Effect of nitrogen fertilizer level on infestations of lepidopterous stemborers and yields of maize in Zanzibar

The effect of nitrogen levels of 0, 60, 120, and 250 kg/ha and insecticide treatment (Furadan) on population densities and parasitism of lepidopteran stemborers, and maize yields were studied in Zanzibar during 2004/05. Chilo partellus (Swinhoe) (Lepidoptera: Crambidae) dominated by 3-fold over Sesamia calamistis Hampson (Lepidoptera: Noctuidae) and 42 fold over Chilo orichalcociliellus Strand (Lepidoptera: Crambidae). Stemborer density per plant and parasitism by Cotesia flavipes (Cameron) (Hymenoptera: Braconidae) increased with nitrogen application level. Percentage of bored internodes per plant caused by stemborer decreased with N levels during the short rainy season. Pesticide application reduced densities of all stemborer species during the short rainy season, when infestations were high. Maize yield increased 2 to 8 times with N level, compared to the zero treatment, but the effect was less pronounced in the protected plots.     

Assessment of the impact of natural enemies on stemborer infestations and yield loss in maize using selected insecticides in Mozambique

The effect of natural enemies on stemborer infestations and maize grain yields was estimated using an insecticide exclusion method. Field experiments were conducted at low, mid and high elevation zones, which vary in the stemborer species composition. Dimethoate was applied to exclude natural enemies and Cypermethrin to suppress stemborers, while other plots served as control. At all study sites more stemborer larvae and pupae were collected when natural enemies were excluded. Parasitism as well as maize grain weight in the unprotected plots were significantly higher than in the exclusion plots. Yield losses increased by 28.9 % in unprotected to 43.3 % in exclusion plots. The most abundant parasitoids of Chilo partellus (Swinhoe) (Lepidoptera: Crambidae) were Cotesia sesamiae (Cameron), Cotesia flavipes Cameron (Hymenoptera: Braconidae) and Dentichasmias busseolae Heinrich (Hymenoptera: Ichneumonidae). While for Busseola fusca (Fuller) (Lepidoptera: Noctuidae) they were C. sesamiae, Sturmiopsis parasitica (Curran) (Diptera: Tachinidae) and Porcerochasmias nigromaculatus Heinrich (Hymenoptera: Ichneumonidae). It was concluded that exclusion of natural enemies caused an increase in stemborer populations, thus, the parasitoids play an important role in suppressing stemborer infestations and increase maize yield.     

Single-step PCR differentiation of Cotesia sesamiae (Cameron) and Cotesia flavipes Cameron (Hymenoptera: Braconidae) using polydnavirus markers

Cotesia sesamiae (Cameron) and Cotesia flavipes Cameron (Hymenoptera: Braconidae) are the main larval parasitoids of cereal stemborers in sub-Saharan Africa. Cotesia sesamiae is endemic to eastern and southern Africa, while C. flavipes was introduced into the region for biological control against the exotic lepidopteran Chilo partellus (Swinhoe) (Lepidoptera: Crambidae). The two are sibling parasitoids, difficult to distinguish morphologically. The introduced insect could potentially lead its African biotype to extinction because of their similar ecological niche. In order to distinguish the two species, multiplex primer-specific and PCR-RFLP tests were developed. Rapid identification of the two species was possible using primer-specific tests on DNA extracts as well as on pieces of tissue in a single PCR step followed by gel electrophoresis. The CRV1 gene of the polydnavirus, a symbiont to the wasps, was used as the marker. The results show that the morphological identifications, validated by molecular tests, are accurate in 93% of cases.     

Larval dispersal of the invasive fall armyworm,Spodoptera frugiperda,the exotic stemborer Chilo partellus,and indigenous maize stemborers in Africa

Larval dispersal either through ballooning or crawling results in a redistribution of the insect population and infestations within and between plants. In addition, invasive species, such as the fall armyworm (FAW), Spodoptera frugiperda (JE Smith) (Lepidoptera: Noctuidae), and the exotic stemborer Chilo partellus (Swinhoe) (Lepidoptera: Crambidae), may displace indigenous stemborers on maize in Africa. To test whether larval dispersal activity may play a role in the displacement of indigenous stemborers, larval dispersal was compared between FAW, C. partellus, and the indigenous species Busseola fusca (Fuller) and Sesamia calamistis (Hampson) (both Lepidoptera: Noctuidae). Twenty potted maize plants were infested with one batch of eggs either from stemborers (B. fusca, S. calamistis, or C. partellus) or from FAW and monitored in the greenhouse for ballooning activities. After egg hatching, both ballooning and non-ballooning larvae were identified according to species and counted. FAW neonate larvae had greater potential for ballooning off than stemborers, irrespective of species. For each species, more females dispersed than males, and their survival rate was higher than that of non-ballooning larvae. In addition, plant-to-plant larval movements were studied using 6.25-m² plots of caged maize in a completely randomized design with five replicates. FAW was found to have wider dispersal and plant damage potential than any of the stemborer species. In conclusion, in contrast to C. partellus, the invasive characteristic of FAW can be explained, in part, by its higher larval dispersal activity compared to stemborers. This difference in larval dispersal might also be considered in sampling plans for monitoring pest density in the field.     

Host Suitability of Four Cereal Stem Borers (Lepidoptera: Crambidae, Noctuidae) for Different Geographic Populations of Cotesia sesamiae (Cameron) (Hymenoptera: Braconidae) in Kenya

This study focused on the suitability of four species of cereal stem borers for the development of five geographic populations of Cotesia sesamiae (Cameron). C. sesamiae, an indigenous larval parasitoid of gramineous stem borers, is widespread in Africa. Four stem borers, Chilo partellus (Swinhoe), Chilo orichalcociliellus Strand (Lepidoptera: Crambidae), Busseola fusca Fuller, and Sesamia calamistis Hampson (Lepidoptera: Noctuidae), were offered to C. sesamiae for oviposition. Parasitoid individuals originated from five locations in Kenya. Biological parameters such as developmental time, percentage parasitism, progeny production, mortality of immature parasitoids, and proportion of female progeny were compared across host species. The two populations from western Kenya developed well on B. fusca. However, populations from the coast and the Eastern Province could not successfully parasitize B. fusca. With the exception of B. fusca, the percentage of hosts successfully parasitized by the different C. sesamiae populations was not different. The size of the host appeared to be an important factor influencing the development and reproductive potential of the parasitoid. We conclude that the different parasitoid populations were adapted to location-specific characteristics. Parasitoid–host compatibility must be evaluated before release for better establishment and colonization.     

Foraging behavior and life history of the stemborer parasitoidCotesia flavipes (hymenoptera: Braconidae)

The gregarious parasitoidCotesia flavipes (Hymenoptera: Braconidae) attacks larvae of pyralid and noctuid stemborers by entering the stemborer tunnel. The short-range foraging behavior of femaleC. flavipes was studied on stemborerinfested plants, in patches with host-related products and in artificial transparent tunnels. In addition, the longevity under specific conditions and the potential and realized fecundity of femaleC. flavipes were determined. Larval frass, caterpillar regurgitate, and holes in the stem are used in host location byC. flavipes. The response to host products byC. flavipes seems not to be host species specific. FemaleC. flavipes respond to frass from four stemborer species and one leaf feeder. No differences are found in the behavior ofC. flavipes on maize plants infested with the suitable host,Chilo partellus (Lepidoptera: Pyralidae), or the unsuitable host,Busseola fusca (Lepidoptera: Noctuidae). Attacking a stemborer larva inside the stem is risky for the parasitoid. The mortality rate of the parasitoids inside the stem is high: 30–40% of the parasitoids are killed by the spitting and biting stemborer larva.C. flavipes is relatively shortlived: without food the parasitoids die within 2 days; with food and under high-humidity conditions they die within 5–6 days.C. flavipes is proovigenic and has about 150 eggs available for oviposition. A relatively large proportion of the available egg load (20–25%) is allocated to each host, so femaleC. flavipes are egg depleted after parasitizing only five or six hosts.     

Superior basal and plastic thermal responses to environmental heterogeneity in invasive exotic stemborer Chilo partellus Swinhoe over indigenous Busseola fusca (Fuller) and Sesamia calamistis Hampson

Lepidopteran stemborers are the most destructive insect pests of cereal crops in sub‐Saharan Africa. In nature, these insects are often exposed to multiple environmental stressors, resulting in potent impact on their thermal tolerance. Such environmental stressors may influence their activity, survival, abundance and biogeography. In the present study, we investigate the effects of acclimation to temperature, starvation and desiccation on thermal tolerance, measured as critical thermal limits [critical thermal minima (CT_min) and maxima (CT_max)] on laboratory‐reared economic pest species Chilo partellus Swinhoe (Lepidoptera: Crambidae), Busseola fusca (Fuller) and Sesamia calamistis Hampson (Lepidoptera: Noctuidae) using established protocols. Low temperature acclimation results in improved CT_min for B. fusca and C. partellus, whereas high temperature acclimation enhances the same trait for B. fusca and S. calamistis. Similarly, high temperature and starvation pretreatment improve CT_max for C. partellus relative to S. calamistis and B. fusca. In addition, starvation and desiccation pretreatments improve CT_min for all stemborer species. Furthermore, rapid cold‐hardening (RCH) enhancs CT_min for B. fusca and C. partellus, whereas rapid heat‐hardening (RHH) improves the same trait for C. partellus. However, RCH and RHH impair CT_max for all stemborer species. These findings show differential thermal tolerances after exposure to heterogeneous environmental stress habitats. Chilo partellus, of exotic origin, shows a higher magnitude of basal thermal tolerance plasticity relative to the indigenous African species S. calamistis and B. fusca. This indicates that C. partellus may have a fitness and survival advantage under climate‐induced heterogeneous environments, and also have a greater chance for geographical range expansion and invasion success compared with the indigenous B. fusca and S. calamistis.     

