Reproductive compatibility of several East and West African Cotesia sesamiae (Hymenoptera: Braconidae) populations and their crosses and backcrosses using Sesamia calamistis (Lepidoptera: Noctuidae) as the host

The relative importance of the braconid Cotesia sesamiae, a gregarious larval parasitoid of lepidopteran stemborers, varies greatly with region in Africa; while the most common parasitoid of noctuid stemborers in eastern Africa, it is rare in western Africa. Thus, several strains of C. sesamiae from Kenya are envisaged for introduction into western Africa. The present study investigates the reproductive compatibility between four populations of C. sesamiae from West Africa and Kenya with the noctuid Sesamia calamistis as the host using reciprocal crosses as well as backcrosses of hybrid females with males of the parental populations. Searching time of the male for the female and mating period varied significantly with couple and ranged between 0.78-1.9 min and 3.4-12.8 s, respectively. Crosses that involved females from inland Kenya (KI) did not yield any female offspring. However, backcrosses of hybrid female bearing a KI male genome with a KI male yielded both female and male offspring. Thus, there was a partial reproductive incompatibility between KI and West African populations which suggested that the latter were infected with Wolbachia sp. However, this should not affect the efficacy of a population introduced from East into West Africa, as there is a high degree of sib-mating in this gregarious parasitoid species. It was concluded that the regional differences in the relative importance of C. sesamiae was due to differences in the insect and plant host range of the different populations.     

Susceptibility of Eldana saccharina (Lepidoptera: Pyralidae), Busseola fusca and Sesamia calamistis (Lepidoptera: Noctuidae) to Bacillus thuringiensis Cry toxins and potential side effects on the larval parasitoid Cotesia sesamiae (Hymenoptera: Braconidae)

Laboratory trials were conducted to determine the efficacy of four Bacillus thuringiensis (Bt) Cry toxins at five different concentrations (0.016, 0.08, 0.4, 2, 10 μg/mL) for controlling three lepidopteran stem-borer species (i.e., the pyralid Eldana saccharina and the noctuids Busseola fusca and Sesamia calamistis) as well as to evaluate their indirect effect on the braconid larval parasitoid Cotesia sesamiae. In addition, larvae from the treatments above, after having been parasitized, were either fed a contaminated (group 1) or a toxin-free (group 2) diet and compared with a control (i.e., parasitized larvae which have never fed on Bt-toxin). All Bt Cry toxins induced larval feeding inhibition. Compared with the control, significant mortality resulted at all concentrations and for all species of Lepidoptera. Cry1Ab was the most toxic with 10 days post treatment mortalities ranging from 81% in B. fusca and S. calamistis to 100% in E. saccharina. In contrast, Cry1Ac had comparatively low toxicity particularly for B. fusca and S. calamistis (e.g., respectively, 54 and 74% mortality at 10 days at the highest concentration). In the toxin-treated group 1, percentages of C. sesamiae cocoon-producing moth larvae were higher compared to group 2 and the control, whereas clutch size was higher than in group 2 but similar to the control. In both groups, 0.016, 0.08 μg/mL CrylAc yielded lower female-biased sex ratios than the control. It was suggested that paralyses of the moth larvae caused by the toxin may have facilitated parasitization leading to higher parasitism and clutch size.     

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.     

Sugar convertibility in the parasitoid Cotesia glomerata (Hymenoptera: Braconidae)

Lack of suitable sugar sources for adult parasitic wasps is an important cause of failure in biological control programs, but the metabolic constraints of sugar feeding are poorly understood. Here we investigated the suitability of 11 naturally occurring sugars as energy sources for the parasitoid Cotesia glomerata (L.) (Hymenoptera: Braconidae). By feeding energy-deprived individuals with given quantities of a 40% (w:w) sugar solution, we assessed recovery time and lifespan after feeding. More than 50% of the wasps recovered within 20 min, and at least 80% within 60 min after uptake of one of the monosaccharides fructose or glucose, the disaccharide sucrose, or the trisaccharide melezitose. Between 40 to 80% of the test insects recovered within an hour after intake of maltose, raffinose, galactose, or mannose. Less than 25% recovered within 1 h after uptake of melibiose, trehalose, rhamnose, or water (control). Parasitoids obtained the highest lifespan benefits after intake of glucose, fructose, sucrose, or melezitose, indicating and confirming their convertibility as an energy source for C. glomerata. In contrast, no lifespan increase was found after consumption of rhamnose and trehalose. The differences in recovery time and lifespan are discussed in terms of parasitoid enzyme activity and metabolic processes.     

