摘要:

Abstract.1. Collards (Brassica oleracea L.) grown in clumps were more difficult for unstarved, early instar cabbage white caterpillars (Pieris rapae L.) to find than collards spaced at regular intervals, although total plant densities were identical.2. Early instar, unstarved larvae are less mobile than later instar larvae (our data) or starved larvae (Jones' 1977 data).3. Starved larvae and late instar larvae tend to find plants more readily than do unstarved or younger larvae.4. We contend that larval mobility governs the success of searching caterpillars and their sensitivity to variations in plant dispersion.5. Our results show that the dispersion of targets can influence searching success even though target density is constant. This means that the degree of clumping in host plants is capable of influencing their availability to herbivores.

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1985.tb00529.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Abstract.1. Movements of nectar and pollen‐foraging bumble bees on inflorescences of Chamaenerion angustifolium (L.) J. Holub (fireweed or rosebay willow herb) were compared with predictions based on reward distributions and optimality principles. Observations suggest that nectar and pollen‐gathering bumble bees behave according to the same set of reward maximization criteria when foraging from flowers of this species.2. Both kinds of foragers matched their arrival points with the vertical positions on inflorescences in which the densities of their respective food resources were greatest. For nectar‐foragers, this point was located at the lowest tier of flowers, whereas for pollen‐foragers it was found in the middle of the inflorescences. Nectar and pollen‐foraging bees both moved upward on inflorescences following gradients from high to low reward availability.3. Nectar‐foragers responded to decreases in inflorescence size over the season by reducing the number of flower visits made on each raceme. Number of flowers visited by pollen‐foragers was low throughout and reflected the scarcity of male‐phase flowers on racemes. Flower revisitation rates were low for both kinds of workers, but were slightly higher for those co

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1985.tb00530.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Abstract.1. The tiger swallowtail butterfly, Papilio glaucus (L.) (Lepidoptera: Papilionidae), is commonly assumed to have a bivoltine life cycle in central New York State and other parts of the northeastern United States. The seasonal abundance of adults in Tompkins County, New York, shows a bimodal pattern in some years, and a skewed unimodal pattern in others. We studied the incidence of diapause, the potential for successful development of two generations in the field, and the dates of adult emergence from overwintering pupae to determine whether these seasonal patterns are the result of bivoltinism.2. Insects from Tompkins County, reared as larvae under 16L:8D photoperiod, uniformly enter pupal diapause.3. Comparison of the heat units required for successful development of two generations with the heat units available in the field during 11 years shows that emergence of non‐diapausing individuals would occur too late in the summer to contribute to the second peak of butterfly abundance. Offspring of non‐diapausing individuals could only rarely complete development before the end of the growth season.4. Diapausing offspring of butterflies collected in early June and late July differed sufficiently in dates of emergence to account for the field pattern of seasonal abundance.5. Electrophoretic studies revealed no evidence of genetic isolation between early and late emerging butterflies.6. These results suggest that polymodal emergence of diapausing insects can masquerade as a bivoltine life cy

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1985.tb00531.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Abstract.1. Ants (Myrmica spp. and Formica lemani) visiting the extrafloral nectaries of bracken, Pteridium aquilinum, imposed heavy mortality on caterpillars of a novel moth species experimentally introduced onto bracken fronds. However, the exclusion of ants from bracken fronds had no significant effect on adapted bracken‐feeding herbivores in Britain.2. The feeding stages of British bracken‐feeding insects are immune to, or can largely avoid, predation by ants in a variety of ways. Gall formers and miners cannot be attacked by these ants. Two other species hide, one inside tied leaves, the other in a mass of ‘spittle’. Another group of species jumps away from, or falls off the plant when touched by ants. Sawfly caterpillars in the genera Strongylogaster, Aneugmenus and Tenthredo have viscous, distasteful haemolymph that repels ants.3. No species of bracken herbivore has an absolute temporal refuge from ants; during their development they all overlap with ants to some degree.4. Ant predation appears to have played a significant role in determining the contemporary structure of British bracken‐feeding insect communities. Distasteful haemolymph in sawfly caterpillars may have evolved in response to selection from ant predation. Other species may fortuitously possess characteristics, evolved in response to a variety of selective forces, that also reduce the impact of ants; without such characteristics, however, we postulate that they would be unable to live on this plant. An absence of external, foliage feeding Lepidoptera early in the spring, a high proportion of sawfly species, and a high proportion of gall‐formers and miners may all be characteristics of the bracken herbivore community which have been influenced by an

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1985.tb00532.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Abstract.1. Field and published data reveal that there are at least twenty‐three species of phytophagous insects associated with Prunus padus L. in Britain. Most of these species occur on the tree between May and September. Interspecific competition does not appear to be severe.2. There are a total of 196 species of phytophagous insects feeding upon the various tissues of P. avium, P. cerasifera, P. cerasus, P. domestica, P. laurocerasus, P. padus and P. spinosa.3. A highly significant species (5)‐distribution (A) relationship of the form In (S+l)=0.92 In A‐2.19, was obtained for the Prunus species examined within Britain (excluding Ireland), i.e. the wider the distribution of the plant the greater the number of insect species associated with it.4. However, critical analysis of the data indicate that P. padus does not support as many different insect species as expected.5. Neither plant form nor age of establishment within the British Isles accounted for this discrepancy.6. The possibility of using a plant's insect fauna to describe its relationship to other plants in the same genus is disc