Host–parasitoid community model and its potential application in biological control of cereal stemborers in Kenya

A two-host–two-parasitoid model was constructed to assess the effects of the introduced larval parasitoid, the braconid Cotesia flavipes, on its primary target host, the invasive crambid Chilo partellus, and on secondary host species, in inter-specific competition with Cotesia sesamiae, the main native parasitoid species of stemborers in Kenya. The model assumed that: (1) there was no host discrimination by either parasitoid species; (2) Cotesia flavipes was the superior competitor that out-competed Cotesia sesamiae when the host was suitable; and (3) Cotesia flavipes could only develop in an unsuitable host if it had been previously parasitized by Cotesia sesamiae. Model parameters were estimated from surveys conducted in Kenya and from laboratory experiments. Different scenarios of host and parasitoid species composition and host suitability occurring in the different ecological zones in Kenya were analyzed. Results indicated that: (1) the coexistence of stemborer host populations are determined by their population growth rates, the degree of aggregation of the parasitoids and their searching efficiency; (2) in the regions where both the invasive and the predominant native host species were suitable to either parasitoid species, stemborer densities would be reduced to and controlled at low densities, and Cotesia flavipes would become the dominant parasitoid species. However, the extinction or predominance of the native stemborer species depends on the ratio of the growth rates of exotic and native stemborers and their relative searching efficiencies; and (3) if the native host species was acceptable but unsuitable to Cotesia flavipes, the parasite would not become established.     

Dominance of spotted stemborer Chilo partellus Swinhoe (Lepidoptera: Crambidae) over indigenous stemborer species in Africa's changing climates: ecological and thermal biology perspectives

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

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.     

Importance of contact chemical cues in host recognition and acceptance by the braconid larval endoparasitoids Cotesia sesamiae and Cotesia flavipes

The ability of the congeneric braconid parasitoids Cotesia sesamiae (Cameron) and Cotesia flavipes Cameron to discriminate between stemborer larval cues upon contact was studied using their natural hosts, namely the noctuid Busseola fusca (Fuller) and the crambid Chilo partellus (Swinhoe), respectively, and the pyralid non-host Eldana saccharina (Walker). When the natural host larvae were washed in distilled water, parasitoid behavior was similar to that displayed when in contact with E. saccharina, characterized by the absence of ovipositor insertion. When washed host or non-host larvae were bathed with water extracts of their natural host, the parasitoids showed a significant increase in ovipositor insertions. However, the water extracts of host-larvae deposited on cotton wool balls did not induce ovipositor insertion in either C. sesamiae or C. flavipes. Nevertheless, the extracts enabled the parasitoids to discriminate between natural and non-hosts as indicated by the intensive antennating of the former. For both parasitoids, frass was found to be important in short-range host recognition as indicated by differences in the time spent on antennating between frass sources. In addition, the regurgitants of B. fusca and C. partellus induced ovipositor insertion in C. flavipes only. These results indicated that C. sesamiae and C. flavipes used different chemical cues for acceptation and oviposition in a stemborer larva, and that B. fusca and C. partellus shared the same chemical cues to induce oviposition in C. flavipes.     

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.     

Geographic differences in host acceptance and suitability of two Cotesia sesamiae populations in Zimbabwe

Three lepidopteran stemborers, Busseola fusca Fuller (Noctuidae), Sesamia calamistis Hampson (Noctuidae), and Chilo partellus (Swinhoe) (Crambidae), were evaluated for their acceptability for oviposition and suitability for development by two populations of the larval endoparasitoid Cotesia sesamiae (Cameron) (Hymenoptera: Braconidae) occurring in the highveld (>1200 m) and lowveld (<600 m) regions of Zimbabwe. Mating studies were also conducted to determine reproductive compatibility between the populations. Both C. sesamiae populations preferred the noctuids to C. partellus for oviposition, possibly reflecting differences in evolutionary history. Although B. fusca was partially suitable for development of lowveld C. sesamiae, all three hosts were suitable for development of the highveld population. Crosses between highveld and lowveld C. sesamiae were compatible, and were generally not different from the intra-population crosses in developmental time, % adult emergence and sex ratio. However, broods were much larger when highveld males were used in the mating combinations. We conclude that although there is host overlap and probably a considerable degree of outbreeding between the two C. sesamiae populations, there are still significant genetic differences between them. Within Zimbabwe, it is unlikely that the deliberate introduction of either population outside its region of occurrence will give meaningful stemborer control.     

