摘要:

The effects of several diel and nondiel photoperiods on the induction of larval diapause of the corn stalk borer,Sesamia nonagrioides(Lefebvre), were explored. The diapause induction curve was found to be of type III (short–long day type). The photoperiodic induction of diapause was not restricted to either specific light–dark ratios or to diel photoperiods. Instead, photoperiods of =6–13 h of photophase combined with =;10–16 h of scotophase resulted in a high incidence of diapause. Light pulses of 1 and 2 h applied at different successive points in time during the 1st part of the scotophase of a diapause–inducing photoperiod of 10:14 (L:D) h greatly reduced diapause. Such pulses, applied to the last part of the scotophase, did not prevent diapause induction. Thus, 1 photosensitive time gate of the scotophase, in which illumination prevents diapause induction, exists. No instar was found to be crucially sensitive to a diapause–inducing photoperiod of short day length. The 6th instar is a partial exception in the sense that its exposure to short day length is a necessary,but not a sufficient, condition for diapause induction. In general, as the number of instars exposed to short–day photoperiod increases, the percentage diapause also increases and vice versa. The commitment (irreversible process), however, to diapause and to nondiapause development were asymmetrical phenomena, as explained in the text. A synergistic effect of short–day photoperiods and low temperatures in the induction of diapause was demonstrated.

ISSN:1754-5692    

DOI:10.1093/ee/24.6.1458

出版商:Oxford University Press    

年代:1995

数据来源: OUP

摘要:

Field studies were conducted at 19 sites in western Montana during 1987 through 1990 to determine the cause and extent of predation onUrophoraspp. larvae in spotted knapweed,Centaurea maculosaLamarck, capitula. The extent of knapweed capitula removal was monitored at all 19 sites, and causes of capitulum removal were assessed at 1 site. Capitula removal and subsequent mortality ofUrophora affinisFrauenfeld larvaeoccurred at all sites, with mean percentage removal ranging from 29 to 64%. In general, the percentage capitula removal increased with each sequential sampling date over all winters. Sampling date, winter,U. affinisgall density, and percentageU. affinis–infested capitula explained most of the variationin the percentage missing capitula.There was no relationship between percentage missing capitula and U.quadrifasciata(Meigen) gall density or percentageU. quadrifasciatainfested capitula. Based on an assessment of bite marks and stem fracture patterns, =74% of the capitulum removal at the Teller Wildlife Refuge was caused by 3 predator/herbivores: the deer mouse,Peromyscus maniculatus(Wagner);the blackcapped chickadee,Parus atricapillusL.; and the white–tailed deer,Odocoileus virginianus(Zimmermann). Approximately 64% of the observed chickadee foraging activityin knapweed–infested areas during winter months was associated with knapweed capitula. Chickadee predation was selective for heavily infested capitula. Vegetation type had limited effect on predation.

ISSN:1754-5692    

DOI:10.1093/ee/24.6.1467

出版商:Oxford University Press    

年代:1995

数据来源: OUP

摘要:

We studied the spread of the newly introduced parasitic mite, VarmajacobsoniOudemans, within California's population of the feral honey bee,Apis mellifera L., by examining worker bees taken from 208 colonies in 1990, 124 of which were examined again in 1993. The samples taken in 1990 did not containV. jacobsonimites. In 1993, 75% of the colonies examined in an area located near Sacramento, CA, no longer existed, and all surviving colonies were infested withV. jacobsoni. In an area located near the Californian central coast, 84% of the nest sites examined were occupied and few colonies contained detectable levels ofV. jacobsoni. The probability of survival for colonies that have not survived a winter yet (founder colonies) has been previously reported to be low in areas with a temperate climate. Data collected in an area with a low level ofVarroamite infestation suggest that the probability of founder colony survival is higher in California with a mostly Mediterranean climate. The data collected in areas with a high level of Varroa mite infestation suggest that the parasite reduces the mean life span of feral honey bee colonies in California to go between 6 mo and 1 yr. The parasite was widely spread in areas with a high density of commercial colonies. This suggests that the fast spread of the parasite is caused mostly by migration of commercial colonies. We discuss the consequences of the decline of the feral honey bee population on pollination and on the invasion of California by Africanized bees.

ISSN:1754-5692    

DOI:10.1093/ee/24.6.1473

出版商:Oxford University Press    

年代:1995

数据来源: OUP

摘要:

Host plant resistance to herbivores is usually measured by visual screening in the field, which is very expensive. We tested an alternative method using 26 varieties of tea,Camellia sinensis, selected from different geographical locations to screen for resistance against the red and black flat mite,Brevipalpus phoenicis(Geijskes); survival and logistically fixed net fecundity schedules (predicted number F1offspring) were compared. Survival schedules of the mites varied among the different varieties, as indicated by a change in the concavity of the survivorship curves and measured in terms of entropy. Varieties were classified according to their level of resistance/susceptibility based on the number of predicted F1offspring. The level of susceptibility was positively correlated with life expectancy and was negatively related to entropy. Varieties that evolved from northeast India were consistently less susceptible, which suggests that a search in this region to identifY genes for resistance might be useful for future breeding programs.

ISSN:1754-5692    

DOI:10.1093/ee/24.6.1481

出版商:Oxford University Press    

年代:1995

数据来源: OUP

摘要:

We investigated the effects of plant density, plant diversity, and light availability on susceptibility of saplings ofStryphnodendron microstachyumPoeppig&Endlicher to attack by herbivores and pathogens in the lowlands of northeastern Costa Rica. Seedlings ofS. microstachyumwere planted at either low or high density. High density stands were planted in 2 environments with 2 plant diversities within each environment: monocultures in abandoned pastures (=sun) and in 5–yr–old secondary forest (=shade), or polycultures in whichS. microstachyumwas planted with 4 other species also in sun and shade. Low density stands consisted of isolated individuals in 4 types of sites (abandoned pasture, secondary forest understory, primary forest understory, and primary forest light gap). Numbers of galls (Diptera: Cecidomyiidae), larvae (Lepidoptera: Noctuidae:Euclystis), and fungal spots (Melanconiales:Pestalotia) were greater in the high density stand than in low density stands, and greater in the shade than in sun. We found no differences in infection between monocultures and polycultures at high density, nor did we findEuclystislarvae or Cecidomyiidae galls in low density stands. Numbers of fungal spots per leaf and density of galls were greater on larger plants. These data suggest that higher plant densities increase the probability of attack by herbivorous insects and leaf pathogens, and that plantations of tropical native tree species in partial shade, as a means of reforestation, run the risk of outbreaks of normally rare plant enemies. Furthermore, the observed positive relation between plant size and attack suggests that plantations of this tree species will become more susceptible to pest outbreaks as the trees mature.

ISSN:1754-5692    

DOI:10.1093/ee/24.6.1487

出版商:Oxford University Press    

年代:1995

数据来源: OUP

摘要:

Incidence,prevalence,and densityof ectoparasites are reported for 3 species of tropical bats,Stenoderma rufumDemarest,Artibeus jamaicensisLeach,Monophyllus redmaniLeach, from the tabonuco forest of Puerto Rico. In addition,patterns of ectoparasite associations were examined with respect to several host characteristics including age and sex, as well as with respect to season. Levels of ectoparasite infestation differed because of host age, but not sex,with juveniles harboring higher numbers than adults. No ectoparasite attribute differed with season. Significantly different assemblages of parasites occurred on adult male, adult female, and juvenileA. jamaicensis. Moreover,S. rufum, A. jamaicensis, andM. redmanieach have a significantly different ectoparasite assemblage.

ISSN:1754-5692    

DOI:10.1093/ee/24.6.1495

出版商:Oxford University Press    

年代:1995

数据来源: OUP

摘要:

The influence of degree–day accumulations and photoperiodic induction of diapause on the phenology ofErythroneura Comes (Say) was investigated. In growth chamber experiments, nymphs reared at photoperiods of710 degree days (DD) before 1 August are required to produce a 2nd generation ofE. comesunder climatic conditions in New York.Variationsin temperature–driven development are hypothesized to strongly influence year–to–year variability in leafhopper abundance. Degree–day accumulations by 30 June correlated well with degree–days by 1 August and may provide a useful early–warningsystem for predicting years in which leafhopper population densities are above average.

ISSN:1754-5692    

DOI:10.1093/ee/24.6.1504

出版商:Oxford University Press    

年代:1995

数据来源: OUP

摘要:

I examined the flight behavior of the Mexican bean beetle,Epilachna varivestisMulsant, at 2 types of simulated patch boundaries, and compared such behavior with the assumption of random movement often incorporated into simple diffusion models. I also examined flight behavior from the patch edge with respect to wind direction and sex. Movement from the patch edge was found to be equally nonrandom for both boundary types, with =2/3 of the beetles flyingin the direction of the host plants. Beetles also displayed a tendency to fly upwind or perpendicular to the wind at low wind speeds and downwind at high wind speeds. Flight behavior was not affected by sex of the beetles. Because observed flight preference did not vary between patch boundary types or between sexes, nonrandom movement from the patch boundary could likely be incorporated into diffusion models without significantly increasing their degree of complexity.

ISSN:1754-5692    

DOI:10.1093/ee/24.6.1515

出版商:Oxford University Press    

年代:1995

数据来源: OUP

摘要:

Colony size, foraging activity, foraging phenology, and selected physiological parameters were evaluated on colonies of the western subterranean termite,Reticulitermes hesperusBanks, in urban and undisturbed habitats. The greatest foraging activity occurred from May to October at the University of California, Riverside urban site, and from late November to January at the Motte–Rimrock natural study site. Foraging activity was related to minimum temperatures at the urban site, and minimum temperatures and precipitation at the undisturbed site. Foraging population was greater in the urban habitat, with estimates ranging from 85,752 to 830,581 foragers compared with 78,930 to 103,758 at the native site. Termites at the urban site had greater initial and dry body weights, but less body fat than their counterparts from undisturbed habitats. No difference in the cuticular permeabilities of termites occurred between locations.

ISSN:1754-5692    

DOI:10.1093/ee/24.6.1520

出版商:Oxford University Press    

年代:1995

数据来源: OUP

摘要:

Estimation of the boundary of the geographic distribution of gypsy moth,Lymantria dispar(L.), populations is important for monitoring and controlling the spread of this species in North America. In this study, gypsy moth population boundaries were estimated from male moths counts in pheromone–baited traps and from egg mass counts in a 5.18– million–ha area in northwestern Virginia and southeastern West Virginia.Population boundaries were estimated for 5 yr (1988–1992) and for different population density thresholds using the following 3 methods: (1) best classification(minimizing the number of grid cell misclassifications),(2) 1st occurrence method, and (3) logistic regression of log population counts versus distance perpendicular to population boundary.All 3 methods generated similar boundaries for male moth counts, and boundaries obtained with the first 2 methods were most correlated. The regression method failed to estimate boundaries of egg mass populations because of their irregular spatial distribution. However,the 2 other methods were successful and yielded similar results. The average gypsy moth spread rate estimated using male counts was 10.7–11.9 km/yr.The minimum spread rate was 3.8–4.9 km in 1991, and the maximum rate was 19.4–22.6 Km in 1989.

ISSN:1754-5692    

DOI:10.1093/ee/24.6.1529

出版商:Oxford University Press    

年代:1995

数据来源: OUP