Multiple Parasitism by Cotesia sesamiae and Cotesia flavipes (Hymenoptera: Braconidae) on Busseola fusca (Lepidoptera: Noctuidae)

Busseola fusca (Fuller) is one of the most important pest of cereals in sub-Saharan Africa. Cotesia sesamiae (Cameron) is the predominant parasitoid attacking B. fusca larvae in many parts of Africa. An exotic parasitoid, Cotesia flavipes Cameron, was introduced into Kenya in 1993 for the control of Chilo partellus (Swinhoe). Laboratory studies indicated that although C. flavipes would search for, and attack B. fusca , it was not able to complete its development in this host. The aim of the present study was to investigate the outcome of multiple parasitism of B. fusca by the two Cotesia species. The study showed that when both parasitoid species stung a B. fusca larva at the same time, both parasitoids emerged from more than half of the host larvae, C. flavipes alone emerged from 17%, and C. sesamiae alone emerged from 9%. When the larvae were parasitized by C. sesamiae first, and then 2 h later by C. flavipes , and vice versa, most of the progeny were C. flavipes . However, when B. fusca larvae were stung by C. sesamiae three days before oviposition by C. flavipes , significantly more C. sesamiae emerged from the larvae. When C. flavipes oviposited first, no larvae produced C. flavipes only. The interaction of parasitoids and the host immune system, and the implications of these results for the biological control of stem borers in East Africa are discussed.     

Resource allocation and bionomics of indigenous and exotic Cotesia (Hymenoptera: Braconidae) species reared on Sesamia calamistis

The braconid larval parasitoids Cotesia chilonis (Matsumura), C. flavipes Cameron and a strain of Cotesia sesamiae (Cameron) from coastal Kenya, reared at the International Centre of Insect Ecology and Physiology, were introduced at the International Institute of Tropical Agriculture in the Republic of Benin for suitability testing on West African stemborers prior to release. C. chilonis was originally collected in Japan while C. flavipes was imported into Kenya from Pakistan. The host species used was the noctuid Sesamia calamistis (Hampson), the most important noctuid maize pest in the region. All three Cotesia species attacked and successfully developed in 2nd to 6th larval instar of S. calamistis but parasitoid-induced mortality was highest on second instars. On most instars, C. sesamiae and C. flavipes produced larger broods than C. chilonis. Larvae parasitized by C. sesamiae developed to the 6th instar and attained an average larval weight of 353 mg, while larvae parasitized by C. chilonis only molted to the 4th instar and attained a maximum weight of 107 mg. The lower developmental threshold estimated from the non-linear regression of temperature on developmental rate was 15.9, 15.9 and 14.9 degrees C for C. chilonis, C. sesamiae and C. flavipes, respectively, while the maximum temperature was 34.2, 35.2 and 33.8 degrees C, respectively. A maximum of four ovipositions were observed per female during a life span ranging from 1.3 days for C. chilonis and C. flavipes to 1.6 days for C. sesamiae. The largest adult progeny, intrinsic rate of increase and net reproductive rates were recorded at 28 degrees C for all species. However, across temperatures, C. flavipes yielded the highest number of offspring, followed by C. sesamiae and C. chilonis. The sex ratios did not vary significantly with species and temperature. Thus, the reproductive potentials of C. sesamiae and C. flavipes were greater than that of C. chilonis.     

Comparative development, longevity and population growth of exotic and native parasitoids of lepidopteran cereal stemborers in Kenya

Studies on the effect of temperature on the development, longevity and population growth of Cotesia flavipes Cameron and Cotesia sesamiae (Cameron) indicated that the development of both Cotesia spp. from oviposition to cocoon formation and adult emergence was inversely related to temperature. The longevity of the parasitoids was also inversely related to temperature. Both parasitoids lived longer when moisture and food (agar + honey/water) were provided. The mean number of females and total adult progeny produced by C. flavipes on two host species were, in most cases, higher than C. sesamiae. The intrinsic rate of natural increase of C. flavipes was higher than that of C. sesamiae.     

