Interspecific competition betweenEupelmus vuilleti andDinarmus basalis, two solitary ectoparasitoids ofBruchidae larvae and pupae

Coexistence of two solitary ectoparasitoids of bruchids may be the result of counter-balanced competition. Some strategies in interspecific competition at the extrinsic level of female behaviour are identified.Dinarmus basalis (Rondani) (Hymenoptera; Pteromalidae) has adapted an evasion strategy to avoid competition. Females ofD. basalis show interspecific discrimination against hosts parasitized byEupelmus vuilleti Crawford (Hymenoptera; Eupelmidae) and lay fewer eggs in the presence of females or hosts parasitized by the latter.Eupelmus vuilleti has adapted an aggressive strategy. In contrast toD. basalis, E. vuilleti concentrates her ovipositions on hosts already parasitized byD. basalis. Females ofE. vuilleti preferably use oviposition holes made by other parasitoids, and are able to kill eggs and larvae ofD. basalis selectively by thrusts of their ovipositor (ovicide and larvicide). Furthermore,E. vuilleti can act as a facultative hyperparasitoid on older larvae ofD. basalis. The number ofE. vuilleti offspring is not affected by the presence ofD. basalis on a host. Our study does not provide insight in the process of larval competition.

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Résumé La coexistence de deux ectoparasito?des solitaires de Bruchidés peut resulter de compétition contrebalancée (Zw?lfer, 1971). Quelques stratégies en situation de compétition interspécifique ont été indentifiées au niveau (extrinsèque) du comportement de femelles.Dinarmus basalis (Rondani) (Hymenoptera; Pteromalidae) a développé une stratégie d'évitement de la compétition. Les femelles deD. basalis montrent une capacité à reconna?tre les h?tes parasités parEupelmus vuilleti Crawford (Hymenoptera; Eupelmidae), et pondent moins d'œufs en présence des femelles d'E. vuilleti ou des h?tes parsités par cette espèce.Eupelmus vuilleti a adapté une stratégie aggressive. Au contraire deD. basalis, E. vuilleti concentre sa ponte sur les h?tes déjà parasités parD. basalis. Les femelles d'E. vuilleti utilisent préférentiellement les orifices de ponte pratiqués par les autres parasito?des. Elles sont alors capables de tuer grace à l'ovipositeur les œufs et les larves deD. basalis (ovicide et larvicide). De plus,E. vuilleti est capable d'hyperparasiter les larves de dernier stade deD. basalis. Le nombre de descendants d'E. vuilleti n'est pas affecté par la présence deD. basalis sur un h?te. Notre étude expérimentale n'a pas permis l'étude du mécanisme de la compétition larvaire.

     

Interspecific Relations Between Two Sympatric Species of Hymenoptera, Dinarmus basalis (Rond) and Eupelmus vuilleti (Crw), Ectoparasitoids of the Bruchid Callosobruchus maculatus (F)

Dinarmus basalis (Rond) and Epelmus vuilleti (Crw) are two Hymenopteran species, which are solitary ectoparasitoids of bruchid larvae. In the presence of seeds of Vigna unguiculata (Walp) containing hosts parasitized by E. vuilleti, a high percentage of D. basalis females avoided multiparasitism whatever the age of the eggs or the larvae present on the host. The least avoidance was observed when the hosts were parasitized by E. vuilleti 30 min beforehand. This avoidance behavior is adaptive and is related to the low survival chances of the D. basalis larvae when they are in interspecific competition with E. vuilleti larvae. The analysis of the behavior of D. basalis demonstrated that the avoidance of multiparasitism could be due to the perception of two signals; an external signal deposited on the surface of the seeds during the E. vuilleti oviposition phase and an internal signal due to the presence of the eggs and larvae at the surface of the hosts. E. vuilleti females did not avoid multiparasitism and multiparasitized the hosts bearing D. basalis eggs or larvae. The behavior of E. vuilleti females was not disturbed by the presence of its competitor. Under these conditions of interspecific competition, the survival chances of E. vuilleti larvae were very high whatever the age of its competitor D. basalis. The two species of parasitoids could move in a column containing healthy seeds of V. unguiculata and patches with seeds containing parasitized or unparasitized larvae. The distribution of D. basalis females introduced into these columns depended on the host quality. They avoided the patches containing the hosts parasitized E. vuilleti and were found in the patches with healthy hosts. The behavior of E. vuilleti females was very different; the distribution of the females and the parasitism and multiparasitism rates were not affected by the quality of the hosts present in the patches. The adaptive significance of the behaviors of these two species was analyzed in relation to the survival chances of their offspring.     

