Organic Mulch Increases Insect Herbivory by the Flea Beetle Species, Disonycha glabrata, on Amaranthus spp.

Roger V Vorsah,Louis E Jackai,Sarah A Fremah,Sudan Gyawaly,Beatrice N Dingha,Mulumebet Worku,Harmandeep Sharma,Arnab Bhowmik

doi:10.3390/insects11030162

Roger V Vorsah, Louis E Jackai + Show 6 more

Open Access

https://doi.org/10.3390/insects11030162

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Abstract

Amaranth (Amaranthus spp.) is an increasingly high-valued niche vegetable crop among small organic growers in North Carolina, due to its increasing demand among diverse immigrant groups. Production is however hampered by insect pests such as the flea beetle (FB), Disonycha glabrata (Coleoptera: Chrysomelidae), that cause significant yield reduction. Chemical insecticides are generally applied for pest control despite their known risks to health and the environment. Integrated pest management (IPM), which is a cost effective and environmentally friendly approach is still under-exploited in vegetable production by small growers. We studied IPM approaches, suitable for organic production of amaranth by screening nine amaranth varieties for resistance to the flea beetle (FB), D. glabrata, grown with, and without, mulch. D. glabrata population was 60% higher in plots with mulch compared to plots without. The amaranth varieties Molten fire and Green Callaloo recorded the lowest and the highest beetle population commensurate with low, and high leaf damage, respectively. Conversely, leaf yields in the mulched plots were 50% less than recorded in the zero-mulch counterpart, with Green Callaloo variety recording the lowest. These findings will serve as building blocks for a sustainable pest management plan that is appropriate for organic production of Amaranthus spp. in North Carolina.

Highlights

Global efforts to feed the ever-growing world population that is predicted to reach 8.1 billion by2025 [1], and the need to attain food security have galvanized the drive to cultivate crops on various scales, including small backyard and community gardens that are mostly organic culture, both in rural areas and among urban dwellers [2,3,4]
The leaf mulch used in the study increased the population of D. glabrata that resulted in higher leaf damage
Compounds that were identified including plant proteins and polyphenols, as well as other possible compounds may account, at least in part, for the differences observed in damage among the different amaranths

Summary

Introduction

Global efforts to feed the ever-growing world population that is predicted to reach 8.1 billion by2025 [1], and the need to attain food security have galvanized the drive to cultivate crops on various scales, including small backyard and community gardens that are mostly organic culture, both in rural areas and among urban dwellers (the new small farmer community) [2,3,4]. Organic vegetable farming faces many challenges [5,6,7]. Organic production practices use methods of pest control that limit, or completely eliminate, the use of high-risk synthetic pesticides and benefit from the use of IPM approaches including the use of various mulches and other biological and cultural approaches, inter alia [8,9]. These approaches seek to mitigate the impact of pests, delay the development of insecticide resistance, curb environmental contamination, and minimize human

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