Forest Restoration and Parasitoid Wasp Communities in Montane Hawai\u27i

Globally, most restoration efforts focus on re-creating the physical structure (flora or physical features) of a target ecosystem with the assumption that other ecosystem components will follow. Here we investigate that assumption by documenting biogeographical patterns in an important invertebrate taxon, the parasitoid wasp family Ichneumonidae, in a recently reforested Hawaiian landscape. Specifically, we test the influence of (1) planting configurations (corridors versus patches), (2) vegetation age, (3) distance from mature native forest, (4) surrounding tree cover, and (5) plant community composition on ichneumonid richness, abundance, and composition. We sampled over 7,000 wasps, 96.5% of which were not native to Hawai\u27i. We found greater relative richness and abundance of ichneumonids, and substantially different communities, in restored areas compared to mature forest and abandoned pasturelands. Non-native ichneumonids drive these differences; restored areas and native forest did not differ in native ichneumonid abundance. Among restored areas, ichneumonid communities did not differ by planting age or configuration. As tree cover increased within 120 m of a sampling point, ichneumonid community composition increasingly resembled that found in native forest. Similarly, native ichneumonid abundance increased with proximity to native forest. Our results suggest that restoration plantings, if situated near target forest ecosystems and in areas with higher local tree cover, can facilitate restoration of native fauna even in a highly invaded system. © 2013 Gould et al

Landscape and farm management effects on Ichneumonidae (Hymenoptera) diversity and parasitism of pests in organic vegetable production

Land conversion and agricultural intensification reduce both on-farm and near-farm non-crop habitat for arthropod biodiversity, with potentially detrimental consequences for biological control of crop pests. The diversity of ichneumonid wasps, a large family of parasitoids, was sampled over three years and parasitism of two insect pests was measured in annual vegetable farms the following year; management practices were described and vegetation and landuse cover within 1.5Km were measured for each farm. Ichneumonidae species richness was positively associated with landscape-scale vegetative cover and field-scale crop diversity, but not with landscape-scale vegetation diversity; subfamily responses to both landscape vegetation classes and crop diversity varied. Species richness within Campopleginae and Cryptinae were positively associated with perennial vegetation and negatively associated with annual cropland, whereas diplazontine richness was positively associated with grasslands and negatively associated with freshwater. Baccharis shrubs and annual crop cover best explain the distribution of ichneumonid species, regardless of subfamily. Three ichneumonid and two braconid wasp species and tachinid flies parasitized Trichoplusia ni larvae, but major mortality was due to Hyposoter exiguae (Ichneumonidae) in May and Microplitis alaskensis (Braconidae) in September. Spring parasitism rates were positively associated with annual crop and grassland cover--an opposite pattern to the abundance and species richness of the Ichneumonidae samples. T. ni parasitism in fall was positively associated with grassland cover, pest control intensity, and decreasing tillage, not perennial vegetation cover. Parasitism of Brevicoryne brassicae was not associated with landscape vegetation or with farm management. Although greater on-farm crop diversity and perennial vegetation conservation in cropland-dominated landscapes were associated with greater richness of Ichneumonidae, neither perennial vegetation nor wasp richness was associated with high parasitism rates of sentinel caterpillars or aphids in the following year. These results suggest that elements of the landscape mosaic are needed to support diverse communities of natural enemies, but pest control services do not necessarily map on to patterns of arthropod diversity. Over the long term, a more diverse community may provide "insurance" against pest outbreaks if a dominant parasitoid is lost, but areas of overlap between biodiversity conservation and agricultural goals must be assessed critically

Perennial Habitat Fragments, Parasitoid Diversity and Parasitism in Ephemeral Crops

Agricultural intensification has led to the removal of semi-wild, perennial vegetation in agricultural landscapes. However, in short-cycle crops, frequent disturbance from insecticides, harvesting and tillage disrupts the establishment of resident communities of natural enemies of pests. Semi-wild perennial vegetation may provide critical habitat for mobile arthropods supporting ecosystem services and sustainable agriculture. We sampled tachinid parasitoids, an important taxon for biological control of vegetable pests, in 35 organic farm fields situated within a mosaic of agricultural, residential and preserved lands in coastal California. Using a GIS, we characterized land-use and vegetative cover within 500 and 1500 m, including grasslands, chaparral, oak woodlands and coniferous forests. The abundance and species richness of tachinid flies captured in Malaise traps in spring and summer were positively associated with the cover of semi-wild perennial vegetation, especially in mesic habitats. The effective number of tachinid species (eH) was correlated positively with semi-wild perennial vegetation cover and negatively with annual crop cover in the landscape in September and May. The richness of parasitoids emerging from sentinel lepidopteran pests exposed on potted plants within farm fields was negatively associated with annual cropland cover. Parasitism rates dropped precipitously as percentage annual crop cover exceeded species-specific thresholds. Synthesis and applications. Maintaining semi-wild, perennial habitat fragments as refugia to support parasitoids can increase biodiversity and provide ecosystem services in annual and short-cycle crop fields. Our results indicated that crop pests escaped parasitism by two important tachinid species in landscapes with greater than 38% and 51% cover of annual cropland, respectively. Landscape-level research is critical for integrating science and policy to conserve biodiversity, promote sustainable agroecosystems and evaluate new anti-wildlife vegetation removal campaigns that may harm biological control agents while targeting microbial food contamination

Do Perennial Habitat Fragments Support Greater Parasitoid Diversity and Pest Regulation in Ephemeral Crops?

