Learning and natal host influence host preference,handling time and sex allocation behaviour in a pupal parasitoid

The host choice and sex allocation decisions of a foraging female parasitoid will have an enormous influence on the life-history characteristics of her offspring. The pteromalid Pachycrepoideus vindemiae is a generalist idiobiont pupal parasitoid of many species of cyclorrhaphous Diptera. Wasps reared in Musca domestica were larger, had higher attack rates and greater male mating success than those reared in Drosophila melanogaster. In no-choice situations, na?ve female P. vindemiae took significantly less time to accept hosts conspecific with their natal host. Parasitoids that emerged from M. domestica pupae spent similar amounts of time ovipositing in both D. melanogaster and M. domestica. Those parasitoids that had emerged from D. melanogaster spent significantly longer attacking M. domestica pupae. The host choice behaviour of female P. vindemiae was influenced by an interaction between natal host and experience. Female P. vindemiae reared in M. domestica only showed a preference among hosts when allowed to gain experience attacking M. domestica, preferentially attacking that species. Similarly, female parasitoids reared on D. melanogaster only showed a preference among hosts when allowed to gain experience attacking D. melanogaster, again preferentially attacking that species. Wasp natal host also influenced sex allocation behaviour. While wasps from both hosts oviposited more females in the larger host, M. domestica, wasps that emerged from M. domestica had significantly more male-biased offspring sex ratios. These results indicate the importance of learning and natal host size in determining P. vindemiae attack rates, mating success, host preference and sex allocation behaviour, all critical components of parasitoid fitness. Electronic Publication     

Clutch size adjustment, information use and the evolution of gregarious development in parasitoid wasps

As larvae, solitary species of parasitoid wasps eliminate rivals, including sibs, through contest competition. In gregarious species, larvae tolerate each other and several individuals can develop from a single host. We report experiments on two congeneric braconid species aimed at understanding how gregarious development evolved in one genus, and the consequences of larval interactions for parental behavior. In the transition from solitary to gregarious development, one possible intermediate stage is if solitary species frequently lay more than one egg per host. If the risk of conspecific superparasitism (another female of the same species oviposits into a single host) is high, optimal clutch size theory predicts the laying of multiple-egg clutches, because a female will increase the probability of the surviving larva being her own. Under the same conditions, theory predicts that gregarious species should reduce their clutch size. In our experiments, the solitary Aphaereta genevensis increased their clutch size under the risk of intraspecific competition for hosts whilst the gregarious A. pallipes reduced their clutch size, as predicted. In A. genevensis, the response to the risk of competition was dependent upon body size, being greatest amongst small females. In A. pallipes, the response did not depend on female body size, but clutch size increased with body size in all treatments, unlike in A. genevensis. Under the risk of competition from the other species, the response differed relative to the intraspecific treatments and differed between species. Thus, our data suggest that: (1) competition for hosts may have contributed to the evolution of gregarious development in this genus; (2) female wasps can combine information from both external and internal cues in complex ways during clutch size adjustment; and (3) the social environment may alter the adaptive response to both external and internal cues in adult females.Communicated by M. Elgar     

Breeding and moulting of barnacles under rearing conditions

The reproductive parameters of three species of barnacles common in warm-water regions,Balanus amphitrite Darwin,B. eburneus Gould andB. trigonus Darwin, cultured singly or in pairs for 2 1/2 yr, were compared. All specimens, collected from Tokyo Bay and studied between 1985 and 1987, were fed on newly hatchedArtemia sp. larvae (Tetra strain) and phytoplankton culture and were maintained under constant temperature (20°C) and controlled photoperiods (10 h light:14 h dark). The breeding frequencies of these three species were equally high, from 2 to 4 broods mo^–1 in the first year; they were relatively high between October and February, averaging 3 broods mo^–1.B. amphitrite, B. eburneus andB. trigonus produced 24, 21 and 11 broods yr^–1, respectively. Brood size was quite variable among the three species examined, yielding 4000 embryos brood^–1 inB. amphitrite andB. eburneus and 6000 inB. trigonus. Brood interval averaged 4 to 9 d. The moult occurred over short intervals of 4 to 10 d moult^–1. Both breeding and moulting frequencies were influenced by low temperature and starvation. Self-fertilization was observed in all species and was more frequent inB. amphitrite than inB. eburneus andB. trigonus. Nutritional condition and temperature seemed to be the main external factors regulating both breeding and moulting processes in barnacles.     

Effects of within- and among-patch experiences on the patch-leaving decision rules in an insect parasitoid

The present study aimed to address how an insect parasitoid makes patch-departure decisions from various types of host patches and how previous patch experiences in the environment modify this decision-making process. Experiments were done with the parasitic wasp Aphidius rhopalosiphi attacking the grain aphid Sitobion avenae. In the experiments, wasps were observed in a laboratory environment containing several patches of various host densities, and behavioural records were analysed using a Coxs proportional hazards model. Consideration of the effect of the within-patch experience gave a classic pattern of patch-leaving decision rules in parasitoids: A. rhopalosiphi used local information on host quality (i.e. numbers of ovipositions or rejections) and availability (i.e. patch density) to determine departure decision. However, consideration of previous patch experiences provided evidence that these departure rules are fundamentally dynamic, responding to the physiological state of the animal and the information it has about its environment. Results showed that A. rhopalosiphi decreased its tendency to leave the visited patch after an oviposition. However, when a female has already laid several other eggs in the environment, such an incremental mechanism gradually switched to a decremental one. Hence, A. rhopalosiphi responded to egg-load depletion by leaving the visited patches sooner and by depositing a smaller number of eggs in those patches, which probably led to a decreased level of superparasitism. Results also indicated that previous experiences enabled wasps to estimate spatial host distribution and then to adjust their behavioural decisions accordingly. Thus, A. rhopalosiphi was shown to adjust its patch residence time according to the quality and the number of the patches previously visited. These proximate mechanistic rules adopted by A. rhopalosiphi females are discussed in the context of general predictions from optimality models.Communicated by D. Gwynne     

Earlier sex change in infected individuals of the protogynous reef fish<Emphasis Type="Italic"> Thalassoma bifasciatum</Emphasis>

Sex allocation theory for sequential hermaphrodites predicts the size at which an individual should change sex, given the different relationships between individual size and reproductive success in the two sexes. We studied a host-parasite system where the myxozoan Kudoa ovivora infects the ovaries of the reef fish Thalassoma bifasciatum, a protogynous sequential hermaphrodite. The parasite sporulates in the hosts eggs and renders them infertile. It is thus expected to reduce the females reproductive success, and could thereby influence host sex change. We present data from marked fish we observed in the field over 4 months. The data suggest that females infected with Kudoa ovivora have a lower reproductive success, change sex earlier and at a smaller size than uninfected females. These results are in agreement with predictions from sex allocation theory, and provide the first example of a possible parasitic influence on the sex allocation of its host.Communicated by P. Heeb     

Egg production by the subtropical copepod Undinula vulgaris

Egg production by Undinula vulgaris, collected off Kaneohe Bay, Hawaii, was measured under field and laboratory conditions on 16 occasions from June to December 1991. In situ rates ranged from 0 to 15.7 eggs female^-1 d^-1, with a mean of 6.4 eggs female^-1 d^-1, 2.1% female body carbon d^-1. Maximum in situ production was 53 eggs female^-1 d^-1, 17.2% C d^-1. Average egg production (Y, eggs female^-1 d^-1) was related to the concentration of particulate carbon (X, g C l^-1) by the Ivlev function, Y=13.9[1-e^{-0.0097 (x-10)}], with R ²=0.96. Individuals with the same feeding history produced more eggs at lower temperatures in the laboratory. Egg production was not significantly correlated with dry weight, and no noticeable temporal trend was found. Despite the elevated habitat temperatures (26 to 27°C) of this subtropical copepod, maximum fecundity of U. vulgaris was comparable to, but average rates were lower than, egg production rates of similarly-sized, temperate and borcal species of the genus Calanus. Our results caution against broad extrapolations of the temperature-growth relationship for temperate coastal copepods to species from poorly studied, oligotrophic regions of the oceans.Contribution No. 3257 from the School of Ocean and Earth Science and Technology, University of Hawaii at Manoa, Honolulu, Hawaii 96822, USA     

Correlations of food distribution and patch size with agonistic interactions in female vervets (Chlorocebus aethiops) and patas monkeys (Erythrocebus patas) living in simple habitats

Food distribution is hypothesized to be important in determining the nature of female relationships within social groups of primates. When food limits female reproductive success, spatially clumped foods are expected to produce strong, linear dominance hierarchies within groups, whereas more spatially dispersed foods are expected to produce weaker or non-existent dominance hierarchies. The association between food distribution and competitive relationships presumably occurs because clumped foods are usurpable but dispersed foods are not. We examined the spatial distribution of food patches (trees) and patch size relative to feeding behavior and agonistic interactions in vervets and patas monkeys, two closely related and sympatric species that nonetheless differ in the strength of the female dominance hierarchy. Food patches of both patas monkeys and vervets were small in size and randomly distributed in Acacia drepanolobium habitat. In contrast, in A. xanthophloea woodland, the habitat type that was exclusively used by vervets, food patches were larger and more spatially clumped. These similarities and differences between and within species were correlated with similarities and differences in the strength and linearity of their dominance hierarchies. Patas monkeys and vervets in A. drepanolobium habitat had dominance hierarchies that were weakly defined because there were relatively few agonistic interactions between females. By contrast, in A. xanthophloea habitat, vervets had a stronger, linear dominance hierarchy characterized by a higher rate of agonistic interactions over food. The covariation of agonistic interactions with patch size is discussed in relation to depletion time, another characteristic that may covary with food distribution, and resource renewal rate, an important determinant of agonistic interactions in insectivorous birds, fishes, insects, and mammals. Received: 18 February 2000 / Revised: 5 September 2000 / Accepted: 26 September 2000     

Oviposition height increases parasitism success by the robber fly Mallophora ruficauda (Diptera: Asilidae)

For parasitoids, host finding is a central problem that has been solved through a variety of behavioural mechanisms. Among species in which females do not make direct contact with hosts, as is the case for many dipteran parasitoids, eggs must be laid in an appropriate part of the host habitat. The asilid fly Mallophora ruficauda lays eggs in clusters on tall vegetation. Upon eclosion, pollen-sized larvae fall and parasitize soil-dwelling scarab beetle larvae. We hypothesized that wind dissemination of M. ruficauda larvae is important in the host-finding process and that females lay eggs at heights that maximize parasitism of its concealed host. Through numerical and analytical models resembling those used to describe seed and pollen wind dispersal, we estimated an optimal oviposition height in the 1.25- to 1.50-m range above the ground. Our models take into account host distribution, plant availability and the range over which parasitic larvae search for hosts. Supporting our findings, we found that the results of the models match heights at which egg clusters of M. ruficauda are found in the field. Generally, work on facilitation of host finding using plants focuses on plants as indicators of host presence. We present a case where plants are used in a different way, as a means of offspring dispersal. For parasitoids that carry out host searching at immature stages rather than as adults, plants are part of a dissemination mechanism of larvae that, as with minute seeds, uses wind and a set of simple rules of physics to increase offspring success.     

Responses of Metaphycussp. nr. flavus to semiochemicals released from a scale host, Coccus hesperidum

Summary. Metaphycus sp. nr. flavus (Encyrtidae: Hymenoptera) is a parasitoid species collected from the Mediterranean region which lays its eggs in the immature stages of several economically important soft scale insects (Hemiptera: Coccidae), including brown soft scale, Coccus hesperidum L. (= host insect). Preliminary tests suggested that the parasitoid is most successful in producing offspring when it oviposits in the younger stages of brown soft scale. In Y-olfactometer bioassays measuring wasp choices and residence times, naïve parasitoids were significantly more attracted to yucca leaves infested with 26, 27, or 28 d-old scale than to uninfested leaves, whereas leaves with older (29-30 d-old) scale were no more attractive than uninfested leaves. Parasitoids also spent significantly more time in the arm with yucca leaves infested with 26 d-old scale than in the arm with uninfested leaves. These results are consistent with observations of the parasitoids reproductive success on scale of different ages, whereby older scale are more likely to encapsulate the developing eggs of M. sp. nr. flavusfemales than are younger scale. Further bioassays determined that yucca leaves that had been infested with 26 d-old scale but from which the scale had been removed were as attractive as infested leaves. In contrast, infested yucca leaves from which scale had been removed and the leaves subsequently washed with distilled water were less attractive than infested leaves. Furthermore, the wash water containing scale residues was attractive to female wasps. In total, these results suggest that Metaphycussp. nr. flavus females utilize volatile, water soluble compounds produced by brown soft scale as cues to locate suitable hosts.     

Parasitic wasps orient to green leaf volatiles

Summary Undamaged plants emit low levels of green leaf volatiles (GLVs), while caterpillar-damaged and artificially damaged plants emit relatively higher levels of certain GLVs. Female braconid parasitoids,Microplitis croceipes, oriented to both damaged plants and to individual GLVs in no-choice tests in a wind tunnel, but seldom oriented to undamaged plants. Female ichneumonid parasitoids,Netelia heroica, also oriented to individual GLVs in a wind tunnel. Males of both wasp species failed to orient to the GLVs. These data show that leaf-feeding caterpillars can cause the release of GLVs, and that parasitic wasps can respond to these odors by flying upwind (chemoanemotactic response), which brings the wasps to their caterpillar hosts. This supports the hypothesis that plants communicate with members of the third trophic level,i.e., plants under herbivore attack emit chemical signals that guide natural enemies of herbivores to sites of plant damage. In this interaction, the GLVs serve as tritrophic plant-to-parasitoid synomones. That parasitoids from two different wasp families oriented to GLVs suggests that the response may be widespread among the Hymenoptera.Mention of a commercial or proprietary product does not constitute an endorsement by the U.S. Department of Agriculture     

Aphid alarm pheromone (E)-β-farnesene: A host finding kairomone for the aphid primary parasitoidAphidius uzbekistanicus (Hymenoptera: Aphidiinae)

Summary The present study aimed to test the possible function of the aphid alarm pheromone (E)--farnesene (EBF) as a host finding kairomone for aphid primary parasitoids. Extracts of volatile emissions of undisturbed aphids and of aphids under parasitoid attack were obtained by air entrainment. Extracts of cornicle secretions were gained by disturbing aphids and taking their secretions into solution. Extracts were compared by gas chromatography. Only air entrainments of aphids under attack and solvent extracts of cornicle secretions contained the alarm pheromone. In Y-tube olfactometer bioassays, femaleA. uzbekistanicus were attracted to aphid groups under attack of parasitoids, presumably by released EBF. High concentrations of synthetic EBF (1.4 µg to 5.7 µg) also attractedA. uzbekistanicus females. Females with oviposition experience reacted more readily to lower concentrations of EBF than females without experience. In experiments designed as Petri-dish bioassays, the test animals could contact filter paper discs that were treated with solutions containing EBF. Behavioural effects like antennation or stinging attack were not observed. With computer video analysis of parasitoid movements, some effects onA. uzbekistanicus behaviour were detected, again indicating attraction to EBF.As the volatile aphid alarm pheromone attractedA. uzbekistanicus females, it can be concluded that this chemical stimulus acts as a host finding kairomone for this parasitoid species. However, its effect over long distances seems to be limited due to the relatively high concentrations required for reactions. Of two other parasitoid species examined (P. volucre andL. testaceipes) onlyP. volucre was also significantly attracted to the volatile EBF in the Y-tube olfactometer.     

