摘要:

A study was conducted in 1986 and 1987 to determine the relationships between habitat characteristics and perturbation from insecticides on population and community dynamics of ground beetles collected with pitfall traps at 29 mixed-grass rangeland plots in northwestern South Dakota. Detrended correspondence analysis (DCA) and correlation analysis were used to define ecological gradients underlying changes in community structure of ground beetles. Results indicated that spatial changes in ground beetle communities occurred along gradients of percentage of clay, sand, and silt in soils and coverage of bare ground but were not related to vegetation. Twenty of the plots, located in two 1,400-ha blocks, were treated aerially with malathion liquid spray or carbaryl–bran bait in early July 1986. Pitfall trap catches of the dominant species declined significantly in one or both treatment blocks. However, catches rebounded to or above pretreatment levels a year after treatments. Results from DCA and multiple regression analysis of communities sampled in both years indicated that specific habitat characteristics were associated with immediate changes in community structure after perturbation; communities in habitats with high coverage ofBuchloe dactyloides(Nutt.) Engelm., low coverage ofBouteloua gracilis(H.B.K.) Lag. ex Steud., and low clay soils were more resistant to change. Community malleability, or the tendency of communities to return to their predisturbed state, was not affected by treatment and was greater in habitats with high coverage ofB. dactyloidesand sedges and low coverage ofB. gracilisand forbs. These variables are undoubtedly associated with other habitat characteristics as well.

DOI:10.1093/ee/20.5.1285

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

Density and population structure of a native cecidomyiid gall midge,Rhopalomyia californicaFelt, and the spatial structure of its parasite guild have returned to normal at Woodside, Calif., several years after ecological disruption caused by repeated applications of malathion bait for eradication of Mediterranean fruit fly,Ceratitis capitata(Wiedemann). Midge larvae develop in terminal galls onBaccharis pilularisDC; galls are multichambered and can contain>50 larvae per gall (one larva per chamber). Samples taken during the summer–fall of 1989 and April 1990 (7–8 yr after the disruption) revealed that the number of larvae per 100 terminals, number of larvae per gall, and number of galls per 100 terminals were comparable at Woodside and the Jasper Ridge Biological Preserve, an adjacent nontreated area. The parasite guild consists of seven solitary species. Analysis of spatial structure of the guild in April 1990 revealed no significant differences (Woodside versus Jasper Ridge) for the following six parameters: parasitization by individual species, total parasitization, number of parasite species per gall (relative frequency), parasite species per gall as a function of gall size, total percent parasitization as a function of number of parasite species per gall (species dependence), and total percent parasitization as a function of gall size (spatial density dependence). The evidence obtained also illustrates how host population structure can influence parasite guild structure (i.e., direct relationship between number of host larvae per gall and number of parasite species per gall), and supports the view that there is a relationship between parasite guild structure and effect on the host population (i.e., direct relationship between number of parasite species per gall and total percent parasitization per gall). Some additional aspects of structure of parasite guilds are discussed.

DOI:10.1093/ee/20.5.1295

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

Larvae, pupae, and adults of ladybird beetles were observed in an insecticide-free and an insecticide-treated block in an apple orchard near Budapest, Hungary during 1980–1982. Species numbers and densities in all developmental stages were higher and species turnover was lower in the insecticide-free block. Diversity and similarity indices showed more diverse and constant assemblages in the insecticide-free block. The adult assemblage was the most rich in species, with 19 species in the insecticide-free and 12 species in the treated block. The most common species overall wereCoccinella septempunctata, Adonia variegata, Adalia bipunctata, andExochomus quadripustulatus. The larval assemblage included nine and eight species for the untreated and treated blocks respectively, whereas the pupal assemblage had eight species in both blocks. Immature stages of 11 species were found in at least 1 yr and 10 of these was able to complete development in the orchard. The rate of success was higher in the insecticide-free block for most species. OnlyA. bipunctatareproduced successfully in both blocks in all three years butA. decempunctataandC. septempunctatawere often successful.

DOI:10.1093/ee/20.5.1301

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

Overwintered Colorado potato beetles,Leptinotarsa decemlineata(Say), collected from the soil at South Deerfield, Mass., in the spring of 1989 were brought to the laboratory and individually fed potato foliage or left unfed. Beetles were tethered to a flight mill for 1h daily to measure the number of flights, their distances, and time per flight when on the mill. Unfed beetles flew more often, for longer periods, and for greater distances (on average, a total of 4,879 m for unfed females compared with 1,346 m for fed females). Many (17 of 27) fed beetles flew for short distances (>5 m) before initiating oviposition; a smaller number (6 of 22) flew>200 m during any flight bout before laying their first eggs. Unfed female beetles laid virtually no eggs, whereas fed females laid an average of 22 eggs/d. Overwintered females that were unmated in the spring did not differ in egg production from spring-mated females, but egg viability was significantly higher. Results show that a single overwintered female constitutes a mobile and fecund founder of populations. The complex life history of the Colorado potato beetle uses migration and diapause to distribute offspring over space and time, thus minimizing reproductive risk.

DOI:10.1093/ee/20.5.1309

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

Survivorship and development rates were determined for cohorts of noctuid larvae caged on irrigated and dryland ‘Braxton’ soybean plants in the Delta of Mississippi. In September 1985, larval survival of fall armyworm,Spodoptera frugiperda(J. E. Smith), was higher in irrigated than in dryland soybean, although no differences were observed for rate of larval development. In July 1986, survival of fall armyworm and soybean looper,Pseudoplusia includens(Walker), was higher and development faster in irrigated than in dryland soybean, whereas no differences were observed for corn earworm,Helicoverpa zea(Boddie), during a period of high temperatures. In September 1986, survival and development rates were similar for these three species. In a study conducted with soybean planted in a nursery in July 1987, survival and rate of larval development of soybean looper, but not beet armyworm,Spodoptera exigua(Hübner), were positively correlated with canopy closure. Irrigation of soybean resulted in a cooler canopy environment or higher leaf water content or both. Irrigation increased survival (in the absence of predators) and optimized larval development of some noctuids, whereas the lack of irrigation had no effect or was favorable for larval development of other noctuid species.

DOI:10.1093/ee/20.5.1315

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

The sunflower moth,Homoeosoma electellum(Hulst), has a distinct eclosion rhythm in either a light–dark constant temperature photoperiod, or in constant darkness, or in constant light with alternating temperatures. Eclosionis arrhythmic in either constant light or constant darkness with constant temperatures. With a 12:12 light–dark, constant-temperature regimen, there is a broad eclosion peak occurring over ≍6 h before lights turn off as well as over the first part of the dark phase. Some individuals eclose during all hours of the day regardless of the regimen. With a regimen of 12 h each at 26° and 17°C. (both in constant light or darkness or light–dark with the low temperature during the dark), a bimodal periodicity of eclosion is initiated with a high peak immediately preceding the temperature drop and a low peak shortly after the temperature rise. The rhythm damps out rather quickly in constant darkness at constant temperatures.

DOI:10.1093/ee/20.5.1322

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

A stochastic model simulated the dispersal of the boll weevil,Anthonomus grandis grandisBoheman, from cotton fields. The model was developed to study various factors influencing the total distance traveled by individual weevils in a population. It describes several behavioral attributes of weevil flight, such as flight speed and duration, and selected atmospheric conditions such as wind speed and direction which affect flight. The dispersing weevil population is generated by a population dynamics model which is initialized with a population of weevils entering the field from overwintering sites. A rule-based expert system adjusts the number of overwintered weevils, larval mortality, insecticide spray threshold, and spray interval in the population model to determine the number of weevils available for flight each day. These values act as input to a flight subroutine, which produces a distance distribution for dispersing weevils from the field. Final displacement of each weevil is calculated by integrating information on random flight heading, speed, and duration given the direction and speed of the wind at different flight altitudes. Sensitivity analyses were performed on model parameters to determine their effect on dispersal distances.

DOI:10.1093/ee/20.5.1327

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

A new method developed for estimating time-varying survival rates was illustrated by examples with numerical data from a population study onListronotus oregonensis(Le Conte). The conformity between field population and simulated larval population ofL. oregonensissuggested that the simulated results represented the true egg survival rate dynamics in the field. Sensitivity analysis demonstrated that this method was not strongly affected by sampling errors or errors from the model parameters. It was adequate for simulating time-varying survival rates. In field experiments,L. oregonensispopulation density was lower and its peaks were later with later sowing of carrots. The mean survival rates calculated by the new method and by Southwood's area under the curve method were similar. The mean egg survival rates were 0.258 in 1987 and 0.382 in 1988. The egg survival rates in 1987 and 1988 followed a similar pattern in plots sowed at different dates, and there was no obvious relation between the egg survival rates and different sowing dates, although the initial egg population density decreased greatly with the later sowing dates. Egg mortality was density-dependent with no obvious time delay. Average larval survival rates for several sowing dates were 0.295 in 1987 and 0.569 in 1988. Larval mortality was generally density independent, whereas pupal mortality was density-dependent.

DOI:10.1093/ee/20.5.1333

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

Effect of crowding on alate production of the Russian wheat aphid,Diuraphis noxia(Mordvilko) was tested using a low-density treatment of 10–20 aphids per plant and a high-density treatment of 150–200 aphids per plant. Student'stdistribution (P<0.01) indicates no significant difference between the low and high density treatments. A pressure chamber was used to quantify the amount of water stress in wheat. Wing pad formation began within the range of −0.51 and −0.61 MPa and ended within the range of −1.21 and −1.31 MPa. From this range in water potential values, six water potential treatment ranges were established. Our results show by curvilinear regression that a positive correlation exists (P<0.01) between alate production and the leaf water potential of wheat, with maximum alate production occurring between −0.79 and −1.03 MPa. These data suggest that a response of the host plant, which in part results from feeding damage, is causing the production of alates.

DOI:10.1093/ee/20.5.1344

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

Cameocephala floridanaBall is an oligophagous leafhopper that switches host plants seasonally and feeds primarily on the salt-marsh cord grass,Spartina alternifloraLoiseleur-Deslongchamps, during the winter. In the laboratory, we examined how variation in foliar nitrogen ofS. altemiflorainfluenced the choice of cord-grass culms byC. floridanaas feeding and oviposition sites. We also examined the effects of host-plant nitrogen on leafhopper oviposition rate, body size, and fecundity. Given a choice among cord-grass culms grown under four fertilization regimes, groups of adult female leafhoppers preferentially fed on culms that were higher in foliar nitrogen. Although the total number of eggs laid was highest on plants of superior quality (as measured by nitrogen content), the rate of oviposition did not differ among plants of different nitrogen levels. Leafhoppers reared from first instar to adult on highly fertilized plants were significantly larger (had higher dry body weight) than those reared on unfertilized or minimally fertilized plants. A significant relationship between body weight and maternal sibship was also found for males, but not for females. Larger body size is advantageous because larger adult females have higher daily oviposition rates than smaller ones. We suggest thatC. floridanathat choose plants with higher nitrogen content under natural conditions enjoy a selective advantage and that choice within a host-plant species (and perhaps among species) is correlated with host-plant nitrogen content.

DOI:10.1093/ee/20.5.1349

出版商:Oxford University Press    

年代:1991

数据来源: OUP