Non-crop Habitats Research Articles

Conservation of biodiversity within Canadian agricultural landscapes: Integrating habitat for wildlife

Industrialized agriculture currently substitutes many of the ecological functions of soil micro-organisms, macroinvertebrates, wild plants, and vertebrate animals with high cost inputs of pesticides and fertilizers. Enhanced biological diversity potentially offers agricultural producers a means of reducing the cost of their production. Conservation of biodiversity in agricultural landscapes may be greatly enhanced by the adoption of certain crop management practices, such as reduced pesticide usage or measures to prevent soil erosion. Still, the vast monocultures comprising the crop area in many Canadian agricultural landscapes are often of limited conservation value, thus the inclusion of appropriate wildlife habitat in and around arable lands is a fundamental prerequisite for the integration of wild species within agricultural landscapes. This review of current literature considers the potential for non-crop areas within agricultural landscapes to be reservoirs of agronomically beneficial organisms including plants, invertebrates, and vertebrate species. Non-crop habitats adjacent to crop land have been identified as significant for the maintenance of plant species diversity, for the conservation of beneficial pollinating and predatory insects, and as essential habitat for birds. A key component for enhancement of biodiversity is the reintroduction of landscape heterogeneity by (1) protection and enhancement of key non-crop areas, (2) smaller fields and farms, and (3) a greater mixture of crops, through rotation, intercropping and regional diversification. The benefits of increased biodiversity within arable lands are reviewed for various species groups. In the Canadian context, any serious attempt to derive significant agronomic benefit from increased biodiversity will require considerable changes in the agricultural programs and policies which shape mainstream industrialized agriculture. The problems of crop depredation by vertebrate species, weed and insect competition, which still represent significant impediments to the creation and proper management of wildlife habitat, are also discussed.

Seasonal Distribution and Overwintering of Orius insidiosus (Say) in Arkansas

The overwintering and seasonal habitats of Orius insidiosus (Say), timing of diapause in field populations, and seasonal population dynamics in selected crop and non-crop habitats were evaluated during 1992 and 1993 at two locations, one on southwestern and the other in central Arkansas. Each location consisted of three square miles (≈ 7.77 km2) of various habitats. Diapause status was determined by dissection. In early spring, females were found primarily on hairy vetch, crimson clover, and hairy buttercup. During that time, these weeds were flowering and were infested with high populations of thrips. During late spring and summer, populations of O. insidiosus increased in association with increasing thrips populations and flowering of corn, grain sorghum, cotton, and soybean. In the fall, population densities declined sharply and became widely dispersed. In the winter, females collected from both locations were in reproductive diapause from early November until mid-March. No males were recovered during the winter or early spring. Females in reproductive diapause were found to overwinter in vegetation, primarily grasses including wheat.

A Review and Synthesis of Habitat Use by Breeding Birds in Agricultural Landscapes of Iowa

Existing information on bird species composition, abundance and nesting sta- tus during the breeding season (May through July) was compiled for habitats characteristic of the agricultural landscapes of Iowa. Data were derived from 60 sources for 144 bird species in 20 habitats. Total numbers of breeding bird species were highest in floodplain forest (107 species) and upland forest (85), and lowest in small grains (31) and herbaceous fencerows (27). Species abundances were standardized and categorized on a scale from 0 (absent) through 5 (very abundant with >250 individual birds/census count/100 ha). Bird species abundances are lowest in some agricultural habitats (e.g., tilled row crops and small grains) and highest in narrow, strip-cover habitats (e.g., railroad rights-of-way, wooded fencerows and farmstead shelterbelts). Species abundance patterns in natural habitats (forest, marsh and prairie) are intermediate between those in agricultural and strip-cover habitats. Twenty-five species occurred only in forest habitats and 14 only in marshes. Other species selectively (through not exclusively) use tilled row crop, grassland or wooded habitats. Principal com- ponents analysis was used to assess the relative similarities in use of the 20 habitats by the assemblage of breeding birds in Iowa. Predicted numbers of nesting species increased from 18 to 93 over four landscape scenarios representing a progression from an intensively farmed row-crop monoculture to a diverse mosaic of crop and noncrop habitats. Although laborious, the approach developed in our study has been useful for standardizing and synthesizing a diverse literature in efforts to conduct ecological risk assessments for farmland birds. It can also provide valuable baseline data for landscape-level research.