Differences in the species- and size-composition of fish assemblages in three distinct seagrass habitats with differing plant and meadow structure

Fish faunas were sampled seasonally using a large and a small beam trawl in three seagrass habitats comprising predominantly Amphibolis griffithii or Posidonia sinuosa or Posidonia coriacea, which differ in seagrass and meadow structure. Amphibolis griffithii and P. sinuosa both produce a relatively dense leaf canopy, but the former exhibits a distinct architecture, with the leaf canopy overlying relatively open spaces surrounding woody stems, compared to the uniformly dense blade-like leaves of P. sinuosa which emerge directly from the sediment. In comparison, P. coriacea provides a landscape of patchy seagrass amongst areas of bare sand. Since the latter seagrass habitat contains large areas of sand, fish were also sampled in adjacent unvegetated areas. The number of species and density of fish were greater (P<0.05) in P. sinuosa than in either A. griffithii or P. coriacea. The mean number of species caught using the large trawl ranged from 16 to 24 in the first of these habitats compared to 14–21 and 9–15 in the last two habitats, respectively, and the mean densities ranged between 78 and 291 fish 1000 m^?2 in P. sinuosa compared to 31–59 fish 1000 m^?2 in A. griffithii and 31–59 fish 1000 m^?2 in P. coriacea. The biomass of fish was greater (P<0.05) in both P. sinuosa and A. griffithii than in P. coriacea (4.2–5.3 kg and 3.3–6.2 kg versus 0.7–1.9 kg 1000 m^?2, respectively). Furthermore, the size-structure of fish differed among these habitats, where the median weight of fish was 72.1 g in A. griffithii, compared to 7.5 g and 19.8 g in P. sinuosa and P. coriacea, respectively. Ordination and ANOSIM demonstrated that the species-composition differed markedly among the three seagrass habitats (P<0.001), suggesting that fish species display a distinct preference for particular seagrasses characterised by different architecture. Differences in species-composition among the seagrass habitats partly reflected the size-composition of fish in each habitat. The open space below the canopy of A. griffthii is likely to allow larger fish to occupy this habitat, whereas only small fish would be able to penetrate the dense foliage of P. sinuosa. Differences in species- and size-composition of fish among these habitats may be the result of settlement-sized larvae discriminating between particular seagrass and meadow structures, or fish being subject to different levels of predation and/or accessibility to food or space. The species-composition in P. coriacea was highly dispersed and did not differ from that of unvegetated areas. While several species were associated with both P. coriacea and bare-sand habitats, some species did display a high affinity with the seagrass P. coriacea. This may reflect an association with the sparse and narrower leaves of this seagrass or with the patchy occurrence of the seagrass Heterozostera tasmanica, which commonly occurs as an understorey in this habitat.     

Nemertean,copepod, and amphipod symbionts of the dimorphic ascidian Pyura stolonifera near Melbourne,Australia: specificities to host morphs,and factors affecting prevalences

On the central coast of Victoria. Australia, the dimorphic ascidian Pyura stolonifera (Heller, 1878) harbors three endosymbionts: the nemertean Gononemertes australiensis Gibson, 1974, the copepod Doropygus pulex (Thorell, 1859), and the amphipod Paraleucothoe novaehollandiae (Haswell, 1880). The specificities of these symbionts to two host colour morphs were studied during 1989 to 1991 as part of a multidisciplinary investigation aimed at determining whether the two morphs are genetically distinct. Distributional surveys revealed that nemerteans and copepods occur only in yellow and brown ascidians, respectively, and that amphipods live in both forms. These specificities held true not only when the two morphs were in allopatry, but also in sympatry. These observations, especially the sympatric data, suggest that the two host morphs might be genetically distinct. For example, the two morphs might have different genetically encoded internal milieus that favour the survival of nemerteans in yellow ascidians, and copepods in brown hosts. In transplant experiments, which involved moving ascidian morphs within and between habitats, the wrong symbionts never colonised the wrong hosts. These results, although consistent with the hypothesis of genetic maintenance of specificity, were deemed inconclusive because of the difficulty of establishing reliable controls (i.e. vacant hosts). The relationships between symbiont prevalences and several factors (season, year, site within host, host individual, host habitat, host size/age, host breeding condition, and co-occurrence of other symbiont species) were also analysed. Both simple (e.g. greater prevalences for large hosts) and complex (e.g. prevalence x season x gonad state of host) interactions were detected for all three symbiont species. These are among the very few quantitative analyses of factors affecting prevalences of ascidicolous nemerteans and amphipods. The present report identifies one of very few definite nemertean-ascidian symbioses. Since no differences in gross condition were ever noticed between occupied and vacant hosts, it is suggested that all three symbionts are commensals rather than parasites or mutuals.     