Hyperparasitisme facultatif de parasitoïdes en cours de développement par les femelles des ectoparasitoïdes Eupelmus vuilleti et Eupelmus orientalis Craw

In a community of three ectoparasitoids, Dinarmus basalis, Eupelmus vuilleti and E. orientalis, the host Callosobruchus maculatus parasitised 48 h before by D. basalis, is accepted by E. vuilleti females after they have eliminated the eggs and neonatal larvae of D. basalis. This ovicidal and larvicidal behaviour enables E. vuilleti to develop on C. maculatus instead of D. basalis. E. vuilleti females are able to parasitise the L5 larval stage and the pupa of D. basalis: their larvae therefore feed at the expense of the developing parasitoid. This trophic level is that of hyperparasitism. However, E. vuilleti females rarely practise hyperparasitism on their own L5 larvae and on those of E. orientalis. This behaviour reveals a high behavioural plasticity enabled by intra- and interspecific recognition of parasitoids used as hosts. Hyperparasitism activity in E. orientalis females is higher than that in E. vuilleti females since they hyperparasitise host parasitoids more frequently without preferential species choice. However, E. vuilleti seems to be free from competitive pressure with E. orientalis, as the former penetrates deeply into a grain store contaminated with C. maculatus in contrast to E. orientalis females, which remain on the surface from where they escaped.     

Response of the parasitoidEupelmus vuilleti to the odours of the phytophagous host and its host plant in an olfactometer

Eupelmus vuilleti (CRW) is a solitary ectoparasitoid which, under our experimental conditions, developed at the expense of the larvae and pupae ofBruchidius atrolineatus (Pic) (Coleoptera, Bruchidae). The larvae of this beetle are found inside the seeds of cowpea,Vigna unguiculata (Walp). Using a tubular olfactometer, we determined the olfactory stimuli involved in the orientation of females of the hymenopterous speciesE. vuilleti towards one of its hosts;B. atrolineatus. Several odours were tested including those from host plants ofB. atrolineatus, from non-host plants, from the host itself and from the waste products of the host. The odours of pods or dry seeds ofV. unguiculata (host plant of the phytophagous insect) affected the locomotor behaviour of females ofE. vuilleti. The odours from the plant in the vegetative stage had no effect. Kairomones from larvae, pupae or faeces ofB. atrolineatus were attractive to the parasitoid females. Odours from adult male or femaleB. atrolineatus, as well as the sex pheromone emitted by females were not attractive toE. vuilleti females. This sex pheromone did however stimulate the locomotor activity of the parasitoid. The adaptive significance of these olfactory stimuli is discussed.

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Résumé Eupelmus vuilleti (CRW) est un ectoparasito?de solitaire qui se développe dans nos conditions expérimentales aux dépens des larves et des nymphes deBruchidius atrolineatus (Pic) (Coléoptère:Bruchidae). Les larves de ce Coléoptère se trouvent à l'intérieur des graines d'une LégumineuseVigna unguiculata (Walp). Grace à un olfactomètre tubulaire, nous avons déterminé les différents stimuli olfactifs intervenant dans l'orientation des femelles de cet hyménoptère, vers l;un de ses h?tes;Bruchidius atrolineatus. Plusieurs odeurs émanant soit de plantes-h?tes ou nonh?tes deB. atrolineatus, soit de l'h?te lui-même ou résultant de son métabolisme ont été testées. Les odeurs de gousses ou de graines sèches deVigna unguiculata Walp (plante-h?te du phytophage) influencent le comportement locomoteur des femelles. Par contre, les odeurs de plantes au stade végétatif n'ont pas d'effet. Les kairomones émanant de larves, nymphes ou fèces de larves deB. atrolineatus exercent un effect attractif sur les femelles parasito?des. Les odeurs émanant d'adultes males ou femelles deB. atrolineatus ainsi que la phéromone sexuelle émise par les femelles ne sont pas attractives pour les femelles deE. vuilleti. Cette phéromone sexuelle, par contre, stimule l'activité locomotrice des parasito?des. La signification adaptative de ces différents stimuli olfactifs est discutée.

