Charles O. Omwega

Diversity of lepidopteran stem borers on monocotyledonous plants in eastern Africa and the islands of Madagascar and Zanzibar revisited.

Surveys were completed in Eritrea, Ethiopia, Kenya, Madagascar, Mozambique, Tanzania, Uganda and Zanzibar to assess the lepidopteran stem borer species diversity on wild host plants. A total of 24,674 larvae belonging to 135 species were collected from 75 species of wild host plants belonging to the Poaceae, Cyperaceae and Typhaceae. Amongst them were 44 noctuid species belonging to at least nine genera, 33 crambids, 15 pyralids, 16 Pyraloidea species not yet identified, 25 tortricids and three cossids. The noctuid larvae represented 73.6% of the total number of larvae collected, with 66.3, 3.5 and 3.8% found on Poaceae, Cyperaceae and Typhaceae, respectively. The Crambidae, Pyralidae, Tortricidae and Cossidae represented 19.8, 1.9, 2.5 and 0.1% of the total larvae collected, respectively, with 90.4% of the Crambidae and Pyralidae collected from Poaceae, and 99.7% of the Tortricidae collected from Cyperaceae. The lepidopteran stem borer species diversity in the wild host plants was far more diverse than previously reported.

Geographic distribution and host plant ranges of East African noctuid stem borers

Abstract Surveys were carried out in Kenya, Tanzania, Uganda and Zanzibar to establish geographic distribution in the main vegetation mosaics and ecological (host plant range, feeding behaviour) characteristics of the East African noctuid stem borers. 49 wild plant species belonging to Poaceae, Cyperaceae and Typhaceae were found to harbour stem borers in the six vegetation mosaics surveyed. A total of 36 noctuid species belonging to nine genera were identified from 14,318 larvae collected, out of which 17 were new to science. The species diversity varied among vegetation mosaics and host plants. Most borer species appeared to be specialised feeders with 24 species being monophagous. Species belonging to the same types (named as the Busseola Thurau 1904 and the Sesamia Guenée 1852 types) or genus harboured common ecological characteristics such as pigmentation and feeding site. The Sciomesa Tams and Bowden 1953 genus was an exception as it had a mixture of these characters.

A review of the introduction and establishment of Cotesia flavipes Cameron in East Africa for biological control of cereal stemborers.

Chilo partellus Swinhoe (Lepidoptera: Pyralidae) is an exotic stemborer of cereal crops in Africa which invaded the continent from Asia earlier this century. In addition to Ch. partellus, several indigenous stemborers are found in Africa. In 1991, Cotesia flavipes Cameron (Hymenoptera: Braconidae), a gregarious endoparasitoid of stemborers in Asia, was introduced into Kenya for biological control of Ch. partellus. Laboratory studies revealed that the parasitoid could successfully parasitise not only the target stemborer, but also two native stemborers that occur sympatrically with Ch. partellus in some locations. Interbreeding studies demonstrated the Co. flavipes would mate with a native congener, Cotesia sesamiae (Cameron), but no female offspring resulted from these matings. Investigations on competition between the two Cotesia spp. indicated that when Ch. partellus was the host, Co. flavipes appeared to be a superior parasitoid. Releases of Co. flavipes were made in 1993 in Kenya. Recoveries in 1994, 1995 and 1996 demonstrated that the parasitoid was firmly established in two regions of Kenya and in northern Tanzania. Preliminary observations suggest that the parasitoid is causing greater mortality to stemborers in southwestern Kenya than in the coastal area.RésuméChilo partellus Swinhoe (Lepidoptera: Pyralidae) est un exotique foreur de tiges des cultures céréalières en Afrique qui envahit le continent en provenance d’Asie au début de ce siècle. En plus de Ch. partellus, plusieurs foreurs de tiges sont rencontrés en Afrique. En 1991, Cotesia flavipes (Hymenoptera: Braconidae), un grégaire endoparasitoïde des foreurs de tiges en Asie fut introduit au Kenya pour la lutte biologique contre Ch. partellus. Des études en laboratoire révélèrent que le parasitoïde pouvait parasiter avec succès non seulement les foreurs cibles mais aussi deux foreurs en occurrence sympatrique avec Ch. partellus dans quelques localités. Des études sur élevage mixte ont démontré que Co. flavipes pouvait s’accouplert avec un congénère indigène, Cotesia sesamiae (Cameron), mais ces accouplemets ne donnèrent pas naissance à une progéniture femelle. Les investigations sur la compétition entre les deux espèces de Cotesia montrèrent que lorsque Ch. partellus était l’hôte, Co. flavipes était un parasitoïde supérieur. Des lâchers de Co. flavipes furent effectués en 1993 au Kenya. Les recouvrements de 1994, 1995 et 1996 montrèrent que le parasitoïde s’était fermement établi dans deux régions du Kenya et au nord de la Tanzanie. Des observations préliminaires suggèrent que le parasitoïde cause une plus grande mortalité chez les foreurs de tiges au sud-ouest que dans la région côtière du Kenya.

