Seasonal development and trapping of coryphodema tristis in eucalyptus nitens

Abstract

Plantation forestry is a significant economic contributor in many countries around the world, accounting for approximately 0.9% of the global GDP according to a 2011 estimate. These exotic commodities are often at risk of being invaded by various pests and diseases, both native and exotic. In Brazil, for example, losses of up to US$6.5 million per annum have been estimated due to infestations of the Sirex wood wasp (Sirex noctilio, Hymenoptera: Siricidae). Management of these biological risks is crucial to curb significant economic losses; however, management strategies can often be complicated and require a thorough understanding of the target pest’s biology and ecology. In South Africa, one of the more important pests in plantation forests is the cossid moth (Coryphodema tristis, Lepidoptera: Cossidae). This wood-boring moth was previously described as a pest of quince and grapevines in the Western Cape region, but has recently been found to infest plantations of Eucalyptus nitens on the Mpumalanga Highveld. Despite its significant impact on E. nitens, few studies have investigated the biological and ecological characteristics of this pest, as well as aspects relating to its management, on this recent host. The aim of this study was to obtain a better understanding of the biological and ecological characteristics of C. tristis on E. nitens, and to use this knowledge to develop an effective management strategy. The dissertation contains three chapters. The literature review in the first chapter provides a summary of wood-boring Lepidoptera as pests in commercial forestry plantations. The review draws on general characteristics present in the groups discussed and includes information on their diversity and distribution, life cycle characteristics, host associations, diet and nutrition, pathways of invasion and early detection mechanisms. Eradication as a control strategy, as well as other management tactics such as biological, chemical and behavioural control, is also discussed. The aim of the first research chapter was to investigate the seasonal development and occurrence of C. tristis in association with E. nitens, on the Mpumalanga Highveld, and to compare these findings to those previously published for the Western Cape area on quince and vines. This was achieved through the regular felling of cossid infested E. nitens trees on the Mpumalanga Highveld over a 23-month period to investigate development of the immature stages, and through the trapping of C. tristis male adults to monitor the flight season(s). Since the previously recorded hosts and environment (quince and vines in the Western Cape) differ from the new host and environment (E. nitens on the Mpumalanga Highveld), differences in the life cycle of C. tristis between the two regions were expected. The broad objective of the second research chapter was to optimise the management of C. tristis using behavioural control tactics. Specifically, we investigated the influence of trapping density on moth captures, using pheromone-baited traps that have recently been used for an experimental mass trapping programme. Six different trap spacing treatments, ranging from 10 m to 60 m between traps, were investigated over a period of 23 months and the mean moth captures per trap and total estimated moth captures per hectare were compared between these treatments. It was expected that the lower trap densities would capture significantly more male moths than the higher trap densities, since inter-trap interference may occur at the higher trap densities. This was the first study to investigate the seasonal development and occurrence of C. tristis on E. nitens. These results, together with results from the trapping density study, will be useful to inform future management strategies for this pest. In addition, this study made an important contribution to the knowledge on economically significant wood-boring moths.