Abstract: Parasitoid wasps often lay male eggs in small hosts and female eggs in larger hosts. The selective advantage of this strategy can be explained by assuming wasp fitness increases with host size and that this fitness increase is greater in females than in males. I conducted experiments to test a model based on this explanation and found the results generally supported the model with one exception; unlike what the model assumed, these wasps were unable to adjust their offspring sex ratios in each generation to different host size distributions. This finding suggests an alternate view as to how selection might operate in the evolution of parasitoid sex ratios.

Abstract: . 1. The ovipositional and egg allocation behaviour of individual females of Aphytis melinus DeBach and A.lingnunensis Compere were compared. 2. Both Aphytis species exhibit the same behavioural sequence during oviposition. 3. Aphytis melinus laid most of its female eggs on the dorsum of a scale-insect beneath its cover, and most of its male eggs under the scale-insect's body. Aphytis lingnanensis also oviposited both dorsally and ventrally on scale-insect hosts, but female and male progeny arose with equal frequency from eggs laid in both locations. 4. Both A.melinus and A. lingnanensis are facultatively gregarious parasitoids. The degree of gregariousness depends on host size, i.e. the larger the host, the more the Iikelihood that several eggs will be deposited at each visit by the parasitoid. 5. When two eggs were laid during the same host visit, both A.melinus and A.lingnanensis laid one female and one male egg more often than would be expected under an assumption of random allocation of sexes. 6. Because A.melinus successfulIy utilize smaller hosts than A.lingnanensis to produce progeny, these parasitoids should not be considered ecological homo-logues, as suggested by DeBach & Sundby (1963).

Abstract: The ability of parasites to influence the behavior of their hosts is an important aspect of parasite-host biology (Price, 1980). Holmes and Bethel (1972) review an extensive literature that documents the influence of parasites on the behavior of their intermediate hosts. They argue that these effects by parasites on their hosts are adaptations of the parasites to increase transmission to subsequent hosts. Holmes and Bethel suggest that parasites affect intermediate host behavior by reducing stamina, increasing conspicuousness, causing disorientation, and altering responses so that hosts are more susceptible to predation by the definitive host of their parasites. Modification of insect hosts by their parasitoids, however, has received little attention. Insect parasitoids, unlike parasites, are of relatively large size, they possess a freeliving stage, and their development kills the hosts; therefore their effect on host population dynamics resembles that of predators (Doutt, 1959). Parasitoids, other than insects, and parasitic castrators show similar characteristics (Kuris, 1974; Trail, 1980). Most insect species are attacked by one or more parasitoid species during their development. The growth, development, and survival of parasitized hosts are of direct consequence to the parasitoids; if the host dies before the parasitoid emerges, so does the parasitoid. Vinson (1975) developed the concept that host regulation is necessary for the parasitoid's success. He stated that growth and development of parasitoids were enhanced by physiological regulation of the host through venoms, hormones and parasitoid feeding. Parasitized hosts may behave differently from unparasitized hosts in predator avoidance responses, microhabitat selection, and developmental and growth rates. Some of these modifications may be adaptively significant, and promote the coevolution between the host and its parasitoid. Here I propose a hypothesis that extends Vinson's host regulation concept to explain the evolution of host modification by insect parasitoids. This hypothesis leads to predictions of the characteristics of hosts that should influence how parasitoids should modify their hosts.

Abstract: 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.

Abstract: The natural history of the parasitoids attacking Asteromyia carbonifera (O.S.) (Diptera: Cecidomyiidae) was studied. Five species were recorded: Platygaster solidaginis (Ashmed)(Hymenoptera: Platygasteridae); Torymus capite (Huber)(Hymenoptera: Torymidae); Tetrastichus fumipennis (Girault); Tetrastichus tesserus (Burkes) (Hymenoptera: Eulophidae); and a eulophid of an unknown genus[3][1]. Three aspects of parasitoid ecology were examined: (1) their trophic relationships with the host and with one another; (2) their temporal sequence of attack; and (3) foraging response to the number of host larvae per gall. All species fed parasitically on the host, but T. capite also feeds on previously parasitized hosts, on gall tissue, and as an adult drinks host haemolymph through a feeding tube. P. solidaginis attacks in the host's egg stage, T. fumipennis during early gall development, and T. capite and T. tesserus later in development. Time of attack may be related to the ability of the parasitoids to penetrate gall tissue. A negative correlation was found between the number of hosts per gall and the percent parasitism inflicted by T. tesserus ; no correlation was found in the cases of T. fumipennis and T. capite . [1]: #fn-1

Abstract: The progeny of Coccygomimus turionellae (L.) varied significantly in size and development time when reared on five host species. Regression analysis revealed that factors other than host weight affected parasitoid development. Within a particular host species, parasitoid size and development time were highly correlated to host weight. The age of the host also influenced its suitability; larval instars did not permit parasitoid development, whereas the late prepupae were 50% as effective as the pupae. There was a significant negative linear relationship between host age and parasitoid size within the pupal stadium. However, the relationship between the parasitoid's developmental period and its size broke down when host age increased. This indicated a relative increase in development period per unit weight with increased host age.

Abstract: . 1. The Caribbean and Central American eulophid wasp, Melittobia sp. 1 (hawaiiensis complex), (Hymenoptera: Chalcidoidea), whose larvae are exophagous on the prepupae of solitary wasps and bees, has three adult female and two adult male morphs. 2. The males, which constituted only 5% of the progeny, had morphs with, and without, ocelli. 3. In the females, brachypterous, negatively phototactic ‘crawlers’ developed mainly at low densities (<8.9 eggs cm-2), while above this density an increasing number and percentage of macropterous, positively phototactic ‘fliers’ were produced. Intermediate ‘jumpers’ were positively phototactic but could not fly. 4. In a typical progeny twenty to thirty ‘crawlers’, twenty to forty ‘jumpers' and up to 400 ‘fliers’ emerged in an overlapping sequence. 5. Experiments demonstrated that the proportions of the three morphs emerging were unrelated to the sequence in which the eggs were laid, to the species of the host and to the quality and absolute amount of food given, but related only to the density experienced by the young larvae. 6. We relate this trimorphism of dispersive female morphs to the three levels of ecological space (food item, patch and distribution of patches) postulated by Hassell & Southwood (1978) and suggest the general ecological conditions necessary for it to evolve.

Abstract: Studies were conducted on behavior, host relationships, immature morphology and population growth potential of Orgilus jenniae Marsh, an exotic parasitoid of the potato tuberworm (PTW), Phthorimae operculella (Zeller). Results were compared with similar studies on the exotic species, O. lepidus Muesebeck and O. parcus Turner, previously colonized but not established in southern California. Stalked eggs of O. jenniae are deposited in the abdominal hemocoel of host larvae. A solitary parasitoid larva develops internally, emerges before host pupation, and constructs a translucent-white cocoon within that of its host. The first of three larval instars is initially caudate- and and finally vesiculate-mandibulate; the last two are hymenopteriform. Immature dimensions and descriptions are presented. Parasitoids preferentially oviposit in first or second instar PTW in potato foliage, but there is an interaction between host age and density in tubers arising from actual parasitoid preference and characteristics of host mines. Developmental time from oviposition to adult parasitoid emergence depends on the host’s age at the time of oviposition, as the first parasitoid molt is synchronized to occurrence of the fourth host instar. Parasitism significantly reduces host larval growth. If O. jenniae has a preoviposition period, it is less than 3-hrs, but female progeny are not produced during the first 6-hrs after adult emergence or mating. A diurnal oviposition rhythm does occur, with progeny production peaking during the last half of the photophase. Courtship, mating, searching and oviposition behaviors are described. The mean fecundity was 375.2 and 436.8 eggs/female, the mean sex ratio, 23.6% and 28.4% females, and the mean adult female longevity, 25.5 and 16.9 days, when hosts were in potato tubers and foliage, respectively, at 25 ± 1 °C, 45 ± 5% RH and 12-hr photoperiod. Parasitoid life tables and statistics for hosts in potato tubers and

Abstract: Superparasitism in Aphis craccivora by Trioxys indicus was observed in the field and in the laboratory. A parasitoid which is ready to oviposit will not so readily lay eggs in parasitised hosts and search-deterring substances may reduce superparasitism. As the number of parasitised hosts in a container increases, the "escape" attempts of the parasitoid are more frequent. After a period of preening and standing-still, the parasitoid returns to the leaf, begins to encounter, prick, and probe the hosts again; the escape tendency apparently decreases. These activities either lower the oviposition threshold or overcome it resulting in superparasitism.

Abstract: Methods of estimating the probability of encounter and probability of parasitism given encounter are described for situations in which a host patch that has not been encountered by a parasitoid cannot be distinguished from one that has been encountered but none of the hosts have been parasitized. These methods provide estimates of quantities which do not vary with host density per patch unless parasitoid behavior changes, and therefore are the appropriate ones to use to detect effects of host density on the intensity of parasitism. An example is given, using published data on the parasitism of Heliothis zea eggs by Trichogramma spp.

Abstract: The occurrence of multiple parasitoid emergence from individual hosts was observed on numerous occasions. Characteristically such a phenomenon is extremely rare. In the observed instances of successful multiple parasitism of Autographa californica the parasitoid life history attributes of partial host consumption, gregariousness and timing of host parasitism are suggested as traits which contributed to certain species being able to coexist within individual hosts.

Abstract: Peristenus stygicusLoan develops inMirinae speciesLygus hesperus,Knight,L. lineolaris, (Palisot de Beauvois) andPolymerus basalis (Reuter),Orthotylinae speciesLabopidicola geminata (Johnston),Phylinae speciesPseudatomoscelis seriatus (Reuter) and partially develops in the mirineDichrooscytus sp. The parasitoids attackMicrophylellus maculipennis (Knight) (Phylinae) and another orthotyline species, but do not develop in these.Taedia johnstoni (Knight) (Mirinae), 2 species ofBrycorinae and 3 species ofLygaeidae are not acceptable as hosts. Olfactometer studies show the parasites are significantly more attracted to lygus nymphs whenPhaseolus vulgaris L. is present than either the nymphs or bean alone. Host color, mobility, size, previously infested plant material, and host plant species are rejected as host selection criteria.

Abstract: The developmental interactions between the gregarious endoparasitoidApanteles ruficrus Hal. and the army worm,Leucania separata Walker were investigated. The parasitoid preferred young host larvae and developed in 9.5 days irrespective of host age at the time of parasitization. The growth of parasitized host larvae were depressed. The net maximum weight of the host larva was positively correlated with the number of parasitoid eggs laid when the 2nd instar was parasitized. And when parasitizing in 2nd instar, the weight of parasitoid was negatively correlated with the number of eggs laid. The parasitoid has an ability to regulate the size of the host and the parasitoid itself according to the number of eggs laid when the host larva is very small.

Abstract: Epipompilis insularis females were found to attack 2 species of hunting spider, Clubiona cambridgei and Salticus sp., and oviposit on them. All spiders were females which had oviposited and were inside their nests with their eggs. After eating the spiders, the larval parasitoids fed on the developing eggs or post-embryos, a facet of behaviour not previously reported for a pompilid wasp.

Abstract: Aspects of the reproductive biology of the larviparous tachinid parasitoid Bonnetia comta were evaluated under laboratory conditions. Adult survivorship and age-specific fecundity curves were developed. Mean fecundity was 413 planidia per female; a small positive correlation was found between female size and fecundity. Thermoperiodic conditions and behavioral responses to photophase were shown to determine diel reproductive cycles. The intensity of larviposition by the fly was found to be governed by the quantity and quality (species) of larvipositional stimulant (host fecal pellets) present. The results demonstrate how a diurnally active parasitoid may obtain access to a nocturnally active, diurnally concealed host, and how certain physical and biological factors are involved in the allocation of reproductive resources in time and space.

Abstract: The ovipositional response of the parasitoid Meteorus leviventris (Wesmael) was examined over five host densities. Fecundity was the same for all host densities tested. Daily oviposition peaked ca. 48 h after emergence, then decreased as parasitoids aged. Both the total number of eggs deposited and the number of hosts parasitized per 12 h were significantly higher during the dark phase of the LD 12:12 cycle. The maximum number of hosts parasitized during a l2-h period for any parasitoid was 8, with an average of 3.5 hosts for parasitoids exposed to 12 hosts per 12 h. With increasing host density, more total hosts were parasitized, resulting in lower numbers of eggs per host and fewer incidences of superparasitism.

Abstract: Observations of Manduca sexta (L.) larvae parasitized by Apanteles smerinthi Riley indicated that parasitism induced only partial host developmental arrest, since host molting was suppressed during parasitoid emergence but not thereafter. After parasitization of first-stage M. sexta larvae, parasitoid emergence usually occurred during the host's fourth larval stage. Two to six days later, host larvae either underwent apolysis in preparation for larval molting or exposed the dorsal vessel; in both cases, the larvae later formed nonviable larval-pupal intermediates. In many hosts, cuticle was secreted over the surface of partly emerged parasitoids. The occurrence of postemergence molting suggests that the host's ecdysteroid titer rises after emergence, in contrast to the low ecdysteroid titers measured after emergence in larvae parasitized by A. congregatus (Say), a highly co-evolved parasitoid. Together with the finding that few A. smerinthi larvae that emerged spun cocoons and eclosed as adults, the observed anomalous effects of parasitism were interpreted as indicative that this species is poorly adapted to using M. sexta as its host even though the parasitoid frequently escapes encapsulation by host hemocytes. This report is the first description of postemergence molting in larval hosts of endoparasitic Hymenoptera.

Abstract: 1) Pachycrepoideus vindemiae Rondami, a pupal parasitoid of Drosphila, accepts puparia containing any stage of the larval parasitoids Asobara tabida Nees and Leptopilina heterotoma (Thomson) in experiments in which it could choose between equal number of puparia containing uparasitized Drosophila pupae and puparia containing some stage of the larval parasitoids. 2) P. vindemiae does not accept all stages of the larval parasitoids equally: stages in which the offspring of P. vindemiae have a higher survival chance and stages which produce larger P. vindemiae are more readily accepted for oviposition than those in which survival chances are lower or hosts which produce smaller wasps, hence, the selective acceptance of larval parasitoids as hosts is functional. 3) Proportionally more male offspring emerged from low quality hosts. The data suggest that this is caused by allocation of more male producing eggs to hosts that represent a lower amount of resource rather than by differential mortality.

Abstract: . Differences in the weight of parasitoid individuals of Brachymeria intermedia (Nees) (Chalcidae) and Coccygomimus turionellae (L.) (Ichneumonidae) were found to be associated with differences in host diet. The availability of the host nitrogen to the parasitoids differed depending on the sex of the host, Lymantria dispar, and its diet. Nitrogen utilization efficiency (NUE) for both parasitoid species were inversely correlated with host weight and with host nitrogen. Values for NUE are lower than those reported for phytophagous insects such as Lepidoptera.

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