Comparative Biology of Cotesia chilonis Hymenoptera: Braconidae on Selected African Gramineous Stemborers

Observations were made on the development, mortality and fecundity of the gregarious endoparasitoid, Cotesia chilonis Matsumura , when reared on four African stemborers, Chilo partellus Swinhoe , C. orichalcociliellus Strand, Sesamia calamistis Hampson and Busseola fusca Fuller . C. chilonsis accepted the four stemborers for oviposition, but parasitoid eggs were encapsulated in B. fusca. The percentage of C. partellus, C. orichalcociliellus and S. calamistis successfully parasitized was not different, and ranged from 65.4 to 73.4 . The mortality of parasitoid larvae was higher and immature development took longer in C. orichalcociliellus compared with S. calamistis or C. partellus. The numbers of ovarian eggs in adult C. chilonis females reared from C. partellus, C. orichalcociliellus and S. calamistis were 125.3, 79.5 and 120.6 respectively.     

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.     

Species richness and parasitism in an assemblage of parasitoids attacking maize stem borers in coastal Kenya

Abstract. 1. Parasitoids were reared from four species of lepidopteran stem borer collected in maize in southern coastal Kenya from 1992 to 1999. The stem borers included three native species, Sesamia calamistis Hampson, Busseola fusca Fuller, and Chilo orichalcociliellus (Strand), and one exotic borer, Chilo partellus (Swinhoe). A total of 174 663 caterpillars was collected, of which 12 645 were parasitised.
2. Twenty-six primary parasitoid species were reared from the exotic borer, C. partellus , indicating a rapid accumulation of native parasitoids on the alien borer.
3. The three most abundant parasitoids were the larval parasitoids Cotesia sesamiae Cameron, Cotesia flavipes (Cameron), and the pupal parasitoid Pediobius furvus Gahan. The pupal parasitoid Dentichasmias busseolae Heinrich and the larval parasitoid Goniozus indicus Ashmead were also common. All used an ingress-and-sting method of attack.
4. Cotesia flavipes , introduced into Kenya in 1993, was found in all seasons from 1997 onwards, and has become the most abundant stem borer larval parasitoid in the area. A native congener, Cotesia sesamiae , appeared in all seasons from 1992 to 1999. Together, these two parasitoids accounted for 83.3% of the parasitised borers.
5. Thirty parasitoid species were recovered in Kilifi district, 27 in Kwale, and 15 in Taita Taveta. Parasitism was much greater in Taita Taveta district than in Kilifi or Kwale districts.     

Intrinsic competition between two oligophagous parasitoids, Sturmiopsis parasitica and Cotesia sesamiae, attacking the same life stages of lepidopteran cereal stemborers

Host acceptability and suitability of four cereal stemborers (Lepidoptera) commonly occurring in eastern Africa, Sesamia calamistis Hampson, Busseola fusca (Fuller) (both Noctuidae), Chilo partellus Swinhoe (Crambidae), and Eldana saccharina Walker (Pyralidae), for a West African strain of Sturmiopsis parasitica (Curran) (Diptera: Tachinidae) were assessed. In addition, the outcome of multi-parasitism was studied using a local strain of the endoparasitic Cotesia sesamiae Cameron (Hymenoptera: Braconidae) as the competing parasitoid. Various parasitism sequences and time intervals between parasitism were chosen. Parasitism increased linearly with the number of planidia used per larvae and was 80% with eight planidia. All species were accepted for larviposition, but suitability varied greatly; parasitism was 75.2, 37.9, 34.8, and 23.8% with S. calamistis , B. fusca , E. saccharina , and Ch. partellus , respectively. Sturmiopsis parasitica outcompeted Co. sesamiae irrespective of the time interval between parasitism, and whether it was the first or second species to parasitize. This was mainly due to a longer egg-to-cocoon development time and a high cocoon-to-adult mortality in Co. sesamiae . The implications of these results for expanding the geographic range of the West African strain of the tachinid in Africa are discussed.     

