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.     

Intraspecific and Interspecific Competition Between Cotesia flavipes and Cotesia sesamiae (Hymenoptera: Braconidae), Gregarious Larval Endoparasitoids of Lepidopteran Stemborers

Super and multiple parasitism of Chilo partellus (Lepidoptera: Pyralidae) and Sesamia calamistis (Lepidoptera: Noctuidae) by Cotesia flavipes Cameron and Cotesia sesamiae (Cameron) (Hymenoptera: Braconidae) were investigated in the laboratory. Progeny production of Co. flavipes increased as a result of increasing the number of ovipositions, from one to three per one Ch. partellus host larva, then decreased as a result of four and five ovipositions per larva. Cocoon weight, sex ratio and emergence of the parasitoid progeny were not affected by superparasitism. Low progeny production of Co. sesamiae and poor survival of Ch. partellus host larvae were found as a result of superparasitism. When S. calamistis was the host, the duration of immature stages of Co. flavipes , parasitoid emergence, progeny production and sex ratio were not affected by superparasitism, but cocoon weight, adult longevity and the potential fecundity of adult females decreased. Superparasitism of S. calamistis by Co. sesamiae did not affect emergence, longevity or sex ratio of adult progeny of the parasitoid, but prolonged immature development, lowered cocoon weight and decreased potential fecundity of adult female progeny. Co. flavipes out-competed Co. sesamiae when Ch. partellus was parasitized by both species. The potential for local displacement of Co. sesamiae by Co. flavipes in areas dominated by Ch. partellus in East Africa is discussed.     

The role of chemical cues in host finding and acceptance by Callosobruchus chinensis

We studied the response of female Callosobruchus chinensis to chemical cues emitted by cowpea seeds at different stages of bruchid infestation (uninfested, egg carrying, L1-, and L4-infested). Olfactory attractiveness was determined in Y-tube olfactometer assays by testing individual seed categories against either clean air or uninfested seeds. Oviposition preferences between uninfested and infested seeds were determined in petri-dish choice-experiments. The olfactometer assays revealed that weevils discriminate between seeds containing different stages of developing bruchids on the basis of olfactory cues. While odors from uninfested and egg-carrying seeds acted as attractants, odors from L1- and L4-infested seeds failed to induce a positive response by the bruchids. When given a choice between uninfested and infested seeds in the olfactometer, weevils preferred uninfested seeds over L1- and L4-infested seeds, but failed to distinguish between uninfested and egg-carrying seeds. In the oviposition experiment as well, bruchids showed a distinct preference for uninfested seeds when offered in combination with L1- and L4-infested seeds. This experiment further showed a reduced acceptance of egg carrying seeds. Our results indicate that C. chinensis females use chemical information during both host searching and host acceptance. Volatiles from uninfested or egg carrying seeds act as attractants, while deterrence increases as development of bruchid immature stages progresses.     

Host refractoriness of the tobacco hornworm, Manduca sexta, to the braconid endoparasitoid Cotesia flavipes

Cotesia flavipes (Hymenoptera:Braconidae) is a gregarious endoparasitoid of several pyralid stemborer larvae of economic significance including the sugarcane borer, Diatraea saccharalis. In this study, the ability of this parasitoid to develop in a sphingid host, Manduca sexta, was tested. First, second, third, fourth, and even pharate fifth instar host tobacco hornworm larvae were readily parasitized by the female C. flavipes parasitoids but no wasp larvae hatched from the eggs in this refractory host. Instead, the parasitoid eggs were invariably encapsulated by the host's hemocytes and, ultimately, no parasitoids emerged from tobacco hornworm hosts. The first stages of encapsulation were evident at 2 h post-parasitization of the host M. sexta larvae, when the beginning stages of capsule formation were seen. The developmental fate of the host larvae with encapsulated parasitoids was variable. Most succumbed as abnormally small fifth instars or as post-wandering prepupal animals, while a few developed normally to the pupal stage. Dissection of all the larvae or pupae with encapsulated wasp eggs showed evidence of hemocytic encapsulation and melanization of the C. flavipes eggs. This report describes the association between C. flavipes and M. sexta, which appears to be an excellent model system for studying the physiological processes accompanying wasp egg encapsulation that result in death of the host as well as the parasitoid. Since the parasitoid egg never hatches, the system offers an excellent opportunity to identify and study the effects of parasitoid-injected polydnavirus and venom on host physiology.     

