Impact of habitat modification on parasitism of African rice gall midge, <i>Orseolia oryzivora</i> (Diptera: Cecidomyiidae) and rice yields in lowland cultivation

The African rice gall midge (AfRGM) (<i>Orseolia oryzivora</i>, Diptera:Cecidomyiidae) poses a significant threat to lowland rice in Africa, causing up to 77% yield loss. This study investigates the potential of habitat modification using <i>Paspalum</i> grass to enhance parasitoid carryover from the non-pest <i>Paspalum</i> gall midge (PGM) (<i>O. bonzii</i>) to AfRGM, as both share the same parasitoids (<i>Platygaster diplosisae</i> and <i>Aprostocetus procerae</i>). The experiments conducted during the 2022 and 2023 wet seasons used a split-plot arrangement fitted into a Randomised Complete Block Design (RCBD). The main plot treatments consisted of rice surrounded by <i>Paspalum</i> grass or without, using four rice cultivars (FARO 44, FARO 66, FARO 67, FARO 37). Results show that rice surrounded by <i>Paspalum</i> grass significantly reduced AfRGM tiller infestation, with FARO 66 and FARO 67 exhibiting lower infestation rates. Parasitism levels on rice galls increased with plant age, and a significant positive correlation was observed between <i>Paspalum</i> galls and parasitism (r = 0.93 in 2022, and r = 0.63 in 2023). Rice fields with <i>Paspalum</i> grass showed significantly higher grain yields (93.66% increase in 2022 and 120.30% in 2023) than those without, with FARO 44 recorded the highest grain yield. AfRGM infestation negatively correlated with panicle number and grain yield. A significant negative correlation was found between AfRGM infestation and both panicle number and grain yield. Hence, planting <i>Paspalum</i> grass around rice fields promotes parasitoid population growth, effectively suppressing AfRGM infestations and enhancing rice productivity.