摘要:

The spruce beetle,Dendroctonus rufipennis(Kirby), has had a major effect on the spruce forests of southcentral Alaska. In one area of the Chugach National Forest, 51% of the Lutz spruce,Picea glauca x lutziiLittle, or nearly 90% of the commercial stand volume was killed by spruce beetles during a 16–yr period. The majority of the tree losses occurred during the first 10 yr of the outbreak. Tree species composition remained essentially the same after the outbreak. Forest structure changed with decreased tree density, and species richness declined significantly on the unburned, spruce beetle–effected plots. This reduction in plant diversity was probably a result of the significant increase, and competitive advantage, of bluejoint grass,Calamagrostis canadensis(Michaux) Beauvois, and fireweed,Epilobium angustifoliumL., in the heavily beetle–effected plots. Although species richness did not change 7 yr after a prescribed fire, species composition did change. Specifically, the occurrence and percentage of blue joint and fireweed cover significantly increased.

DOI:10.1093/ee/24.6.1539

出版商:Oxford University Press    

年代:1995

数据来源: OUP

摘要:

Herbivory by leafmining insects is notoriously difficult to manipulate for ecological studies because eggs and larvae generally cannot be moved easily among plants without damaging plant tissue and killing larvae. We report on the effectiveness of stem implants of acephate (O,S dimethyl acetylphosphoramidothioate)for protecting turkey oak,Quercus laevisWalter,foliage from leafminer,Brachys tesselatusF., herbivory. Implanting acephate capsules into the stem of turkey oak trees before budbreak significantly reduced overall leafminer damage (both adult foliage feeding and larval mining) without any evident negative effects on tree acorn production (number and weight of acorns). This technique is currently being used to examine long–term costs of leafminer herbivory on growth and reproduction of turkey oak. It is likely that a similar approach can be used to manipulate leafminer densities for ecological studies on other tree species, as has been shown for herbivores on conifers and numerous crop species.

DOI:10.1093/ee/24.6.1548

出版商:Oxford University Press    

年代:1995

数据来源: OUP

摘要:

Many insects lay their eggs in clutches on discrete patches of resource that represent the only food available to progeny. The ability of females to distinguish resource patches of variable size and adjust their clutch size accordingly may enable these insects to reduce sibling conflict and exploit resources optimally.Stator bealiJohnson is an unusual seed beetle because it lays eggs in clutches rather than singly.Within a natural population, clutch size varied from 1 egg to>19 eggs on seeds of Texasebony,Chloroleucon ebano(Berlandier). We examined the heritability of clutch size inS. beali, and then determined the extent to which females can adjust clutch size in response to seed size.We obtained conflicting evidence as to whether clutch size variation is heritable; a standard parent–offspring regression analysis suggested that the heritability of clutch size was not different from 0 (h2 = 0.10 ± SEM 0.18), whereas an analysis of full sibs suggested that it was substantially greater than 0 (h2 = 0.33 ± 0.12). This discrepancy is likely the result of large nongenetic effects on clutch size. When presented with both a large and a smallC. ebanoseed, females preferentially laid eggs on the large seed. When forced to lay eggs on seeds of a specific size, females presented with 5 large seeds laid larger clutches (mean ± SEM, 6.7 ± 0.4 eggs) than those presented with 5 small seeds (5.2 ± 0.5 eggs). Females also actively avoided superparasitism in the laboratory when alternative, nonparasitized seeds were available. However, most seeds collected in the field (56%) were superparasitized, and many (15%) had>2 clutches on them, suggestingthat seeds are a limited resource for ovipositing females.