Importance of plant physical cues in host acceptance for oviposition by Busseola fusca

Plant and surrogate stems exhibiting specific combinations of physical cues were used to determine which plant‐related stimuli influence the oviposition of Busseola fusca (Fuller) (Lepidoptera: Noctuidae). The number of eggs and egg batches laid per female increased with an increase in diameter of both natural and artificial stems. Direct observations of the oviposition behaviour (walking, antennating, and sweeping with the ovipositor) indicated that the female moths preferred oviposition supports with a large diameter and non‐pubescent or smooth surfaces over pubescent or rough ones. Pubescence and rough surfaces significantly affected the behavioural steps leading to oviposition by interfering with the ovipositor sweep process necessary to find a suitable oviposition site. Furthermore, more eggs and egg batches were laid on soft than rigid supports. The rigidity of the support affected the proper insertion of the ovipositor for egg deposition. Our results underline the importance of physical stimuli in B. fusca's choice of an oviposition site, which may facilitate the identification of potential host plants or preferred oviposition sites on a plant for this species.     

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.     

Oviposition in Yponomeuta cagnagellus: the importance of contact cues for host plant acceptance

Small ermine moths (Yponomeutidae: Lepidoptera) are specialist herbivores. Species within the genus Yponomeuta are each specialized on a limited number of plant species, mainly within genera belonging to the Celastraceae. European Yponomeuta species have developed new specialized host affiliations, mainly on rosaceous hosts. Since these host shifts are reputed to be of consequence for speciation, the role of the ovipositing female is of particular interest. Study of the pre-oviposition behaviour of gravid Y. cagnagellus (Hb.) moths on host (Euonymus europaeus), non-host (Crateagus monogyna) and artificial oviposition substrates, provided information on the nature of the cues used for host plant acceptance and the insect’s perception of these cues. Host selection by adult females occurs with contact chemoreceptors probably located on the antennae or tarsi. MeOH-soluble, non-volatile phytochemical compounds washed from the host plant’s surface and applied on an artificial twig are sufficient to stimulate a complete sequence of behavioural elements leading to oviposition. Volatiles do not have a large effect on the pre-oviposition behaviour.     

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%.     

Sensilla on antennae,ovipositor and tarsi of the larval parasitoids,Cotesia sesamiae (Cameron 1906) and Cotesia flavipes Cameron 1891 (Hymenoptera: Braconidae): a comparative scanning electron microscopy study

Two braconid parasitoids of cereal stemborers in eastern Africa, Cotesia sesamiae and Cotesia flavipes, have been shown to display a similar hierarchy of behavioural events during host recognition and acceptance. In order to understand the mechanisms underlying host recognition and acceptance, the morphology of antennal sensilla on the last antennomeres, on the ovipositor, and on the fifth tarsomere and pretarsus of the prothoracic legs tarsi were studied using scanning electron microscopy followed by selective silver nitrate staining. It appeared that female C. sesamiae and C. flavipes shared the same types and distribution of sensory receptors, which enable them to detect volatiles and contact chemical stimuli from their hosts. In both parasitoids, four types of sensilla were identified on the three terminal antennomeres: (i) non-porous sensilla trichodea likely to be involved in mechanoreception, (ii) uniporous sensilla chaetica with porous tips that have gustatory functions, (iii) multiporous sensilla placodea, which are likely to have olfactory function, and (iv) sensilla coeloconica known to have thermo-hygroreceptive function. The tarsi of both parasitoids possessed a few uniporous sensilla chaetica with porous tips, which may have gustatory functions. The distal end of the ovipositor bore numerous dome-shaped sensilla. However, there were no sensilla coeloconica or styloconica, known to have gustatory function in other parasitoid species, on the ovipositors of the two braconid wasps.     

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.     

