摘要:

Abstract.1The western spruce budworm,Choristoneura occidentalisFreeman, and Douglas‐fir,Pseudotsuga menziesii(Mirb.) Franco, have been used to test the hypothesis that variation in levels of foliar sugars form part of the basis for plant resistance to herbivore attack.2Budworm population growth was evaluated on artificial diets with 2–45% sucrose using a three generation bioassay. Diets with 1.2% and 3.9% N were tested to determine if responses to sugar were dependent on levels of protein. The 3.9% N diets were supplemented with a mineral salt mixture, so they had high levels of N and minerals.3The response of budworm population growth to sucrose concentrations ≤20% was convex at 1.2% N and flat for 3.9% N. Population growth on the 1.2% N diet, which had levels of N and minerals similar to host foliage, was good with only 2% sugar, but optimal at the 6% sucrose level; the number of F1, F2and F3larvae produced declined substantially when sugar was increased to 11% and 20%. On the 3.9% N diets, population growth was equivalent for diets with 2% and 11% sucrose. Sucrose concentrations ≥29% were detrimental to the budworm at both N levels.4Sugar concentrations in Douglas‐fir foliage varied between 5.7% and 18.4%. Thus, results from the 1.2% N experiment indicated that budworm performance was best on diets with sugar concentrations near the lower limit observed for host foliage. This implies that plants with higher foliar sugar may be inferior hosts for the budworm. Field observations supported this conclusion, as putatively resistant Douglas‐fir trees had significantly higher levels of sugars in their foliage than nearby paired susceptible trees. Variation in foliar sugars among individual trees may be part of the mechanism in Douglas‐fir resistance toC.occid

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1992.tb01047.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract.1Three aspects of prey utilization are documented in a guild of spider‐hunting pompilid wasps at a Breckland heath site: female phenology, size, and microhabitat utilization.2Twenty‐four species were present at the site, 59% of the British fauna. Ten species individually represented more than 1% of the guild.3Pompilid abundance peaked in early July and mid‐late August.Anoplius viaticushad a different life‐history from other common guild members, making its inclusion in the guild questionable.4Most species represented by large samples occurred in all microhabitats and time intervals, and all species overlapped in size with all other species exceptA. viaticus. Arachnospila ancepswas numerically dominant in all microhabitats and most time intervals.5Mean pair‐wise overlaps in phenology and microhabitat utilization were significantly lower than predicted by null models, consistent with the idea that interspecific competition has been important in determining guild structure.6Female size is highly correlated with prey size, but the distribution of mean female sizes did not generally differ from null expectations.7Interpretation of comparisons with null models is problematic, particularly because it is difficult to quantify evolutionary ‘favourability’ of different resource states. Null models are currently of limited use because the patterns expected to result from key processes such as competition are uncertain in multi‐dime

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1992.tb01048.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract.1Egg cannibalism is a form of infanticide that has been implicated in the evolution of guarding of eggs and immatures in some species of insects. The milkweed leaf beetle,Labidomera clivicollis(Coleoptera: Chrysomelidae), exhibits three types of egg cannibalism in the field: siblicide, cannibalism of eggs by older larvae from earlier hatching egg clutches, and cannibalism of eggs by adult females. Unlike their close relative,L.suterella(Choe, 1989), femaleL.clivicollisdo not guard their eggs or immatures. They move slowly about a patch of milkweeds laying multiple egg clutches.2First instar and older larvae cannibalized eggs in two geographically separated study populations (subspecies) in Austin, Texas, and Bridgeport, New York, U.S.A. Although adult females of both populations cannibalized eggs in the laboratory, only the Texas subspecies,L.c.rogersii, exhibited such cannibalism in the field.3In the field, correlates of siblicide varied both temporally (within subspecies) and spatially (between subspecies) in terms of whether they were statistically significant, but trends were all in the same direction. Group size was positively correlated with hatching success and siblicide, but negatively correlated with other types of predation. Siblicide was also positively correlated with egg density in a laboratory study of the Texas subspecies,L.c.rogersii.4In the laboratory, an average of 15–17% ofL.c.clivicolliseggs never developed embryos. Although these were almost always cannibalized, some viable eggs were also eaten and there is no evidence that females increased the proportion of infertile eggs they laid to increase siblicide.5Field data and laboratory experiments showed that adult femaleL. c.rogersiicannibalized eggs while males rarely did. Females preferentially ate the eggs of other females over their own eggs in an experiment that removed spatial cues.6Although the selective context of cannibalism is not demonstrated here, I suggest that females may increase siblicide by increasing egg density and may cannibalize eggs to protect their own eggs from being eaten by second and third instar larvae produced by other female

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1992.tb01049.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract.1The effects of density, feeding regime, and body size on interference competition in the pit‐digging larvae of the ant‐lionMacroleon quinquemaculatus(Hagen) were investigated in laboratory experiments.2Competition had little effect on the pit size of winners but losers constructed much smaller pits than isolated larvae. Losers were less likely to dig or maintain pits and more likely to move than winners.3Competition was much stronger between well‐fed larvae than between hungry ones, and well‐fed competitors showed reduced growth rates. Well‐fed larvae orientated themselves so that they could throw sand into their neighbour's pit whereas hungry larvae faced away from each other. Differences in hunger level reversed the competitive advantage of larger larvae only when individuals were of similar size.4Cannibalism was density‐dependent and most frequent in hungry, similar‐sized, larvae; the smaller larva was usually the victim.5Displays/challenges between larvae affected the distance between pits. Body size was the main determinant of contest outcome though pit ownership and hunger level also

