Parasitism by Pteromalus cerealellae (Hymenoptera: Pteromalidae) on the Cowpea weevil, Callosbruchus maculatus (Coleoptera: Bruchidae): Host density, temperature effects, and host finding ability

Studies on interactions between a larval parasitoid, Pteromalus cerealellae (Boucek) and one of its hosts, Callosobruchus maculatus (F.) were carried out in the laboratory. The number of host larvae parasitized by P. cerealellae increased with host larvae at low densities and tended to a plateau at a density of 25 larvae per female parasitoid. Each parasitoid was able to parasitize more hosts and produced more offspring at 20 and 25 °C than at 30 °C. The number of non-infested seeds mixed with seeds infested with the last instar of C. maculatus did not preclude P. cerealellae from identifying infested seeds and attacking larvae inside them. When infested seeds were tightly packed, several host larvae escaped parasitism. P. cerealellae may be a useful biological control agent in newly harvested cowpea with low C. maculatus infestation, and lowering the temperature of the storage system may enhance the effectiveness of this parasitoid.     

The effect of host size on the sex ratio of Syngaster lepidus, a parasitoid of Eucalyptus longhorned borers (Phoracantha spp.)

The solitary larval ectoparasitoid, Syngaster lepidus Brullé, parasitizes the cryptic larvae of two wood-boring beetles, Phoracantha recurva Newman and Phoracantha semipunctata F. The objective of this study was to determine how the female parasitoids allocated the sex of progeny when presented with larval hosts of uniform size classes. Host size was directly correlated with age of the Phoracantha larval hosts. Groups of Phoracantha larvae of a single age class (2-, 3-, 4-, or 5-week-old) were exposed to parasitoids, and sex ratios of the resulting parasitoid progeny from each host age class were determined. A significant relationship was observed among the sizes of P. recurva and P. semipunctata hosts and the sex ratio of emerging parasitoids. Parasitized 2-week-old beetle larvae of both Phoracantha spp. produced only male S. lepidus progeny, whereas older larval hosts produced increasing proportions of female parasitoids (up to 80% females from 5-week-old hosts). Two-week-old Phoracantha larvae of both species produced fewer parasitoids than host larvae 3–5-week-old. The size of parasitoid progeny consistently increased with host larval age (size), and female parasitoids were larger than males across all host size classes. Male S. lepidus developed in approximately 25 days from 2-week-old hosts, and 19–21 days in 3–5-week-old hosts. Female S. lepidus developed in 22–25 days, with developmental time increasing with host size.     

Parasitoid–Pathogen–Pest Interactions of Chelonus insularis, Campoletis sonorensis, and a Nucleopolyhedrovirus in Spodoptera frugiperda Larvae

In this study we examined interactions between two solitary endoparasitoids, the braconid Chelonus insularis and the ichneumonid Campoletis sonorensis, and a multiple-enveloped nucleopolyhedrovirus infecting Spodoptera frugiperda larvae. We examined whether ovipositing females minimize interference by discriminating amongst hosts and examined the outcome of within-host competition between parasitoid species and between the parasitoids and the virus. The egg–larval parasitoid Ch. insularis did not discriminate between virus-contaminated and uncontaminated S. frugiperda eggs; all S. frugiperda larvae that emerged from surface-contaminated eggs died of viral infection prior to parasitoid emergence. The larval parasitoid C. sonorensis also failed to discriminate between healthy and virus-infected S. frugiperda larvae or between larvae unparasitized or parasitized by Ch. insularis. Host larvae parasitized in the egg stage by Ch. insularis were suitable for the development of C. sonorensis when they were multiparasitized by C. sonorensis as first, second, third, and fourth instars, whereas emergence of Ch. insularis was dramatically reduced (by 85 to 100%) in multiparasitized hosts. Nonspecific host mortality was significantly higher in multiparasitized hosts than in singly parasitized hosts. The development time and sex ratio of C. sonorensis in multiparasitized host larvae were unaffected by the presence of Ch. insularis larval stages. Both Ch. insularis parasitized and nonparasitized larvae of the same instar (second, third, or fourth instars) had a similar quantitative response to a challenge of virus inoculum. All host larvae that ingested a lethal dose of virus were unsuitable for Ch. insularis development. In contrast, C. sonorensis did not survive in hosts that ingested a lethal virus dose immediately after parasitism, but parasitoid survival was possible with a 2-day delay between parasitism and viral infection and the percentage of parasitoid emergence increased significantly as the interval between parasitism and viral infection increased. The development time of C. sonorensis was significantly reduced in virus-infected hosts compared to conspecifics that developed in healthy hosts. C. sonorensis females that oviposited in virus-infected hosts did not transmit the virus to healthy hosts that were parasitized subsequently. Field applications of virus for biocontrol of S. frugiperda may lead to substantial mortality of immature parasitoids, although field experiments have not yet demonstrated such an effect.     