Life history traits and foraging behaviour of Cotesia nonagriae (Olliff) (Hymenoptera: Braconidae), a newly recognised member of the Cotesia flavipes complex of stemborer parasitoids

Cotesia nonagriae (Olliff) from Australia, a parasitoid of the incidental native pest of sugarcane, Bathytricha truncata (Walker) (Lepidoptera: Noctuidae), was previously thought to be a synonym of Cotesia flavipes Cameron. However, recent studies using DNA sequences, morphology and preliminary biological information show that this parasitoid is clearly a different species than C. flavipes and other members of the species complex. Here we further examine differences in the biology of these species by undertaking a detailed study of the life history traits of C. nonagriae , including adult longevity and the potential and realised fecundity of females. In addition, the influence of learning on microhabitat location and foraging behaviour were investigated. Duration of the larval stages and adult longevity of C. nonagriae were longer than previously recorded for other members of the species complex. The potential fecundity of females was similar to C. flavipes (∼200 eggs); however, C. nonagriae oviposited a average of over 100 eggs into each host, almost three times more than for other species in the C. flavipes complex (30–40). The propensity of C. nonagriae to allocate a large number of eggs to each host may be an evolutionary strategy due to the high mortality rate (50–57%) of ovipositing adult wasps. During microhabitat location, both naïve and experienced females demonstrated a strong response towards the plant host complex, with experienced wasps benefiting by having a more rapid response time to host-induced volatiles and cues.     

Establishment of Cotesia flavipes (Hymenoptera: Braconidae) in sugarcane fields of Ethiopia and origin of founding population

Cotesia flavipes (Cameron) (Hymenoptera: Braconidae) is used as a classical biological control agent against Chilo partellus (Swinhoe) (Lepidoptera: Crambidae), a serious exotic pest of cereal crops in eastern and southern Africa. This parasitoid has been introduced into several African countries for the control of C. partellus in maize, Zea mays L., and sorghum, Sorghum bicolor (L.), but it has never been released in Ethiopia. It is hypothesized that it spread into Ethiopia from populations released in Kenya and Somalia to become the predominant parasitoid of C. partellus in maize and sorghum fields of the country. In recent surveys conducted in Ethiopia, C. flavipes was recovered from C. partellus in sugarcane, Saccharum L. spp. hybrids, at a site >2,000 km from the nearest known release sites in Kenya and Somalia. These findings question published hypotheses that estimate the dispersal rate of C. flavipes to be 60 km per year in Africa, and they suggest that since its release in Africa this parasitoid has developed strains adapted to searching particular host plants infested by particular stem borers. The anomalies between our results and previous reports evoked the hypothesis that C. flavipes in Ethiopian sugarcane might be a different strain. To test this hypothesis, we compared partial COI gene sequences of C. flavipes collected from sugarcane in Ethiopia and those of specimens from other African countries to determine the origin of the Ethiopian population. In addition, COI sequences were obtained for C. flavipes from other continents. The C. flavipes population established in Ethiopian sugarcane is most closely related to the populations released against C. partellus in maize in other parts of Africa, which were derived from the original population imported from Pakistan. The dispersal rate of the parasitoid was estimated to be >200 km per year.     

