摘要:

Predation rates for the predatorPodisus maculiventris(Say) on third-instarEpilachna varivestisMulsant were measured in field cages in soybeans,Glycine maxL., over 3 yr. Attack rates in the first 2 yr averaged 0.47 attacks per predator per day and were consistently low at low prey density. Area searched by predators was estimated from attack rates, and the estimated search area decreased as prey density increased. In a third field season, attack rates averaged 0.5 attacks per day at low prey density and increased linearly at high density. A negative exponential function was used to develop a model that described search area as a function of prey density. The model estimated that area searched ranged from a maximum of 0.50 m2at zero prey density to an asymptotic minimum of 0.055 m2at high prey densities. Searching less area as prey density increases keeps attack rates low and consistent at low prey density, and searching a constant amount of area at high prey density results in increasing attack rates at higher prey density. The search strategy may result from balancing energetic costs and predation risks with the benefits gained from attacking prey. Also, the strategy may reflect the budgeting of time between searching and other time-consuming activities (e.g., reproduction) by the predator. Determining the search strategy of predators may provide a better understanding of the requisites of generalist predators living in ephemeral crop systems.

ISSN:1754-5692    

DOI:10.1093/ee/21.1.1

出版商:Oxford University Press    

年代:1992

数据来源: OUP

摘要:

Developmental times, survival, and adult dry weights for two clones of the pea aphid,Acyrthosiphon pisum(Harris), were determined at constant temperatures from 5 to 28°C1. These data were used to test the hypotheses that genetic variation in the developmental threshold or the effect of temperature on the nutritional value of food could account for nonlinearity in the relationship between developmental rate and temperature at low temperatures. Neither of these hypotheses was supported by the data and the relationship probably is inherently nonlinear. The consequences of this nonlinearity were investigated in relation to estimating developmental thresholds. Developmental thresholds based on the traditional linear method of estimation are not adequate when they are used to quantify a life history trait, but probably are adequate in pest management. Alternative methods for estimating a developmental threshold and degree-day requirement were developed based on the parameters of a nonlinear equation. The approach was validated by comparing methods for 21 diverse species of insects.

ISSN:1754-5692    

DOI:10.1093/ee/21.1.10

出版商:Oxford University Press    

年代:1992

数据来源: OUP

摘要:

This study examines the feasibility of markingLygus hesperusKnight adults externally by submersion in rabbit immunoglobulin G(IgG) solution. Rabbit IgG retention time was measured in the laboratory on insects submerged in an IgG solution. We marked insects with rabbit IgG and ran an enzyme-linked immunosorbent assay (ELISA) with its complementary antibody (antirabbit IgG). We concurrently ran an ELISA assay using the same samples against an egg-specificL. hesperusmonoclonal antibody (MAb)to measure the presence ofL. hesperusegg antigen in the insect. A previously developed egg-specific MAb toL. hesperusenabled us to assay simultaneously adult females (which possess the egg antigen) and adult males for the presence ofL. hesperusegg antigen. This combination of techniques will enable us to examine the gut contents of potential predators ofL. hesperuseggs or adult females using whole body macerates while simultaneously evaluating the efficiency of lab-reared predators for augmentative biological control.

ISSN:1754-5692    

DOI:10.1093/ee/21.1.20

出版商:Oxford University Press    

年代:1992

数据来源: OUP

摘要:

A comparative analysis of three natural enemy guilds is used to illustrate a conceptual framework for guild analysis and to derive predictions for applied biological control. The guilds consist of: a natural, coevolved guild of parasites (seven species) associated with a native cecidomyiid midge,Rhopalomyia californicaFelt, which develops in galls onBaccharis pilularisDC in northern California; a diverse parasite guild (12 species), believed to have been restructured by the addition of an exotic species, associated with a native diaspidid,Melanaspis obscura(Comstock) (obscure scale), on pecan in southern Texas; and a synthetic or anthropogenic guild of phytoseiid mites (four commercially available species) released against twospotted spider mite,Tetranychus urticaeKoch, on bean plants in northern California. These guilds are analyzed according to the following framework: ecological-evolutionary history, empirical patterns in space and time (e.g., spatial distribution of species per host patch), factors affecting guild structure (e.g., interspecific competition, structure of host population), ecological effect on the host population (e.g., spatial density dependence), and relationship between guild structure and ecological effect (e.g., species-dependent mortality). It is suggested that analysis of natural enemy guilds may be of value in deriving introduction strategies in both classical and augmentative biological control. The importation ofEncarsia aurantii(Howard) into California for control of obscure scale is described as a case in point. Some additional implications of guild analysis for biological control are discussed.

ISSN:1754-5692    

DOI:10.1093/ee/21.1.26

出版商:Oxford University Press    

年代:1992

数据来源: OUP

摘要:

Rye,Secale cerealeL., used as a winter cover crop was killed by the herbicide paraquat or by mowing with a rotary mower. In subsequent no-till corn,Glyptapanteles militaris(Walsh) (Hymenoptera: Braconidae) andPeriscepsia laevigata(Wulp) (Diptera: Tachinidae) were the most abundant of twelve species of parasitoids that emerged from field-collected larvae of the armyworm,Pseudaletia unipuncta(Haworth). No effects of cover crop suppression practices were detected for parasitism rates for any individual species or for total armyworm parasitism. Seasonal parasitism rates ranged from 32 to 45%. Higher numbers ofPterostichusspp. andScaritesspp. (Coleoptera: Carabidae), and wolf spiders (Araneae: Lycosidae) occurred early in the corn season in the mowed cover crop treatment compared with the herbicide killed cover crop treatment. Subsequent reduction of larval densities of amryworm in mowed plots following higher predator densities suggests the role of these generalist predators in biological control of armyworm.

ISSN:1754-5692    

DOI:10.1093/ee/21.1.41

出版商:Oxford University Press    

年代:1992

数据来源: OUP

摘要:

A plate enzyme-linked immunosorbent assay (ELISA) using the biotinavidin system was developed for identifying larvae of the spotted tentiform leafminer,Phyllonorycter blancardella(F.), parasitized byPholetesor ornigis(Weed). Host larvae were chemically extracted, without trituration, directly in antibody-coated ELISA plate wells containing sodium dodecyl sulfate, mercaptoethanol, and EDTA buffered with TRIS. Detergents were used in the extraction buffer to prevent loss of serological activity and to reduce nonspecific reactions. The assay was accurate using fresh or frozen specimens. The correlation between parasitoid size and ELISA value was highly significant down to a parasitoid length of ≍0.34mm. Parasitoid eggs or early-stage larvae were not detectable with antiserum prepared to cocoons.

ISSN:1754-5692    

DOI:10.1093/ee/21.1.50

出版商:Oxford University Press    

年代:1992

数据来源: OUP

摘要:

Male and female adults of fall armyworm,Spodoptera frugiperda. (J. E. Smith), were exposed to a substerilizing dose (10 krads) of radiation, and their progeny were reared on corn,Zea maysL., foliage and meridic diets with varying concentrations of resistant corn silk. Mean leaf damage ratings for all corn entries were higher for plants infested with larvae from nonirradiated adults than for plants infested with larvae from irradiated males crossed with normal females. However, the rate of larval establishment on foliage of all corn entries was not affected by the larval treatment. Larvae from irradiated males crossed with normal females were equally competitive with normal larvae in all measured parameters of laboratory bioassays. Larvae from irradiated females also were competitive with normal larvae except in early larval development and time to adult eclosion. The results suggest that host plant resistance and inherited sterility would be compatible strategies for managing populations of the fall armyworm.

ISSN:1754-5692    

DOI:10.1093/ee/21.1.57

出版商:Oxford University Press    

年代:1992

数据来源: OUP

摘要:

The effect of vegetational diversity on ants and herbivores was studied in a maize-bean(Zea mays-Phaseolus vulgaris)biculture and a maize monoculture in Nicaragua. Three basic hypotheses were examined: (1) the abundance of herbivores on maize would be less in the biculture than in the monoculture, (2) ant foraging activity would be higher in the biculture, and (3)the effect of ants as natural enemies of maize pests would account for differences in the abundance of those pests in the bicultures. The effects of plant diversity on the abundance ofSpodoptera frugiperda(J. E. Smith), the fall armyworm, andDalbulus maidis(De Long&Wolcott), the corn leafhopper, were examined. Ant-foraging activity was estimated as the proportion of tunafish baits occupied by ants in monocultures and bicultures. The effect of ants on the maize herbivores was investigated by excluding ants through selective poisoning. Cropping patterns significantly influenced the numbers of fall armyworm and corn leafhopper, but in different ways. The corn leafhopper was more abundant in bicultures, and the fall armyworm was more abundant in monocultures. No significant difference was found in the proportion of baits occupied by ants in maize monocultures and maize- bean bicultures. Ants had a significant effect on the two main maize pests,S. frugiperdaand D.maidis. There were significantly higher numbers of both pests in plots where ant foraging activity was reduced with insecticide. These results suggest the possibility of using ants as agents of biological control in the maize agroecosystem in Nicaragua.

ISSN:1754-5692    

DOI:10.1093/ee/21.1.61

出版商:Oxford University Press    

年代:1992

数据来源: OUP

摘要:

Temperature and seasonal changes affected endophyte concentration, peramine concentration, and antixenosis to greenbug in perennial ryegrass infected withAcremonium loliiLatch, Christensen&Samuels. Endophyte and peramine concentrations and degree of greenbug antixenosis to endophyte-infected tillers were lower at 7 and 28%C compared with 14 and 21%C in three genotypes of perennial ryegrass; antixenosis was related to peramine and to endophyte concentration. Genotype differences were greater than differences associated with temperature. Field data collected every 3–6 wk indicated highest endophyte concentrations in spring and fall, when mean daily temperatures averaged 15%C in the previous 4 wk. These data suggest that it is possible to produce cultivars with low or high endophyte concentrations as needed for pastures or turf.

ISSN:1754-5692    

DOI:10.1093/ee/21.1.68

出版商:Oxford University Press    

年代:1992

数据来源: OUP

摘要:

Population densities and relative abundances of spider families were estimated on Douglas-fir,Pseudotsugata menziessiivar.glauca(Beissn.) Franco and true firs,Abiesspp., in three geographical provinces of the interior Pacific Northwest: the Southern Cascades, the Northern Cascades, and the Blue Mountains. Mean densities, estimated by sampling tree foliage on lower branches in June 1981, were 9.96, 5.21, and 6.03 spiders per square meter of branch area for the three areas, respectively. Eleven families were represented in the sample. Over half of all individuals were hunting spiders of the families Salticidae and Philodromidae, of which several species are believed to be important predators of defoliating insects. The rest were web-spinners, mostly of the families Dictynidae, Araneidae, Linyphiidae, and Theridiidae. The relative abundance of families had a consistent statistical pattern in which their frequencies were apportioned according to a log series distribution. This suggests that arboreal spider communities of interior Pacific Northwest fir stands have a similar familial structure, probably determined by the branch and foliage characteristics of their habitat.

ISSN:1754-5692    

DOI:10.1093/ee/21.1.75

出版商:Oxford University Press    

年代:1992

数据来源: OUP