data could be used as reference data should resistance in these species be suspected in the future. Both species were able to detoxify DDT to DDE with D. cucumis having a greater capability than D. tryoni. In both species penetration of C‐DDT over a post‐treatment period of 72 hr was biphasic. In the initial phase of rapid penetration, the rate of penetration followed first‐order kinetics. As the post‐treatment temperature was increased from 21 to 25 to 30°C both the rate of absorption and metabolism of DDT increased, but metabolism increased relatively more than absorption

Effects of artificial shade on attack by the mahogany shoot borer, Hypsipyla robusta (Moore)

Swietenia macrophylla King (Meliaceae: Swietenioideae) provides one of the premier timbers of the world. The mahogany shoot borer Hypsipyla robusta Moore (Lepidoptera: Pyralidae) is an economically important pest of S. macrophylla throughout Asia, Africa and the Pacific. No viable method of controlling this pest is known. Previous observations have suggested that the presence of overhead shade may reduce attack by H. robusta, but this has not been investigated experimentally. This research was therefore designed to assess the influence of light availability on shoot-borer attack on S. macrophylla, by establishing seedlings under three different artificial shade regimes, then using these seedlings to test oviposition preference of adult moths, neonate larval survival and growth and development of shoot borer larvae.\ud \ud \ud Oviposition preference of shoot borer moths was tested on leaves from seedlings grown under artificial shade for 63 weeks. A significant difference in choice was recorded between treatments, with 27.4 ± 1.5 eggs laid under high shade and 87.1 ± 1.8 under low shade.\ud \ud Neonate larval survival on early flushing leaflets of S. macrophylla did not differ significantly between shade treatments. Larval growth rate, estimated by measuring daily frass width, was significantly higher for those larvae fed on seedlings from the high and medium shade treatments (0.1 mm/day), than the low shade treatment (0.06 mm/day). In laboratory-reared larvae, the total mass of frass produced was significantly higher in the high shade treatment (0.4 g) than under the low shade treatment (0.2 g).\ud \ud Longer tunnel lengths were bored by larvae in plants grown under high shade (12.0 ± 2.4 cm) than under low shade (7.07 ± 1.9 cm). However, pupal mass under low shade was 48% higher than that under the high shade treatment, suggesting that plants grown under high shade were of lower nutritional quality for shoot borer larvae.\ud \ud These results indicate that shading of mahogany seedlings may reduce the incidence of shoot borer attack, by influencing both oviposition and larval development. The establishment of mahogany under suitable shade regimes may therefore provide a basis for controlling shoot borer attack using silvicultural approaches