     

Intraguild interactions between two egg parasitoids exploring host patches

Intraguild interactions between two egg parasitoids, Trissolcus basalis (Hymenoptera: Scelionidae) and Ooencyrtus telenomicida (Hymenoptera: Encyrtidae), exploring egg masses of the Southern Green Stink Bug (SGSB) Nezara viridula (Heteroptera: Pentatomidae), were investigated in laboratory conditions by single, simultaneous and sequential host attack experiments. Mortality of N. viridula eggs was higher in simultaneous and sequential releases compared to single species releases. In simultaneous host exploitations, T. basalis females displayed an aggressive behavior against O. telenomicida females. The outcome of multiparasitism showed that interspecific larval competition was dominated by O. telenomicida regardless of the sequence in which oviposition occurred and which parasitoid was or was not simultaneously released in the patch. Finally, O. telenomicida can successfully develop in hosts already parasitized by T. basalis up to seven days earlier, acting as a facultative hyperparasitoid, so that intraguild predation (IGP) also occurred. The ecological factors that allow species coexistence and the role played by competition in biological control programs are discussed.     

Sex ratio regulation in the waspEupelmus vuilleti (crwf.), an ectoparasitoid on bean weevil larvae (Hymenoptera: Pteromalidae)

In Africa, the seeds and/or pods ofVigna unguiculata andVigna radiata (Papilionacea) are attacked in fields and storage structures by bruchid beetlesCallosobruchus maculatus andBruchidius atrolineatus, on which parasitoid communities can develop. One of these parasitoids is the solitary ectoparasitoidEupelmus vuilleti (Eupelmidae). The storage conditions ofV. unguiculata andV. radiata favor the overlapping of all host stages during several months. These conditions suggest that female parasitoids would vary the sex ratio of their offspring according to the different sizes or developmental stages of hosts. The sex ratio ofE. vuilleti was strongly related to the developmental stage of the hostC. maculatus. Under our experimental conditions, where superparasitism is rare, the proportion of daughters varied between 5 and 25% on the third larval stage but reached 70 to 90% on the pupae. The increase in the proportion of daughters was also observed in the absence of superparasitism. In this case, there was an absolute coincidence between the sex ratio of eggs laid and that of emerged adults. Manipulation of the sex of the egg by the females seems to take place at the time of the egg's fertilization. The relation between host weight and egg sex showed that the male eggs are preferentially laid on lighter host larvae and the female eggs on heavier ones.     

Intra- and interspecific host discrimination in two closely related egg parasitoids

Intraspecific host discrimination is frequently found in solitary parasitoids, but interspecific host discrimination, where female parasitoids recognize hosts already parasitized by females of other species, is rare. This particular behaviour appears to be adaptive only under specific circumstances. In this paper, we quantified intraspecific host discrimination in Anaphes n. sp. (Hymenoptera: Mymaridae), an endoparasitoid of the eggs of Listronotus oregonensis (LeConte) (Coleoptera: Curculionidae) and interspecific host discrimination toward eggs parasitized by Anaphes sordidatus (Girault), a sympatric species competing for the same resource in similar habitats. To examine host discrimination, choice experiments were used where the females had to choose between different categories of eggs (unparasitized, parasitized by Anaphes n. sp. or A. sordidatus). Superparasitism and multiparasitism were avoided in experiments where the female had a choice between unparasitized hosts and hosts parasitized by the same female, by a conspecific or by a female A. sordidatus. When all hosts available were parasitized, conspecific superparasitism occurred more often than self-superparasitism or multiparasitism. These results indicated that females Anaphes n. sp. were capable of self-, conspecific and interspecific discrimination. Self-discrimination followed recognition of an external marking while interspecific discrimination occurred mostly after insertion of the ovipositor. Interspecific discrimination could result from the recent speciation of these species and could be associated with a genotypic discrimination. This behavior appears to be adaptive because of the competition for common hosts between the two parasitoid species.     