Distribution and relative importance of cereal stem borers and their natural enemies in the semi-arid and cool-wet ecozones of the Amhara State of Ethiopia

The distribution and relative importance of lepidopteran and coleopteran stem borers and their natural enemies on maize and sorghum were studied in cereal growing zones of the Amhara State of Ethiopia from 2003 to 2004. Sorghum is the major crop in semi-arid eastern and maize in the cool-wet western zones of the Amhara state. Four administrative zones, 10 districts and 88 localities in the semi-arid ecozone (SAE) and four zones, 19 districts and 71 localities in the cool-wet ecozone (CWE) were chosen for the study. In SAE, the species composition was 91% Chilo partellus (Swinhoe) (Lepidoptera: Crambidae), 8% Busseola fusca (Fuller) (Lepidoptera: Noctuidae) and 1% Sesamia calamistis Hampson (Lepidoptera: Noctuidae). In the CWE, maize and sorghum are grown in different ecozones and thus B. fusca was the dominant species on sorghum, whereas 61% B. fusca and 39% S. calamistis were recorded on maize. Borer density generally increased with crop growth stage. C. partellus parasitism by C. flavipes Cameron (Hymenoptera: Braconidae), which occurred only in SAE, varied among districts ranging from 5% to 39%. In the CWE, unidentified nematodes parasitized medium-sized B. fusca larvae during the wet months. Population of native parasitoids was very low. The coleopteran borer, Rhynchaenus niger (Horn) (Coleoptera: Rhynchophoridae), attacked sorghum plants in both regions. Sorghum yields were negatively related to plant damage variables and positively to larval parasitism and plant growth variables. On maize, plant damage was too low to affect yields. Taylor’s power law indicated aggregated distribution for C. partellus and B. fusca larvae and pupae combined.     

Acceptance and suitability of four lepidopteran stemborers for the development of the pupal parasitoid Xanthopimpla stemmator (Hymenoptera: Ichneumonidae)

Xanthopimpla stemmator (Thunberg), a solitary endoparasitoid of lepidopteran stemborer pupae, was recently imported into East Africa as a candidate biological control agent of gramineous stemborers. Suitability of Busseola fusca Fuller, Chilo partellus (Swinhoe), Eldana saccharina (Walker) and Sesamia calamistis Hampson, for the development of X. stemmator was studied in the laboratory. One- to 6-day-old laboratory reared pupae of the four stemborer species were exposed to naïve X. stemmator females. All host pupae and ages were acceptable for oviposition. The parasitoids inflicted multiple probe wounds on 67.8% of pupae exposed. B. fusca, C. partellus and S. calamistis were equally suitable with 56.4, 59.4 and 52.3%, respectively, of probed pupae leading to emergence of adult parasitoids. E. saccharina was less suitable with only 22.6% of probed pupae producing parasitoids. Emergence of parasitoids did not differ significantly across the six pupal ages for B. fusca and S. calamistis, but varied for C. partellus and E. saccharina. No parasitoids emerged from 6-day-old E. saccharina pupae. Realized fecundity of females reared on the four stemborer pupae showed that fewer progeny were produced by females emerging from E. saccharina than females reared on the other three stemborer species. Eldana saccharina may be a poor host for X. stemmator in Kenya, but this parasitoid is a potential candidate for biological control of B. fusca, C. partellus and S. calamistis.     

Effect of Bt corn leaf suspension on food consumption by Chilo partellus and life history parameters of its parasitoid Cotesia flavipes under laboratory conditions

Laboratory scale experiments were conducted in order to assess the potential effect of Bacillus thuringiensis‐corn leaf material on the parasitized herbivore Chilo partellus Swinhoe (Lepidoptera: Crambidae) and on its parasitoid Cotesia flavipes (Cameron) (Hymenoptera: Braconidae). Food consumption and relative consumption rate of parasitized hosts exposed to Bt‐corn leaf‐material were strongly reduced compared to the control. The number of hosts allowing parasitoid larvae to complete their development was also reduced in the Bt group. Moreover, the fresh weight of parasitoid pupae and the dry weight of parasitoid adults was lower than in the control. Only in the Bt group, were strong negative correlations found between food intake by the host, and the number of parasitoid cocoons. Strong positive correlations were also only found in the Bt group, between food intake and parasitoid development time. As effects of Bt on the oviposition behaviour of C. flavipes could be excluded, differences between the Bt group and the control could only be due to the effect of Bt toxin on the parasitoid larva developing inside the host. Whenever food consumption can be measured, the methods used in this study are proposed as a model for future risk assessments on different types of insect‐resistant transgenic plants, herbivores, parasitoids, and predators.     

