The temporal correlation and spatial synchrony in the stemborer and parasitoid system of Coast Kenya with climate effects

The spatial synchrony and the temporal auto-correlationship of the exotic stemborer Chilo partellus (Swinhoe) (Lepidoptera: Crambidae) and the indigenous Sesamia calamistis Hampson (Lepidoptera: Noctuidae) and Chilo orichalcociliellus (Strand) (Lepidoptera: Crambidae), and crosscorrelationship with their indigenous and introduced larval parasitoids Cotesia sesamiae (Cameron) and Cotesia flavipes Cameron (Hymenoptera: Braconidae) was studied using 3-year data collected in coastal Kenya. An autoregressive model was used to study the effect of climatic stochasticity or population density-dependent factors on stemborer populations. It appeared that rainfall did have a direct impact on stemborers in the south coast and an indirect one in the north coast. Spatial nonparametric correlation functions (SNCF) and cross-correlation functions (SNCCF) were applied for spatial synchrony analysis. The regional synchrony of Ch. partellus and S. calamistis decreased and that of Ch. orichalcociliellus increased after the introduction of Co. flavipes. The positive crosscorrelation coefficient between stemborers and parasitoids suggests a synchrony between the pest and its natural enemy.     

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.     

Close-Range Host Searching Behavior of the Stemborer Parasitoids <Emphasis Type="Italic">Cotesia sesamiae</Emphasis> and <Emphasis Type="Italic">Dentichasmias busseolae</Emphasis>: Influence of a Non-Host Plant <Emphasis Type="Italic">Melinis minutiflora</Emphasis>

Studies were conducted on the host searching behavior of the larval parasitoid Cotesia sesamiae (Cameron) (Hymenoptera: Braconidae) and the pupal parasitoid Dentichasmias busseolae Heinrich (Hymenoptera: Ichneumonidae), both of which attack lepidopteran (Crambidae, Noctuidae) cereal stemborers. The behavior of D. busseolae was observed in a diversified habitat that consisted of stemborer host plants (maize, Zea mays L. and sorghum, Sorghum bicolor (L). Moench (Poaceae)) and a non-host plant (molasses grass, Melinis minutiflora Beauv. (Poaceae)), while C. sesamiae was observed separately on host plants and molasses grass. In previous olfactometer studies, C. sesamiae was attracted to molasses grass volatiles while hboxD. busseolae was repelled. The aim of the present study was to investigate the influence of molasses grass on close-range foraging behavior of the parasitoids in an arena that included infested and uninfested host plants. Dentichasmias busseolae strongly discriminated between host and non-host plants, with female wasps spending most of the time on infested host plants and least time on molasses grass. Likewise, C. sesamiae spent more time on uninfested and infested host plants than it did on molasses grass in single choice bioassays. While on infested plants, the wasps spent more time foraging on the stem, the site of damage, than on other areas of the plant. Overall, the results indicate that presence of the non-host plant does not hinder close range foraging activities of either parasitoid.     

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.     

Increase in cereal stem borer populations through partial elimination of natural enemies

An insecticide exclusion method was used to evaluate the effect of parasitoids on level of infestation by the stem borers, Busseola fusca (Fuller) and Chilo partellus (Swinhoe), in grain sorghum. In field trials conducted at Brits and at Delmas, South Africa, a selective organophosphate insecticide, dimethoate, was applied twice weekly at each site to three subplots whereas three other identical subplots served as controls. Twelve plants were randomly selected from each subplot at weekly intervals and removed from the field. In the laboratory all plants were dissected to record borer infestation. In order to determine parasitism levels egg batches were kept in Petri dishes and all borer larvae and pupae were kept individually in vials until either parasitoids or moths emerged. At Brits ca. 97% of borers were C. partellus and 3% B. fusca, whereas at Delmas 37.5% were C. partellus and 62.5% B. fusca. The most abundant parasitoids of B. fusca were Cotesia sesamiae (Cameron) and Bracon sesamiae Cameron. The dominant parasitoids of C. partellus at both sites were C. sesamiae, Stenobracon spec., Dentichasmias busseolae Henrich and Pediobius furvus (Gahan). No egg parasitoids were found. At both sites, infestation levels in the sprayed plots were significantly higher than in the untreated plots. On the other hand, parasitism levels of borers in the unsprayed plots were significantly higher than in the treated plots. It was concluded that the higher infestation level of sorghum by stem borers in the sprayed plots was because of partial elimination of parasitoids and possibly other natural enemies by the pesticide.     

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.     