Flight Orientation of Diabrotica virgifera virgifera and D. barberi (Coleoptera: Chrysomelidae) at Habitat Interfaces

The short-range flight orientation behavior of adult western corn rootworms, Diabrotica virgifera virgifera LeConte, and adult northern corn rootworms, D. barberi (Smith & Lawrence), was observed within plots of corn, Zea mays L. and soybean, Glycine max (L.) Merr., and at the interface between corn and other crop and noncrop habitats. The direction of flight was random within corn and soybeans, but at the interface between early- and late-planted corn, beetles of both species generally oriented more toward flowering corn than vegetative or post-flowering corn. Beetles also oriented toward corn rather than soybean, wheat (Triticum aestivum L.), and sweet clover (Melilotus officinalis (L.) Lam.) mixed with weeds, independent of the developmental stage of the corn. In general, flight orientation behavior did not differ with sex, and flight direction was not modified by wind or the presence of the observer. It appears that, although movement within a homogeneous habitat is random, movement at the boundaries of dissimilar habitats is nonrandom. This behavior should be considered in the development of models for predicting large-scale dispersal of these insects within the corn ecosystem.

Influence of Landscape Structure on Abundance and Within-Field Distribution of European Corn Borer (Lepidoptera: Pyralidae) Larval Parasitoids in Michigan

Studies were conducted at eight locations in Ingham County, Michigan, during 1989–1990 to determine the within-field distribution of European corn borer, Ostrinia nubilalis (H¨bner), larval parasitism. O. nubilalis larval sampling was conducted at multiple locations on three transects across large 1st-yr corn fields during the F1 and F2 generations. Plants were destructively sampled to determine O. nubilalis abundance and larvae were returned to the lab to determine parasitism. Eriborus terebrans (Gravenhorst) (Hymenoptera: Ichneumonidae) was the dominant parasitoid of O. nubilalis in the sampled fields, accounting for 92.5% of the F1 and 99.2% of the F2 parasitism during 1989; and for 92.2% of the F1 and 99.1% of the F2 during 1990. Average parasitism by E. terebrans ( n = 4 fields) was 4.9 and 18.7% of F1, 10.2 and 9.1% of F2 larvae during 1989 and 1990 respectively. The maximum E. terebrans parasitism observed (37.4%) of the O. nubilalis larvae in one field (F1 1990), is the highest level reported for this species in the Midwest. Parasitism by E. terebrans during the F1 generation was greater along field margins than in field interiors in most fields during both years. During 1990, O. nubilalis larvae near wooded edges had significantly higher E. terebrans parasitism than those near nonwooded edges or field interiors. In the F2 generation, parasitism did not vary significantly from field margins to field interiors in either year. There was no consistent relationship between O. nubilalis larval density per infested plant and E. terebrans parasitism. These data suggest that local landscape structure, including proximity of particular noncrop habitats, plays an important role in the effectiveness of this natural enemy.

The Ecology of Myzus persicae

This review has been suggested by the Scientific Committee of the In­ ternational Biological Programme as part of a project on the population dy­ namics and biological control of Myzus persicae. In order to contain this review within a reasonable number of pages, information on transmission of virus diseases is virtually omitted; it could easily form a review of equal length. Work on other aphids which is relevant to the ecology of M. persi­ cae has been included in sections where knowledge of M. persicae is lacking or inadequate. A few insect species seem very well adapted to exploit the ephemeral crop environment. They include some aphid species of regional (Aphis fabae, A. gossypii, A. craccivora and Rhopalosiphon maidis as well as other grass aphids) or of almost world-wide importance (Brevicoryne brassicae, Macrosiphum euphorbiae, Myzus persicae) (2). M. persicae is outstanding in distribution, in host plant range (57, 67, 81, 103,148, 149,221,389,422,428,432,444, 525), and as a pest which causes not only direct damage but is able to transmit over 100 virus diseases of plants on about thirty different families including many major crops such as beans, sugar beet, sugar cane, brassicas, potatoes, tobacco and citrus (281). The use of chemical methods to prevent spread of viruses by controlling their aphid vectors has been either unsuccessful or only partially successful. Thus, there is a special need for the integrated control approach which will lower the numbers of the vector especially at times when viruses are spread. Control of the aphid by natural enemies in the noncrop or alternative crop habitat is therefore particularly important, but biological control by natural enemies and by manipulating the host plant could also be enhanced in the crop. Although there is a large background of knowledge on the biology of natural enemies of aphids, their significance in control in both the funda­ mental and applied senses is little understood, except perhaps for Thel'­ ioaphis maculata in California. Quantitative effects of natural enemies and of other factors which help to regulate numbers are partly understood for a few aphids (A. fabae, B. brassicae) during periods when they are pests on crops, but little relevant data is available for M. persicae. Even less atten-