Superparasitism in Cotesia glomerata: response of hosts and consequences for parasitoids

Abstract.  1. Superparasitism occurs in Cotesia glomerata (Hymenoptera: Braconidae), a gregarious endoparasitoid of Pieris spp. (Lepidoptera: Pieridae). The response of P. brassicae larvae to superparasitism and the consequences for the parasitoid were examined in order to elucidate the ecological significance of this behaviour.
2. Field surveys of a Swiss population revealed that C. glomerata brood sizes from P. brassicae larvae ranged from three to 158, and both the female ratio and the body weight of emergent wasps correlated negatively with brood size. In the laboratory, single oviposition on P. brassicae larvae did not produce any brood size larger than 62, but brood size increased with superparasitism.
3. Laboratory experiments demonstrated that both naive and experienced female wasps were willing to attack hosts that had been newly parasitised by themselves or conspecifics. Superparasitism reduced survivorship but increased food consumption and weight growth in P. brassicae larvae. Superparasitism lengthened parasitoid development and prolonged the feeding period of host larvae.
4. Despite a trade-off between maximising brood size and optimising the fitness of individual offspring, two or three ovipositions on P. brassicae larvae resulted in a greater dry female mass than did a single oviposition on the host. Thus, superparasitism might be of adaptive significance under certain circumstances, especially when host density is low and unparasitised hosts are rare in a habitat.     

Feasibility of using an alternative larval host and host plants to establish Cotesia flavipes (Hymenoptera: Braconidae) in the temperate Louisiana sugarcane ecosystem

Attempts to establish Cotesia flavipes Cameron (Hymenoptera: Braconidae) in Louisiana sugarcane fields to control the sugarcane borer, Diatraea saccharalis (F.) (Lepidoptera: Crambidae) have been unsuccessful. Experiments were conducted to investigate the feasibility of using an alternative larval host and host plants to overcome barriers preventing establishment. In addition, we evaluated C. flavipes' ability to search for D. saccharalis in sugarcane without above-ground internodes. Diatraea evanescens Dyar (Lepidoptera: Crambidae) was investigated as an alternative host for C. flavipes. Cotesia flavipes was reared for five generations on D. evanescens without any indication of diminishing fitness as measured by days to parasite pupation and average cocoon mass weight. However, there was a significant reduction in percent parasitism, cocoon mass weight, and percent emergence when C. flavipes parasitized D. evanescens as compared with D. saccharalis, resulting in a 75% reduction in the gross reproductive rate (R(0)). Greenhouse studies indicated little difference in parasitism of D. saccharalis on the weed hosts johnsongrass, Sorghum halepense (L.), and vaseygrass, Paspalum urvillei Steud. However, when planted as refuge plots, we found it difficult to establish infestations of D. saccharalis in either of these hosts, or in two energy sugarcanes. After 3 yr of infesting host plants and releasing parasitoids only one parasitized D. saccharalis larvae was recovered within the johnsongrass refuge. Diatraea evanescens readily established in vaseygrass; however, these larvae appear inaccessible to C. flavipes. In contrast, parasitism of D. saccharalis by C. flavipes infesting young sugarcane was 30%.     

The effect of nitrogen fertilizer application to maize and sorghum on the bionomics of Chilo partellus (Lepidoptera: Crambidae) and the performance of its larval parasitoid Cotesia flavipes (Hymenoptera: Braconidae)

Laboratory and field trials were conducted to evaluate the effect of plant species (maize, sorghum), plant age (young, middle, old) and four different nitrogen fertilization levels (N0-N3) on the bionomics of the invasive crambid Chilo partellus and the performance of its braconid larval parasitoid Cotesia flavipes. Plant N varied significantly between N0 and N1-N3, but the differences among the latter were not significant. Intrinsic rates of increase and net-reproductive rates of C. partellus followed the same trends: they were lowest with N0 and similar among the other treatments. On maize only, mortality of C. partellus and parasitism by C. flavipes tended to decrease with age of the plant while the percentage of borers reaching adulthood (i.e. pupation) increased. Borer mortality and parasitism was lower and pupation higher on sorghum than on maize. On both host plants, percent dry matter content of frass, which could affect ingress of the parasitoid into the borer tunnel, did not vary with nitrogen level but varied with age of the host plants: on maize, it was highest on young plants and on sorghum on old plants. Tunnels were shorter on young maize and sorghum plants; longer tunnels on older plants indicated compensatory feeding by the larva as a result of lower nutritive value of the food source. Consequently, larval weight was lower on older than younger plants. The level of nitrogen fertilization had no effect on food conversion efficiency of C. partellus. Nitrogen did not affect number of C. flavipes progeny while egg load of progeny increased significantly with nitrogen level, on both plant species. Differences in egg load between sorghum and maize were mostly not significant. It was concluded that on depleted soils only, an increase in nitrogen via mulching, rotation with a leguminous crop or fertilization would increase survival of C. partellus on both maize and sorghum and an increase in acreage of maize and in application of nitrogen fertilizer in an area would also increase the parasitism of C. flavipes.     

Wolbachia infection dynamics in experimental laboratory populations of Metaseiulus occidentalis

The present study examined the acceptability and suitability of Old World stemborers (Chilo partellus and C. orichalcociliellus) for the development of New World parasitoids (Apanteles deplanatus and A. minator) and New World stemborers (Diatraea saccharalis and D. grandiosella) for the development of Old World parasitoids (Cotesia sesamiae, C. flavipes and C. chilonis). Results revealed that acceptance and suitability were high in old associations. In new associations, parasitoids accepted about 60% of the new association hosts. In addition, 10 out of 17 new associations were successful. Apanteles species appeared to be more physiologically host specific than Cotesia species. For example, two of four new association hosts were accepted by A. deplanatus and only one (D. saccharalis) was partially suitable for progeny development. Among the Cotesia species, Cotesia flavipes appeared to have a wider host range than the two other species. It attacked all hosts offered and successfully parasitized all but one (D. grandiosella). Diatraea saccharalis was accepted and was a suitable host for the development of all parasitoid species tested, whereas D. grandiosella was unsuitable for the development of four out of five parasitoid species tested. No clear pattern was observed as behavioral acceptance did not always agree with the pattern of physiological suitability. Implications of these findings for importation biological control of stemborers are discussed.     

Fitness consequences of superparasitism and mechanism of host discrimination in the stemborer parasitoid Cotesia flavipes

The fitness consequences of superparasitism and the mechanism of host discrimination in Cotesia flavipes, a larval parasitoid of concealed stemborer larvae was investigated. Naive females readily superparasitized and treated the already parasitized host as an unparasitized host by allocating the same amount of eggs as in an unparasitized host. However, there was no significant increase in the number of emerging parasitoids from superparasitized hosts due to substantial mortality of parasitoid offspring in superparasitized hosts. Furthermore, the developmental time of the parasitoids in a superparasitized host was significantly longer than in a singly parasitized host and the emerging progeny were significantly smaller (body length and head width). Naive females entered a tunnel in which the host was parasitized 4 h previously and accepted it for oviposition. Experienced females (oviposition experience in unparasitized host) refused to enter a tunnel with a host parasitized by herself or by another female. In experiments where the tunnel and/or host was manipulated it was demonstrated that the female leaves a mark in the tunnel when she parasitizes a host. The role of patch marking in C. flavipes is discussed in relation to the ecology of the parasitoid.     