Host suitability of the New World stalkborer Diatraea considerata for three Old World Cotesia parasitoids

Biological control ofstalkboring Lepidoptera often has beensuccessful when the braconid parasitoids in thegenera Cotesia and Apanteles werethe natural enemies of choice. Constraints inusing these gregarious, koinobiont,endoparasitoids have included host suitability,especially as influenced by the host's immuneresponse. The suitability of a novel host, theNew World stalkborer Diatraeaconsiderata (Lepidoptera:Pyralidae), for parasitization by three OldWorld braconids, Cotesia chilonis, C. flavipes and C. sesamiae (Hymenoptera: Braconidae), wascompared to the suitability of another NewWorld novel host, Diatraea saccharalis. D. considerata was less suitable for allthree parasitoids than was D.saccharalis. The frequent occurrence ofparasitized D. considerata larvae thatdid not yield parasitoids, or pupate within anappropriate time interval, suggestedencapsulation of the parasitoid progeny, whichwas visible through the host cuticle. Giventhe suitability results, these threeparasitoids would not be appropriate candidatesfor use against D. considerata. Theresults also have important implications forthe narrow host range expressed by theseparasitoids.     

Occurrence and direct control potential of parasitoids and predators of the fall armyworm (Lepidoptera: Noctuidae) on maize in the subtropical lowlands of Mexico

Abstract 1 Native natural enemies have the potential to control fall armyworm Spodoptera frugiperda (Smith) in tropical maize grown in Mexico, where this insect pest causes severe economic losses to farmers. It has been proposed that enhancing herbivore‐induced volatile emissions in maize plants may help to increase the effectiveness of natural enemies, which use these volatiles to locate their prey. This will only be of immediate benefit to farmers if the activity of the natural enemies results in a direct reduction in herbivory. Here we report on field surveys for the most common natural enemies in a tropical maize‐growing region in Mexico and the potential effects of these enemies on herbivory by fall armyworm. 2 Caterpillars were collected in maize fields near Poza Rica in the state of Veracruz during January and February 1999, 2000 and 2001. Plants were either naturally infested by S. frugiperda, or artificially infested with laboratory‐reared larvae. Ten species of parasitoids emerged from the collected larvae and eight species of predators that are known to feed on larvae and eggs were observed on the plants. Campoletis sonorensis (Cameron) (Hymenoptera: Ichneumonidae) was the dominant parasitoid species, in 1999 and 2001. 3 Of the nine larval parasitoids collected, six (all solitary) are known to reduce herbivory, whereas one causes the host to eat more (for two species this is not known). This implies that enhancing the effectiveness of solitary endoparasitoids may benefit subsistence farmers in developing countries by immediately reducing herbivory. The overall benefit for the plant resulting from parasitoid activity also has important implications for the evolutionary role of parasitoids in contributing to selection pressures that shape indirect defences in plants.     

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.     

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.     

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.     

Species diversity of lepidopteran stem borer parasitoids in cultivated and natural habitats in Kenya

Field surveys were conducted during 2005 to 2007 to assess the species diversity of stem borer parasitoids in cultivated and natural habitats in four agroecological zones in Kenya. In total, 33 parasitoid species were recovered, of which 18 parasitized six stem borer species feeding on cereal crops, while 27 parasitized 21 stem borer species feeding on 19 wild host plant species. The most common parasitoids in cultivated habitats were Cotesia flavipes Cameron, Cotesia sesamiae (Cameron), Pediobius furvus Gahan and the tachinid Siphona sp., whereas in natural habitats, Siphona sp. was the most common. The majority of parasitoids were stenophagous species; only five species –Cotesia sp., Enicospilus ruscus Gauld and Mitchell, Pristomerus nr. bullis, Sturmiopsis parasitica (Curran) and Syzeuctus ruberrimus Benoit – were monophagous. In both cultivated and natural habitats, parasitoid species diversity was highest on the most dominant stem borers Busseola spp. and Chilo spp. On cereal crops, parasitoid diversity was highest on maize and among wild host plants, it was highest on Setaria spp. The ingress‐and‐sting attack method was the most common strategy used by parasitoids in both habitats. In all agroecological zones, parasitoid species diversity was significantly higher in natural than in cultivated habitats. Furthermore, the majority of parasitoid species were common to both cultivated and natural habitats. It was concluded that natural habitats surrounding cereal crops serve as refugia for sustaining the diversity of stem borer parasitoids from adjacent cereal fields.     

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.     

