Quantifying the contribution of birds to the control of arthropod pests on kale,<i>Brassica oleracea acephala</i>, a key crop in East African highland farmland

Ndang’ang’a, Paul K.; Njoroge, John B.M.; Vickery, Juliet A.

doi:10.1080/09670874.2013.820005

Cited by 20 publications

(22 citation statements)

References 49 publications

(50 reference statements)

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“…This result may seems surprising, as birds are known to decrease free-feeding caterpillar abundances and their leaf damage in kale agroecosystems (Hooks et al 2003;Ndang'ang'a et al 2013). However, similarly significant avian predation on aphids has been observed in kale fields of other regions of Kenya, yet only during the dry season (Ndang'ang'a et al 2013). This difference in predation pressure with relation to the season cautions that effects found in a single season such as with our study can not necessarily be generalised as year-round mechanisms.…”

Section: Effects Of Bird Predation On Pestscontrasting

confidence: 43%

Section: Effects Of Bird Predation On Pestsmentioning

confidence: 53%

“…As bird predation has been found to reduce aphid populations, constrain parasitism and reduce plant damage by free-feeding caterpillars in other systems (Hooks et al 2003;Martin et al 2013;Ndang'ang'a et al 2013), these variables were assessed by performing a bird exclusion experiment. Four pairs of kale plants per field were randomly selected.…”

Section: Parasitism and Predationmentioning

confidence: 99%

“…Crucifers are known to host more pests than most other crops. Aphids (Hemiptera: Aphididae) and moth caterpillars, including the diamondback moth Plutella xylostella L. (Lepidoptera: Plutellidae), are among the most abundant pests in Kenyan brassica crops (Kibata 1997;Badenes-Perez and Shelton 2006;Ndang'ang'a et al 2013). These pests are mainly managed with insecticides, which are used by at least 80% of all Kenyan farmers producing crucifers (Nyambo et al 1996;Badenes-Perez and Shelton 2006).…”

Section: Introductionmentioning

confidence: 99%

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Shade trees decrease pest abundances on brassica crops in Kenya

2017

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Agroforestry practices may mitigate the current loss of biodiversity and ecosystem services due to deforestation and agricultural intensification. To examine the effects of agroforestry on the ecosystem service of pest regulation, we assessed pest abundances and biological control potential in shaded and open kale (Brassica oleracea L. acephala) fields in Western Kenya. Specifically, we compared the abundance of pest aphids and caterpillars, ground-dwelling ants, spiders and predatory beetles, and examined aphid parasitism rates, predation rates on diamondback moth eggs, attack rates on surrogate caterpillars and bird predation on aphids. Shade trees effectively reduced abundances of aphids, caterpillars and increased abundances of spiders and predatory beetles, but neither affected ant abundances, or predation and parasitism rates. Our results suggest that presence of shade trees can decrease pest abundances, but that this is not only due to improved biological control by natural enemies but also due to microclimatic conditions affecting pest performance and bottom-up processes such as changes in plant quality and soil conditions. We encourage studies exploring simultaneously how top-down and bottom-up processes affect pest regulation in agroforestry settings.

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Section: Effects Of Bird Predation On Pestscontrasting

confidence: 43%

Section: Effects Of Bird Predation On Pestsmentioning

confidence: 53%

Section: Parasitism and Predationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Shade trees decrease pest abundances on brassica crops in Kenya

2017

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“…In part, this owes to relatively fewer studies that highlight insectivorous birds as agents of crop herbivory reduction (Borkhataria, Collazo & Groom, ; Garfinkel & Johnson, ; Perfecto et al., ) compared with studies on predacious arthropod's role in this regard (e.g., Bianchi, Booij & Tscharntke, ; Tscharntke et al., ; more). Most studies regarding birds’ arthropod regulation role relate to the Americas, with only a few in tropical Africa (Guenat, ; Milligan, Johnson, Garfinkel & Smith, ; Ndang'ang'a, Njoroge & Vickery, ).…”

Section: Introductionmentioning

confidence: 99%

Maize‐field complexity and farming system influence insectivorous birds’ contribution to arthropod herbivore regulation