Background/Question/Methods To examine the role of native perennial vegetation in agricultural landscapes in providing critical habitat for supporting ecosystem services and sustainable agriculture, we sampled mobile arthropods in short-cycle, organically-managed crops in California. These agroecosystems are notoriously challenging for achieving conservation biological control because frequent disturbance precludes the establishment of resident communities of natural enemies of pests. Tachinidae, a diverse and ubiquitous family of parasitoid flies, were sampled for three seasons in 35 organic farm fields situated within a mosaic of agricultural and preserved lands in coastal California. Using a GIS, we characterized land-use and vegetative cover within 500m and 1500m, including grasslands, chaparral, oak woodlands, and coniferous forests. Results/Conclusions The abundance and species richness of tachinid flies captured in field crops in spring and summer were positively associated with the cover of semi-wild perennial vegetation, and the species richness of parasitoids emerging from sentinel lepidopteran pests exposed on potted plants in these organic vegetable fields was negatively associated with annual cropland cover. We discuss the importance of maintaining semi-wild, perennial habitat fragments as refugia to support parasitoids that provide ecosystem services in annual and short-cycle crop fields, and distinctions between fragments dominated by native versus introduced plants

Do Perennial Habitat Fragments Support Greater Parasitoid Diversity and Pest Regulation in Ephemeral Crops?

Background/Question/Methods To examine the role of native perennial vegetation in agricultural landscapes in providing critical habitat for supporting ecosystem services and sustainable agriculture, we sampled mobile arthropods in short-cycle, organically-managed crops in California. These agroecosystems are notoriously challenging for achieving conservation biological control because frequent disturbance precludes the establishment of resident communities of natural enemies of pests. Tachinidae, a diverse and ubiquitous family of parasitoid flies, were sampled for three seasons in 35 organic farm fields situated within a mosaic of agricultural and preserved lands in coastal California. Using a GIS, we characterized land-use and vegetative cover within 500m and 1500m, including grasslands, chaparral, oak woodlands, and coniferous forests. Results/Conclusions The abundance and species richness of tachinid flies captured in field crops in spring and summer were positively associated with the cover of semi-wild perennial vegetation, and the species richness of parasitoids emerging from sentinel lepidopteran pests exposed on potted plants in these organic vegetable fields was negatively associated with annual cropland cover. We discuss the importance of maintaining semi-wild, perennial habitat fragments as refugia to support parasitoids that provide ecosystem services in annual and short-cycle crop fields, and distinctions between fragments dominated by native versus introduced plants

Perennial Habitat Fragments, Parasitoid Diversity and Parasitism in Ephemeral Crops

Agricultural intensification has led to the removal of semi-wild, perennial vegetation in agricultural landscapes. However, in short-cycle crops, frequent disturbance from insecticides, harvesting and tillage disrupts the establishment of resident communities of natural enemies of pests. Semi-wild perennial vegetation may provide critical habitat for mobile arthropods supporting ecosystem services and sustainable agriculture. We sampled tachinid parasitoids, an important taxon for biological control of vegetable pests, in 35 organic farm fields situated within a mosaic of agricultural, residential and preserved lands in coastal California. Using a GIS, we characterized land-use and vegetative cover within 500 and 1500 m, including grasslands, chaparral, oak woodlands and coniferous forests. The abundance and species richness of tachinid flies captured in Malaise traps in spring and summer were positively associated with the cover of semi-wild perennial vegetation, especially in mesic habitats. The effective number of tachinid species (eH) was correlated positively with semi-wild perennial vegetation cover and negatively with annual crop cover in the landscape in September and May. The richness of parasitoids emerging from sentinel lepidopteran pests exposed on potted plants within farm fields was negatively associated with annual cropland cover. Parasitism rates dropped precipitously as percentage annual crop cover exceeded species-specific thresholds. Synthesis and applications. Maintaining semi-wild, perennial habitat fragments as refugia to support parasitoids can increase biodiversity and provide ecosystem services in annual and short-cycle crop fields. Our results indicated that crop pests escaped parasitism by two important tachinid species in landscapes with greater than 38% and 51% cover of annual cropland, respectively. Landscape-level research is critical for integrating science and policy to conserve biodiversity, promote sustainable agroecosystems and evaluate new anti-wildlife vegetation removal campaigns that may harm biological control agents while targeting microbial food contamination

Perennial habitat fragments, parasitoid diversity and parasitism in ephemeral crops. Applied Ecology 49(6