Diversity and distribution of lepidopteran stemborer species and their host plants in Botswana

Lepidopteran stemborers are amongst the most important insect pests of maize, sorghum and sugarcane in sub-Saharan Africa. With the exception of Chilo partellus (Swinhoe), which was accidentally introduced into Africa, the other stemborer pests are indigenous to the continent and have co-evolved with native grasses and sedges. In addition to pest species, wild habitats harbour diverse non-economic stemborer species, some of which are new to science. However, the diversity and distribution of both non-economic and pest species of stemborer are currently mostly unknown in Botswana. Accordingly, country-wide surveys were conducted during 2014/15 and 2015/16 austral summer to determine species diversity and distribution in cultivated and wild host plants of stemborers in Botswana. A total of 1597 stemborer larvae and 228 pupae were collected, constituting 63.1 and 36.9 larvae and 84.8 and 15.2% pupae from cultivated versus wild habitats, respectively. In addition to C. partellus, Sesamia calamistis Hampson and Eldana saccharina Walker which were previously reported, 12 more stemborer species were recorded for the first time in Botswana, including nine undescribed species. These species were from the Sciomesa, Sesamia and Conicofrontia genera and Tortricidae and Pyralidae families. Fourteen wild host and two cultivated host plant species of stemborers were recorded. Chilo partellus was most abundant (89.5%) in cultivated habitats whilst E. saccharina (33.6%) was most abundant in wild habitats. Stemborer species diversity was higher in wild habitats than cultivated. Current results highlight the significance of wild, especially wetland habitats for ecological functions and conservation of lepidopteran stemborer biodiversity.     

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

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.     

Olfactory responses of Cotesia flavipes (Hymenoptera: Braconidae) to target and non-target Lepidoptera and their host plants

The attraction of Cotesia flavipes Cameron to volatiles from a range of non-target lepidopteran larvae and their host plants (grasses and trees) or food substrate (honeycomb) was evaluated using a Y-tube olfactometer. The non-target host larvae used in the study included Galleria mellonella (L.), Charaxes cithaeron Felder, Bombyx mori L., and Eldana saccharina Walker. The target insects, Chilo partellus (Swinhoe) and Chilo orichalcociliellus (Strand), were used as controls. Host plants included Afzelia quanzensis Welw., Morus alba L., Cyperus papyrus L., Pennisetum purpureum Schumach, and Zea mays L. The response of C. flavipes to volatiles from the non-target larvae and their food was variable. Attraction to uninfested maize was not significantly different from uninfested plants of non-target hosts or honeycomb. Only maize and honeycomb were preferred over clean air. C. partellus infested maize plants were significantly more attractive than M. alba, A. quanzensis, and honeycomb infested with their herbivores. Infested maize and C. papyrus were more attractive than uninfested ones. When odors from naked larvae were tested, C. flavipes preferred odors from C. partellus larvae over those of E. saccharina and C. cithaeron and larvae of C. partellus and G. mellonella were preferred to clean air. The implications of these findings for biological control and its effect on non-target organisms are discussed.     

Dispersal of the exotic parasitoid Cotesia flavipes in a new ecosystem

A study on the dispersal of the exotic larval endoparasitoid, Cotesia flavipes Cameron (Hymenoptera: Braconidae), was conducted in a maize field in the northern Kilifi District in the coastal area of Kenya. Because C. flavipes did not previously occur in the release area, it was possible to use a unique indirect method to estimate dispersal by examining the distribution of parasitised hosts. Parasitoids released in the centre of the field moved as far as 64 meters during their life span, and dispersal was dependent on wind direction. The level of parasitism was influenced by the location of hosts in plants. The majority of parasitised stemborers (88.4%) were found inside the plant (stems and tassel stems), where 74.3% of the suitable hosts were found, which indicates that female parasitoids were not searching randomly for hosts. Aggregation of parasitoids in response to plants with different host densities was not detected. Implications of the release of C. flavipes on stemborers population in the agroecosystem of East Africa are discussed.