Effect of differential host exposure on reproduction in the solitary ectoparasitoid Eupelmus vuilleti

We examined self-superparasitism in Eupelmus vuilleti (CRW.), a solitary ectoparasitoid of larvae of Callosobruchus maculatus (F.) which develop in cowpea seeds. The reproduction of isolated females was analysed in the presence of seeds containing 10 or 30 hosts for 24, 48, and 72 h. At the two host densities, female reproductive activity increased with host exposure time, but variations in offspring number per female were limited. The propensity of the females to self-superparasitise their hosts after long exposure times could explain these results. The offspring sex ratio was female biased but tended to 0.5 for longer exposure times. The absence of host renewal for a 3-day period was followed by an increase in self-superparasitism which reduced the parasitoid survival rate and by emergence of a lower number of females in the offspring. The offspring production was then analysed when females were provided with ten hosts a day or with 30 hosts every three days throughout their life span. The reduction of host renewal frequency did not affect male production but caused a reduction in the number of females emerging from the seeds. The importance of a high rate of self-superparasitism on the population biology of this parasitoid is discussed.     

Parasitism of the grasshopper Melanoplus sanguinipes by a sarcophagid fly, Blaesoxipha atlanis: influence of solitary and gregarious development on host and parasitoid

Blaesoxipha atlanis (Aldrich) (Diptera: Sarcophagidae) is a common parasitoid of the grasshopper Melanoplus sanguinipes (F.) (Orthoptera: Acrididae) in western Canada. We tested the hypothesis that B. atlanis can develop as either a solitary or a gregarious parasitoid, and assessed the influence of parasitism on the growth and survival of infected grasshoppers. Males and females of M. sanguinipes were parasitized manually with one, two, or three first-instar larvae of B. atlanis in the laboratory. Parasitism was more deleterious to males than females of M. sanguinipes; females are larger than males. Host survival and longevity declined with the number of larvae per host in a sex-specific manner. In females, 39%, 24%, and 8% of hosts containing, respectively, one, two, and three sarcophagid larvae survived parasitism. Although 41% of single-parasitized males survived, all males containing more than one larva died. Variations in host quality as measured by dry mass explained much of the response to parasitism in male, but not female, hosts. Parasitoid larvae, apparently, did not cause significant physical damage to host organs and tissues but instead functioned as a metabolic sink. The greater metabolic activity associated with egg production could account for the relatively higher tolerance to parasitism of female, as opposed to male, grasshoppers. Developmental time, adult size, and percentage survival of B. atlanis declined with the intensity of parasitism, especially in parasitoids developing in male hosts. Females developing gregariously contained fewer ovarioles at eclosion than counterparts developing as solitary larvae. The mean body size of field-collected B. atlanis did not differ from that of laboratory-reared parasitoids developing singly in a host. Gregarious development is an alternative strategy to solitary development that may enable B. atlanis to maintain population numbers during periods of grasshopper scarcity.     

Fecundity and oviposition ofEucelatoria bryani, a gregarious parasitoid ofHelicoverpa zea andHeliothis virescens

We examined longevity, fecundity, and oviposition strategies ofEucelatoria bryani Sabrosky (Diptera: Tachinidae), a gregarious endoparasitoid ofHelicoverpa zea (Boddie) andHeliothis virescens (F.) (Lepidoptera: Noctuidae). Longevity of adult femaleE. bryani was not related to body size. In contrast to longevity, largerE. bryani females had greater potential fecundity than smaller females, as determined by the number of embryonated eggs present in the common oviduct. However, female parasitoid size did not affect primary clutch size (number of eggs deposited in a host). Because embryos in eggs located in the ovisac were larger than those located elsewhere in the common oviduct, maximum primary clutch size may be physiologically limited by the number of fully mature eggs a female has available at one time.E. bryani females adjusted primary clutch size in response to host size, for bothH. zea andH. virescens. This adjustment appears to be adaptive because females did not overexploit hosts by depositing more larvae than a host could support. Adult emergence was not related to host size. Although host weight positively influencedE. bryani progeny weight, increases in progeny size with host size were counterbalanced by increases in primary clutch size with host size.     