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1992.tb01050.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract.1Substantial intraspecific variation exists inSalix viminalisresistance to the gall midgeDasineura marginemtorquens.Earlier work has found this variation to have a large genetic component. Willow clones are stable in their resistances between midge generations and different nutrient levels in both field and laboratory culture.2This study reports the results of laboratory experiments on female oviposition choice and larval survival on potted plants from clones that are very different in resistance as determined in field studies.3In choice experiments using pairs of plants, the average female midge did not prefer susceptible willow clones over resistant ones for oviposition. In about one third of the replicates, midges actually laid more eggs on the resistant clone. Further work is necessary to examine the nature of variation among midges in discrimination of these plant types.4Resistance is manifested as great differences in larval survival. Six days after oviposition survival was 92% on susceptible plants but only 6% on resistant ones. Galls developed on all of the susceptible plants, while in 73% of the resistant plants galls were not even initiated.5The plant traits causing resistance are enigmatic. Larval behaviour suggests that resistant plants interfere with feeding behaviour. On resistant plants, most larvae wander for more than 24 h without initiating any galls before dying. On susceptible plants many first instar larvae begin feeding and initiate galls within this period.

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1992.tb01051.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract.1We test the hypothesis that a solitary parasitoid wasp may gain in fitness if she lays more eggs in a host.2Using heterospecific superparasitism (=multiparasitism) between the solitary aphid parasitoids,Aphidius smithiSharma&Subba Rao andEphedrus californicusBaker, we show that (i) a superparasitizing female's chance that her offspring will survive competition is an increasing function of egg density, and (ii) survival among same‐aged larvae is independent of the oviposition sequence.3These findings on asymmetric larval competition provide indirect evidence that supports two fundamental, but untested, assumptions underlying models of adaptive superparasitism between conspecific wasp

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1992.tb01052.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract.1Tortoise beetle larvae possess a shield composed of exuviae and faeces which functions as an effective defence against some invertebrate predators.2In the laboratory,Charidotella bicolor, Deloyala guttataandChelymorpha cassidealarvae with their shields experimentally removed did not exhibit enhanced performance (i.e. decreased development time, increased body mass, or higher survival) compared to control larvae with shields intact.3Disturbance caused during shield removal did not adversely affect larvae because performance did not differ among controls (undisturbed larvae with intact shields), disturbance controls (shield removal simulated, but shield left in place), and larvae with shields removed.4Larvae without shields did not exhibit compensatory feeding to reconstruct the shield following its removal.5In a field experiment in which predators were excluded, larvae with shields removed did not develop faster than controls; in fact, survival was slightly reduced (10%) for larvae without shields and may have resulted from desiccation.6For slow‐moving tortoise beetle larvae, the cost of bearing the shield is minimal. Thus, larval shields, composed of recycled waste products, provide an inexpensive mode of protection from some natural enemie

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1992.tb01053.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract.1Hadenamoths drink nectar from, pollinate, and oviposit into the flowers of the genusSilene.In the gynodioeciousSilene vulgaris(Moench) Garcke (Caryophyllaceae), eggs were laid byHadena confusa(Hufn.) females both in male phase flowers, which could not be pollinated by the moth at the time of oviposition, and in female phase and female flowers that allowed pollination.2Flowers in which an egg had been laid had a lowered probability of receiving a second egg laid by another female during the same night.3The degree of flower discrimination by the moth with respect to the presence of eggs was positively correlated with the proportion of flowers containing eggs.4The oviposition behaviour ofH.confusais moulded by four factors: (1) a high probability of chosen male phase flowers later becoming pollinated by other moths, (2) the presence of conspecific eggs and risk for larval competition, (3) probability of presence of conspecific eggs also in neighbouring flowers, (4) capability of larvae to move to adjacent flowers.

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1992.tb01054.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract.1Definitions were adopted for the identification of the extinction and foundation of populations in data from the Butterfly Monitoring Scheme from 1976 to 1991. The data are indexes of abundance, not population estimates.2The frequency of extinctions and foundations for twenty‐eight butterfly species was assessed in relation to characteristics of their population fluctuations, as indicated by fluctuations in the index values.3Using multiple regression, the best predictive equation for the number of extinctions plus foundations included the number of test data available, the mean index per site and the first serial correlation. Two measures of variability were included in the analysis, but were not retained in the best predictive equation.4Some results for individual species are described and the potential of the approach for the study of effects of climatic warming is emphasize

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1992.tb01055.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract.1The spatial distributions of two tephritid flies (Urophora stylata(Fabricius) andTerellia serratulaeL.) attacking thistle flower heads and the levels of parasitism from their associated parasitoid guilds were studied over a 7‐year period.2Using these data it is possible to seek both temporal, density dependent relationships between average levels of parasitism and host density per generation, and also any spatial patterns of parasitism contributing to stability that may be operating within the same field system.3Parasitism by the two most important generalist parasitoids ofT.serratulaeis a direct function of averageT.serratulaedensity per year. There is little evidence of any stabilizing heterogeneity arising from the spatial distribution of parasitism within generations.4Temporal density dependence ofUrophora stylatacannot be confirmed from the 7 years of study but there is evidence of spatial heterogeneity which may have an important effect on the dynamics of the host populatio

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1992.tb01056.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY