摘要:

Abstract.1Caterpillars of the facultatively myrmecophilous butterflyPolyommatus icaruswere reared on inflorescences, or foliage, of four natural hostplant species and on an artificial diet to study dietary effects on larval growth and secretory capacity.2Caterpillars achieved highest weights and relative growth rates when fed flowersof Medicago sativa, Lotus corniculatusorMelilotus officinalis.Larvae reared onCoroniüa varia(flowers and leaves), foliage ofM.sativaand on the artificial diet pupated at lower weights and achieved lower growth rates.3In standardized experiments with the ant speciesLasius flavus, secretion rates from the dorsal nectar organ (DNO) were 2 times higher among flower‐fed caterpillars than among foliage‐fed siblings or caterpillars on the artificial diet. Larvae reared onC.variaflowers were superior to all other food treatments with respect to secretion rates.4High water content of larval diet, as in flowers, appears to be important for lycaenid caterpillars to achieve high secretion rates, whereas the correlation between myrmecophily and nutrient availability, as evidenced by growth rates, was less pronounced.5Using experimental data on larval growth and secretion rates, the lifetime volume of secretions from the DNO is estimated to range from 2 to 5 μl in most food treatments. Only onC.variaflowers (5.5–8.7 μl) and onM.sativaleaves (0.9–1.1 μl) did the caterpillars deviate in their absolute investment in myrmecophily.6The estimated lifetime investment accounted for 1.6–5.5% of prepupal fresh weight in all food treatments except onC.variaflower

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1996.tb00259.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract.1There was little overlap in the species composition of carabid beetle assemblages sampled below 450 m and above 800 m on an altitude transect and the first axis of a DECORANA ordination was closely correlated with altitude (r11= 0.93,P<0.001), probably reflecting the differing temperature requirements of different species.2Life‐cycle strategies of two low‐altitude species, found predominantly below 600 m, and two species caught above 600 m a.s.l., have been determined, using mandible wear to identify whether the females breed in the calendar year that they emerge as adults or in the year following.3Nebria salinahas an annual cycle at 630 m.Pterostichus madidusandCalathus fuscipeswere both biennial at altitudes above 300 m although predominantly annual at low altitude.N.gyllenhaliwas biennial above 600 m and it is not known whether it is able to switch to an annual cycle at low altitude.4BothN.salinaandN.gyllenhaliceased activity soon after emergence, an adaptation which preserves their mandibles from wear.5At altitudes of 305 m and 430 m,P.madidusandC.fuscipesentered the breeding season with 33% and 56% reduction in mandible tip length, possibly reducing their reproductive output.6The necessity for relatively sharp mandibles on entry into the breeding season may restrict the capacity of carabids to respond to a temperature change by switching from annual to biennial cycles, and vice versa, adding support to the suggestion that carabids are more likely to respond to climate change by shifting distributions than by physiological adaptat

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1996.tb00260.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract.1The reproductve biology ofVarroa jacobsoni, whose females infest honeybee brood, was studied in natural and transparent artificial brood cells. These investigations were made under the headings of maturation behaviour and fertilization, and the influence of infestation rate of brood cells on the number of mated females produced per infestingVarroa.2Mating ofVarroadaughters, observed in the transparent brood cells with time‐lapse video, occurs just after ecdysis and as soon as they arrive on the faecal accumulation prepared by the mother. Such females are remated for as long as no other freshly moulted daughter arrives on the faecal accumulation.3The number of spermatozoa stocked in the spermatheca increases with remating, a strong indication for sperm mixing in this species when brood cells contain more than oneVarroafoundress.4The number of daughters per infesting mother decreases at higher rates of infestation per cell, but the proportion of such daughters with a mate rises sharply due to the higher probability of finding a male within multi‐infested cells. The number of mated daughters per mother is maximal in cells with two foundressVarroafemales.5The frequency distributions of infesting mites in drone cells are aggregated, and approximate to negative binomial distributions.6We postulate from the above that the observed non‐random infestation byVarroain drone brood augments the mite's mean reproductive success through the production of a higher number of mated daughters than the corresponding Poisson distributions

