摘要:

It is widely believed that population outbreaks of the southern pine beetle (Dendroctonus frontalisZimm.) are caused by vagaries of climate, such as periods of severe drought. According to this view,D. frontalispopulation dynamics are dominated by density-independent processes. We have statistically analyzed a 30-yr record ofD. frontalisactivity in east Texas and have assessed the relative roles of density-independent and density-dependent factors in beetle population fluctuations. Regressions of the rate of population change on three climatic variables were not significant. By contrast, both time-series and regression analyses provided strong and consistent evidence for delayed density regulation ofD. frontalispopulations. Thus, in contrast to previous analyses, we conclude thatD. frontalisoutbreaks are driven not by stochastic fluctuations of weather, but by some unknown population process acting in a delayed density-dependent manner. This result provides a starting point for a current study that will experimentally test various hypotheses concerning the role of natural enemies inD. frontaliscycles.

ISSN:1754-5692    

DOI:10.1093/ee/20.2.401

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

Substantial variation among experimental units may occur in studies that address effects of the host plant on insect performance or preference. Efficiency in demonstrating host effects can be enhanced by recognizing that variation among insects is often important and, more particularly, by using an experimental design appropriate for these conditions. Performance data from studies that address local adaptation in phytophagous insects are often analyzed with a two factor ANOVA, testing for host species, population, and host species × population effects. Local adaptation to different hosts would be indicated by a significant interaction term. Commonly, a completely randomized design is employed. A repeated measures design involving an allocation of siblings across host species can provide considerably more powerful tests on the host × population interaction than a completely randomized design. Allocation of relatives across host species can induce positive correlations among hosts and, depending upon magnitude of correlations, provide conditions suitable for powerful tests of the interaction term. We develop power curves for several patterns of correlation to describe the amount by which the repeated measures design will be more powerful than the completely randomized design. A literature review indicates that conditions appropriate for repeated measures analysis are very common. Finally, we provide an example using two populations of a phytophagous beetle feeding on three plant species, and show that the repeated measures design demonstrates host × population effects missed by the more traditional design.

ISSN:1754-5692    

DOI:10.1093/ee/20.2.410

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

This study describes the courtship behavior sequence under wind tunnel conditions ofHeliothis subflexa(Guenée) and selected backcross insects (generations 5 and 6) obtained from hybridization withHeliothis virescens(F.). The rhythmic release of pheromone byH. subflexa, H. virescensand backcross females was correlated with the response rhythm of males. The behavioral courtship sequence ofH. subflexamales (P<0.05) included oriented flight, landing, antennation, attempted copulation, and mating behaviors. Backcross insects did not antennate, but they fully displayed their hairpencils as did males ofH. virescens. Factors that increased the probability of successful matings were identified as an acquiescent female, antennating byH. subflexamales, full hairpencil display (backcross males) and the male's ability to clasp the female genitalia. Overall, 63% ofH. subflexaand 33% of backcross pairs culminated the courtship sequence with successful mating. The tendency of backcross males to settle down after limited flight activity contributed greatly to the increased proportion of unsuccessful males.

ISSN:1754-5692    

DOI:10.1093/ee/20.2.419

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

Synergism of permethrin and fenvalerate by piperonyl butoxide for fourth instars of the Colorado potato beetle,Leptinotarsa decemlineata(Say) fed on different host plants was used as an indicator of allelochemical-mediated induction of the cytochrome P-450. Beetles collected from Parry Sound, Ontario, were fed on potato (Solanum tuberosumL.), tomato (Lycopersicon esculentumMill.), buffalo bur (S. rostratumDunal), and climbing nightshade (S. dulcamaraL.). Combined LD50's were used to calculate and compare synergistic ratios. The mean weight of the larvae in each bioassay (replication) was used as a covariate in calculation of combined 72-h LD50's and the approximate 95% CI for the synergistic ratios was calculated. For permethrin, the only significant difference found was between synergistic ratios of larvae fed on buffalo bur (10.5) and climbing nightshade (5.9,P<0.001). For fenvalerate, larvae fed on climbing nightshade showed the highest resistance factor, but larvae fed on buffalo bur showed the highest synergistic ratio (29.2), which was significantly different from that of potato (14.7,P<0.01). LD50's for larvae fed on potato were lowest for both insecticides, but feeding on the other host plants increased the LD50. Implications of this response to allelochemicals in alternate host plants to breeding for resistance to Colorado potato beetle is discussed.

ISSN:1754-5692    

DOI:10.1093/ee/20.2.427

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

The production of sexual morphs by the greenbug,Schizaphis graminum(Rondani), in response to long scotophases was studied using eight clones of the aphid from one locality in California, one clone from Nebraska (biotype E), and one from Oklahoma (biotype C). The temporal and quantitative differences found in the polymorphism of these clones confirmed that considerable variability in biological traits exists between aphids from local as well as regional populations. The groupings to which the clones could be assigned on the basis of their photoperiodic responses differed from previous groupings based on performance of the clones on different varieties of sorghum.

ISSN:1754-5692    

DOI:10.1093/ee/20.2.433

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

Developmental velocities of European corn borer,Ostrinia nubilalis(Hübner), colonies collected at four geographically separate locations (Delaware, Iowa, Missouri, and North Dakota) were compared. Each colony was reared under five or six constant temperature regimes. Mean developmental times and standard deviations about the means were determined. Developmental velocities were used to formulate both linear and sigmoid developmental velocity equations. Because the sigmoid and linear functions exhibited similar fits to the data, the latter were used in a European corn borer phenology model that predicts the period of second generation oviposition. The resulting predicted oviposition periods are reported for model runs using developmental velocity equations generated for the four colonies. The resulting predictions suggest that developmental rates are similar among the four geographically separate European corn borer populations. For European corn borers reared at 32°C, however, developmental times and developmental threshold temperatures during the period of larval eclosion to adult emergence appeared different among the colonies.