A review of sugarcane stem borers and their natural enemies in Asia and Indian Ocean Islands: an Australian perspective

This paper provides a review on lepidopteran stem borer pests of graminaceous crops in Asia and Indian Ocean Islands which have the potential to invade Australia. Information on the geographical distribution, host plants and potential of invading Australia is provided for 36 stem borer species. A literature review of all natural enemies of 18 key pest species is provided. A knowledge of possible biological control options is essential to determine which natural enemies are to be considered for introduction following an incursion. The Braconid, Cotesia flavipes Cameron (Hymenoptera: Braconidae), stands out as a promising candidate for introduction into Australia following a borer incursion. Studies are currently being conducted on a native Cotesia species in Australia, which may be able to parasitize larvae of exotic borers, therefore minimizing the need for other parasitoids introductions.     

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.     

Food web associations and effect of trophic resources and environmental factors on parasitoids expanding their host range into non‐native hosts

Trophic interactions and environmental conditions determine the structure of food webs and the host expansion of parasitoids into novel insect hosts. In this study, we investigate plant–insect–parasitoid food web interactions, specifically the effect of trophic resources and environmental factors on the presence of the parasitoids expanding their host range after the invasion of Chrysodeixis chalcites (Esper) (Lepidoptera: Noctuidae). We also consider potential candidates for biological control of this non‐native pest. A survey of larval stages of Plusiinae (Lepidoptera: Noctuidae) and their larval parasitoids was conducted in field and vegetable greenhouse crops in 2009 and 2010 in various locations of Essex and Chatham‐Kent counties in Ontario, Canada. Twenty‐one plant–host insect–host parasitoid associations were observed among Trichoplusia ni (Hübner) (Lepidoptera: Noctuidae), C. chalcites, and larval parasitoids in three trophic levels of interaction. Chrysodeixis chalcites, an old‐world species that had just arrived in the region, was the most common in our samples. The larval parasitoids Campoletis sonorensis (Cameron) (Hymenoptera: Ichneumonidae), Cotesia vanessae (Reinhard), Cotesia sp., Microplitis alaskensis (Ashmead), and Meteorus rubens (Nees) (all Hymenoptera: Braconidae) expanded their host range into C. chalcites changing the structure of the food web. Copidosoma floridanum (Ashmead) (Hymenoptera: Encyrtidae) was the most common parasitoid of T. ni that was not found in the invasive species. Plant species, host abundance, and agro‐ecosystem were the most common predictors for the presence of the parasitoids expanding their host range into C. chalcites. Our results indicate that C. sonorensis, C. vanessae, and C. floridanum should be evaluated for their potential use in biological control of C. chalcites and T. ni.     

Experimental analysis of the influence of pest management practice on the efficacy of an endemic arthropod natural enemy complex of the diamondback moth

Maximizing the contribution of endemic natural enemies to integrated pest management (IPM), programs requires a detailed knowledge of their interactions with the target pest. This experimental field study evaluated the impact of the endemic natural enemy complex of Plutella xylostella (L.) (Lepidoptera: Yponomeutidae) on pest populations in commercial cabbage crops in southeastern Queensland, Australia. Management data were used to score pest management practices at experimental sites on independent Brassica farms practicing a range of pest management strategies, and mechanical methods of natural enemy exclusion were used to assess the impact of natural enemies on introduced cohorts of P. xylostella at each site. Natural enemy impact was greatest at sites adopting IPM and least at sites practicing conventional pest management strategies. At IPM sites, the contribution of natural enemies to P. xylostella mortality permitted the cultivation of marketable crops with no yield loss but with a substantial reduction in insecticide inputs. Three species of larval parasitoids (Diadegma semiclausum Hellén [Hymenoptera: Ichneumonidae], Apanteles ippeus Nixon [Hymenoptera: Braconidae], and Oomyzus sokolowskii Kurdjumov [Hymenoptera: Eulophidae]) and one species of pupal parasitoid Diadromus collaris Gravenhorst (Hymenoptera: Ichneumonidae) attacked immature P. xylostella. The most abundant groups of predatory arthropods caught in pitfall traps were Araneae (Lycosidae) > Coleoptera (Carabidae, Coccinelidae, Staphylinidae) > Neuroptera (Chrysopidae) > Formicidae, whereas on crop foliage Araneae (Clubionidae, Oxyopidae) > Coleoptera (Coccinelidae) > Neuroptera (Chrysopidae) were most common. The abundance and diversity of natural enemies was greatest at sites that adopted IPM, correlating greater P. xylostella mortality at these sites. The efficacy of the natural enemy complex to pest mortality under different pest management regimes and appropriate strategies to optimize this important natural resource are discussed.     