2019

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The contribution of insectivorous birds to reducing crop damage through suppression of herbivory remains underappreciated, despite their role as cropland arthropod predators. We examined the roles of farming system, crop cover pattern, and structural configuration in influencing assemblage composition of insectivorous birds and their herbivorous arthropod prey across maize fields, and determined how bird exclusion affects crop herbivory levels. To achieve these objectives, we collected data across a sample of organic and conventional small‐scale non‐Bt maize farms in western Kenya. Assessments of abundance, diversity, and richness of insectivorous birds and abundance of their arthropod prey were compared between organic and conventional small‐scale non‐Bt maize on monocultured and inter‐cropped farms. We also employed bird exclusion experiments to assess impacts of bird predation on herbivorous arthropod abundance. Results showed that higher structural heterogeneity supported higher insectivorous bird richness, particularly under organic systems, dense trees, large woodlots, and thick hedgerows. Bird abundance further increased with crop diversity but not in relation to cropping method, hedgerow type, or percent maize cover per se. Conversely, herbivorous arthropod abundance and richness increased on conventional farms and those with higher percent maize cover, but were unaffected by cropping methods, tree, or hedgerow characteristics. Birds’ arthropod prey was more abundant under completely closed experimental plots compared with open or semi‐closed plots, confirming a significant linkage between birds and herbivorous arthropod suppression. In this study, we demonstrate importance of structural heterogeneity in agricultural landscapes, including diverse croplands and on‐farm trees to maximize insectivorous birds’ contribution to reducing crop arthropod herbivory. Abstract in Swahili is available with online material.

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Multiscale habitat mediates pest reduction by birds in an intensive agricultural region

Heath

Long²

2019

Ecosphere

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Habitat augmentation on farms is predicted to conserve biological diversity and support beneficial animals that reduce crop pests. Effectiveness of local habitat enhancement and subsequent pest reduction services can be mediated by the amount of habitat at larger scales. We tested whether the presence and increase of local and landscape scale bird habitat increased avian predator abundance and pest reduction by birds. We surveyed birds and performed a sentinel prey exclosure experiment in walnut orchards in the Sacramento Valley, California, USA—comparing predation probability between orchards with (n = 10) and without (n = 10) woody habitat in uncultivated orchard margins. We digitized seminatural habitat cover in landscapes around orchards to test the effectiveness of avian predators in reducing sentinel prey along a seminatural cover gradient of 0–38%. Experimental prey were diapausing larvae of Cydia pomonella (L.) (Lepidoptera: Tortricidae; codling moth), a significant pest of walnuts, which overwinter in cocoons in orchards, emerge as adults, and produce larvae that feed on the nuts the following spring. Permitting bird access to cocoons increased larval predation from 11% (caged) to 46% (no cage), and predation increased with increasing proportions of seminatural habitat within 500‐m of orchard transects. Predation also increased as the size and bark furrow depth of walnut trees increased, likely because these characteristics were associated with increasing abundance of avian predators with functional traits specific to consuming tree‐dwelling cocoons (e.g., woodpeckers). The presence and increasing complexity of local margin habitat increased the species richness and abundance of avian predators but was not predictive of cocoon predation. Consistent with intermediate landscape‐complexity hypothesis predictions, the effect size of woodpecker abundance on predation was large in simple landscapes (1–20% seminatural cover) and low in complex landscapes (>20% cover). Contrary to predictions, effect size was large in cleared landscapes (<1% cover), suggesting that orchards supported predators in cleared landscapes, with positive effects on pest reduction. We provide evidence that increasing the abundance of avian predators with traits specific for consuming target pests—by retaining old trees and seminatural cover—can increase orchard pest reduction services in an intensive agricultural region.

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Quantifying the contribution of birds to the control of arthropod pests on kale,Brassica oleracea acephala, a key crop in East African highland farmland

Cited by 20 publications

References 49 publications

Shade trees decrease pest abundances on brassica crops in Kenya

Shade trees decrease pest abundances on brassica crops in Kenya

Maize‐field complexity and farming system influence insectivorous birds’ contribution to arthropod herbivore regulation

Multiscale habitat mediates pest reduction by birds in an intensive agricultural region

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