DOI:10.1093/ee/24.6.1557

出版商:Oxford University Press    

年代:1995

数据来源: OUP

摘要:

The suitability of the whiteflyBemisia argentifoliiBellows&Perring and the potato aphid,Macrosiphum euphorbiae(Thomas), as prey for 2 indigenous species of Chrysopidae,Chrysoperla rufulabris(Burmeister) andCeraeochrysa cubana(Hagen), was examined. The developmental time and percentage mortality were compared for each prey separately and mixed. Prey preference was also tested for each predator using 2 preference models as well as a pairedt–test. The developmental period for C. rufulabris was shortest on a mixed diet of aphids and whiteflies, suggesting that the nutritional quality of each prey alone was inferior to that of the combined prey. Development ofC. cubanawas slowest and mortality was greatest on the aphid diet. Both species of chrysopids were able to complete development on immature life stages of the whitefly alone. Both species consumed greater numbers of whiteflies than aphids; however, the consumption of aphids increased with each new instar. This trend indicates that prey selection was strongly influenced by increases in body size. The results of the pairedt–test and probability model, coupled with the developmental responses in feeding trials, lead us to conclude thatC. cubanaexhibited a preference beyond that which was associated with body size forB. argentifoliioverM. euphorbiae, whereasC. rufulabrisdemonstrated little or no such preference.

DOI:10.1093/ee/24.6.1562

出版商:Oxford University Press    

年代:1995

数据来源: OUP

摘要:

In northern New Zealand, greedy scale,Hemiberlesia rapax(Comstock),infests kiwifruit,Actinidia deliciosa(Chevalier) C. F. Liang et A. R. Ferguson varietydeliciosa, by aerial invasion from adjacent host plants such as taraire,Beilshmiedia tarairiBentham&Hooker. Greedy scale was monitored over 3 seasons using leaf samples from taraire trees adjacent to a commercial kiwifruit orchard. The seasonality of stage–specific population peaks and troughs was estimated using a Bayesian smoothing technique for both degree–day (DD) accumulations and Julian days. Two generations were observed with peaks for the 1st, 2nd, 3rd instars, and mature stages occurring on 30 December, 4 February, 17 March, and 18 April, respectively, for the summer generation, and 12 March, 13 April, 3 June, and 2 July, respectively, for the winter generation. Field populations of greedy scale were well described by physiological time; therefore, opportunities exist for predicting stage–specific events. Total developmental time using a base temperature of 9.3°C was estimated at 1,056DD with a standard error of 34 DD.

DOI:10.1093/ee/24.6.1569

出版商:Oxford University Press    

年代:1995

数据来源: OUP

摘要:

We tested the hypothesis that an endophytic fungus,Acremonium starrii(White&Morgan–Jones), deters redlegged grasshoppers,Melanoplus femurrubrum(De Geer), from feeding on Arizona fescue,Festuca arizonica(Vasey), a native grass. Arizona fescue plants were screened and classified according to their level of endophyte infection. In the laboratory, we presented grasshoppers with grass clippings from plants of high or low endophyte infection levels either simultaneously (choice) or separately (no choice), and we measured the amount of each eaten by the grasshoppers. In the field, we monitored the mass of grasshoppers placed in cages built around plants of high or low levels of infection. In all cases, we found that grasshoppers consumed similar amounts of grasses with high and low infection levels, contrary to the prediction that endophytic fungi deter herbivores. Our results question whether theA. starriiendophyte alters the interactions of native populations of Arizona fescue with a native grasshopper.

DOI:10.1093/ee/24.6.1576

出版商:Oxford University Press    

年代:1995

数据来源: OUP

摘要:

Survey data from 5 commercially managed apple orchards in West Virginia showed that spirea aphid,Aphis spiraecolaPatch, was the more abundant species and that apple aphid,A. pomiDe Geer, was present primarily during the late summer when apple is least suitable as a host for aphids. There was no significant positive or negative interaction between the distribution of the 2 species within orchards. In the laboratory, adult apple aphid survived longer at 15°C than spirea aphid but produced the same total number of progeny. At 25 and 28°C, spirea aphids produced more total progeny and more progeny per day than apple aphids. In an unsprayed orchard that had apple aphids introduced in the autumn of 1990, both species were equally abundant in the spring of 1991, but by the end of that summer spirea aphid was the only aphid species present. In a 2–species population model, reproductive differences between the species were sufficient for spirea aphid to dominate the guild quickly. Several different insecticide schedules marginally increased the rate at which spirea aphid replaced apple aphid. The model that most closely resembled field data had a delay in apple aphid immigration and a reduced rate of emigration as compared with spirea aphid. The reduced tendency to emigrate from apple is the one competitive advantage of apple aphid permitting them to remain in the system despite their reproductive disadvantage and greater susceptibility to insecticides. The use of insecticides that produce higher mortality of apple aphid have added to displacement by spirea aphid.