A comparison of strike and prey capture kinematics of three species of piscivorous fishes: Florida gar ( Lepisosteus platyrhincus), redfin needlefish ( Strongylura notata), and great barracuda ( Sphyraena barracuda)

Ram feeding is the process by which a predatory fish uses a high-velocity lunge or chase to overtake its prey. This study compares the strike and prey capture behaviors and kinematics of three species of ram-feeding fishes: Florida gar Lepisosteus platyrhincus, redfin needlefish Strongylura notata, and great barracuda Sphyraena barracuda. These ram-feeding piscivores are morphologically similar with fusiform bodies, posteriorly placed dorsal and anal fins, and large, conical teeth. Strike and prey capture kinematics for five individuals of each species were recorded with high-speed video. Pre-strike behavior in L. platyrhincus consists of a slow stalk, resulting in the close, lateral positioning of the predators head relative to the prey. Lepisosteus employ a sideways lunge of the head during the strike, which lasts only 25–40 ms and is the most rapid strike among these three species. Strongylura notata and Sphyraena barracuda exhibit longitudinal orientation to the prey before the strike, followed by a high velocity, head-on lunge, initiated by an s-start in Sphyraena barracuda. Prey capture in adult L. platyrhincus and Strongylura notata is characterized by the jaws closing on the prey, with the prey held orthogonal to the jaws. This is followed by manipulation using the inertia of the prey to reposition the prey head first, and then suction transport into the buccal cavity. Prey capture in juvenile Sphyraena is accomplished by closing the jaws after the prey has entered the buccal cavity, resulting in possible ram transport of the prey with no oral manipulation under these experimental conditions. Although these three species all employ ram feeding for prey capture of elusive prey, each species has a unique repertoire that appears to minimize hydrodynamic constraints and prey response, utilize locomotory capabilities, and may be suited to each species specific habitat.Communicated by P.W. Sammarco, Chauvin     

Ultrastructure of the mature spermatozoon of the coconut crabBirgus latro (Coenobitidae: Paguroidea: Decapoda)

The spermatozoon ofBirgus latro (Linnaeus, 1767) is approx 14µm in length. It is composed of a large multi-layered oblong-ovoid acrosome which is capped by a conical operculum and lies anterior to a small ring of cytoplasm and an amorphous nucleus which is drawn out into a series of arms or extensions. Originating from the cytoplasmic area are three further long microtubular arms. The sperm ofB. latro is very similar to the sperm of the only other genus in the Coenobitidae,Coenobita, of whichC. clypeatus is a representative species. They share a suite of ultrastructural characters including: a long, cylindrical, capsule-bound acrosome containing an inner acrosome core, a large acrosome ray zone and a thin outer acrosome zone; an apical operculum anterior to a subopercular zone divided into two areas of differing density; an invaginated perforatorial zone with a bipartite granular matrix; microvillus-like extensions of the inner acrosome core projecting into the perforatorial invagination; a ring of cytoplasm, around the base of the acrosome, containing numerous mitochondria, extensive lamellar systems and the bases of three microtubular arms; granular nuclear material forming irregular arms; and at the posterior portion of the cell membrane a combination of nuclear and plasma membranes. Some ultrastructural characters which separate the two genera are: a domed operculum inC. clypeatus as opposed to a conical one inB. latro; inB. latro there is some residual cytoplasm external to the operculum and centrioles are absent from the mature spermatozoon; inC. clypeatus the inner acrosome core does not appear to invest the perforatorium and a series of dense rods are found subjacent and internal to the operculum. Similarities between the two coenobitids are greater than those shared with the paguridEupagurus bernhardus. In this latter species, the acrosome is more ovoid than cylindrical and the acrosome zones are less conspicuous; the operculum is absent from the mature sperm (although present during spermiohistogenesis); no subopercular zone is present; the perforatorium contains longitudinally arranged microtubules and extends the full length of the acrosome; and the nuclear material does not form separate nuclear arms. Sperm ultrastructure supports monophyly of the Paguroidea, while distinguishing coenobitids from pagurids within this superfamily.     

Diversity, ecosystem function, and stability of parasitoid-host interactions across a tropical habitat gradient

Global biodiversity decline has prompted great interest in the effects of habitat modification and diversity on the functioning and stability of ecosystem processes. However, the applicability of previous modeled or mesocosm community studies to real diverse communities in different habitats remains ambiguous. We exposed standardized nesting resources for naturally occurring communities of cavity-nesting bees and wasps and their parasitoids in coastal Ecuador, to test the effects of host and parasitoid diversity on an ecosystem function (parasitism rates) and temporal variability in this function. In accordance with predictions of complementary host use, parasitism rates increased with increasing diversity, not simply abundance, of parasitoids. In contrast, parasitism decreased with increasing host diversity, possibly due to positive prey interactions or increased probability of selecting unpalatable species. Temporal variability in parasitism was lower in plots with high mean parasitoid diversity and higher in plots with temporally variable host and parasitoid diversity. These effects of diversity on parasitism and temporal stability in parasitism rates were sufficiently strong to be visible across five different habitat types, representing a gradient of increasing anthropogenic modification. Habitat type did not directly affect parasitism rates, but host and parasitoid diversity and abundance were higher in highly modified habitats, and parasitoid diversity was positively correlated with rates of parasitism. The slope of the richness-parasitism relationship did not vary significantly across habitats, although that for Simpson's diversity was significant only in rice and pasture. We also show that pooling data over long time periods, as in previous studies, can blur the effect of diversity on parasitism rates, and the appropriate spatiotemporal scale of study must be considered.     

Parasitoid learning during interactions with ants: how to deal with an aggressive antagonist

Pauesia picta, P. pinicollis and P. silvestris (Hymenoptera: Aphidiidae) are common parasitoids of the conifer aphid Cinara pinea, which is regularly attended by red wood ants (Formica spp.). In this study, I tested whether females of these parasitoid species learned during interactions with honeydew-collecting Formica polyctena workers that caution is not necessary if searching behaviour is adapted, and whether parasitoids benefit from being able to learn. When searching on Scots pines, naive females of P. picta and P. pinicollis generally retreated to a pine needle when making contact with a honeydew-collecting ant, did not approach ants from the side or from the front and kept a ”safe distance” from ants when sitting on needles. After some non- aggressive ant encounters, experienced female parasitoids changed their behaviour: they reduced their searching speed, approached ants from the side and even from the front, retreated less often in response to an approaching ant and reduced the ”safe distance”. These experienced females had a significantly higher rate of oviposition than naive females or females foraging for an unattended host. Thus, the ability of the parasitoid to learn during interactions with an antagonist led to a prolonged retention time and a higher oviposition rate. By contrast, there was no evidence of learning in P. silvestris. Females of this species showed no behavioural change in response to ant encounters, and there was no difference in the foraging success of naive and experienced female parasitoids. Received: 7 December 1999 / Revised: 23 September 2000 / Accepted: 10 March 2000     

A survey of identified kairomones and synomones used by insect parasitoids to locate and accept their hosts

Summary The host utilization process of insect parasitoids can be described by three stages of (1)habitatlocation, (2)host-location, and (3)host-acceptance andoviposition. There are 19 systems in which chemicals used inhabitat-location have been identified, 12 systems in which chemical cues leading tohost-location have been identified, and 16 systems in which chemicals elicitinghost-acceptance andoviposition have been identified. Both the chemical class and the source of the infochemical change with the stage of the host utilization process. Semiochemicals identified in thehabitatlocation stage were predominantly aldehydes, alcohols, sulfur-containing compounds, esters and terpenes, and were equally likely to be from the host-plant of the host, or from the host itself. Semiochemicals identified in thehost-location stage were sugars, alkanes, terpenes and heterocyclic aromatic compounds and 3/4 of them were host-produced cues. In thehost-acceptance andoviposition stage the identified semiochemicals were all produced by the host and were proteins, amino acids, triglycerides and salts. The importance of recognizing specific cues involved in host utilization by parasitoids is discussed, and suggestions for future research are made.     