Interspecific competition between two endoparasitoids Cotesia vestalis (Hymenoptera: Braconidae) and Oomyzus sokolowskii (Hymenoptera: Eulophidae)

Two endoparasitoids, Cotesia vestalis and Oomyzus sokolowskii, parasitize the same host, larvae of Plutella xylostella. These two species have evolved different parasitization strategies. O. sokolowskii expresses a single factor, venom, and exerts virtually no detrimental effects on the development of its host. C. vestalis, on the other hand, injects polydnavirus (PDV) and venom during oviposition, and teratocytes are released into the host's hemolymph after egg hatching. Parasitization suppresses host immune reactions and redirects its developmental program. Because both these species parasitize the same stage of their hosts, there is the possibility of multiparasitism in nature. Only one species survives multiparasitism and because of its parasitic strategy, we hypothesized that C. vestalis would invariably be the stronger competitor. We designed competition experiments which revealed that C. vestalis is a stronger competitor than O. sokolowskii. We also show that C. vestalis survives intrinsic competition with O. sokolowskii through two mechanisms: physical attack and physiological suppression. We discovered melanized wounds on O. sokolowskii eggs and larvae, which is strong evidence of physical attacks. The physiological suppression is due to PDV and venom injected by C. vestalis. To test this idea more rigorously, we designed a pseudoparasitization experiment which revealed that no O. sokolowskii emerged from multiparasitized hosts when infertile C. vestlais eggs and normal O. sokolowskii larvae are both present inside the same host. These results support our hypothesis that C. vestalis is the stronger competitor and demonstrate two mechanisms that account for the outcome of intrinsic competition between these two endoparasitoids.     

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.     

Single-locus sex determination in the parasitoid wasp Cotesia glomerata (Hymenoptera: Braconidae)

The parasitoid Cotesia glomerata usually produces female-biased sex ratios in the field, which are presumably caused by inbreeding and local mate competition (LMC); yet, sibling mating increases the production of males, leading to the male-biased sex ratio of broods in the laboratory. Previous studies have suggested that the sex allocation strategy of C. glomerata is based on both partial LMC in males and inbreeding avoidance in females. The current study investigated the presence of single-locus complementary sex determination (sl-CSD) as a sex-determining mechanism in this species through inbreeding experiment, cytological examination and microsatellite analysis. Cytological examination detected diploid males in nine of 17 single pairs of sibling mating, thus in agreement with the proportion of matched matings predicted by the sl-CSD model. Sex ratio shifts in these matched sibling matings were consistent with the sl-CSD model with less viable diploid males. The haploid males have a single set of maternal chromosomes (n = 10), whereas diploid males possess a double set of chromosomes (2n = 20). Microsatellite analyses confirmed that diploid males produced from the matched matings inherited segregating genetic materials from both parents. Thus, this study provides the first solid evidence for the presence of sl-CSD as a sex-determining mechanism in the braconid genus Cotesia.     

Factors affecting the rate of attack by Cotesia rubecula (Hymenoptera: Braconidae)

Abstract. 1. The relationship between responses of the insect parasitoid Cotesia rubecula (Marshall) to kairomones produced by the feeding activities of its host, Pieris rapae (L.), and patterns of parasitism were investigated under field conditions.
2. Parasitoid adults aggregated in patches with the highest densities of host larvae but there was no commensurate increase in the rate of attack in these patches.
3. The rate of attack was not limited by the availability of eggs.
4. The rate of parasitoid attack was highest where feeding damage by the host was highest, irrespective of current host density.
5. The rate of parasitoid attack was further influenced by host age distribution. Late instar larvae were less susceptible to parasitism than were early instar larvae. The rate of attack on early instar larvae occupying the same plants as late instar larvae was reduced. This reduction in rate of attack was due to limitations on parasitoid search time imposed by the increased feeding damage associated with large host larvae and by the increased time the parasitoid required to recover from an attack on these large host larvae.     

Characterization and Generation of Male Courtship Song in Cotesia congregata (Hymenoptera: Braconidae)

Background

Male parasitic wasps attract females with a courtship song produced by rapid wing fanning. Songs have been described for several parasitic wasp species; however, beyond association with wing fanning, the mechanism of sound generation has not been examined. We characterized the male courtship song of Cotesia congregata (Hymenoptera: Braconidae) and investigated the biomechanics of sound production.

Methods and Principal Findings

Courtship songs were recorded using high-speed videography (2,000 fps) and audio recordings. The song consists of a long duration amplitude-modulated “buzz” followed by a series of pulsatile higher amplitude “boings,” each decaying into a terminal buzz followed by a short inter-boing pause while wings are stationary. Boings have higher amplitude and lower frequency than buzz components. The lower frequency of the boing sound is due to greater wing displacement. The power spectrum is a harmonic series dominated by wing repetition rate ∼220 Hz, but the sound waveform indicates a higher frequency resonance ∼5 kHz. Sound is not generated by the wings contacting each other, the substrate, or the abdomen. The abdomen is elevated during the first several wing cycles of the boing, but its position is unrelated to sound amplitude. Unlike most sounds generated by volume velocity, the boing is generated at the termination of the wing down stroke when displacement is maximal and wing velocity is zero. Calculation indicates a low Reynolds number of ∼1000.

