摘要:

Diploid males are known to occur in several braconid and ichneumonid species. These diploid males are the result of a single-locus, sex-determination mechanism. Heterozygotes at this sex locus develop into females, whereas hemizygotes (haploids) and homozygotes (diploids) develop into males. Diploid males have a low fertility and their frequency drastically increases with small populations or inbreeding. The implications of this sex-determining mechanism for the use of parasitoids in biological control are explored. Production of diploid males leads to male-biased sex ratios and can reduce rates of establishment and population growth. Taxa in which a single-locus sex determination has been found (e.g., Ichneumonidae and Braconidae) often experience extreme male-biased sex ratios in mass rearing and have been more difficult to establish than taxa with other modes of sex determination (e.g., Chalcidoids). The effect of laboratory rearing on the number of sex alleles, frequency of diploid males, and population growth rates is explored by computer simulation. Methods of rearing and release that can enhance the number of sex alleles and the establishment of parasitoids are discussed. Furthermore, additional small-scale releases may enhance the effectiveness of already established populations by increasing number of sex alleles and the rate at which their population grows.

ISSN:1754-5692    

DOI:10.1093/ee/21.3.427

出版商:Oxford University Press    

年代:1992

数据来源: OUP

摘要:

Models that describe the distance traveled in a fixed time of a dispersing insect population are well-known. The gamma distribution is presented as a model for the inverse variable, namely the time required to travel a fixed distance. The use of the model is illustrated by fitting it to data on the consecutive northernmost captures ofApis melliferaswarms through Guatemala and Mexico. Point and interval estimates of predicted arrival time are obtained. The methodology is general and may be applied to other locations and species. The model also provides a tractable basis for the stochastic modeling of insect population density.

ISSN:1754-5692    

DOI:10.1093/ee/21.3.436

出版商:Oxford University Press    

年代:1992

数据来源: OUP

摘要:

The generation time ofCydia pomonella(L.), measured as the number of degree-days occurring from the start of a flight to the start of the following flight, was estimated for 176 generations in walnuts, apples, pears, and other hosts at several locations throughout California. The results show that the accumulated number of degree-days during the first generation (, 595.62 DD [≥ 10°C])was significantly lower than the number of degree-days for the second and third generations ($\bar x$, 677.68 and 685.06 DD [≥ 10°C], respectively). There was no significant difference among hosts within flights, but significant differences did exist among locations. Five published degree-day models were compared using the data set. Model accuracy, reported as root mean square error (RMSE), ranged from 6.3 to 10.8 d across generations. A degree-day model using 10°C as the lower threshold, 31.1°C as the upper threshold (horizontal cutofI), and a generation time of 619 DD provided an adequate fit to the data when all generations were considered. The median predicted duration of the first generation was 4 d too long; however, 72% of the predictions were within ≍7d of their observed date. The median predicted duration of the second generation was 2 d too short; however, 82% of the predictions were within ≍7d of their observed date.

ISSN:1754-5692    

DOI:10.1093/ee/21.3.441

出版商:Oxford University Press    

年代:1992

数据来源: OUP

摘要:

In 1983, large populations ofKorscheltellus gracilis(Grote) were discovered in soil in the boreal zone of Camels Hump Mountain, Vt. A monitoring procedure was developed to evaluate population dynamics and abundance. The insect was most abundant at elevations of 1,000–1,150 m where red spruce and balsam fir grow and spruce decline is most evident. Flight occurs from late June through early August, andK. gracilisadults were trapped in 19 of 20 sites in the Green Mountain National Forest. They were significantly more abundant at high elevations and on even years.

ISSN:1754-5692    

DOI:10.1093/ee/21.3.447

出版商:Oxford University Press    

年代:1992

数据来源: OUP

摘要:

Microplots (2.5 m long) of sprouting onion bulbs planted 5 cm deep received an average of 2,300Delia antiqua(Meigen) eggs during 3 wk in a field trial. Plots with bulbs resting on the soil surface, planted with their neck at the soil surface, or at 12-cm depth, received 280, 1,530, and 980 eggs, respectively. In the laboratory, damage to sprouting bulbs caused by slicing, maggot infestation, or both did not enhance or diminishD. antiquaoviposition compared with intact bulbs. Egg laying was equivalent for all treatments as long as green, moist foliage was present. The simultaneous use of an ovipositional deterrent (cinnamaldehyde) and diversionary cull onions to protect seedling onions fromD. antiquawas tested using a factorial experiment in the greenhouse. The interaction between deterrent and culls was consistent with a multiplicative model where the probability of an onion maggot fly accepting seedlings was reduced independently by the presence of deterrent or culls. Collectively, these experiments suggest that insect control by stimulo-deterrent diversion is a valid concept, albeit not yet practical forD. antiqua.

ISSN:1754-5692    

DOI:10.1093/ee/21.3.453

出版商:Oxford University Press    

年代:1992

数据来源: OUP

摘要:

Interspecific associations of rangeland grasshoppers studied in Gallatin Valley, Mont., during 1988–1990 when regional densities were low, showed a great deal of spatial variation. Although ≥40 rangeland grasshopper species were collected valley-wide throughout this study, mean species richness at the habitat type level ranged from ≍10–17; results suggest that species replacement occurred over the gradient of habitat types sampled. Based on the results of this and previous research, it appears that rangeland grasshopper communities consist of facultative assemblages of species. At the valley level, it was possible to distinguish between species groups in terms of their general distribution characteristics (i.e., broadly, intermediately, or narrowly distributed). Although there appeared to be a maintenance in the proportion of the species in each of the three distribution groups among the six habitat types studied, proportions differed from those found at the valley level. Similar to other studies in plant and insect ecology, a positive relationship between species abundance and the number of sites collected was found at both the habitat type and valley levels. Because of the differences found in species composition at the habitat type level, the generalization of detailed experimental studies, beyond the habitat type level, must be done with caution. Lastly, it is clear that to understand rangeland grasshopper communities in general, large-scale observational studies designed to depict pattern must be conducted together with small-scale studies designed to elucidate process.

ISSN:1754-5692    

DOI:10.1093/ee/21.3.461

出版商:Oxford University Press    

年代:1992

数据来源: OUP

摘要:

The spatial patterns of association between spider mites and some of their natural enemies and the potential changes in these association patterns through the season, between years, and as a result of pesticides targeting both the spider mites and their natural enemies were studied in cotton. Included in the study were the spider mites,Tetranychusspp.; western flower thrips,Frankliniella occidentalis(Pergande); big-eyed bugs,Geocoris pallensStål andG. punctipes(Say); and the minute pirate bug,Orius tristicolor(White). Association patterns were modeled using a log-linear statistical model. Co-occurrence patterns for most species pairs were significantly nonrandom and mostly positive and were seen to change over the season. In general, associations tended to become increasingly positive (or less negative) as the season progressed. Pesticide treatments (dicofol, permethrin) were not found to affect associations. Observed spatial association patterns fit the known biological relationships of the species.

ISSN:1754-5692    

DOI:10.1093/ee/21.3.471

出版商:Oxford University Press    

年代:1992

数据来源: OUP

摘要:

Tritrophic-Ievel studies of predator–prey interactions on leaves have emphasized the role of plant secondary chemistry, but leaf morphology can also influence predation. We found that domatia, structures with mite-sized spaces in the vein axils of leaves on many woody angiosperms, often sheltered predatory mites (Phytoseiidae and Stigmaeidae). Leaves with domatia generally had much higher numbers of phytoseiid mites, especially their eggs, than those without domatia. This occurred within plant species, between congeners, and across unrelated species of rain forest trees and vines with and without domatia. When leaf domatia of a rain forest tree,Elaeocarpus reticulatusSmith, were blocked with a bitumen paint, numbers of phytoseiid mites per leaf were reduced to 24% of controls. These results show that morphological traits of plants can have a strong effect on the distribution and abundance of predators. Such predator enhancement may complement plant allelochemical defenses.

ISSN:1754-5692    

DOI:10.1093/ee/21.3.478

出版商:Oxford University Press    

年代:1992

数据来源: OUP

摘要:

The phytophagous arthropod community in three apple orchards was sampled for the first 5 yr (1984–1988) after planting. One orchard was unmanaged, one was partially managed with pruning and weed control, and one was under full commercial management. For the first 2 yr there were no significant differences in arthropod diversity among the three orchards. In the third and subsequent years, diversity, as measured by species richness and Williams' index, was significantly lower in the commercially managed orchard than in the two reduced management orchards. In the fifth year, the commercially managed orchard had the most uneven distribution of species abundances and the partially managed orchard the most even. Within-year evenness values were more variable in the commercially managed orchard than in either of the reduced management orchards. Mean annual diversity in both reduced management orchards increased in the first 4 yr of community development and remained constant in the fifth year. In the commercially managed orchard, diversity increased in the second year, then declined and remained low. Within each year, diversity generally peaked in all orchards in middle to late summer. There were subtle differences between communities in the unmanaged and partially managed orchards. In the partially managed orchard, trees were larger and more vigorous than trees in the unmanaged orchard. The community in this orchard was dominated by species that were able to exploit the abundant succulent branch terminals, such as aphids (Homoptera: Aphididae) andLyonetia speculella(Lepidoptera: Lyonetiidae).

ISSN:1754-5692    

DOI:10.1093/ee/21.3.485

出版商:Oxford University Press    

年代:1992

数据来源: OUP

摘要:

Insect fauna from the heads (capitula) and stems of six native sunflower species in eastern North Dakota and western Minnesota are reported. Eight insect species in six families of Coleoptera, Diptera, and Lepidoptera were recovered from the heads of six species ofHelianthus. Heads ofHelianthus annuusL. contained the greatest diversity of insect species. Insect species collected were also commonly found as pests of cultivated sunflower heads. Two major pests of commercial sunflower in the Great Plains—the red sunflower seed weevil,Smicronyx fulvusLeConte; and the banded sunflower moth,Cochylis hospesWalsingham—were collected from the heads of all six nativeHelianthusspecies, although they were most common inH. annuus.Neotephritis finalis(Loew) also occurred in the heads of allHelianthusspp. examined. Insects from seven overwintering species were recovered from the stems of all sixHelianthusspp. Insect stem fauna diversity was greatest inH. maximilianiSchrader, and least inH. rigidus subrhomboideus(Rydberg). The sunflower stem weevil,Cylindrocopturus adspersus(LeConte), was the only major insect pest of cultivated sunflower that was recovered from sunflower stems. It was most abundant inH. annuus. A single species of parasitoid,Nealiolus curculionis(Fitch), was reared from sunflower stem weevil larvae. Results suggest that some species ofHelianthushave high potential as sources of insect resistance for incorporation into commercial sunflower.

ISSN:1754-5692    

DOI:10.1093/ee/21.3.493

出版商:Oxford University Press    

年代:1992

数据来源: OUP