亚致死剂量阿维菌素和氟虫睛处理小菜蛾对寄生蜂菜蛾绒茧蜂生长发育的影响

分别在小菜蛾体内的菜蛾绒茧蜂处于卵期、早期幼虫和中期幼虫时,饲喂小菜蛾2龄幼虫亚致死剂量（＝LC₁₀）的阿维菌素和氟虫睛,研究上述杀虫剂处理对寄主体内菜蛾绒茧蜂结茧率和羽化率的影响。结果表明： 在菜蛾绒茧蜂处于卵期、早期幼虫和中期幼虫时,饲喂小菜蛾LC₁₀剂量阿维菌素处理的菜叶后,菜蛾绒茧蜂的结茧率分别下降26.6%,22.8%和5.8%,饲喂小菜蛾LC₁₀剂量氟虫睛处理的菜叶后,菜蛾绒茧蜂的结茧率分别下降76.9%,42.5%和18.5%。上述阿维菌素处理对菜蛾绒茧蜂成虫羽化率影响不显著,但上述氟虫睛处理可显著抑制菜蛾绒茧蜂成虫羽化率,在菜蛾绒茧蜂处于卵期、早期幼虫和中期幼虫时,饲喂小菜蛾LC₁₀ 剂量氟虫睛处理的菜叶可导致菜蛾绒茧蜂成虫羽化率分别下降53.1%,36.1%和47.8%。结果显示,即便是对寄主小菜蛾幼虫很低的剂量（LC₁₀剂量）也会显著危害小菜蛾幼虫体内的菜蛾绒茧蜂的生长发育。此外,饲喂小菜蛾幼虫亚致死剂量杀虫剂对菜蛾绒茧蜂生长发育的影响与杀虫剂种类及蛾绒茧蜂发育阶段有关。     

螟黄足盘绒茧蜂复合群支序系统学研究（膜翅目：茧蜂科：小腹茧蜂亚科）

对螟黄足盘绒茧蜂复合群Cotesia flavipes complex (膜翅目：茧蜂科：小腹茧蜂亚科)分布全世界的5个种和外群侧沟茧蜂Microplitis 及荻茧蜂Diolcogaster 的25个性状,以及复合群5个种和外群螟蛉盘绒茧蜂Cotesia ruficrus、粘虫盘绒茧蜂Cotesia kariyai、粉蝶盘绒茧蜂Cotesia glomerata 的24个性状,分别进行比较研究,并运用支序分析的方法探讨该复合群内5个种种间的系统发育关系。支序分析表明螟黄足盘绒茧蜂复合群是一单系群,二化螟盘绒茧蜂C. chilonis 和大螟盘绒茧蜂C. sesamiae 近缘,芦螟盘绒茧蜂C. chiloluteelli 和汉寿盘绒茧蜂C. hanshouensis 近缘,螟黄足盘绒茧蜂C. flavipes相对独立。 以上研究表明无论是以近缘属作外群还是以同属其它种作外群,所得结果基本上都能反映螟黄足盘绒茧蜂复合群各种之间的分类地位。     

寄主抗药性对菜蛾绒茧蜂生物学特性的影响

以小菜蛾Plutella xylostella敏感品系SP作寄主饲育的菜蛾绒茧蜂Cotesia plutellae SC品系分别寄生于小菜蛾的SP品系(SC-SP组合)或抗性RP品系(SC-RP组合),还以小菜蛾RP品系作寄主饲育的菜蛾绒茧蜂RC品系分别寄生于小菜蛾的SP品系(RC-SP组合)或RP品系(RC-RP组合),均在幼虫中期施用氰戊菊酯,考察了药剂对该蜂生物学特性的影响。结果发现：在不施用杀虫剂时,SC-RP组合中蜂的结茧率为45.8%,显著低于其它组合, 所结茧长0.76 mm,育出雌蜂前翅和后足胫节长分别为3.28 mm和2.33 mm,也分别小于其它各组合的结果,表明寄主抗药性对该蜂有不利影响;施用杀虫剂后,RC-RP、SC-RP组合中,蜂的结茧率分别为95.5%和37.8%,显著高于SC-SP和RC-SP组合中蜂的结茧率（22.5%,25.8%）,表明寄主抗性能保护其体内的幼蜂少受杀虫剂的影响;RC-SP组合在受到和未受到杀虫剂作用时茧的羽化率分别为95.2%和93.6%,无显著差异,卵+幼虫及雌蛹的发育历期在处理和对照间也无显著差异,表明用抗性寄主饲育的菜蛾绒茧蜂在寄生敏感寄主时仍表现一定的耐药性,有利于该蜂抗药性的发展,即寄主 寄生蜂之间在抗药性方面存在协同进化。     