Response of a parasitoid fly, Gymnosoma rotundatum (Linnaeus) (Diptera: Tachinidae) to the aggregation pheromone of Plautia stali Scott (Hemiptera: Pentatomidae) and its parasitism of hosts under field conditions

We studied the attraction of a tachinid fly, Gymnosoma rotundatum (Linnaeus) to the male-produced aggregation pheromone of the brown-winged green bug, Plautia stali Scott, its parasitism on the bug, and its seasonal occurrence in the field. The tachinid fly was continuously attracted to the aggregation pheromone from spring to autumn and utilized the bugs as hosts. Our field experiment to clarify the effect of the pheromone on parasitism demonstrated that parasitism occurred only in female bugs baited with synthetic aggregation pheromone and did not occur in females without the pheromone. The parasitoid flies therefore appeared to use the bug’s pheromone as a host-finding kairomone. The pheromone attracted not only female flies but also males. Male flies may increase their chance of encountering pheromone-attracted females by waiting near pheromone sources. The tachinid develops multiple generations in active hosts from spring to autumn and overwinters in dormant hosts. Thus, G. rotundatum seems to be highly adapted to using P. stali as its host, and it is a potentially important biological control agent of P. stali populations in the field.     

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.     

Does superparasitism improve host suitability for parasitoid development? A case study in the Microplitis rufiventris-Spodoptera littoralis system

Superparasitism refers to the oviposition behavior of parasitoid females who lay their eggs in an already parasitized host. Recent studies have shown that allocation of additional eggs to an already parasitized host may be beneficial under certain conditions. In the present work, mortality of Microplitis rufiventris wasps was significantly influenced by both host instar of Spodoptera littoralis larvae at parasitism and level of parasitism. In single parasitization, all host instars (first through sixth) were not equally suitable. Percentage of emergence success of wasp larvae was very high in parasitized first through third (highly suitable hosts), fell to 60% in the fourth instar (moderate suitable) and sharply decreased in the penultimate (5th) instars (marginally suitable). Singly parasitized sixth (last) instar hosts produced no wasp larvae (entirely unsuitable), pupated and eclosed to apparently normal adult moths. The scenario was different under superparasitism, whereas supernumerary individuals in the highly suitable hosts were almost always killed as first instars, superparasitization in unsuitable hosts (4th through 6th) had significant increase in number of emergence success of wasp larvae. Also, significantly greater number of parasitoid larvae successfully developed in unsuitable hosts containing three wasp eggs than counterparts containing two wasp eggs. Moreover, the development of surplus wasp larvae was siblicidal in earlier instars and nonsiblicidal gregarious one in the penultimate and last “sixth” instars. It is suggested that the optimal way for M. rufiventris to deal with high quality hosts (early instars) is to lay a single egg, while the optimal way to deal with low quality hosts (late instars) might be to superparasitize these hosts.     

Host Location of Hyssopus pallidus, a Larval Parasitoid of the Codling Moth, Cydia pomonella

The effectiveness of parasitoids as biological control agents depends largely on their host location behavior. In this study we describe the host-searching behavior of Hyssopus pallidus (Askew), a larval parasitoid of the codling moth Cydia pomonella L. We observed parasitoid behavior on mature apples (a potential host patch) and elucidated some of the stimuli which determine host location. Female wasps showed more complex and intensive searching on infested apples than on mechanically damaged or noninfested apples. Wasps were able to enter infested apples through the calyx or the tunnel made by the host larvae and parasitize them. Area-restricted searching was observed on infested apples, in particular on areas contaminated with host frass. In a further bioassay, we confirmed that host frass contains a host location kairomone. The kairomone appears to be produced by the host independently from its diet, even though frass produced by hosts fed on an apple are more attractive than frass produced by hosts fed on a fruit-devoid artificial diet. The capability of H. pallidus to locate its host inside apples makes the foraging strategy of this species potentially useful as a biological control agent.     