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1996.tb00261.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract.1Female parasitoid wasps (Hymenoptera) must search for hosts to reproduce, but only require mates if their broods are to contain female progeny. In outbreeding species, females locate mates after dispersal from the emergence site. Unmated females may therefore face a trade‐off between searching for hosts and searching for mates, if hosts and mates are spatially separated.2In the outbreeding parasitoidBracon hebetorSay (Hymenoptera: Braconidae), males and females are spatially segregated in the field. Females are found primarily below the surface of stored corn where they search for hosts, whereas males are found on or above the surface.3Wasps placed in laboratory observation chambers designed to mimicB.hebetor'sstored corn habitat distributed themselves in a manner consistent with field observations. Males remained on the surface of the grain, whereas females moved below the surface to attack hosts.4In the laboratory, female distribution was influenced by their mating status, the presence of males or hosts, and female age. Virgin females were more reluctant to move into the corn than were mated females, younger females foraged deeper than older females, and all females moved deeper into the com when males were present.510% of all females did not mate even when males were present in the chambers, a percentage consistent with previous observations from the field. IfB.hebetorfaces a trade‐off between host‐searching and mate‐searching, the trade‐off seems to be part of 'split sex ratio strategies', with some females remaining constrained to producing only male

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1996.tb00262.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract.1Leaf folding is a common behaviour among caterpillars that has many potential benefits such as creation of a favourable microclimate and protection from predation or dislodgment.2One cost of leaf folding which has not previously been quantified is the reduction in growth rate that might result from the energetic expenditures of producing silk and applying it to fold leaves.3On caged goldenrods in field and forest habitats, early‐instarDichomeris leuconotella(Busck) caterpillars that were repeatedly forced to spin new leaf refuges (either folds or webs of silk) actually had higher growth rates than caterpillars left undisturbed.4This surprising result apparently reflected the fact that disturbed caterpillars chose relatively young green leaves for new refuges, whereas undisturbed caterpillars tended to remain in their webs or folds on ageing leaves.5In a glasshouse experiment using plants that underwent little senescence, growth rates were unaffected by the amout of refuge‐making effort, indicating that the costs of such effort were either negligible or easily compensated for by these caterpillars.6On glasshouse plants, caterpillars periodically forced to change refuges had higher disappearance rates than those left undisturbed, despite the absence of predators. Wandering or falling from plants is evidently a major hazard of frequent refuge changes.7Thus, early‐instarDichomeriscaterpillars face a trade‐off in which risks of predation or loss of contact with the host favour the observed low rate of refuge changes, but in which growth rates could actually be improved with more refuge

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1996.tb00263.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract.1We examine the conventional wisdom among biological control practitioners that destructive host feeding is a desirable attribute in parasitoids employed for classical biological control, using both the predictions of population dynamics theory and historical data on biological control introductions of Hymenoptera against Homoptera.2Population dynamics theory predicts that destructive host feeders, compared with other parasitoids, are (a) either just as likely or more likely to become established, and (b) unable to depress host equilibria as strongly.3Analyses of the B IOC AT database suggest that among parasitoids of Homoptera destructive host feeders are superior to other parasitoids with respect to both establishment rate and success rate.4We present likely explanations for the disparity between the predictions of population dynamics theory and the results of database analysis. A partial explanation for the mismatch between theory and observation with respect to the degree of pest suppression may be that females of destructive host feeding parasitoids rely less upon hosts as a food source when alternative foods such as honeydew and nectar are plentiful.5We conclude that, despite the predictions of population dynamics theory, destructive host feeders are probably better biological control agents than other parasitoids, and certainly no worse, but that it would imprudent to use destructive host feeding as the sole, or even primary, selection criterion when seeking agents for classical biological control.

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1996.tb00264.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract.1A univoltine herbivorous ladybird beetleEpilachna niponica(Coleoptera: Coccinellidae) shows a large variation in adult size within a population.2Large adults had higher survival from emergence to the reproductive season, and the size‐dependent adult survival was most apparent during hibernation. On the other hand, adult survival during pre‐hibernation contributed little to size‐dependent overall survival.3Neither reproductive lifespan nor lifetime fecundity were a function of adult size, though large females produced larger size of egg batches.4Size of adult beetles was significantly reduced by leaf damage to plants on which they grew up on larval stage. Since leaf herbivory increases through the season, late emerged adults that were subjected to food deterioration during the larval period were smaller than early‐emerged indi

