Inventory of insect pests of rice in agro-ecosystems of far north region of Cameroon

The entomofauna vector of rice yellow mottle virus was studied from June to September 2023 in the rainfed rice ecosystem of Maroua and in the main irrigated rice ecosystems of Yagoua and Maga in the Far North Region, Cameroon . Insect vector sampling was conducted in rainfed and irrigated rice fields every two weeks using a sweep net and a D-Vac (vacuum trap). From the samples obtained in the different rice-growing sites, the dominant structure of insect vectors of rice yellow mottle as well as their natural enemies was analyzed according to the phenology of rice. It appears from the inventory of insects in irrigated rice (Maga, Yagoua) and rainfed rice (Maroua) that this crop harbors many vectors of the rice yellow mottle virus. In the different rice-growing sites, we have numbers of vector insect individuals captured of 267, 286 and 385 respectively in Maroua (rainfed rice), Maga and Yagoua (irrigated rice). The vector insects captured are distributed as follows, eight species of vector insects in irrigated rice in Maga belonging to five families divided into three orders: Chnootriba similis (Coleoptera: Coccinellidae), Chaetocnema pulla (Coleoptera: Chrysomelidae), Locris rubra ( Hemiptera: Cicadellidae), Nephotettix nigropictus (Hemiptera: Cicadellidae), Sogatella furcifera (Hemiptera: Delphacidae), Cofana spectra (Hemiptera: Cicadellidae), Niparvata lugens (Hemiptera: Delphacidae) and Diopsis thoracica (Diptera: Diopsidae). In irrigated rice in Yagoua, eleven species of vector insects belonging to seven families divided into three orders were collected: Chnootriba similis (Coleoptera: Coccinellidae), Chaetocnema pulla (Coleoptera: Chrysomelidae), Locris rubra (Hemiptera: Cicadellidae), Nephotettix nigropictus (Hemiptera: Cicadellidae), Sogatella furcifera (Hemiptera: Delphacidae), Cofana spectra (Hemiptera: Cicadellidae), Recilia dorsalis (Hemiptera: Cicadellidae), Niparvata lugens (Hemiptera: Delphacidae), Leptocorisa oratorius (Hemiptera: Alydidae), Diploxys spp. (Hemiptera: Pentatomidae) and Diopsis thoracica (Diptera: Diopsidae). As for rainfed rice in Maroua, thirteen vector insect species belonging to seven families and three orders were collected: Chnootriba similis (Coleoptera: Coccinellidae), Chaetocnema pulla (Coleoptera: Chrysomelidae), Trichispa sericea (Coleoptera: Chrysomelidae), Locris rubra (Hemiptera: Cicadellidae), Nephotettix nigropictus (Hemiptera: Cicadellidae), Sogatella furcifera (Hemiptera: Delphacidae), Cofana spectra (Hemiptera: Cicadellidae), Recilia dorsalis (Hemiptera: Cicadellidae), Niparvata lugens (Hemiptera: Delphacidae) and Diopsis thoracica (Diptera: Diopsidae). These species proved to be particularly important by the size of their populations at the tillering stage of rice. The irrigated rice ecosystems of Yagoua and Maga are the most infested by insect vectors of rice yellow mottle virus and among these insect vectors Nephotettix nigropictus (Hemiptera: Cicadellidae) is the abundant species with 87 and 90 individuals collected respectively from Maga and Yagoua. Nephotettix nigropictus (Hemiptera: Cicadellidae) was collected in abundance at the tillering stage of rice. As for the predators and parasitoids present in the rice fields, there were spiders Araneus sp. (Araneae: Araneidae), Tetragnatha sp. (Araneae: Tetragnatidae), Pardosa injucunda (Araneae: Lyconidae) and lady beetles Xanthadalia effusa (Coleoptera: Coccinellidae) as predators and Hydrellia griseola (Diptera: Ephydridae), Bracon sp. (Hymenoptera: Braconidae), Xiphosomella sp. (Hymenoptera: Braconidae), Platygaster sp. (Hymenoptera: Platygasteridae) as parasitoids. The parasitoid species Hydrellia griseola (Diptera: Ephydridae) and the predatory species Araneus sp. (Araneae: Araneidae) are the most abundant natural enemies in the rice ecosystems of the Far North.