▪ Abstract Many agroecosystems are unfavorable environments for natural enemies due to high levels of disturbance. Habitat management, a form of conservation biological control, is an ecologically based approach aimed at favoring natural enemies and enhancing biological control in agricultural systems. The goal of habitat management is to create a suitable ecological infrastructure within the agricultural landscape to provide resources such as food for adult natural enemies, alternative prey or hosts, and shelter from adverse conditions. These resources must be integrated into the landscape in a way that is spatially and temporally favorable to natural enemies and practical for producers to implement. The rapidly expanding literature on habitat management is reviewed with attention to practices for favoring predators and parasitoids, implementation of habitat management, and the contributions of modeling and ecological theory to this developing area of conservation biological control. The potential to int...

Habitat Management to Conserve Natural Enemies of Arthropod Pests in Agriculture

▪ Abstract Many terrestrial communities include omnivorous arthropods that feed on both prey and plant resources. In this review we first discuss some unique morphological, physiological, and behavioral traits that enable omnivores to exploit such dissimilar foods, and we explore possible evolutionary pathways to omnivory. We then examine possible benefits and costs of omnivory, describe the relationships between omnivory and other high-order complex trophic interactions, and consider the stability level of communities with closed-loop omnivory. Finally, we explore some of the implications of omnivory for crop damage and for biological, chemical, and cultural control practices. We conclude that the growing realization of the ubiquity of omnivory in nature may require a change in our view of the structure and function of ecological systems.

Omnivory in terrestrial arthropods: mixing plant and prey diets.

Most biological control systems involve a diverse community of natural enemies. We investigated how specialist and generalist natural enemies differ as biological control agents of pea aphids (Acyrthosiphon pisum), and how interactions among natural enemies affect successful control. In alfalfa, pea aphids are attacked by a specialist parasitoid wasp, Aphidius ervi, and a guild of generalist predators primarily made up of Nabis and Orius bugs, coccinellid and carabid beetles, and web-building spiders. In three field experiments, we manipulated the parasitoid, then the generalist predator guild, and finally both classes of natural enemy, and recorded resulting impacts on pea aphid population control. The parasitoid caused little immediate reduction in aphid population growth but caused a large decline after a delay corresponding to the generation time of the parasitoid. In contrast, the generalist guild caused an immediate decline in the aphid population growth rate. However, the generalists did not exert density-dependent control, so aphid densities continued to increase throughout the experiment. The third field experiment in which we simultaneously manipulated parasitoids and predators investigated the possibility of “nonadditive effects” on aphid control. Densities of parasitoid pupae were 50% lower in the presence of generalist predators, indicating intraguild predation. Nonetheless, the ratio of parasitoids to aphids was not changed, and the impact of the two types of natural enemies was additive.

We constructed a stage-structured model of aphid, parasitoid, and predator dynamics and fit the model to data from our field experiments. The model supports the additivity of parasitoid and predator effects on aphid suppression but suggests that longer-term experiments (32 d rather than 20 d) would likely reveal nonadditive effects as predation removes parasitoids whose response to aphid densities occurs with a delay. The model allowed us to explore additional factors that could influence the additivity of parasitoid and predator effects. Aphid density-dependent population growth and predator immigration in response to aphid density would likely have little influence on the additivity between parasitism and predation. However, if a parasitoid were to show a strong Type II functional response, in contrast to A. ervi whose functional response is nearly Type I, interactions with predators would likely be synergistic. These analyses reveal factors that should be investigated in other systems to address whether parasitism and predation act additively on host densities.

Corresponding Editor: E. Evans.

https://www.jstor.org/stable/pdfplus/3108000.pdf

Interactions between specialist and generalist natural enemies: parasitoids, predators, and pea aphid biocontrol

Glucophagy.- The Functions of Non-Prey Foods in the Diets of Entomophagous Species.- The Sugar Feeders.- Floral Nectar.- Extrafloral Nectar.- Honeydew.- Pollinivory.- The Pollen Feeders.- Adaptations to Pollen feeding.- Pollen Nutrition and Defense.- Granivory.- The Seed Feeders.- Adaptations to Granivory.- Seed Nutrition and Defense.- Seed-Associated Food Bodies.- Seed Preferences of Natural Enemies.- Fungi and Microorganisms.- Mycophagy.- Symbioses with Microorganisms.- Applied Aspects of Non-Prey Foods for Natural Enemies.- Non-Prey Foods and Biological Control of Arthropods.- Plant-Incorporated Pest Resistance and Natural Enemies.- Biological Control of Weed Seeds in Agriculture Using Omnivorous Insects.- Conclusions and the Relative Quality of Non-Prey Foods for Natural Enemies.

Relationships of Natural Enemies and Non-prey Foods

It is well established that plants provide alternative foods to predators of herbivorous arthropods. This provision may facilitate protection against herbivory. However, plants often cannot prevent other organisms from utilizing these foods as well. There are many examples of herbivorous arthropods that can feed on plant-provided foods such as extrafloral nectar and pollen. The question therefore arises whether individual plants still gain protection when not only the predators, but also the herbivores, can feed on these foods. We investigated this question using a mathematical model and experiments that assessed the impact of supplementary pollen on the dynamics of predatory mites (Iphiseius degenerans (Berlese)) and herbivorous thrips (Frankliniella occidentalis (Pergande)), two arthropods capable of using pollen for reproduction. Replicated greenhouse experiments showed that addition of pollen every two weeks to one young mature leaf of a male-sterile cucumber plant increased predator population growth...

How plants benefit from providing food to predators even when it is also edible to herbivores

Coleomegilla maculata (DeGeer) is an abundant, polyphagous predator in corn fields; it can develop and reproduce on a diet of only corn pollen. We used sweet corn ( Zea mays L.) in field experiments to investigate the effect of pollen abundance on C. maculata population densities, predation by C. maculata on Helicoverpa zea (Boddie) eggs, and egg cannibalism by C. maculata . Plots designated as "no-pollen plots" were detasseled immediately before anthesis, whereas tassels were left intact in "pollen plots." In both years, when pollen was absent in all plots (i.e., before and after anthesis) there were no significant differences in C. maculata population density, H. zea egg predation, or C. maculata egg cannibalism between pollen and no-pollen plots. During anthesis in 1996, C. maculata egg and larval densities were significantly higher in pollen plots compared with no-pollen plots, but not in 1995. Predation on H. zea eggs was significantly lower in pollen plots than in no-pollen plots in 1995, but not in 1996. During anthesis in both years, egg cannibalism was lower in pollen plots compared with no-pollen plots and significantly so in 1996. Even when abundant pollen led to increased C. maculata larval populations in pollen plots (i.e., in 1996), predation on H. zea eggs and cannibalism of C. maculata eggs was not higher in the pollen plots, suggesting that abundant pollen diverts C. maculata from carnivory. Thus, even though C. maculata populations may increase during anthesis in corn, this increased abundance is not likely to translate into increased predation on H. zea eggs.

Effect of Pollen on Coleomegilla maculata (Coleoptera: Coccinellidae) Population Density, Predation, and Cannibalism in Sweet Corn

Solving the Complementarity Dilemma: Evolving Strategies for Simultaneous Hermaphroditism

The polyphagous predator, Coleomegilla maculata (DeGeer) (Coleoptera: Coccinellidae), commonly oviposits on the native weed, Acalypha ostryaefolia Riddell (Euphorbiaceae), in and around Kentucky sweet corn fields. Cannibalism of eggs by C. maculata adults and larvae is drastically lower on A. ostryaefolia than on nearby sweet corn plants. We examined ovipositional preference of C. maculata for A. ostryaefolia plants or sweet corn plants, dispersal of larvae from A. ostryaefolia plants, capability for dispersal of larvae across bare soil (e.g., to nearby plants), ability of larvae to climb from ground level up A. ostryaefolia plants or sweet corn plants, and effect of A. ostryaefolia borders adjacent to sweet corn plots on C. maculata population density in sweet corn. The ovipositional preference study revealed that C. maculata laid more eggs on A. ostryaefolia than on corn. First-instar C. maculata that hatched from egg clusters on A. ostryaefolia dispersed predominantly by falling, rather than crawling, to the ground. Glandular trichomes on A. ostryaefolia petioles and stems apparently inhibited intraplant movement of first instars, resulting in those larvae falling directly from leaves to the ground. Some first instars were capable of moving at least 8 m across bare soil in 24 h. From the ground, significantly more first instars climbed sweet corn plants than climbed A. ostryaefolia plants. Significantly more larvae were present in sweet corn plots bordered by A. ostryaefolia plants than in sweet corn plots without an A. ostryaefolia border. These findings show that physical attributes of companion plants can significantly influence natural enemy populations on crop plants by affecting interplant dispersal of natural enemies.

Factors influencing dispersal of larval Coleomegilla maculata from the weed Acalypha ostryaefolia to sweet corn

We investigated the density of Coleomegilla maculata (DeGeer), predation by C. maculata on Helicoverpa zea (Boddie) eggs, and egg cannibalism by C. maculata when the weed Acalypha ostryaefolia Riddell was grown in stands of sweet corn ( Zea mays L.). Densities of C. maculata eggs and larvae were significantly higher in weedy plots than in weed-free plots during each of the 3 yr the study was done. Pupal density was significantly higher in weedy plots in 1995 and 1996, but not in 1997. Adult C. maculata density was significantly higher in weedy plots in 1995, but not in 1996 or 1997. Egg cannibalism by adult and larval C. maculata is common on sweet corn plants in Kentucky. C. maculata frequently oviposits on A. ostryaefolia in and around sweet corn plots, and our preliminary observations suggested egg cannibalism was less frequent on A. ostryaefolia than on sweet corn plants. There was a trend for higher abundance of C. maculata eggs on corn plants in weed-free plots than on corn plants in weedy plots; in weedy plots, >85% of eggs were on A. ostryaefolia plants rather than on corn plants. However, larvae were always more abundant on corn plants in weedy plots than on corn plants in weed-free plots and significantly so in 1995 and 1997. Predation of H. zea eggs was significantly higher on corn plants in weedy plots than on corn plants in weed-free plots, whereas cannibalism of C. maculata eggs was significantly higher on corn plants in weedy plots only during 1 of the 3 yr. Thus, presence of A. ostryaefolia in sweet corn plots increased C. maculata egg and larval population densities and predation of H. zea eggs. Direct observations of H. zea egg predation and egg cannibalism by C. maculata revealed that adults predominantly were diurnal but larvae fed day and night.

Influence of a native weed, Acalypha ostryaefolia (Euphorbiaceae), on Coleomegilla maculata (Coleoptera: Coccinellidae) population density, predation, and cannibalism in sweet corn

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Effect of Pollen on Coleomegilla maculata (Coleoptera: Coccinellidae) Population Density, Predation, and Cannibalism in Sweet Corn

Solving the Complementarity Dilemma: Evolving Strategies for Simultaneous Hermaphroditism

Factors influencing dispersal of larval Coleomegilla maculata from the weed Acalypha ostryaefolia to sweet corn

Influence of a native weed, Acalypha ostryaefolia (Euphorbiaceae), on Coleomegilla maculata (Coleoptera: Coccinellidae) population density, predation, and cannibalism in sweet corn