Influence of two successive learning processes on the response ofEupelmus vuilleti Crw (Hymenoptera: Eupelmidae) to volatile stimuli from hosts and host plants

Eupelmus vuilleti (Crw) is a solitary ectoparasitoid of several bruchid species which develop inside Leguminosae seeds. In this hymenopteran a preemergence learning process is responsible for a specific response of females toward the host and host-plant volatiles. This learning occurs after the imaginal molt, while the adult remains in the larval chamber of its host. The persistence of the response toward host and host-plant volatiles of females reared onBruchidius atrolineatus (Pic) larvae developing inVigna unguiculata (Walp) seed was investigated in this study. In the absence of any reinforcement, the response towardB. atrolineatus larvae persisted for 6 days after female emergence from the seeds, whereas the response towardV. unguiculata seed volatiles was maintained for 7 days. Our experiments showed that a later learning process also takes place inE. vuilleti. An ovipositional experience on a given plant-host complex enabled females to learn the stimuli from that complex. This learning occurred even if the complex experienced during oviposition differed from the one on which females were reared. After an ovipositional experience on a new plant-host complex, the response acquired through preemergence learning was maintained. These experiments demonstrate that theE. vuilleti females can memorize cues from several species during successive learning processes. The adaptive significance of these learning capacities, which confer an important behavioral plasticity to this generalist parasitoid, is discussed.     

Impact of mating status on egg-laying and superparasitism behaviour in a parasitoid wasp

Most parasitoid female wasps can distinguish between unparasitized and parasitized hosts and use this information to optimize their progeny and sex allocation. In this study, we explored the impact of mating on oviposition behaviour (parasitism and self‐ and conspecific superparasitism) on both unparasitized and already parasitized hosts in the solitary parasitoid wasp Eupelmus vuilleti (Crw.) (Hymenoptera: Eupelmidae). Virgin and mated females had the same oviposition behaviour and laid eggs preferentially on unparasitized hosts. The sex ratio (as the proportion of females) of eggs laid by mated females in parasitism and conspecific superparasitism was 0.67 ± 0.04 and 0.57 ± 0.09, respectively. Likewise, females laid more eggs in conspecific superparasitism than self‐superparasitism under our experimental conditions. These experiments demonstrate that E. vuilleti females can (i) discriminate between unparasitized and parasitized hosts and adapt the number of eggs they lay accordingly, and (ii) probably discriminate self from conspecific superparasitized hosts. Finally, mating does not appear to influence the host discrimination capacity, the ovarian function, or the oviposition behaviour.     

Superparasitism and host discrimination in the solitary ectoparasitoid Dinarmus basalis

In the solitary ectoparasitoid, Dinarmus basalis (Hymenoptera: Pteromalidae), the occurrence of superparasitism according to the unparasitised host density, and the nature of the host(s) provided was investigated in laboratory studies. In this species superparasitism was observed whatever the experimental conditions used, but the degree of superparasitism depended on the density of its host, Bruchidius atrolineatus (Coleoptera: Bruchidae). Superparasitism was due to successive egg-laying phases on the same host. However, females were able to discriminate between unparasitised hosts and hosts parasitised from 8 h to 72 h beforehand by themselves or by conspecifics. There was no conclusive evidence that superparasitism in the presence of a host parasitised 30 min before was linked to an absence of host discrimination. Host discrimination in this species is achieved by host-quality markers. These are individual-specific markers since conspecific superparasitism rates were often higher than self superparasitism rates. One deterrent substance is emitted by the females during oviposition onto the egg or released by the 16 to 24 h-old egg itself. Another host-quality marker is associated with the presence of a larva on its host. On the other hand, host discrimination ability did not always imply avoidance of superparasitism. In D. basalis there exists a positive relationship between the survival probability of the second egg and the tendency to superparasitise, and superparasitism could therefore result in a significant fitness gain. Under our experimental conditions, D. basalis females exhibited a wide range of oviposition behavioural plasticity in relation to the parasitoid developmental stage, the type of superparasitism, and the encounter rate with unparasitised hosts.     

Interspecific host discrimination and competition in Apoanagyrus (Epidinocarsis) lopezi and A.(E.)diversicornis, parasitoids of the cassava mealybug Phenacoccus manihoti

Abstract.

• 1 Choice experiments on interspecific host discrimination in A.lopezi and A. diversicornis were carried out on discs of cassava leaf containing four hosts (P.manihoti) that had been parasitized by the other species and four unparasitized hosts.
• 2 A.lopezi accepted both host types equally for oviposition, whereas A.diversicornis accepted fewer hosts that had been parasitized by A.lopezi than unparasitized ones. A.diversicornis is therefore capable of interspecific host discrimination, but such a capability was not demonstrated for A.lopezi.
• 3 Survival probability in singly parasitized hosts was 0.85 for both parasitoid species. When the time interval between ovipositions was 2 h or less, survival in multiparasitized hosts was 0.68 for A.lopezi and 0.17 for A.diversicornis, irrespective of priority. Increasing A.lopezi priority to 24±2h did not increase A.lopezi survival. A.diversicornis survival, however, increased to 0.43 when A.diversicornis was given 24 ± 2 h priority. A.diversicornis eggs took 19 h longer than A.lopezi eggs to hatch. This could explain the difference in competitive abilities in multiparasitized hosts.
• 4 The observed difference in host selection behaviour between A.lopezi and A.diversicornis is in accordance with the different benefits of multiparasitism: A.lopezi gains more than A.diversicornis because of its superior within-host competitive abilities.
• 5 Neither species avoided multiparasitism completely. The low survival probability of A.diversicornis in multiparasitized hosts may partly explain its failure to establish when introduced into Africa as part of a biological control programme of P.manihoti.

     

Behavioural and physiological responses to conflicting oviposition stimuli in a synovigenic parasitoid

The behavioural and physiological responses of the synovigenic parasitoid, Dinarmus basalis (Rond.) (Hymenoptera: Pteromalidae), were investigated whilst the wasps were submitted to conflicting oviposition stimuli: an environment which induced them to restrict egg-laying and a physiological factor, egg-load pressure, which induced them to lay eggs. When individual females depleted patches containing hosts parasitized 24 h or 72 h beforehand, they laid preferentially on unparasitized hosts and the number of eggs laid decreased significantly. Although they remained for several days in such patches, egg-load pressure did not lead them to modify their strategy (i.e. to accept all the available hosts including the already parasitized ones). In this synovigenic species, the oviposition constraint resulted in the retention of oocytes. Dissection and histological observation showed that the unlaid eggs are resorbed, a reproductive regulatory process which has seldom previously been reported in the presence of unparasitized hosts. This physiological response was induced by the mere presence of the parasitized hosts rather than their density. The females’ response was also influenced by the presence of conspecifics. They still avoided laying on parasitized hosts but the number of eggs laid daily became comparable to that observed in patches containing only unparasitized hosts. Thus, D. basalis females adapted their strategy in response to their environment, in which the most significant factor seemed to be the quality of the hosts provided, and their physiology. The originality and the importance of these results are discussed.     

Storage of Pentatomid Eggs in Liquid Nitrogen and Dormancy of Trissolcus basalis (Wollaston) and Telenomus podisi Ashmead (Hymenoptera: Platygastridae) Adults as a Method of Mass Production

The eggs of pentatomid species were evaluated to parasitism by Trissolcus basalis (Wollaston) and Telenomus podisi Ashmead after storage in liquid nitrogen. Adults which emerged from stored eggs were kept at 18°C for 120 and 180 days to investigate whether adult dormancy could be associated with host egg storage in liquid nitrogen as a method of mass production of these egg parasitoids. Eggs of Nezara viridula (L.) and Acrosternum pengue (Rolston) were successfully parasitized by T. basalis, as well as Piezodorus guildinii (Westwood) and Dichelops furcatus (F.) by T. podisi. The eggs of Edessa meditabunda (F.) were not parasitized by T. basalis. The emergence of T. podisi from eggs of Euschistus heros (F.) and Podisus nigrispinus (Dallas) stored for 6 months was lower than the control. Females of T. basalis and T. podisi that emerged from stored eggs were kept in dormancy at 18°C. Longevity of T. basalis was influenced by the storage time and sex, but not by the interaction of sex and storage time. For T. podisi, longevity was influenced by the storage time, sex, and by the interaction of sex and storage time. For T. basalis, storage in liquid nitrogen did not affect the fecundity of quiescent females, while the number of parasitized eggs by T. podisi decreased after storage. By the joint use of these techniques, it is possible to optimize mass production of T. basalis so that its life cycle can be monitored and synchronized with the life cycle and availability of hosts.     

Egg resorption behaviour by the solitary egg parasitoid Anaphes nitens under natural conditions

We investigated under outdoor conditions and inside a climate chamber: (i) whether Anaphes nitens Girault (Hymenoptera: Mymaridae), an egg parasitoid of the Eucalyptus snout beetle, Gonipterus scutellatus Gyllenhal (Coleoptera: Curculionidae), experienced egg resorption, and (ii) how various treatments (location, food, and/or host supply) and body size influenced egg load, egg resorption, fecundity, and longevity. One‐day‐old females were mated and randomly assigned to five groups: (A) honey + hosts, (B) water + hosts, (C) only honey, (D) only water, and (E) control females killed at emergence. We compared the egg load of the newly emerged females, which represent the control group (egg load = ovarian eggs present at emergence), with the lifetime egg load (i.e., ovarian eggs + emerged offspring + not emerged offspring) of the females with various host and diet treatments, by dissection of the ovaries to find evidence of egg resorption. All groups reared outdoors had fewer eggs than the control, while indoors there was no significant difference. Outdoors, starved but host‐provided wasps (B) experienced the highest reduction of the lifetime egg load (51%). Groups without access to food (B + D) resorbed more eggs than groups provided with honey (A + C). Females with honey and hosts (A) had the highest lifetime fecundity, but those with water and hosts (B) showed a higher daily realized fecundity. Host‐deprived females with access to food (C) attained the longest lifespan. Our results suggest that under stress conditions, such as low temperature and food shortage, A. nitens females practice egg resorption, probably to save energy.     

Biology of Australian and United States strains of Trissolcus basalis,a parasitoid of the green vegetable bug,Nezara viridula

Strains of Trissolcus basalis (Wollaston) Hymenoptera: Scelionidae, an egg parasitoid of the green vegetable bug, Nezara viridula (L.), were obtained from three regions of Australia and from Homestead, Florida (USA). Percent parasitoid emergence was approximately the same for freezer-stored (-75°C) and fresh eggs, and freezer-stored eggs were suitable hosts for a longer time. Optimum host age, oviposition and emergence patterns, mean number of progeny per female, sex ratio and longevity were examined and certain comparisons were made between the Australian and USA parasitoids. Genetic crosses made between males and females of each strain revealed that reproductive isolation did not occur. Higher fecundity of the Australian strains may make them more successful than indigenous (USA) strains for controlling pest populations of N. viridula in the southern USA.     

Egg-laying, pre-imaginal growth dynamics, and mortality in Eupelmus orientalis and Dinarmus basalis, two solitary ectoparasitoids of Callosobruchus maculatus

In Eupelmus orientalis and Dinarmus basalis, two ectoparasitoid species of Callosobruchus maculatus larvae, pre-imaginal development occurs within a leguminous seed, and is then impossible to observe directly. Offspring sex ratio is normally determined when adults emerge, and mortality during pre-imaginal stages remains unknown. By using translucent gelatine capsules containing a host larva to mimic the seed, we conducted an experimental study of offspring production and sex ratio with measurements of growth and pre-imaginal mortality. Mated females were allowed to lay eggs on hosts in seeds or in gelatine capsules. In the gelatine capsules the parasitoid was observed daily and measured to assess if the offspring sex ratio can be determined before emergence of adults. When seeds are replaced with gelatine caps, the number of egg-laying females decreases (48% in Eupelmus orientalis and 72% in Dinarmus basalis of females ovipositing on seeds lay eggs on gelatine capsules), and the offspring output changes qualitatively in Eupelmus orientalis (egg numbers constant, sex ratio diminishing from 0.75 to 0.46) and quantitatively in Dinarmus basalis (egg numbers diminishing, sex ratio maintained about 0.7). In Eupelmus orientalis, pre-imaginal mortality occurs principally in the first three days, the critical stage is hatching, and the final mortality is 30.1%. In Dinarmus basalis, mortality of larvae increases gradually from the 2nd to the 7th day, the final mortality being 13.6%. (3) In both species sex of the offspring can be determined before emergence but only after most mortality has occurred.     

Egg allocation of the autoparasitoid encarsia tricolor at different relative densities of the primary host (Trialeurodes vaporariorum) and two secondary hosts (Encarsia formosa and E. tricolor)

Parasitism, offspring sex ratio and superparasitism of the facultative autoparasitoid Encarsia tricolor Foërster (Hymenoptera: Aphelinidae) when given access to arenae with different proportions of the primary host (Trialeurodes vaporariorum (Westwood)) and two species of secondary hosts (E. tricolor and Encarsia formosa Gahan) were studied.Parasitism and offspring sex ratio were not affected by female age in the range 3–10 days old. When the secondary hosts were young E. tricolor pupae, eggs were mostly laid on primary hosts, so the offspring sex ratio was more female-biased than expected, and secondary hosts were not superparasitized at all. When the secondary hosts were fully grown E. formosa larvae, superparasitism was small and offspring sex ratio was more male-biased than expected. E. tricolor females were able to discriminate between hosts previously parasitized by themselves and non-parasitized hosts.     