Conclusions and Significance

Acoustic pressure is proportional to velocity for typical sound sources. Our finding that the boing sound was generated at maximal wing displacement coincident with cessation of wing motion indicates that it is caused by acceleration of the wing tips, consistent with a dipole source. The low Reynolds number requires a high wing flap rate for flight and predisposes wings of small insects for sound production.     

Polymorphic microsatellite loci in the parasitic wasp Cotesia glomerata (Hymenoptera: Braconidae)

Five polymorphic microsatellite loci were isolated in a gregarious endoparasitoid, Cotesia glomerata, using an enrichment protocol. We detected two to 15 alleles per locus in a sample of 50 female wasps collected from a field population near Zürich, Switzerland. The observed heterozygosities ranged from 0.21 to 0.92. These markers are currently being used in our studies of sex determination in this species.     

Quality control of Cotesia flavipes (Cameron) (Hymenoptera: Braconidae) from different Brazilian bio-factories

The goal of this study was to evaluate the quality of Cotesia flavipes from different bio-factories as biological control agents. We evaluated biological characteristics of the parasitoids throughout their lifespan, and measured the body length and width, abdomen width, thorax width and width and length of the right forewing of female and male parasitoids. Our results showed that the number of males and pupal viability were similar among the bio-factories; the number of emerged females was greater in bio-factories I and II; the egg-pupa period and the pupal period were shorter in bio-factory IV; and a greater longevity was found in bio-factories II and III. Sex ratio (at approximately 60% females) was satisfactory (in terms of suitability for release) across all bio-factories. For morphometric measurements, the body, abdomen and wing widths were similar in males; however, thorax width was greater in the males from bio-factory I; bio-factory III produced females with the highest body length; bio-factory I produced females with the greatest abdomen width; bio-factories III and IV produced females with the greatest wing length. Among the bio-factories studied, bio-factory IV produced the best quality C. flavipes, with respect to the greatest number of parasitoids per pupal mass (a mean of 57% more parasitoids) in a satisfactory sex ratio, and with the shortest developmental time, which facilitates faster rearing in the laboratory. Studies such as this, which assess the quality of a mass-produced C. flavipes, are crucial for the continued use of this parasitoid in controlling Diatraea saccharalis in the field.     

Behavioural evidence for a female sex pheromone in Cotesia flavipes (Hymenoptera: Braconidae)

Abstract.  The mating behaviour of Cotesia flavipes Cameron, 1891 (Hymenoptera: Braconidae) was observed under laboratory conditions. The results demonstrate that chemical stimuli play an important role in bringing males and females together for mating. Females from this species release chemical compounds to attract males, which exhibit a distinct courtship behaviour divided into three main steps: (i) antennation, (ii) lateral bouncing and (iii) wing fluttering. Ethological tests using hexane extracts from two different parts of the female's body (head plus thorax and abdomen) demonstrate that males are more attracted and also display a courtship behaviour when a filter paper containing hexane extracts from the abdomen is presented to them, indicating that the abdomen is the source of the sex pheromone of this species. Naive males of this species respond to hexane extracts of this gland by displaying courtship behaviour. Furthermore, additional tests show that C. flavipes females mate only once, whereas virgin males do not show any preference for virgin or mated females, suggesting that mated females of this species continue to produce sex attractants after mating.     

Postemergence learning in the insect parasitoid,Cotesia congregata (Say) (Hymenoptera: Braconidae)

Exposing newly emerged females of Cotesia congregata(Say) to wild cherry, an inherently unattractive plant, and their host larvae at 0–4 h after adult emergence induced a positive searching response to wild cherry and an inhibited response to cabbage, an attractive plant. Inherent responses were not affected when females were exposed to their hosts at 0–12 h and to cherry at 8–12 h after emergence. The induced response to cherry was constant until its disappearance at 6–7 days;inhibition of the response to cabbage was released at 4–5 days after emergence. Postemergence exposure to cherry and parasitoid cocoons induced similar but weaker searching responses. Induced searching responses exhibit features of associative learning and receptor modification. In addition to its presumed role in foraging, postemergence experience with plants may encourage assortative mating of C. congregatawithin suitable host habitats and, thus, facilitate local adaptations to specific plants.     

