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

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