The role of intercropping different cereal species in controlling lepidopteran stemborers on maize in Kenya

Abstract:  The effects of mixed cropping systems containing maize, sorghum, millet and beans on infestations of cereals by lepidopteran stemborers and on associated parasitoids, as well as on yields and land equivalent ratios (LER) were assessed during four consecutive rainy seasons at two sites in the semi‐arid eastern region of Kenya. Systems containing the non‐host bean were more efficient in reducing pest densities than those with millet or sorghum only. Higher parasitism in diversified systems compared to monocrops was due to density‐dependent effects rather than superior suitability of such systems to parasitoids. The maize–bean system, which had the highest proportion of bean plants, had LERs >1.65 while most other systems had LERs <1. It is concluded that mixed cropping with several cereal species has little advantages in terms of yield loss abatement due to stemborers and land use efficiency. However, including the drought‐tolerant crops such as sorghum and millet in the system stabilizes food security in drought‐prone areas such as eastern Kenya.

Cereal yield losses caused by lepidopterous stemborers at different nitrogen fertilizer rates in Ethiopia

Abstract:  Field trials were carried out at three locations in the cool‐wet western and one location in the semiarid eastern ecozones of the Amhara State of Ethiopia to determine the effects of nitrogen fertilizer on pest infestation and yield losses caused by lepidopterous stemborers in maize and sorghum. Three N fertilizer levels, i.e. 60, 120 and 180 kg/ha for maize, and 41, 64, and 87 kg/ha for sorghum, were compared with a zero N treatment. The dominant pest species were the noctuid Busseola fusca (Fuller) and the invasive crambid Chilo partellus (Swinhoe). Leaf N content was positively related to N fertilizer dosage. In general, pest density, parasitism, plant growth and borer damage variables increased with crop growth stage. On sorghum, in the cool‐wet western Amhara, increasing levels of N fertilizer also tended to increase pest density, plant growth and damage variables. In the semiarid ecozone, parasitism by the exotic parasitoid Cotesia flavipes Cameron tended to increase with N level. In the cool‐wet ecozone, sorghum yields increased by up to 74% because of fertilization; losses caused by stemborers decreased linearly with N dosage from 49% to 36%. In maize, because of low borer densities, there were no discernable trends for pest infestation and yield losses. In the cool‐wet ecozone, sorghum yields were positively related to insecticide application and plant height, and negatively to damage variables such as tunnelling and peduncle damage. In semiarid eastern Amhara, the effects of fertilizer on pest, damage and yield were low on both crops because of the higher soil fertility. The results indicate that the profitability of nitrogen fertilizer as an integrated pest management tactic in the control of cereal stemborers depends, among others, on the severity of borer damage and the soil fertility status prevailing in an area. It is concluded that N fertilizer helps minimize the impact of borers on grain yields, especially on sorghum and in the cool‐wet ecozone.

Evidence of the establishment of Cotesia flavipes (Hymenoptera: Braconidae), a parasitoid of cereal stemborers, and its host range expansion in Ethiopia.

Three lepidopteran cereal stemborers, Chilo partellus (Swinhoe) (Crambidae), Busseola fusca Fuller, and Sesamia calamistis Hampson (Noctuidae) were collected from maize and sorghum in Ethiopia. The noctuid stemborers are indigenous to Africa while C. partellus is an introduced species from Asia. In 1999, the Asian stemborer parasitoid, Cotesia flavipes Cameron (Braconidae) was found to be widespread in Ethiopia, even though it had never been released in the country. In addition to attacking Chilo partellus, Cotesia flavipes was reared from B. fusca and S. calamistis. The origin of C. flavipes in Ethiopia may have been Somalia where it was released in 1997 near the border with eastern Ethiopia. Percent parasitism of borers by C. flavipes was higher in eastern Ethiopia than other surveyed regions, and parasitism was higher in 2000 than 1999. Parasitism was higher when cereals were intercropped with other plants and when wild grass hosts of stemborers were present.

Effect of wild grasses planted as border rows on stemborer infestations in maize in Uganda)

Abstract The presence of wild grasses in the vicinity of maize fields has been associated with reduced stemborer incidence on the maize crop. This study evaluated the impact of border rows with wild grasses on stemborer infestations and parasitism. Field trials were conducted in East and Central regional Agricultural Research Institutes in Uganda for three seasons. The four grass species planted as border rows included Pennisetum purpureum Schumach, Pennisetum polystachion (L.) Schult, Panicum maximum Jacq. and Sorghum arundinaceum (Desv.) Stapf. (Poaceae) were used. A pure maize stand without a grass border was planted as control. Busseola fusca Fuller (Lepidoptera: Noctuidae) and Chilo partellus Swinhoe (Lepidoptera: Crambidae) were the major stemborers found. Maize with P. purpureum and P. maximum borders reduced stemborer infestations and damage compared to the pure maize stand. The results were however, not consistent for all the three seasons. Yield per plot was higher in pure maize stand compared to plots with grass borders. The usefulness of this technique in stemborer management is discussed.

Release and establishment of Cotesia flavipes Cameron (Hymenoptera: Braconidae) an exotic parasitoid of Chilo partellus (Swinhoe) (Lepidoptera: Crambidae) in East and Southern Africa

Abstract Cotesia flavipes Cameron (Hymenoptera: Braconidae) was first imported into Kenya in 1991 from Pakistan for control of Chilo partellus (Swinhoe) (Lepidoptera: Crambidae). First releases were made at the Kenya coast in 1993 and a few recoveries of the parasitoid were made the following year. Additional foreign exploration for C. flavipes was conducted in central India in 1996 and 1998, which resulted in additional importation of the parasitoid for subsequent releases in eastern and southern Africa. Region-wide releases commenced with releases in Mozambique in 1996, Somalia in 1997 and Uganda in 1998. By 2005, many releases had been made in 10 countries in East and Southern Africa with establishment being reported in all of them except Eritrea but including Ethiopia where releases had never been made. This paper describes the progress made in the release and establishment of C. flavipes in East and Southern Africa and quantifies the rate of spread from the initial release sites in Kenya.

Cereal stemborer distribution and abundance, and introduction and establishment of Cotesia flavipes Cameron (Hymenoptera: Braconidae) in Mozambique.

Field surveys carried out in Mozambique showed that two indigenous cereal stemborers, Busseola fusca Fuller (Lepidoptera: Noctuidae), Sesamia calamistis Hampson (Lepidoptera: Noctuidae) and one exotic stemborer, Chilo parteltus (Swinhoe) (Lepidoptera: Pyralidae), are the main pests of maize and sorghum in the country. Busseola fusca was abundant at high altitudes (> 800 m) and Ch. partellus was abundant at low altitudes (< 800 m). Sesamia calamistis occurred at all elevations but in low numbers. Of the three stemborers, Ch. partellus was the most widespread and abundant pest of maize followed by B. fitsca. Therefore, a programme was initiated to introduce the exotic parasitoid Cotesia flavipes Cameron (Hymenoptera: Braconidae) to increase natural suppression of Ch. partellus populations. Cotesia flavipes was introduced into southern Mozambique for the first time in November 1996. Additional releases were subsequently carried out in several places in southern and central Mozambique from 1998–2000. The parasitoid was recovered from all localities sampled 1 to 3 years after its introduction, indicating that this exotic parasitoid had established in the southern and central regions of Mozambique.RésuméDes enquêtes menées sur le terrain au Mozambique ont montré que les foreurs des tiges de céréales indigènes Busseola fusca Fuller (Lepidoptera: Noctuidae) et Sesamia calamistis Hampson (Lepidoptera: Noctuidae) et un foreur des tiges exotique, Chilo Partellus (Swinhoe) (Lepidoptera: Pyralidae), sont les principaux ravageurs du maïs et du sorgho dans le pays. Busseola fusca est abondant à hautes altitudes (> 800 m) and Ch. partellus est abondant à basses altitudes (< 800 m). Sesamia calamistis est présent à toutes les altitudes mais en faible nombre. Parmi les trois foreurs des tiges, Ch. partellus est le ravageur le plus largement répandu et le plus abondant suivi par B. fusca. Aussi, un programme a été lancé pour introduire le parasitoïde exotique Cotesia flavipes Cameron (Hymenoptera: Braconidae) afin d’augmenter la régulation naturelle des populations de Ch. partellus. Cotesia flavipes a été introduit dans le sud du Mozambique pour la première fois en novembre 1996. Des lâchers supplémentaires ont été par la suite réalisés dans plusieurs localités du sud et du centre du Mozambique entre 1998 et 2000. Le parasitoïde a été retrouvé dans toutes les localités échantillonnées 1 et 3 ans après son introduction, indiquant qu’il s’est établi dans les régions du sud et du centre du Mozambique.

Yield loss due to the stemborer Chilo partellus (Swinhoe) (Lepidoptera: Crambidae) at different nitrogen application rates to maize

Abstract Field trials were conducted at Kibaha and Morogoro in eastern Tanzania during two seasons to evaluate the effect of nitrogen fertilization (0, 50, 75, 100 kg [N]/ha) on pest abundance, plant damage and yield loss of maize due to stemborers. In general, ear and grain weights increased linearly with nitrogen level. In the infested plot, grain weight increased 2.5 and 1.8 fold from 0 to 100 kg [N]/ha in the short and long rainy season, respectively, at Kibaha, and 1.4 and 1.6 times at Morogoro. Yield loss decreased with an increase in nitrogen application and the effect was stronger under high than low borer infestation levels. The results show the beneficial effect of nitrogen on the plant’s ability to compensate for borer damage. Analysis of economic benefits of applying fertilizer and insecticide treatment indicated that using insecticides is not profitable under high-pest-low-soil fertility conditions.