DOI:10.1093/ee/24.6.1581

出版商:Oxford University Press    

年代:1995

数据来源: OUP

摘要:

Laboratory tests involving termite response to rising water levels demonstrated that subterranean termites (Reticulitermesspp.) do not try to escape being submerged. Studies in which termites were completely submerged in water provided LT50sof 19.6 h for eastern subterranean termites,Reticulitermes flavipes(Kollar), 13.9 h forR. virginicus(Banks), and 11.1 h for, Formosan subterranean termites,Coptotermes formosanusShiraki. These data suggest that subterranean termites, in the field, escape drowning not by seeking higher ground but by entering a state of quiescence when confronted with excessive amounts of water in their subterranean habitat. Under normal rainfall conditions, water should move through the soil profile within several hours. If this does not occur, then high termite mortality could result. In the summer of 1992, we characterized the foraging populations of 5 subterranean termite colonies using the triple mark–recapture technique. These colonies averaged 99,000 (range, 157,000–14,000) foraging termites per colony. In the spring 1993, these same colonies were recharacterized and their populations averaged 21,000 (range, 53,000–1000) foraging termites per colony. This represents a 77% reduction in the average foraging populations for these colonies. In this article we provide empirical evidence that these population reductions were a result of heavy rainfall in west–central Georgia during the winter of 1992–1993.

DOI:10.1093/ee/24.6.1592

出版商:Oxford University Press    

年代:1995

数据来源: OUP

摘要:

Development time and life table parameters ofThrips palmiKarny, a pest new to the continental United States, were measured at 3 temperatures on 4 host plants. Net reproductive rate was the highest because of greatest survival and highest egg production when thrips were reared at 26°C on winter melon,Benincasa hispida(Thunb.) Cogn., eggplant,Solanum melongenaL., and cucumber,Cucumis sativus L., compared with bell pepper. However, because of shorter development time, the intrinsic rates of natural increase forT. palmiwere highest when individuals were reared at 32°C on these 3 host plants. Although development times were similar on all 4 hosts at 26°C, survival and reproduction were much lower for thrips reared on bell pepper,Capsicum annuum L., leaves. At 15 and 32°C, these differences were even greater, with only 40 and 48% of thrips reared on bell pepper surviving at the respective temperatures.T. palmiwas able to tolerate the low temperature (56% mortality when held at O°C for 15 h) much better than the high temperature (100% mortality at 40°C for 15 h), which may partially explain whyT. palmipopulations are high in winter and spring and low in the summer in Florida. This study provides information needed to understand population dynamics of thrips in important vegetable crops, information which will be valuable in developing and evaluating cultural and biological controls for this extremely damaging pest.

DOI:10.1093/ee/24.6.1598

出版商:Oxford University Press    

年代:1995

数据来源: OUP

摘要:

Thirteen pear,Pyrusspp., cultivars were evaluated under field and laboratory conditions for resistance toCacopsylla pyri(L.). In field studies, population growth was quantified over a I–mo period of development. In the laboratory, the mode of host resistance was investigated by estimating oviposition and antibiosis. One cultivar and 3 pear species were found to be resistant to pear psylla (‘Hosui’,P. betulaefolia, P. pyrifolia, andP. ussuriensis); the remaining ones may be classified as susceptible (Doyennée du Comice, ‘Williams’, ‘Général Leclerc’, and ‘Moonglow’). Antibiosis was a main factor determining resistance in the test pears, and preference for oviposition was involved to a much lesser degree.

DOI:10.1093/ee/24.6.1604

出版商:Oxford University Press    

年代:1995

数据来源: OUP