Host preference: parasitism, emergence and development of Trissolcus semistriatus (Hym., Scelonidae) in various host eggs

Abstract: Trissolcus semistriatus is an important egg parasitoid of the sunn bug, Eurygaster integriceps. Conservation and the supportive augmentation of populations of egg parasitoids appears to offer high potential for the biological control of sunn bug in an integrated pest management system. The present study was conducted to determine the host preference of T. semistriatus on various heteropteran host eggs. When each host species was examined separately, the eggs of E. integriceps, Dolycoris baccarum, Graphosoma lineatum, Carpocoris pudicus and Holcostethus vernalis, were parasitized at high levels, namely 88.0, 83.6, 94.8, 87.3 and 80.8%, respectively, whereas a smaller portion of Eurydema ornatum eggs were parasitized (24.0%). There was no parasitism in Nezara viridula eggs by T. semistriatus. Similar high rates were recorded for the percentage of adult emergence in each host species, with the exception of E. ornatum. The average development time was shorter for males than for females. The average development period for both male and female was significantly longer in eggs of E. ornatum than in those of the other host species. These results and observations recorded during the experiments showed that G. lineatum and D. baccarum were available, cheap hosts and it was demonstrated that these hosts could be used for the mass production of egg parasitoids.     

Superparasitism in mass reared Diachasmimorpha longicaudata (Ashmead) (Hymenoptera: Braconidae), a parasitoid of fruit flies (Diptera: Tephritidae)

Superparasitism frequency and its effects on the quality of mass-reared Diachasmimorpha longicaudata (Ashmead) parasitoids were investigated under laboratory conditions. Percentage of adult emergence, sex ratio, survival, fecundity and flight ability of adult parasitoids that emerged from Anastrepha ludens (Loew) pupae with different levels of superparasitism were determined. A high prevalence of superparasitism was observed. The number of scars per pupa, produced by insertion of the parasitoid ovipositor, ranged from 1 to 30, with an average (±SD) of 8.3 ± 6.2. Adult parasitoid emergence decreased as the level of superparasitism increased. However, the fraction of females rose with increasing superparasitism and the flight ability was lower in adults emerging from pupae with only one scar, compared with adults emerging from superparasitized hosts. Female longevity and fecundity were not affected by superparasitism. Our results support the hypothesis that superparasitism in D. longicaudata might be adaptive, since adults emerging from hosts with moderate levels of superparasitism showed the highest percentage of emergence and there were no significant differences in the other quality control parameters tested. Our findings are relevant to the mass rearing process, where the ratio of hosts to parasitoids can be optimized as well as the distribution of eggs deposited in host larvae. This contributes to efficient mass rearing methods for augmentative biological control programs.     

Efficiency,intrinsic competition and interspecific host discrimination of Copidosoma desantisi and Trichogramma evanescens,two parasitoids of Phthorimaea operculella

Trichogramma evanescens West. (Hymenoptera: Trichogrammatidae) and Copidosoma desantisi Annecke & Mynhardt (Hymenoptera: Encyrtidae) are potential parasitoids of the potato tuber moth (PTM), Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae) in Egypt. Discrimination of a parasitized host from an unparasitized host would prevent wasting of time, eggs and reduce competition with conspecifics or heterospecifics. Therefore, we evaluated interspecific host discrimination, multiparasitism and intrinsic competition between the two wasp species. In a choice test, females of T. evanescens showed high interspecific host discrimination only when they were offered 2-day-old C. desantisi parasitized and unparasitized PTM eggs. In contrast, C. desantisi showed high host discrimination and preferred unparasitized eggs to PTM eggs harboring 2-h- or 2-day-old T. evanescens’ eggs. We also evaluated the effect of different introduction sequences on the efficacy of the two wasps. Dissection data indicated that the two parasitoids had a negative impact on each other. There was a significant reduction in the total number of deposited eggs as well as total number of parasitized hosts by each parasitoid. Regarding the rearing experiment, the total number of T. evanescens-induced black eggs or C. desantisi formed mummies in combined treatments was significantly lower than in single parasitoid treatments (control). Moreover, C. desantisi was inferior and did not develop from any multiparasitized host regardless of oviposition order. It was suggested that combined release of the two wasps would not elevate rate of parasitism over that of single parasitoid treatments and competition between them would reduce their efficacy.