Vine mealybug sex pheromone increases citrus mealybug parasitism by Anagyrus sp. near pseudococci (Girault)

The present study was aimed at elucidating the role of lavandulyl senecioate (LS), the sex pheromone of Planococcus ficus, in host selection of the parasitoid Anagyrus sp. near pseudococci. Field trials were carried out in Portugal, Italy and Israel. The effect of LS on the parasitism rate of the wasp was determined by exposing sentinel mealybugs combined with pheromone dispensers impregnated with LS, in comparison with other baits: lavandulyl isovalerate (LI); planococcyl acetate (PAc); and unbaited control traps. In addition, in order to study the host location behavior of A. sp. near pseudococci, pheromone dispensers were placed at three different distances: inside the trap, 30 or 60 cm away from the trap. The number of parasitoid females inside the traps, the number of parasitized mealybugs, and the number of days required for the first parasitoid emergence were recorded. The response of A. sp. near pseudococci females to different doses of LS (25–1350 μg) was also evaluated using sticky plate traps. The rate of mealybug parasitism by A. sp. near pseudococci was significantly increased by LS in the three parasitoid populations. PAc and LI had no significant effect on the wasp parasitism rate in most of the trials. However, the Italian population of the parasitoid responded to PAc, showing apparently a different behavioral pattern. The number of parasitoid females trapped did not significantly differ between tested doses of LS. The use of LS as an arrestant in host location by the A. sp. near pseudococci female is discussed.     

Does aggregation behavior of codling moth larvae,Cydia pomonella,increase the risk of parasitism by Mastrus ridibundus?

Mastrus ridibundus is a specialist hymenopteran parasitoid that parasitizes last-instar larvae or prepupae of the codling moth, Cydia pomonella. Foraging females eavesdrop on an aggregation pheromone produced by cocooning larvae. We investigated whether larvae that cocoon in aggregation experience a greater rate of parasitism than larvae that cocoon in isolation. In wind tunnel experiments, 10 larvae in aggregations were more readily located by female M. ridibundus than 10 larvae well separated from each other. Similarly, aggregations of 30 larvae were more attractive to female M. ridibundus than those of 3 larvae. In cage experiments, larval cocooning in aggregation or isolation had no effect on the mean rate of parasitism and the mean number of eggs deposited per parasitized host. In Petri-dish experiments, the location of larvae within an aggregation significantly affected their rate of parasitism, with those in the center of an aggregation completely shielded from parasitism. Our data suggest that aggregation behavior by C. pomonella larvae does not appear to increase the rate of parasitism. The increased risk of aggregated larvae to be detected by M. ridibundus is likely offset by diluted parasitism risk and structural refugia effects that larvae in aggregation experience. As an egg-limited parasitoid, female M. ridibundus can parasitize on average only one larva in an aggregation, with the likelihood of parasitism for each larva being inversely proportional to the number of larvae in that aggregation.     

Pupation site and emergence time influence the mating success of bagworm females,Oiketicus kirbyi

In commercial oil palm plantations in Costa Rica, we tested the hypotheses that pupation site and emergence time affect the mating success of protogynous female bagworms,Oiketicus kirbyi (Guilding) (Lepidoptera: Psychidae). Greater proportions of female than male pupae on upper leaves of oil palms and greater proportions of mated females in the upper rather than lower crown strata support the hypothesis that selection of pupation site by female larvae influences the mating success of adults. Increasing captures of males with increasing trap height further suggest that enhanced mating success of females in tree tops may be attributed either to most effective dissemination of sex pheromone on higher sites, or to males foraging predominantly in the upper strata of oil palms. As the majority of females pupated in the middle rather than upper crown of oil palms, selection of pupation site by females may be affected by additional as yet unknown factors. Emergence of females significntly preceded emergence of males. Increasing proportions of mated females throughout the emergence seasons probably resulted from an increased ‘availability’ of males. In tropical rainforests with local variations inO. kirbyi developmental time and stage, protogyny may represent an evolutionary strategy that furthers outbreeding.     

Influence of water-stressed cassava on Phenacoccus herreni and three associated parasitoids

The influence of cassava Manihot esculenta Crantz grown under condition of water-stress on development and reproduction of the cassava mealybug, Phenacoccus herreni Cox & Williams, and levels of parasitism of three encyrtid parasitoids, Apoanagyrus diversicornis Howard, Aenasius vexans Kerrich, and Acerophagus coccois Smith, were studied in the laboratory. Two cassava cultivars were used: CM 507-37 (drought-tolerant) and CMC 40. A 30 day period of water stress, imposed by reducing the irrigation volume, led to a reduction in shoot development and stomatal conductance of leaves of both cassava genotypes. Phenacoccus herreni development and reproduction were favoured by cassava under water shortage. Parasitism decreased and water stress appeared to enhance the encapsulation of parasitoid eggs or larvae by the mealybug. In the case of the parasitoid A. diversicornis, there was a decrease in size of female progeny, suggesting a lower fitness in this species on cassava plants under water stress. All results indicated that cassava grown under low water availability favoured P. herreni development and reproduction, and affected the success of parasitism and, depending on the species, parasitoid development. The drought-tolerance characteristic of cassava genotypes and parasitoid species most suitable for controlling P. herreni in drought-stricken areas are discussed.     