Geographic variation in male courtship acoustics and genetic divergence of populations of the Cotesia flavipes species complex

Courtship behaviors of insect populations can vary across the range of a species. Populations exhibiting divergent courtship behavior may indicate genetic divergence or cryptic species. Courtship acoustic signals produced by male wing fanning and genetic structure (using amplified fragment length polymorphisms) were examined for seven allopatric populations of the Cotesia flavipes (Hymenoptera: Braconidae) species complex, using four C. sesamiae (Cameron) and three C. flavipes Cameron populations. Members of this species complex parasitize lepidopteran pests in gramineous crops including sugarcane, maize, and rice . Significant variation was detected in courtship acoustic signals and genetic structure among populations of both species. For C. sesamiae, courtship acoustic signals varied more between populations of two biotypes that were collected near an area of sympatry. The two biotypes of C. sesamiae were also genetically divergent. For C. flavipes, significant differences in acoustic signals and genetic structure occurred among allopatric populations; these differences support the recent designation of one population as a new species. Courtship acoustics play a role in reproductive isolation in this species complex, and are likely used in conjunction with chemical signals. Ecological factors such as host range and host plant use may also influence the divergence of both courtship acoustic signals and genetic structure among populations in the C. flavipes complex.     

Calyx fluid proteins of two Cotesia sesamiae (Cameron) (Hymenoptera: Braconidae) biotypes in Kenya: implications to biological control of the stem borer Busseola fusca (Fuller) (Lepidoptera: Noctuidae)

Cotesia sesamiae (Cameron) (Hymenoptera: Braconidae) is an indigenous larval endoparasitoid of Busseola fusca (Fuller) (Lepidoptera: Noctuidae) in sub-Saharan Africa. In Kenya, reports suggest that C. sesamiae occurs as two biotypes. Biotype avirulent to B. fusca gets encapsulated by haemocytes in this host and is unable to complete development. Biotype virulent to B. fusca is able to overcome immune defences. Factors present in the calyx fluid such as the PolyDNAviruses (PDV), venom and calyx fluid proteins have been implicated in the variation of C. sesamiae virulence against B. fusca. In the present study, calyx fluid proteins of the two C. sesamiae biotypes were compared using 2-D gel electrophoresis. More protein spots were observed in the virulent parasitoid calyx fluid, but some proteins were specifically observed in the avirulent parasitoid calyx fluid while others were observed in both. To study changes in proteins due to parasitism of B. fusca larvae by the two strains, SDS-PAGE gel were performed on fat body tissues and the haemolymph at three time points. Differences between the two strains were observed in both the fat body and haemolymph tissues. Parasitism-specific protein bands were detectable in fat body tissues of B. fusca larvae parasitized by the two C. sesamiae strains. These proteins were absent in unparasitized larvae. Implications for using C. sesamiae as a biocontrol agent of B. fusca in Africa are discussed.     

Role of volatiles emitted by host and non-host plants in the foraging behaviour of Dentichasmias busseolae, a pupal parasitoid of the spotted stemborer Chilo partellus

The role of volatiles from stemborer host and non‐host plants in the host‐finding process of Dentichasmias busseolae Heinrich (Hymenoptera: Ichneumonidae) a pupal parasitoid of Chilo partellus (Swinhoe) (Lepidoptera: Crambidae) was studied. The non‐host plant, molasses grass (Melinis minutiflora Beauv. (Poaceae)), is reported to produce some volatile compounds known to be attractive to some parasitoid species. The studies were conducted to explore the possibility of intercropping stemborer host plants with molasses grass in order to enhance the foraging activity of D. busseolae in such a diversified agro‐ecosystem. Olfactometric bioassays showed that volatiles from the host plants maize, Zea mays L., and sorghum, Sorghum bicolor (L.) (Poaceae), were attractive to the parasitoid. Infested host plants were the most attractive. Volatiles from molasses grass were repellent to the parasitoid. Further tests showed that volatiles from infested and uninfested host plants alone were preferred over those from infested and uninfested host plants combined with the non‐host plant, molasses grass. In dual choice tests, the parasitoid did not discriminate between volatiles from maize infested by either of the two herbivore species, C. partellus or Busseola fusca Fuller (Lepidoptera: Noctuidae). Volatiles from sorghum infested by C. partellus were preferred over those from C. partellus‐infested maize. The study showed that the pupal parasitoid D. busseolae uses plant volatiles during foraging, with those from the plant–herbivore complex being the most attractive. The fact that volatiles from molasses grass were deterrent to the parasitoid suggested that intercropping maize or sorghum with molasses grass was not likely to enhance the foraging behaviour of D. busseolae. Volatiles from the molasses grass may hinder D. busseolae's host location efficiency.