Host recognition by the egg–larval parasitoid Chelonus inanitus: effects of physical and chemical cues

Parasitoid wasps are widely used as biocontrol agents. For successful deployment, it is important to know how they search for and recognize their hosts. They often use chemical cues in host searching and recognition. Little attention has been paid to the use of physical cues, particularly when combined with chemical cues, though a combination of cues may improve searching efficiency. Chelonus inanitus L. (Hymenoptera: Braconidae) is a solitary, egg–larval parasitoid wasp that parasitizes various lepidopteran species, including serious crop pests. In this study, effects of physical and/or chemical cues on host recognition were investigated in C. inanitus by observing its antennal searching, ovipositor probing, and the duration of arrestment. In a physical cue test, egg-mass models with glass beads differing in size were used, and a single-egg model with a specific size of bead. Egg-mass models with beads of 0.4–1.0 mm in diameter arrested C. inanitus, in accordance with egg size and arrangement of the host. In a chemical cue test, extract from egg masses of the host Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae), equivalent to half of a host egg mass and extract diluted 100-fold were used, and the undiluted extract stimulated C. inanitus. Untreated egg-mass models (0.2-mm-diameter glass beads) and diluted egg extract arrested C. inanitus less effectively; however, when glass beads were treated with the diluted extract, arrestment increased to the same degree as the undiluted extract. These results suggest that C. inanitus uses both physical and chemical cues to recognize eggs of its host, S. litura, and that these stimuli act synergistically.     

Learning of host searching cues by the larval parasitoid Microplitis croceipes

We conducted laboratory experiments using a wind tunnel to determine the effects of prior experience on the learning and retention of learned responses in the larval parasitoid Microplitis croceipes (Cresson) (Hymenoptera: Braconidae). Although most females that had either antennated host frass or oviposited in a host in the presence of vanilla odor, made oriented flight to the odor from downwind in the wind tunnel at 30 min after experience, only those that had oviposited in a host with the odor responded to the odor at 24 h after experience. Females that had oviposited in the non‐natural host beet armyworm (BAW) larva with or without the odor did not respond to the odor at 30 min after experience. These results indicate that an oviposition in the host in the presence of odors strongly affects associative learning and the persistence of learned response to the odors. When females were allowed to antennate host frass in the presence of vanilla and to subsequently oviposit in a host within an interval of 5 min or less, their learned response to vanilla also persisted for 24 h. Similarly, when females were conditioned to link vanilla with host frass and then allowed to make an ovipositor contact with host hemolymph, their learned response persisted for 24 h. However, antennal contact with hemolymph after such conditioning of vanilla with host frass did not improve the persistence of learned response to the odor. These results indicate that ovipositor contact with host hemolymph during oviposition is partially responsible for an increased retention of learned response. Females responded to vanilla 48% of the time at 30 min after antennating host frass without the odor, but their response to the odor significantly decreased after oviposition in a BAW larva subsequent to the antennation of host frass. This result indicates that oviposition in a BAW larva decreases subsequent response to general odors. Based on the results, we discuss the foraging behavior of M. croceipes dependent on learning and subsequent experiences.     

Role of chemical cues and natal rearing effect on host recognition by the parasitic wasp Melittobia digitata

Parasitoids are expected to have the ability to find, recognize, and perhaps to discern potential hosts that can best support the development of their progeny. Melittobia Westwood (Hymenoptera: Eulophidae) are gregarious ectoparasitoids, which primarily attack mud daubers (Hymenoptera: Sphecidae). How Melittobia females locate their host is not well known, but the process may involve host‐related chemical signals. In this study, we investigated the roles of host chemical cues and natal rearing effect in host recognition by Mel. digitata Dahms. In an olfactometer that contained prepupae of Trypoxylon politum Say (Hymenoptera: Sphecidae), Megachile rotundata (Fabricius) (Hymenoptera: Megachilidae), puparia of Neobellieria bullata (Parker) (Diptera: Sarcophagidae), empty or intact host cocoons, or nest mud, Mel. digitata females spent significantly more time in air fields that contained T. politum (prepupae + cocoon) and Meg. rotundata (prepupae + cocoon) than in N. bullata and control fields. Nest mud and natal host had no attraction for parasitoid host choice. Most first and last choices of Mel. digitata females in the olfactometer were not consistent, suggesting an initial random dispersion, although they responded positively towards hosts in cocoons.     

