Evaluation of four insecticides to protect Nauclea diderrichii (Rubiaceae) seedlings against Orygmophora mediofoveata (Lepidoptera: Noctuidae) shoot borer damage

2017

English

Journal

Nauclea diderrichii (DeWild and Th. Dür.) (common name Kusia and trade name, Opepe) is an evergreen tree found throughout the tropical rainforests of West Africa. It is heavily exploited for its timber and listed as vulnerable on the IUCN Red List of Threatened Species. The shoot borer Orygmophora mediofoveata Hamps, which attacks the nursery stage, has hampered attempts to establish N. diderrichii plantations in Ghana. This study examined the potential of four insecticides to protect N. diderrichii seedlings from O. mediofoveata attack and damage. Four insecticides–Pyrinex (chlorpyrifos), Dursban (chlorpyrifos), Cerox (dimethoate) and Golan (acetamiprid)–were applied to four-monthold N. diderrichii seedlings growing in full sunlight and under shade (80% of normal light), to evaluate their effects on incidence of attack, survival, severity of damage and growth. Insecticide treatment and light conditions had variable effects on the damage and growth of the seedlings after six months of evaluation. Seedling survival was not significantly influenced by the insecticide treatment. Percent survival of insecticide-treated seedlings did not differ significantly from that of control seedlings in full sun; however, under shade survival of treated seedlings was significantly higher than control seedlings. Nonetheless, control seedlings in full sun had higher survival (92.5%) than those under shade (62.5%). Insecticide-treated seedlings in full sun had lower incidence of shoot borer attack than those under shade. In full sun, dieback incidence following shoot borer attack was significantly lower for insecticide-treated than control seedlings. Growth in height and girth of seedlings was influenced positively by both insecticide and light, with girth especially being significantly lower under shade conditions. Currently, N. diderrichii seedlings are typically raised under shade; however, this study shows that raising seedlings in full sun with insecticide application could result in faster and better growth.

Bosu, P. P.; Acquah, E.; Boamah, R. O.