Abstract:
Botswana is a country which depends mainly on cereal agriculture, done mostly by rural farmers as their major income stream. However, lepidopteran stemborers are a major constraint in the rural farmers’ cultivation of cereal crops. Species diversity and distribution of these insects of economic concern is currently unknown in Botswana. Through a survey, I catalogued the diversity of stemborers, host plant interactions and their associated parasitoids across Botswana. A total of 1597 stemborer larvae and 228 pupae were recorded; 63.1% and 36.9% larvae from cultivated versus wild hosts respectively and, 84.8% and 15.2% pupae from cultivated versus wild host plants respectively. In addition to Chilo partellus Swinhoe, Sesamia calamistis Hampson and Eldana saccharina Walker which were previously reported in Botswana, 15 ‘new’ stemborer species were recorded for the first time, including 10 species which have never been described before. These species are: Sesamia jansei Tams & Bowden, Sesamia perplexa, Sesamia nonagrioides Lefebvre, Sesamia perplexa es nov sp 4, Sesamia sp nr perplexa, Sesamia nov sp 41 nr nonagrioides, Sesamia sp. Mythimna loreyi,Conicofrontia nov sp 1 nr sesamoides, Tortricidae sp1, Tortricidae sp2, Tortricidae sp3, Tortricidae sp. and a Schoenobiinae. These were collected from a variety of plants ranging from cultivated Zea mays L., Sorghum bicolor (sorghum), Sorghum bicolor L. Moench (sweet sorghum) to wild Schoenoplectus corymbosus Roth ex Roem. & Schult, Chrysopogon nigritanus (Vetiver), Typha latifolia L., Cyperus papyrus L., C. dives Delile, Vossia cuspidata (Roxb.) Griff., Eriochloa fatmensis (Hochst. & Steud.) Clayton, Echinochloa pyramidalis (Lam.) Hitchc. & Chase and Oryza longistaminata A.Chev. & Roehr. Busseola fusca Fuller, previously reported to be one of the common stemborers in the country, was not recorded in this work. Chilo partellus had the highest relative abundance of 62.1% in Z.mays, grain sorghum, sweet sorghum, E. pyramidalis and C. dives; followed by S. calamistis at 11% in Z. mays, E. pyramidalis, grain sorghum, P. macronium, S. corymbosus, C. papyrus and C.nigratinus; with Mythimna loreyi (Z. mays) and S.perplexa es nov sp4 (E. pyramidalis) having the lowest abundance of 0.7%. Stemborer diversity index for the wild host plant species was found to be greater than that of the cultivated crops. In cultivated habitats, the most common larval parasitoids were Cotesia flavipes Cameron, Cotesia sesamiae Cameron (Hymenoptera: Braconidae), Euvipio rufa Szepligeti (Hymenoptera: Braconidae) and pupal parasitoids were Pediobius furvus Gahan (Hymenoptera: Eulophidae) and Gambroides nimbipennis Seyrig (Hymenoptera: Ichneumonidae). However, larval parasitoids Chelonus curvimaculatus Cameron (Hymenoptera: Braconidae), and Goniozus indicus Ashmead (Hymenoptera: Bethylidae) and a pupal parasitoid, Dentichasmias busseolae Heinrich(Hymenoptera: Ichneumonidae) were common in natural habitats. Furthermore, larval and pupal predatory ants (Linepithema humile Mayr (Hymenoptera: Formicidae), Crematogaster peringueyi Emery (Hymenoptera: Formicidae) and Aenictus species) were identified in both cultivated and natural habitats. Cultivated Poaceae- Zea mays L., Sorghum bicolor (Sweet sorghum), S. bicolor (sorghum); wild Poaceae- Echinochloa pyramidalis (Lam.) Hitchc. & Chase, Sorghum bicolor subsp arundinaceum (Desv.) de Wet & Harlan; wild Typhaceae- Typha latifolia L. and wild Cyperaceae- Schoenoplectus corymbosus (Roth ex Roem. & Schult.) J.Raynal, and Cyperus dives Delile were the major plants harbouring these natural enemies and their host insects. Stemborers C. partellus and Sesamia spp. were the major parasitoid hosts with C. partellus hosting most parasitoids in cultivated habitats and S. jansei in natural habitats. Larval parasitism ranged between 2.1-48.9% and 3.7-23.5% in cultivated and natural habitats respectively, with C. flavipes and C. curvimaculatus Cameron the predominant parasitoids respectively. Pupal parasitism ranged between 5.9-15% in cultivated and 6.7-11.1% in natural habitats with P. furvus Gahan and D. busseolae the predominant parasitoids respectively. Larval and pupal parasitoids relative abundance ranged between 1.1- 47% with C. flavipes and P. furvus the dominant larval and pupal parasitoids respectively. Overall, this work reports Botswana landscapes host diverse stemborer species across wild and agro-ecosystems, and a significant diversity of natural enemy/parasitoid faunal diversity that may be worth conserving for future efficacy of biological control programmes.