The effect of feeding behavior of the gastropods<Emphasis Type="Italic"> Batillaria zonalis</Emphasis> and<Emphasis Type="Italic"> Cerithideopsilla cingulata</Emphasis> on their ambient environment

Feeding behaviors of the gastropods Batillaria zonalis, a suspension and deposit feeder, and Cerithideopsilla cingulata, an obligate deposit feeder, were studied to examine their effect on dynamics of suspended materials, total nitrogen (TN) and total organic carbon (TOC) in sediments. Suspension feeding in B. zonalis was observed in detail visually, as it had been previously unreported. An experimental system where B. zonalis and C. cingulata were cultured for 10 weeks, using previously frozen microalgae Nannochloropsis oculata as food, was then constructed. During feeding observations, the suspension-feeding B. zonalis formed a mucus food cord to entangle particulate materials, which were subsequently ingested. The feeding mode of B. zonalis is hence categorized as ctenidial filter feeding. For the culture experiments, decreases in suspended materials were seen only in the B. zonalis cultures, while the control (no gastropods) and C. cingulata cultures remained nearly unchanged. Sediment TN and TOC showed no significant differences between B. zonalis (with mean TN at 0.0345% and mean TOC at 0.261%) and control cultures (with TN at 0.0389% and TOC at 0.331%), but the sediments in C. cingulata cultures had lower levels (with TN at 0.0204% and TOC at 0.156%). The C/N ratios were similar for both B. zonalis (7.55) and C. cingulata (7.68) cultures, and both were lower than the control cultures (8.55). The filtration rate for B. zonalis was lower than that previously observed in bivalves inhabiting the same intertidal flat (e.g. Cyclina sinensis, Grafrarium tumidum and Barbatia virescens). However, Batillaria zonalis occurs at higher abundances than these bivalves. Therefore, it is expected that this species has a large affect upon the transport of suspended materials to the sediments. The addition of TN and TOC to sediments in B. zonalis cultures was probably caused by biodeposition, but deposit feeding by B. zonalis may have restrained the accumulation of those components. The impact of deposit feeding in Cerithideopsilla cingulata cultures was most probably stronger than sedimentation and biodeposition, because of the lower sediment TN and TOC. Bioturbation by both B. zonalis and C. cingulata yields the same effect on sediment quality, as indicated by the low C/N in the culture sediment of both treatments, despite difference in feeding modes. This paper demonstrates, for the first time, the importance of gastropods in bioturbation and removal of suspended materials in subtropical tidal flat habitats.Communicated by T. Ikeda, Hakodate     

Cleptoparasitism increases the host finding ability of a polyphagous parasitoid species,<Emphasis Type="Italic"> Rhopalicus tutela</Emphasis> (Hymenoptera: Pteromalidae)

Host finding abilities were investigated in the braconid Coeloides bostrichorum and the pteromalid Rhopalicus tutela, two ectoparasitoid wasps attacking the late instar of the bark beetle Ips typographus. Under laboratory conditions, important differences in the host-searching behaviour of these species were found, R. tutela being highly mobile as compared to C. bostrichorum. In the presence of C. bostrichorum, R. tutela behaved as a cleptoparasitoid, displacing the females from their oviposition sites and stealing the hosts previously located by the braconid. This behaviour facilitated host finding in R. tutela and could partly explain the relative success of the polyphagous R. tutela when occurring with the more specialised C. bostrichorum.Communicated by R.F.A. Moritz