Summary 1. Agricultural intensification has led to the removal of semi-wild, perennial vegetation in agricultural landscapes. However, in short-cycle crops, frequent disturbance from insecticides, harvesting and tillage disrupts the establishment of resident communities of natural enemies of pests. Semi-wild perennial vegetation may provide critical habitat for mobile arthropods supporting ecosystem services and sustainable agriculture. 2. We sampled tachinid parasitoids, an important taxon for biological control of vegetable pests, in 35 organic farm fields situated within a mosaic of agricultural, residential and preserved lands in coastal California. Using a GIS, we characterized land-use and vegetative cover within 500 and 1500 m, including grasslands, chaparral, oak woodlands and coniferous forests. 3. The abundance and species richness of tachinid flies captured in Malaise traps in spring and summer were positively associated with the cover of semi-wild perennial vegetation, especially in mesic habitats. The effective number of tachinid species (e H ) was correlated positively with semi-wild perennial vegetation cover and negatively with annual crop cover in the landscape in September and May. 4. The richness of parasitoids emerging from sentinel lepidopteran pests exposed on potted plants within farm fields was negatively associated with annual cropland cover. Parasitism rates dropped precipitously as percentage annual crop cover exceeded species-specific thresholds. 5. Synthesis and applications. Maintaining semi-wild, perennial habitat fragments as refugia to support parasitoids can increase biodiversity and provide ecosystem services in annual and short-cycle crop fields. Our results indicated that crop pests escaped parasitism by two important tachinid species in landscapes with greater than 38% and 51% cover of annual cropland, respectively. Landscape-level research is critical for integrating science and policy to conserve biodiversity, promote sustainable agroecosystems and evaluate new anti-wildlife vegetation removal campaigns that may harm biological control agents while targeting microbial food contamination

Disturbance, Resources, and Exotic Plant Invasion: Gap Size Effects in a Redwood Forest

Volume: 57Start Page: 11End Page: 1

Habitat Eradication and Cropland Intensification May Reduce Parasitoid Diversity and Natural Pest Control Services in Annual Crop Fields

California’s central coast differs from many agricultural areas in the U.S., which feature large tracts of monoculture production fields and relatively simple landscapes. Known as the nation’s salad bowl, and producing up to 90% of U.S. production of lettuces, broccoli and Brussels sprouts, this region is a mosaic of fresh vegetable fields, coastal meadow, chaparral shrubs, riparian and woodland habitat. We tested for relationships between the percent cover of crops, riparian and other natural landscape vegetation and the species richness of parasitic wasps and flies foraging in crops, such as broccoli, kale and cauliflower, and interpreted our results with respect to the decrease in natural habitat and increase in cropland cover prompted by a local microbial contamination event in 2006. Our key results are that: (1) as cropland cover in the landscape increased, fewer species of parasitoids were captured in the crop field, (2) parasitoid richness overall was positively associated with the amount of riparian and other natural vegetation in the surrounding 500m, (3) different groups of parasitoids were associated with unique types of natural vegetation, and (4) parasitism rates of sentinel cabbage aphid and cabbage looper pests were correlated with landscape vegetation features according to which parasitoids caused the mortality. Although individual species of parasitoids may thrive in landscapes that are predominantly short season crops, the robust associations found in this study across specialist and generalist parasitoids and different taxa (tachinid flies, ichneumon wasps, braconid wasps) shows that recent food safety practices targeting removal of natural vegetation around vegetable fields in an attempt to eliminate wildlife may harm natural enemy communities and reduce ecosystem services. We argue that enhancing biological diversity is a key goal for transforming agroecosystems for future productivity, sustainability and public health

Habitat Eradication and Cropland Intensification May Reduce Parasitoid Diversity and Natural Pest Control Services in Annual Crop Fields

California’s central coast differs from many agricultural areas in the U.S., which feature large tracts of monoculture production fields and relatively simple landscapes. Known as the nation’s salad bowl, and producing up to 90% of U.S. production of lettuces, broccoli and Brussels sprouts, this region is a mosaic of fresh vegetable fields, coastal meadow, chaparral shrubs, riparian and woodland habitat. We tested for relationships between the percent cover of crops, riparian and other natural landscape vegetation and the species richness of parasitic wasps and flies foraging in crops, such as broccoli, kale and cauliflower, and interpreted our results with respect to the decrease in natural habitat and increase in cropland cover prompted by a local microbial contamination event in 2006. Our key results are that: (1) as cropland cover in the landscape increased, fewer species of parasitoids were captured in the crop field, (2) parasitoid richness overall was positively associated with the amount of riparian and other natural vegetation in the surrounding 500m, (3) different groups of parasitoids were associated with unique types of natural vegetation, and (4) parasitism rates of sentinel cabbage aphid and cabbage looper pests were correlated with landscape vegetation features according to which parasitoids caused the mortality. Although individual species of parasitoids may thrive in landscapes that are predominantly short season crops, the robust associations found in this study across specialist and generalist parasitoids and different taxa (tachinid flies, ichneumon wasps, braconid wasps) shows that recent food safety practices targeting removal of natural vegetation around vegetable fields in an attempt to eliminate wildlife may harm natural enemy communities and reduce ecosystem services. We argue that enhancing biological diversity is a key goal for transforming agroecosystems for future productivity, sustainability and public health