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1985.tb00533.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Abstract.1. Developmental times from egg to adult eclosion were established for eight Dalbulus leafhopper species on maize (Zea mays) and its perennial, gamagrass relative, Tripsacum dactyloides. Experiments were conducted with a 16 h day (25–27°C) and an 8 h night (21–22°C).2. Developmental times were shortest for the maize specialists, c. 26 days for D. maidis and c. 27 days for D. elimatus, and longest for the Tripsacum specialists, c. 32 days for D. tripsacoides, c. 34 days for D. quinquenotatus and c. 40 days for D. guzmani. Developmental times were intermediate for D. gelbus, D. longulus and D. guevarai, species that utilize both maize and Tripsacum as field hosts.3. For all species, development was significantly faster on maize (species mean 29 days) than on T. dactyloides (species mean 34 days).4. D. maidis and D. elimatus developed significantly faster (c. 3 days) on maize than on its close perennial relative, Z. diploperennis.5. As measured by a 48 h oviposition period, D. maidis, D. elimatus and D. gelbus produced significantly more progeny on maize than on gamagrass. D. quinquenotatus produced more progeny on T. dactyloides than on maize. D. maidis and D. elimatus produced more progeny on maize than on Z. diploperennis.6. These studies provide support for the hypothesis which predicts that herbivorous insects that specialize on annual plants will have a shorter generation time and be more fecund than perennial specialists. The genus Dalbulus appears to be composed of species that fit an r‐K continuum, with maize specialists and Tripsacum specialists at opposite ends of the co

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1985.tb00534.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Abstract.1. Predator avoidance mechanisms of adult tiger beetles (Cicindela spp.) were investigated in the Sulphur Springs Valley of southeastern Arizona, U.S.A.2. The predators were found to be robber flies, lizards, and birds.3. Effective antipredator characters included body size, orange abdomens, defence chemicals, flight and gregariousness.4. The number of these five major antipredator mechanisms exhibited by each tiger beetle species varied with habitat.5. The function and number of antipredator mechanisms was a complex interaction of deterrents; some were effective only in combination and some were characters that each deterred a different type of predator; in several cases, the characters that reduced the probability of attack by one type of predator simultaneously increased the probability of attack by another type of predator.

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1985.tb00535.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Abstract.1. The effects of leaf toughness on mandibular wear of the leaf beetle Plagiodera versicolora Laich. (Coleoptera: Chrysomelidae) were evaluated by feeding adult beetles young (tender) and old (tough) leaves of Salix babylonica and S. alba ‘Tristis’.2. Tough leaves erode the cutting surface of beetle jaws more so than tender leaves.3. Beetles with worn jaws consumed leaves at a slower rate than ones with less mandibular wear.4. Because rates of leaf consumption and egg production are positively correlated, increased mandibular wear may reduce beetle fecundity.5. These results support the belief that leaf toughness may act as a potent defence affecting morphology, feeding behaviour, and ultimately spatial and temporal patterns of herbivo

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1985.tb00536.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Abstract.1. The adaptive significance of the timing of growth and reproduction by honeybee, Apis mellifera L., colonies in cold climates was studied by describing the seasonal patterns of food storage, brood rearing, and swarming, and then observing the consequences of experimentally perturbing the seasonal cycles of brood rearing and swarming.2. Colonies consume large amounts of food over winter (20+ kg of honey), but have only a brief period (about 14 weeks) for food collection each year.3. The honeybee's striking habits of starting brood rearing in midwinter and swarming in late spring evidently help colonies achieve maximum use of the short summer season. Colonies whose onset of‐brood rearing was experimentally postponed until early spring showed greatly retarded colony growth and swarming. Other experiments demonstrated that late swarms starve more often during winter than do early swarms.4. We conclude that the timings of colony growth and reproduction are essential elements in the honeybee's suite of adaptations for winter surviva

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1985.tb00537.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Abstract.1. The acceptability of sucrose solutions to Formica lugubris Zett. in the field was tested by offering droplets of known concentrations to ants tending aphids.2. A probit model fitted to the data allowed the computation of the Median Effective Concentration (ED50) and its confidence limits.3. In spring and early summer ED50was about 0.15 M sucrose, but the ED50rose in 1 week at the end of June from 0.2 M to 0.9 M. The change was simultaneous on pine and birch trees. The ED50fell gradually to about 0.4 M in early November.4. The increase in ED50is related to the production of the summer apterae in the aphids tended, Cinara pini (L.) on pines and Symydobius oblongus (von Heyden) on birch. This increases the ‘quality’ of food resource so that low sucrose concentrations can no longer compete for ant attendance.5. The increase in ED50may limit the attendance of wood‐ants at the nectaries of bracken, Pteridium aquilinum (L.) Kuhn. and at colonies of some other aphid species which are attended only in early s

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1985.tb00538.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY