Mbita Point Field Station Research Articles

Impact of a Habitat Management System on Diversity and Abundance of Maize Stemborer Predators in Western Kenya

—Studies were conducted in farmer’s field, Lambwe School of the Deaf, and Mbita Point Field Station of ICIPE (ICIPE-Mbita) in western Kenya during the long rains of 2001 and 2002 to assess the impact of a diversionary stemborer management strategy on the pest’s predators. Treatments consisted of a maize monocrop (control) and an intercrop of maize and desmodium, Desmodium uncinatum Jacq., with Napier grass, Pennisetum purpureum (Schumach), as trap crop around the field (‘push-pull’) in the farmer’s field and Lambwe School of the Deaf. Sudan grass, Sorghum vulgare sudanense (Pers.), was used in place of Napier on the station. A combination of sticky traps, direct observation and hand-collection methods were employed. Predator groups encountered included 12 families from 7 insect orders and 4 families from one arachnid order, with most of the foregoing represented in both maize monocrop and ‘push-pull’ plots. A Cheilomenes sp. and Chrysopa sp. were, however, recovered from ‘push-pull’ plots only. Ants, earwigs and spiders were the main predators encountered. Both overall and individual group populations of these predators as well as ant diversity were significantly higher in ‘push-pull’ than monocrop plots in all the sites during the vegetative, flowering and mature maize growth stages (P < 0.05, t-test). The results thus indicate a numerical enhancement of stemborer predators by use of this habitat management system.

Pattern and rate of within-field dispersal and bionomics of the cowpea aphid, Aphis craccivora (Aphididae), on selected cowpea cultivars

Comparative field studies were conducted during the rainy and dry seasons at the Mbita Point Field Station of ICIPE in southwestern Kenya, to investigate the pattern and rate of dispersal of Aphis craccivora on aphid-resistant (ICV-12) and aphid-susceptible (ICV-1) cowpea cultivars in relation to key weather factors. The effects of the dispersal trends on crop performance and aphid population dynamics were analysed. Treatments consisted of initial aphid releases at the north, south, west, east and centre of test plots and uninfested controls maintained on plants for 22 days. Parameters recorded included: pattern (direction of spread of aphids) and rate (number of aphid-infested plants at a given time) in test plots; crop growth and yields and associated factors such as incidence of sooty mould and plant mortality, and aphid density and associated factors, including the incidence of natural enemy species, particularly coccinellids. Dispersal was fastest when releases were made in the west, north and centre of plots, and resulted in adveVse effects on ICV-1 growth and yields. Infestations of ICV-12 did not significantly affect crop performance. There was an apparent direct, positive relationship between wind direction and pattern of spread of aphid infestations, but this pattern was more apparent during the rainy season, when wind speeds were higher, than during the dry season. The incidence of natural enemy species correlated with the spread of aphid infestations, while the abundance of coccinellids correlated with aphid density.

Combining Ability of Resistance to the Sorghum Shootfly, Atherigona soccata and Stemborer Chilo partellus in Grain Sorghum, Sorghum bicolor

Combining ability of resistance to the sorghum shootfly, Atherigona soccata and spotted stemborer, Chilo partellus in grain sorghum was analysed on a seven-parents diallel in a field trial at the ICIPE Mbita Point Field Station, western Kenya during the 1990 long rainy season. Lines with best performance for each of the four measured resistance parameters were also found to be the best general combiners. Resistance to leaf damage and number of holes/metre were controlled by additive gene effects whereas resistance to deadheart and stem tunnelling were controlled by additive and non-additive gene effects. Parents IS-1044, IS-12308 and IS-2269 with their good level of resistance, and desirable general combining ability (GCA) effects are proposed for utilisation as resistant combiners in breeding programmes for shootfly and stemborer resistance in grain sorghum.

Phenotypic stability of sorghum hybrids for resistance to the spotted stemborer, Chilo partellus (Swinhoe)

The phenotypic stability of resistance to the stemborer, Chilo partellus and grain yield in 10 newly developed sorghum hybrids namely HYD-1, HYD-2, HYD-3, HYD-4, HYD-5, HYD-6, HYD-7, HYD-8, HYD-9 and HYD-10, and two local checks, Serena (tolerant) and IS-1044 (resistant), were evaluated for seven seasons at the International Centre of Insect Physiology and Ecology (ICIPE) Mbita Point Field Station and Ungoye Field Site in western Kenya. Two stability parameters were determined: (1) The linear regression (b1) of an entry mean on an environmental index, and (2) the deviation from regression (S2d). The significance found for the linear component of environment implies that the variation over the different environments is adequate to test for cultivar stability. Hybrids HYD-1, HYD-5, HYD-8 and HYD-10 were identified as the most suitable genotypes for future commercial production.

Survival and development of Chilo partellus (Swinhoe) on sorghum cultivars

AbstractSurvival and development of Chilo partellus were studied on five sorghum cultivars (IS-18363, IS-18520, ICS-1, ICS-2 and IS-4660) in the laboratory at Mbita Point Field Station, Kenya, at 26 ± 2°C and 65 ± 5% RH. Larval developmental period differed significantly on different cultivars. Number of instars was numerically greater for the females than for the males on all cultivars. Average pupal weight varied with sex; females were twice as heavy as males. The pupal period was longer for males than for females on all cultivars, with the exception of ICS-1, where the pupal period of males was equal to that of females. Ovipositional period was significantly longer on IS-18520 (5.18 ± 0.30 days) than on other cultivars. The shortest ovipositional period (3.70 ± 0.27 days) was recorded on IS-4660. There were no statistically significant differences in adult longevity. Sex ratio of the moths also did not affect the adult longevity of C. partellus reared on the five sorghum cultivars. The variations found in the development of C. partellus on different cultivars were attributed to the nutritional value of the food source.

Natural Enemies of the Legume Pod Borer, Maruca Testulalis Geyer (Lepidoptera: Pyralidae) in Small Scale Farming Systems of Western Kenya

Studies at ICIPE’s Mbita Point Field Station (site 1) and a farmer’s field in Lambwe Valley (site 2) in Western Kenya, revealed the presence of at least seven parasitoids, two predators, one nematode and several microorganic pathogens attacking Maruca testulalis on cowpea crop. Some parasitoids and pathogens were also recovered from M. testulalis cadavers collected on wild host plants of the pest. A pupal endoparasitoid, Antrocephalus sp. was the most predominant, while the pathogens Nosema sp. and Bacillus sp. caused the highest natural mortality on M. testulalis in this region. Parasitoids and pathogens contributed 40.65 and 35.6% to the total generation mortality (K) at sites 1 and 2 respectively. Observed parasitism only contributed 3.25% at site 1 and 3.8% at site 2 of the generation mortality. Mortality due to disappearance which included predation accounted for 59.35 and 64.8% of K at the respective sites. Life table data and survival curves for the pest revealed high generation mortality (ca. 98%), most of which occurred in the early life stages of the pest. The results suggest a high potential for utilizing biocontrol agents in IPM of the pest.

Population monitoring of Chilo partellus (Swinhoe) (Lepidoptera: Pyralidae) using pheromone traps

The flight phenology of the stem borer, Chilo partellus (Swinhoe) at the ICIPE’s Mbita Point Field Station (MPFS) and on a nearby farmer’s field was monitored using pheromone traps. The relation between pheromone trap catches of males and sorghum plant age, infestation, larval/pupal population density and sorghum cultivars used was examined. At MPFS C. partellus males were caught throughout the year in pheromone traps. Fluctuations of trap catches indicated that the pest completes two main generations on each of the long and short rain sorghum crops. On farmers’ fields, males continued to be caught in large numbers after harvest, implying that the pest continues to breed on the sorghum stalks and tillers. Significantly lower observed catches of males occurred only on one (MB-3) of the eight different sorghum cultivars, during the period of 2–6 weeks after plant emergence. In general, positive correlations were observed between the number of males caught in pheromone traps and larval pupal population density, males and percentage plants infested, and males and plant age. However, the pheromone trap appeared to be less effective under high population density, particularly during the flight of the second generation moths, due to competition between pheromone trap and wild females. But the flight phenology as monitored by pheromone traps appeared to reflect major events in population development of C. partellus. Pheromone traps would be useful in detecting C. partellus and for monitoring its flight phenology.

Bioecological studies on Dentichasmias busseolae Heinrich and its potential for biological control of Chilo partellus Swinhoe

Studies were carried out at Mbita Point Field Station, South Nyanza, western Kenya from 1984 to 1987 to determine the role of Dentichasmias busseolae Heinrich in the population dynamics of Chilo partellus Swinhoe and its potential as a biological control agent against the stem borer. D. busseolae is a solitary endoparasitoid which parasitizes and completes its development in the pupa of C. partellus. The developmental period ranged from 64.5 ± 9.5 days at 15°C to 12.0 ± 1.5 days at 30°C for males, and from 66.7 ± 9.8 days to 13.1 ± 2.1 days for females, respectively.The intrinsic rate of natural increase of the parasitoid was 0.1375, and the population multiplied 24.21 times in the mean generation time of 28 days. The functional response was curvilinear.Field parasitism in maize and sorghum was evident 7 weeks after plant emergence (APE). Thereafter, parasitism was persistent until crop harvest. The range of parasitism was 0 to 45.5% (x = 23.3%) on maize and 9.7 to 90% ( X = 36.0%) on sorghum respectively. Using laboratory and field observations, a model for the host searching process of D. busseolae has been constructed. The potential of the parasitoid in biological control programmes of C. partellus is also discussed.

Prevalence of microorganisms in field-sampled borers on sorghum, maize, and cowpea in Western Kenya

A survey carried out over Western Kenya in order to determine the prevalence of microorganisms in cereal stem borers and legume pod borer showed the presence of a large number of insect pathogens in the dead larvae. Larval cadavers were recovered from all sampling sites. Bacterial and fungal microorganisms were highly prevalent. Other major groups of microorganisms were also recovered, although at a low level. Viruses (polyhedral inclusion bodies and granulosis viruses) occurred at 2.7% at the Mbita Point Field Station, and 1.1% in the field. Mermithids and rhabditids occurred at 0.4% in the station and 0.6% in the field, whereas the protozoans (microsporidia and gregarines) were more prevalent in the station than in the farmers’ fields (9.4 and 1%, respectively). The spotted stalk borer, Chilo partellus was the most common borer sampled, but Busseola fusca and legume pod borer, Maruca testulalis were sampled in most sites too. Sesamia calamistis and Eldana saccharina were recorded at a low level, and C. orichalcoceliellus was recorded only at the Kenya coast.

Monitoring of lepidopterous stem-borer population by pheromone and light traps

Preliminary observations were made in the attraction of moths of Chilo partellus Swin., Busseola fusca Fuller, Sesamia calamistis Hmps. and Maliarpha separatella Rag. to light traps and to traps baited with virgin females of these species. The observation was conducted from January 1981 to April 1982 at Mbita Point Field Station in western Kenya. M. separatella showed the highest attraction to light traps followed in descending order by C. partellus, E. saccharina, S. calamistis and B. fusca. The mean catches/trap/night in pheromone traps was highest for M. separatella, followed by C. partellus and B. fusca. The period of atttraction of the moths during the night and effect of moonlight on trap catches were also studied. Catches from light and pheromone traps indicated that attraction of C. partellus and M. separatella was greatest between 23:00 and 03:00hr. The effect of moonlight on light trap catches was greater than on pheromone trap catches.

Screening of local and exotic maize lines for stem-borer resistance with special reference to Chilo partellus

After field screening local germplasm for stem-borer ( Chilo partellus , Swin.) resistance for four seasons in two years we identified two sources of resistance, Katumani and Kitale. A cross between them performed better than either of the parents. When exotic lines from CIMMYT, Mexico, reported to be resistant to South and Central American stem-borers were screened at Mbita Point Field Station, to test and confirm their resistance to East African stem-borers, a number of them were found to be resistant to Chilo . It was also noted that the level of their resistance was higher and more broadly based than the local source. This shows that the source of origin is always full of genetic variability. This finding now suggests that a cross between the local and exotic sources should offer a wide scope in the multiple resistance or the multiline approach towards pest management.

Studies on the legume pod-borer, Maruca testulalis (Geyer)—VIII. Cowpea phenology and yield loss assessment: effect of loss of leaves, shoots, flowers and pods on cowpea yield in Western Kenya

Preliminary studies were conducted using four varieties of potted cowpea (Ex-Luanda, Katuli 107. Vita 1, TVx66-2H) to determine plant response to injury to foliar and reproductive structures. Several levels of leaf loss were simulated at two plant growth stages; flowers were excised manually for 10. 15 and 20 consecutive days post-flowering; and pods were removed at several levels, 7–10 days after flowering. Similar tests were carried out during the short rains of Mbita Point Field Station (MPFS) and on a farmer’s field at Kodiera, near Homa Bay, using two varieties—a local indeterminate dual purpose type (Ex-Luanda) and a determinate grain cultivar (TVu 1509). Defoliation significantly decreased plant weight and pod and grain production, but not branching and pod dimensions of potted plants. Flower and pod loss did not markedly lower plant weight, pod and seed production, and the effect on branching was negligible. The response of field plants was strongly influenced by crop variety and environment, notably agronomic practices and location. These results have implications for integrated pest management (IPM) which are explored in the context of increased grain legume production.

Occurrence and abundance of rice stem borers at Mbita Point in Western kenya

Surveys on the stem borer complex of rice were initiated at Mbita Point Field Station during 1980–1981. Stem borers collected and identified so far included Maliarpha separatella Rag; Diopsis thoracica West; Sesamia calamistis Hmps., and Chilo partellus Wlk. Among these four species, M. separatella was the most abundant and showed highest infestation during the reproductive and ripening phases of the rice crop. D. thoracica was found to cause greatest damage on the crop during the crop’s tillering phase. It is suggested that there may be differences in Maliarpha infestation due to rice varieties.