ISSN:1754-5692    

DOI:10.1093/ee/20.2.441

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

Sex attractants and behavioral antagonists comprising C20and C21triene hydrocarbons and chiral epoxydienes are reported for male moths of two noctuid and six geometrid species. Moths of the noctuidIdia americalis(Guenée) were attracted to lures containing a 1:1 mixture of 3Z,9Z-6S,7R-epoxy-eicosadiene (3Z,9Z-6S,7R-epoxy-20:H) and 3Z,9Z-6S,7R-epoxy-21:H. Moths of the noctuid speciesBleptina caradrinalis(Guenée) were specifically attracted to a blend consisting of a 1:1 mixture of the enantiomers of 3Z,9Z-cis-6,7-epoxy-20:H and to a 4:1 mixture of the enantiomers of 3Z,9Z-cis-6,7-epoxy-21:H. The following geometrid moth species were also caught (optimum lure components in parentheses):Plagodis alcoolaria(Guenée) (3Z,9Z-6R,7S-epoxy-20:H + 3Z,6Z,9Z-20:H),Xanthorhoe munitataHübner (3Z,9Z-6S,7R-epoxy-21:H + 3Z,6Z,9Z-21:H),X. abrasaria aquilonaria(Herrich-Schäffer) (3Z,9Z-6S,7R-epoxy-21:H + 3Z,6Z-9S,10R-epoxy-21:H),X. ferrugata(Clerck) (3Z,9Z-6S,7R-epoxy-21:H),Mesoleuca ruficillata(Guenée) (3Z,6Z,9Z-20:H or 3Z,6Z,9Z-21:H or both), andAnticlea vasiliata(Guenée) (3Z,6Z,9Z-21:H). Chiral and achiral attractants for one species often acted as antagonists for closely related or sympatrie species, indicating how discrete chemical communication channels may be maintained.

ISSN:1754-5692    

DOI:10.1093/ee/20.2.450

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

The relationship between temperature and development ofUraba lugensWalker and between temperature, host size, and development of its parasitoids,Cotesia urabaeAustin and Allen andDolichogenidea eucalyptiAustin and Allen, were investigated.U. lugensunderwent from 6 to 14 instars before pupation. The number of instars affected the allometry of head capsules. Females had more instars than males, and both sexes had more instars at lower temperatures. Thermal requirements for larval and pupal development ofU. lugensdiffered between sexes; male larvae had lower temperature thresholds and male pupae higher temperature thresholds than females. Egg–larval rate of development ofC. urabaeafter oviposition in small hosts was much slower than that after oviposition in midsize hosts and differed between sexes. Pupal development ofC. urabaewas faster for males than females. Egg–larval development ofD. eucalyptiafter oviposition in small hosts was more rapid than that ofC. urabaefrom small hosts, whereas pupal development ofD. eucalyptiwas slightly longer than that ofC. urabae. WhenD. eucalyptiwere reared at 15°C, some individuals pupated when predicted by degree-day summation, and others delayed emergence from the host by a further 120–182 d, indicating a physiological delay in development. Simulation of the phenologies ofU. lugens, C. urabae, andD. eucalyptiin the Adelaide region using thermal constants showed good fit between field-observed and predicted durations of life stages and confirmed the presence of a physiological delay in emergence ofD. eucalyptiin winter and during its second generation in summer.

ISSN:1754-5692    

DOI:10.1093/ee/20.2.458

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

The epicuticular lipids of alfalfa (Medicago sativaL.) were analyzed by gas chromatography to determine if the distribution of alfalfa leaf epicuticular lipid and its components could be correlated with the previously reported preference of spotted alfalfa aphids,Therioaphis maculata(Buckton), for leaves on lower portions of alfalfa sterns. Older leaves near the crowns of alfalfa sterns, on which spotted alfalfa aphids prefer to feed, were covered with less epicuticular lipid per unit of leaf area than those farther up the stern. These differences were primarily due to differences in amounts of the primary alcohol, triacontanol, found in epicuticular lipids. In addition, leaves near the crown had greater aldehyde/alcohol ratios than did those at the top of sterns. Scanning electron micrographs of alfalfa leaf surfaces confirmed that lower leaves on stems contained large patches of leaf surface which were not covered with the crystalline lipid that formed a nearly uniform layer on leaves arising from the upper nodes of stems.

ISSN:1754-5692    

DOI:10.1093/ee/20.2.470

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

Methyl (2E,4Z)-decadienoate was isolated and identified as the major male-specific volatile ofEuschistus conspersus, E. tristigmus, E. servus, E. politus, andE. ictericus. In a sixth species,E. obscurus, this ester is a relatively minor male-specific component, with the major component being tentatively identified as methyl 2,6-dimethyltetradecanoate. Females, males, and nymphs ofE. conspersus, E. tristigmus, E. servus, andE. polituswere significantly attracted to methyl (2E,4Z)-decadienoate in field tests conducted in California and Maryland. Tests in Maryland also demonstrated that parasitic tachinid flies use theEuschistusunsaturated methyl-ester as a host-finding kairomone. It is not yet clear what role minor volatile components ofEuschistusplay in reproductive isolation.

ISSN:1754-5692    

DOI:10.1093/ee/20.2.477

出版商:Oxford University Press    

年代:1991

数据来源: OUP