Differential expression of the CrV1 haemocyte inactivation-associated polydnavirus gene in the African maize stem borer Busseola fusca (Fuller) parasitized by two biotypes of the endoparasitoid Cotesia sesamiae (Cameron)

Polydnaviruses are rarely studied for their natural variation in immune suppressive abilities. The polydnavirus harboring braconid Cotesia sesamiae, a widespread endoparasitoid of Busseola fusca and Sesamia calamistis in sub-Saharan Africa exists as two biotypes. In Kenya, the western biotype completes development in B. fusca larvae. However, eggs of the coastal C. sesamiae are encapsulated in this host and ultimately, no parasitoids emerge from parasitized B. fusca larvae. Both biotypes develop successfully in S. calamistis larvae. Encapsulation activity by B. fusca larvae towards eggs of the avirulent C. sesamiae was detectable six hours post-parasitization. The differences in encapsulation of virulent and avirulent strains were associated with differences in nucleotide sequences and expression of a CrV1 polydnavirus (PDV) gene, which is associated with haemocyte inactivation in the Cotesia rubecula/Pieris rapae system. CrV1 expression was faint or absent in fat body and haemolymph samples from B. fusca parasitized by the avirulent C. sesamiae, which exhibited encapsulation of eggs. Expression was high in fat body and haemolymph samples from both B. fusca and S. calamistis larvae parasitized by the virulent C. sesamiae, encapsulation in the former peaking at the same time points as CrV1 expression in the latter. Non synonymous difference in CrV1 gene sequences between virulent and avirulent wasp suggests that variations in B. fusca parasitism by C. sesamiae may be due to qualitative differences in CrV1-haemocyte interactions.     

Active defence of herbivorous hosts against parasitism: Adult parasitoid mortality risk involved in attacking a concealed stemboring host

Phytophagous insects have several defence strategies to defend themselves against attack by parasitic wasps. Larval lepidopteran hosts can defend themselves actively to prevent oviposition by the parasitoid. Among the aggressive kinds of behaviour exhibited by hosts against parasitoids are violent wriggling, biting and spitting. The behaviour of the braconid parasitoid Cotesia sesamiae attacking stemboring larvae inside their feeding tunnel in the plant stem was investigated in maize and sugarcane stem pieces and transparent artificial tunnels. Attacking a defending stemborer host inside the confined space of a tunnel was shown to be risky for the female parasitoid. A considerable proportion (25%) of female wasps were killed in their attempt to attack the spitting and biting host. No difference was found in the behaviour of C. sesamiae attacking the suitable host Sesamia calamistis or the unsuitable host Eldana saccharina. The consequences of this high mortality risk involved in each host attack is discussed in relation to the ecology of the parasitoid.     

Variability in the reproductive biology and in resistance against Cotesia sesamiae among two Busseola fusca populations

Two mitotypes of Busseola fusca (Fuller) (Lepidoptera: Noctuidae) named KI and KII, co‐exist in Kenya. Individuals of KII are more widely distributed than those of KI. The present study assessed whether this was due to differences in their reproductive potential and/or in their resistance to the braconid Cotesia sesamiae Cameron, which is the most common larval parasitoid of B. fusca in the region. Two populations of the parasitoid, one from the coastal and one from the inland regions of Kenya, which differ in their ability to develop in B. fusca, were tested. Virgin KII females started to call sooner during the night than KI females. Female fecundity and egg viability were significantly lower for the heterogamous than the homogamous crosses. Cotesia sesamiae from the inland produced larger progeny in KI than in KII host. Cotesia sesamiae from the coast did not develop in either host. Despite their long time co‐existence in the same geographical area, KII and KI conserved biological differences in terms of time of calling, fecundity, fertility and resistance against the larval parasitoid, C. sesamiae. This might explain the wider distribution of KII as compared to KI in Kenya.