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.     

Host specificity of the egg pupal parasitoid Fopius arisanus (Hymenoptera: Braconidae) in La Reunion

Fopius arisanus is a polyphagous parasitoid of Tephritidae, which has been recently introduced to La Réunion Island as part of a classical biological control programme. We carried out laboratory experiments to assess the host specificity of this parasitoid, initially reared on Bactrocera zonata, and then offered for parasitization the eight local tephritid pest species. Naive or experienced parasitoid females were given tephritid eggs in no choice tests. Fopius arisanus females parasitize all fly species but parasitism varies with host species. No adult wasps emerge from Bactrocera cucurbitae and the survival of this species is only slightly affected by parasitism. Dissections show that the late instars of this fly may eliminate the parasitoid by encapsulation. When developing on Ceratitis capitata, Ceratitis rosa, Dacus ciliatus, Dacus demmerezi, and Neoceratitis cyanescens, parasitoid survival rate ranges from 10 to 25%. Bactrocera zonata and Ceratitis catoirii are the best hosts, yielding parasitoid survival rates of more than 70% with no premature mortality. The egg-larval mortality of C. capitata, C. rosa, D. ciliatus, and N. cyanescens, and the pupal mortality of D. demmerezi, are significantly increased by parasitism. The size of emerging adults is affected by host species and is correlated to pupal weight. Bactrocera zonata would be a favorable host to support routine colonization of F. arisanus for mass production of this parasitoid.     

栗山天牛天敌花绒寄甲在栎林中的种群保持机制

花绒寄甲(Dastarcus helophoroides)(鞘翅目:寄甲科Bothrideridae)是寄生栗山天牛(Massicus raddei)中老龄幼虫和蛹的重要天敌,但其寄主栗山天牛世代周期长(3年1代)、发育比较整齐,不利于寄生性天敌种群数量的稳定.为了解利用花绒寄甲防治栗山天牛后,其种群能否在栎树林间长期保持较高的种群数量,达到持续控制栗山天牛的防治效果,调查研究了花绒寄甲在栎树林间的转主寄主和种群保持机制.结果表明,在东北辽东栎树干和树枝上除了栗山天牛外,还有其他8种天牛危害:双簇天牛(Moechotypa diphysis)、四点象天牛(Mesosa myops)、中华薄翅锯天牛(Megopis sinica)、锯天牛(Prionus insularis)、双带粒翅天牛(Lamiomimus gottschei)、八字绿虎天牛(Chlorophorus tohokensis)、日本绿虎天牛(C.japonicus)和拟蜡天牛(Stenygrinumquadrinotatum).其中以栗山天牛、双簇天牛、四点象天牛和拟蜡天牛数量较多,而花绒寄甲在辽东栎树干上的垂直分布与栗山天牛、双簇天牛和四点象天牛的垂直分布重叠较多.室内研究表明,花绒寄甲对四点象天牛老熟幼虫的寄生率达到26.67％,对蛹的寄生率达到了43.33％;对双簇天牛老熟幼虫的寄生率达到20.00％,对蛹的寄生率为6.67％.对双簇天牛和四点象天牛在林间的生活史调查和研究发现,花绒寄甲可寄生的这两种天牛的中老龄幼虫和蛹,在花绒寄甲不适宜寄生的栗山天牛幼龄幼虫期大量存在,表明双簇天牛和四点象天牛是花绒寄甲在栎树林中的主要转主寄主.由于这些转主寄主的存在,花绒寄甲在不利于其寄生的栗山天牛卵期、幼龄幼虫期可转移寄生这些寄主,从而在栗山天牛危害的栎树林间保持了较高的种群数量,达到对栗山天牛长期而有效的持续控制效果.     