Mitochondrial DNA phylogeography of the Cotesia flavipes complex of parasitic wasps (Hymenoptera: Braconidae)

The Cotesia flavipes species complex of parasitic wasps are economically important worldwide for the biological control of lepidopteran stem borers. The complex currently comprises three species: Cotesia flavipes Cameron, C. sesamiae (Cameron) and C. chilonis (Matsumura) (Hymenoptera: Braconidae), which appear morphologically similar. Despite their economic importance, little is known about the genetic diversity and phylogeography of these parasitoids. Differences in the biology of geographic populations have generally been interpreted as genetic divergence among strains, but direct genetic evidence is lacking. In Australia, several stem borer pests in neighbouring countries have been identified as significant threats to the sugar industry. However, the status of C. flavipes in Australia is unknown. To examine the genetic variation among worldwide populations of the C. flavipes complex and investigate the status of the Australian C. flavipes-like species, partial sequence data were generated for mitochondrial gene regions, 16S rRNA and COI. Parsimony, minimum evolution and Bayesian analyses based on 21 geographic populations of the complex and four outgroups supported the monophyly of the complex and the existence of genetically divergent populations of C. flavipes and C. sesamiae. The geographically isolated Australian haplotypes formed a distinct lineage within the complex and were ~3.0% divergent from the other species. The results indicated that historical biogeographic barriers and recent biological control introductions play an important role in structuring lineages within these species. This study provides a phylogeographical context for examining adaptive evolution and host range within biologically divergent strains of the C. flavipes complex.     

New species of Allorhogas Gahan (Hymenoptera: Braconidae) reared from galls on Lycium cestroides Schltdl. (Solanaceae) in Argentina

Allorhogas cordobensis sp. nov. (Hymenoptera: Braconidae: Doryctinae) is described from the province of Córdoba, Argentina. Its representatives can be distinguished from all other known species of the genus by the unusual morphology of the ovipositor tip and the expanded clypeus apically. Remarkably, this species is also characterized by having a tridentate mandible, a feature known only in exodont braconids, mostly of the subfamily Alysiinae. The new species was reared from stem galls on Lycium cestroides, which constitutes the second record of an Allorhogas species associated with galls on representatives of the plant family Solanaceae.     

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.     

闭弯尾姬蜂与菜蛾盘绒茧蜂寄生菜蛾幼虫时的种间竞争

在室内25℃下,以菜蛾3龄初幼虫作寄主,研究了菜蛾盘绒茧蜂Cotesia plutellae和半闭弯尾姬蜂Diadegma semiclausum的种间竞争。当寄主供2种蜂同时产卵寄生时,2种蜂各自的寄生率与其单独寄生时无显著差异,合计寄生率比一种蜂单独存在时有所提高,但差异不显著。2种蜂均能产卵寄生已被另一种蜂寄生了的寄主幼虫。当寄主被2种蜂寄生的间隔时间很短（少于10 h）时,所育出的蜂绝大部分（80%以上）为绒茧蜂;当寄主先被绒茧蜂寄生,并饲养2天以上再供弯尾姬蜂寄生时,所育出的全为绒茧蜂;当寄主先被弯尾姬蜂寄生,并饲养2天以上再供绒茧蜂寄生时,寄主幼虫绝大部分不能存活,只有少部分能育出寄生蜂,且多为弯尾姬蜂。当2种蜂的幼虫存在于同一寄主体内时,2种蜂的发育均受到另一种蜂的抑制;绒茧蜂1龄幼虫具有物理攻击能力,能将弯尾姬蜂卵或幼虫致死。这些结果表明,菜蛾盘绒茧蜂与半闭弯尾姬蜂在同一寄主中发育时,前者具有明显的竞争优势。     

Differential parasitism of Plutella xylostella (Lepidoptera: Plutellidae) larvae by the parasitoid Cotesia plutellae (Hymenoptera: Braconidae) on two host plant species

Laboratory experiments were conducted to examine host selection by Cotesia plutellae Kurdjumov when larvae of its host, Plutella xylostella (Linnaeus), fed on Chinese cabbage, Brassica campestris L. ssp. pekinensis and those fed on common cabbage, Brassica oleracea L. var. capitata were provided simultaneously, and to investigate the roles of plant and host volatiles in mediating host selection. When C. plutellae were provided with equal numbers of host larvae on plants of the two species in one arena, the parasitoid parasitized 4- to 15-fold more host larvae on Chinese cabbage than on common cabbage. This preference changed little with host density. However, an experience of searching coupled with an oviposition in a host larva on a leaf of the less-preferred plant, common cabbage, significantly increased the preference for parasitizing host larvae on this plant and resulted in twice as many host larvae parasitized on this plant than on Chinese cabbage. Dual choice tests with a Y-tube olfactometer showed that plant volatiles from Chinese cabbage were more attractive to female C. plutellae than those from common cabbage when plants of both species were either intact or infested. In parallel to the increased parasitism on common cabbage following experience, oviposition in a host larva on this less-preferred plant significantly increased the response to volatiles emanating from that plant. These results indicate that host plants may strongly influence the foraging behaviour of C. plutellae, but their differential attractiveness to the parasitoid may be altered by experience of the parasitoid.     

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.