Encapsulation and hemocyte numbers in three lepidopteran stemborers parasitized by Cotesia flavipes-complex endoparasitoids

Determination of the potential and actual host range of a natural enemy is crucial before its importation and release for biological control. We studied some of the factors that are important in determining the physiological host range of insect parasitoids attacking lepidopteran hosts. Our experimental system consisted of novel host-parasitoid associations, with two New World pyralid stalk borers, Diatraea saccharalis and D. grandiosella; one Old World crambid borer, Ostrinia nubilalis as hosts; and three Old World microgastrine braconids, Cotesia chilonis, C. sesamiae, and C. flavipes as parasitoids. Experiments on the chronology of encapsulation of the parasitoid progeny by host hemocytes indicated that lepidopteran stemborers that are taxonomically, behaviorally and ecologically very similar differ in their ability to encapsulate a parasitoid species. D. saccharalis encapsulated C. flavipes sometimes, whereas D. grandiosella consistently encapsulated C. sesamiae and C. flavipes. C. chilonis was not encapsulated by either Diatraea host. If encapsulation occurred it did not start until four days after parasitization and continued during the following days. O. nubilalis was an unsuitable host for all three parasitoid species; parasitoid eggs were killed within 24 hours of parasitization. O. nubilalis had nearly twice as many hemocytes present in the hemolymph compared to the Diatraea species. In many of the host-parasitoid combinations, there was an initial increase of hemocyte number soon after parasitization, which was not due to mechanical damage at oviposition. There was no correlation between total numbers of hemocytes present in the host hemolymph and the observed encapsulation levels. By understanding the encapsulation response we may be able to make better predictions about the host range of a parasitoid species before its release as a biological control agent.     

Olfactory cues used in host‐habitat location and host location by the parasitoid Cotesia urabae

There is a growing body of evidence that many hymenopteran parasitoids make use of olfaction as the primary mechanism to detect and locate hosts. In this study, a series of bioassays was conducted to investigate the orientation behaviour of the gum leaf skeletonizer larval parasitoid Cotesia urabae Austin & Allen (Hymenoptera: Braconidae) in both Y‐tube and four‐arm olfactometers. In a Y‐tube olfactometer, male C. urabae were attracted only to virgin conspecific females. Host‐plant leaves, damaged leaves, host larvae, and host larvae feeding on leaves were highly attractive to female C. urabae, whereas host frass and conspecific males were not. The multiple‐comparison bioassay conducted in a four‐arm olfactometer clearly indicates that C. urabae females were significantly more attracted to the host Uraba lugens Walker (Lepidoptera: Nolidae) larvae feeding on Eucalyptus fastigata H Deane & Maiden (Myrtaceae) leaves than to any other of the odour sources tested. The results of this study show that C. urabae individuals responded to chemical cues specific to the host plant and target host insect, and support hypotheses that unreliable cues are not utilized for host location by specific natural enemies.     

Interspecific competition between the braconid endoparasitoids Glyptapanteles porthetriae and Glyptapanteles liparidis in Lymantria dispar larvae

The effect of interspecific competition between the solitary endoparasitoid Glyptapanteles porthetriae Muesebeck (Hymenoptera: Braconidae) and the gregarious Glyptapanteles liparidis Bouché (Hymenoptera: Braconidae), was investigated in larvae of Lymantria dispar L. (Lepidoptera: Lymantriidae). Host larvae were parasitized by both wasp species simultaneously in premolt to the 2^nd or the 3^rd host instar or in an additional approach with a 4‐day delay in parasitization by the second wasp species. Host acceptance experiments revealed that both wasp species do not discriminate between unparasitized host larvae and larvae parasitized previously by the same or the other species. In more than 90% female wasps parasitized the larva they encountered first. During the period of endoparasitic development, larvae of the competing parasitoid species never attacked the egg stage of the other species. When host larvae were parasitized simultaneously by both wasp species, the rate of successful development of both species depended on the age of the host larva at the time of its parasitization; G. liparidis emerged successfully from 44% of host larvae parasitized during the premolt to 2^nd instar, G. porthetriae from 28%, and in 20% of the hosts both parasitoid species were able to develop in one gypsy moth larva. However, when host larvae were parasitized simultaneously during premolt to the 3^rd instar, G. liparidis was successful in 90% of the hosts, compared to 8% from which only G. porthetriae emerged. In the experiments with delayed oviposition, generally the species that oviposited first succeeded in completing its larval development. Larvae of the species ovipositing with four days delay were frequently attacked and killed by larvae of the first parasitizing species or suffered reduced growth. As the secondary parasitoid species, G. porthetriae‐larvae were never able to complete their development, whereas G. liparidis developed successfully in at least 12,5% of the multiparasitized host larvae. Thus, multiparasitism of gypsy moth larvae by both Glyptapanteles species corresponds to the contest type; however, G. porthetriae is only able to develop successfully as the primary parasitoid of young host larvae.     

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.