Developmental biology and field performance of Platygaster diplosisae Risbec (Hymn: Platygasteridae) an egg-larval parasitoid of african rice gall midge Orseolia oryzivora Harris and Gagn (Diptera: Cecidoymiidae)

Abstract

The developmental biology and field performance of Platygaster diplosisae an endoparasitoid of African rice gall midge (AfRGM) Orseolia oryzivora were investigated. Experiments were conducted in the screen house, laboratory and fields during 2006/2007 farming seasons. The pre-oviposition period averaged 12.1 h. The mean number of eggs laid per female was 95.2 and mean oviposition period was 3.5 days. The average incubation period was 13.0 days with a hatchability of 67.3%. There were three larval instars with developmental duration averaging 2.2, 0.5 and 2.5 days for the 1st, 2nd and 3rd larval respectively. The prepupa and pupa developmental period lasted for 2.4 and 6.7 days respectively. The longevity of males and females were 3.0 and 4.1 days respectively without food, which varied when food was given. The parasitoid has total developmental period of 27.3 days. The results showed that P. diplosisae has an impact as a bio-control agent of AfRGM, but the percentage parasitism of the host was low at the beginning of the season and increased significantly later in the season with a peak in October of each season. It was recommended that mass rearing or conservation of the parasitoid be adopted to improve its efficiency in control of AfRGM. Key words: Biology, Platygaster diplosisae, bio-control, field impact, Orseolia oryzivora