Survival of the navel orangeworm, Amyelois transitella (Lepidoptera: Pyralidae), on pistachio in South Africa
The navel orangeworm, Amyelois transitella (Pyralidae) (Walker), is the most damaging Lepidoptera larva found on pistachio nuts (Pistacia vera L., Anacardiaceae). Pistachios have only relatively recently been planted in South Africa at Green Valley Nuts, a division of the Industrial Development Corporation, near Prieska in the Northern Cape Province. The navel orangeworm causes direct damage to pistachio nut clusters by feeding on individual nut kernels and contaminating nuts with their faecal excretions. In the process the quality of the nuts is reduced and the nuts are rendered more susceptible to fungal infection. After harvest, navel orangeworm larvae overwinter inside fallen nuts on the orchard floor, as well as inside nuts left behind on trees. The prevalence of navel orangeworm in mummy nuts was studied from May to September in 2008 and 2009 at Green Valley Nuts. The potential survival of the larvae in these nuts was estimated from nuts sampled under trees of three different pistachio cultivars (Ariyeh, Sirora and Shufra). Orchard row management practices were investigated to determine the effect of cover crops, mulch and hydro-cooling on navel orangeworm survival. This was done by monitoring emergence cages and light traps for the presence of navel orangeworm adults emerging from mummy nuts. In both years, navel orangeworm was noted overwintering in mummy nuts. The highest occurrence of navel orangeworm over the two year study period was recorded in nuts from Sirora, a cultivar planted in an orchard lacking inter-tree row cover crops, mulch and hydro cooling. The results support the assumption that these orchard row management practices have a suppressing effect on navel orangeworm development, causing high mortality rates due to mummy nut decomposition. Research was also conducted to observe the life cycle and behaviour of the pest under laboratory conditions. The complete life cycle duration of the navel orangeworm ranged from 50 to 84 days. A single life cycle which gave rise to a next generation was successfully tracked.