The effect of host age ofLymantria dispar larvae [Lep.: Lymantriidae] on the development ofGlyptapanteles liparidis [Hym.: Braconidae]

The endoparasitic development ofG. liparidis was examined in 3 different host stages of gypsy moth larvae. Hatching ofG. liparidis-larvae occurred 3 to 5 days after oviposition in hosts parasitized during their premoulting period, and after 5 to 7 days in those parasitized in the 3^rd midinstar state. The parasites generally moulted to the 2^nd larval instar between the 11^th and 13^th day in the first group, and between the 13^th and 15^th day in the latter, when they had reached a volume of 0.04–0.05 mm³. The positive correlation between host ecdysis and the ecdysis of 1^st stadium larvae to L₂ suggested that host moulting influenced the development of the parasitoid larvae. Emergence from the host larvae occurred at 20°C after 27 days on average, and coincided with the parasites moulting to the 3^rd instar. Five to 7 days after spinning their cocoons near the developmentally arrested host larva, the male, and 1 to 2 days later the female wasps eclosed. Due to the variation in the number of parasites per host, no difference was observed between the hosts parasitized at various stages; however, a tendency for later parasitized hosts to contain more parasite larvae was evident. The nutritional conditions of the moth parental generation influenced both host and parasite development. On the other hand no influence of host age was observed on emergence dates of larvae and wasps.      

寄主大小及寄生顺序对蝇蛹佣小蜂寄生策略的影响

寄主大小模型认为寄生蜂后代性比与寄主大小相关,寄生蜂倾向于在大寄主上产出更多雌性后代,在小寄主上产出更多雄性后代.探讨了以家蝇蛹为寄主时,蝇蛹佣小蜂后代产量和性比变化;单次寄生情况下,寄主大小及寄生顺序对寄生蜂后代性比等影响.结果表明,蝇蛹佣小蜂的产卵期为(8.93±3.34)d,单头雌蜂能产雌性后代(34.11±16.34)头和雄性后代(11.04±8.87)头,且雄性百分比为0.24±0.11.随成蜂日龄的增大,寄生蜂产生雄性后代的比率显著增加.蝇蛹佣小蜂在寄生家蝇蛹时,会优先选择寄生个体较大的蛹;在单次寄生的情况下,蝇蛹佣小蜂倾向于在较大的家蝇蛹内产出更多的雌性后代.     

Acceptance and suitability of different host stages of Ceratitis capitata (Wiedemann) (Diptera: Tephritidae) and seven other tephritid fruit fly species to Tetrastichus giffardii Silvestri (Hymenoptera: Eulophidae)

Tetrastichus giffardii Silvestri is a gregarious eulophid endoparasitoid of several tephritid fruit fly species. Host stage suitability was studied using nine age groups of Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), namely, eggs less than 24 h and between 24 and 48 h old, and 1- to 7-day-old larvae. Life table studies for T. giffardii using C. capitata as host were done at 26 ± 5 °C and 55–60% RH. Egg load in relation to age of the female parasitoid was also assessed as was the effect of host deprivation on adult longevity. Host acceptance and suitability were examined with respect to eight species of tephritids. Potential hosts so tested were five Ceratitis species, the Medfly, C. capitata, the mango fruit fly, Ceratitis cosyra (Walker), the Natal fruit fly, Ceratitis rosa Karsch, Ceratitis fasciventris (Bezzi), and Ceratitis anonae Graham; two Bactrocera species, the melon fruit fly, Bactrocera cucurbitae (Coquillett) and the newly invasive Bactrocera invadens Drew, Tsuruta, and White; and one Dacus species, the lesser pumpkin fly, Dacus ciliatus Loew. No parasitoids were obtained from eggs while all larval stages were suitable though at varying degrees. Parasitism and number of progeny was related to host age in a curvilinear manner with maxima at 4- to 5-day-old larvae. By contrast, development time decreased with age of host larvae while sex ratio was not affected. The intrinsic rate of increase was 0.17 ± 0.01; gross and net reproductive rates were 64.9 ± 4.3 and 44.9 ± 3.8, respectively. Non-ovipositing females lived significantly longer than ovipositing ones. The females accepted all host species tested, but only C. capitata, D. ciliatus and, to a much lesser extent, C. cosyra were suitable. In the remaining host species, most eggs were encapsulated. In C. capitata and D. ciliatus, percent parasitism was similar, but number of progeny was lower and the sex ratio, as the proportion of females, was higher when the parasitoid was reared on D. ciliatus. Progeny per puparium were also similar for the two hosts. In the light of these results it can be concluded that T. giffardii has a narrow host range, but it attacks and successfully develops in larvae representing a wide range of ages.