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1996.tb00265.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract.1Temporal changes in host adaptation were followed in a local population of the pea aphid,Acyrthosiphon pisum.Aphid clones were collected in one alfalfa and one clover field at three different times. In the spring, first‐generation females were collected. Later, in the autumn, females belonging to the last parthenogenetic generation were collected. Lastly, sexual females were collected after mating in autumn and allowed to produce eggs which were hatched. The performance was evaluated on alfalfa and clover. The spring‐collected individuals were also assessed on peas.2On the overwintering hosts clover and alfalfa, the clones performed best on the plant of origin, i.e. negative correlations in performance. Correlations between performance on the temporary summer host, pea, and that on clover/alfalfa were weak or nonsignificant.3Significant variation in host performance was found within both host fields at spring, which is a prerequisite for changes in clone composition due to selection/migration.4The clones from alfalfa showed an increase in mean performance on alfalfa between spring and autumn, whereas no changes among the clones from the clover field were observed. This difference in seasonal response between the two fields could have been the result of larger variation in performance among the alfalfa clones and/or a differential tendency to migrate among clones in both fields.5After sexual recombination in the autumn, mean performance in the alfalfa field returned to the spring level, probably as a result of emergence of new genetic combinations. In the clover field, mean performance did not change significantly over t

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1996.tb00266.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract.1Whenever parasitism by more than one female occurs, larvae of parasitoids not only have to resist host defence but also face competition with other (unrelated) larvae. Competition is particularly important in solitary parasitoids where only one larva is able to complete its development. Such a situation is found in Conopidae (Diptera) parasitizing adult bumble bees where larvae of two species of conopid flies,Sicus ferrugineusL. andPhysocephala rufipesF. often compete within the common hostBombus pascuorumScopoli. This study analysed the larval development of the two species and asks how competition among larvae may be regulated.2Parasitized workers ofB.pascuorumwere caught in the field and kept according to different experimental schedules in the laboratory. This provided stage‐structured data for the temporal course of development of the parasitic larvae. For the analysis, a simulation model was constructed that estimated the duration of all parasitic stages (Manly, 1990, first method). In both species the egg stage was found to be approximately 2 days, first instar 3 days, second instar 4 days, and third instar 3 days. The total development time is an estimated 10.8 days from oviposition inS.ferrugineusand 11.4 days inP.rufipes. S.ferrugineusdevelops faster in the beginning, probably because of its larger egg size, whereasP.rufipespupates at larger size. First‐instar larvae of both species possess strong, pointed mandibles.3The success of conopid larvae seems only marginally affected by host defence, for a single larva per host almost always completes development. Under competition, however, mortality rate increases substantially, and most larvae die in their first instar. Moreover, they show signs of melanization. The estimates for developmental times and the patterns found in this study suggest that conopid larvae seem capable of physical attacks, particularly during the first instar, when elimination of competitors is most common, and thatS.ferrugineushas a time advantage because of its faster early development. Because most studies have previously been carried out with hymenopteran parasitoids, this study provides new information about the other large group of parasitoid insects, the Diptera, and demonstrates convergent patte

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1996.tb00267.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract.1Rapid and substantial changes have occurred in the parasitoid and inquiline community associated with the agamic gallsof Andricus quercuscalicissince it invaded Britain in the late 1950s. The number of parasitoid and inquiline species has risen from one to thirteen over a 15‐year period. Although the number of species has been relatively consistent over the last 8 years, the species composition has changed considerably and in a highly characteristic way during this period.2The parasitoid complex can be divided into two broadly distinct sets of parasitoid species; one set attacks only the gall former whereas the other set concentrates on the inquilines living in the wall of the gall.3The most dramatic change, however, is in the abundance of inquilines which were reported to be virtually absent in earlier studies on this community in Britain. Over a period of only 5 years, between 1988 and 1993, inquiline attack rose from less than 0.01 to an average of 0.26 inquilines per gall. The intensity of inquiline attack is geographically heterogenous, with high inquiline numbers restricted to south‐east England. Because of the relatively high specificity of the parasitoids, high inquiline abundance is positively correlated with parasitoid species richness in knopper galls.4Parasitism rates, particularly on the gall former, were generally low (<10%). Over the last 5 years, however, seven parasitoid species have been consistently recorded and the mortality caused by these species has increased continuously. The species composition of the community associated with this alien gall wasp in Britain has quickly converged to the community known from its native range in continental Europe. Parasitoid species known to attack the galls ofA.quercuscalisison the continent have been recorded from it in Britain for the first time mainly in areas where inquilines have recently become abundant.5Since rates of parasitism of the gall former are still low, parasitoids are unlikely to play a major role in the population dynamics of this invading gall wasp at present, but the rapidly increasing inquiline and parasitoid attack could be a source of increased mortality for native cynipid species which are the alternative hosts of those parasitoid spec

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1996.tb00268.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY