Efficacy of aqueous and oil formulations of a specific Metarhizium anisopliae isolate against Aphis craccivora Koch, 1854 (Hemiptera: Aphididae) under field conditions

Abstract

Cowpea (Vigna unguiculata) production is constrained by biotic and abiotic factors, among which Cowpea aphid (Aphis craccivora) is ranked a key insect pest that severely limits its potential for provision of food and nutritional security to millions of people in sub‐Saharan Africa. The use of entomopathogenic fungi for A. craccivora management has been recently demonstrated at laboratory and field levels as alternative to synthetic insecticides, but with low adoption in Africa. This study assessed the efficacy of aqueous and oil formulations of Metarhizium anisopliae ICIPE 62 against A. craccivora under field conditions. Metarhizium anisopliae formulations and a commonly used insecticide Duduthrin® were applied using knapsack sprayers with target output of 350 L/ha. Data on aphid infestation levels were collected weekly. ICIPE 62 efficacy in inducing mortality was also assessed 24 hr post‐treatment coupled with mycosis test. Further, leaf and grain yields were determined. After six weeks post‐treatment in the wet season, there was no significant reduction in aphid density in fungus‐treated plots compared to control and Duduthrin®‐treated plots. However, in the dry season six weeks after applying the treatments, oil formulation spray resulted low aphid density compared to control and Duduthrin®‐treated plots. ICIPE 62 formulations did not negatively affect the natural enemies’ population. Leaf yield from the various treatments did not differ significantly in the wet season, but the two fungal formulations recorded higher yields in dry season compared to other treatments. Grain yields in wet and dry seasons were lower in control and Duduthrin®‐treated plots compared to both ICIPE 62 formulations. This study showed that both M. anisopliae ICIPE 62 formulations are effective in suppressing A. craccivora population under field conditions without adverse effects on its beneficial insects. The study also revealed that efficacy of fungal‐based biopesticides is highly dependent on environmental conditions.

Exploring entomopathogenic fungi from South Sumatra (Indonesia) soil and their pathogenicity against a new invasive maize pest, Spodoptera frugiperda

“…The symptoms of the infected insects due to the entomopathogenic fungal infections vary depending on favorable environmental conditions, for example, relative humidity higher than 62% (Gutiérrez-Cárdenas et al 2019), then the mycelia and mature conidia can grow well and cover the entire body of the insect, and the condition of unfavorable mycelia and conidia does not appear (El-Ghany 2015). Metarhizium had been reported to be effective against Aphis craccivora (Mweke et al 2019), Spodoptera litura (Gustianingtyas et al 2020), and Sitophilus oryzae (Kavallieratos et al 2015).…”

Integrated Management of Aphis craccivora in Cowpea Using Intercropping and Entomopathogenic Fungi under Field Conditions

“…The fungus Metarhizium anisopliae isolate ICIPE 62 with a known pathogenicity to A. craccivora [17] was obtained from icipe's Arthropod Pathology Unit Germplasm Centre and used in this study.…”

“…Lambdacyhalothrin-based insecticides are used in management of aphids in Kenya and come under different trade names such as Duduthrin (Twiga Chemical Industries Ltd., Nairobi, Kenya), and are easy to access and use. Although aphids are susceptible to pesticides, application of the chemicals does not always result in effective suppression of their population because of their high fecundity, and also they have been reported to develop resistance to some of these chemicals [14][15][16][17]. Moreover, synthetic chemicals pose health risks due to toxic residues, especially on leafy vegetables that are harvested regularly [11,17,18], killing natural enemies of A. craccivora and leading to pest resurgence and the need for further pesticide application [14,19].…”

“…Although aphids are susceptible to pesticides, application of the chemicals does not always result in effective suppression of their population because of their high fecundity, and also they have been reported to develop resistance to some of these chemicals [14][15][16][17]. Moreover, synthetic chemicals pose health risks due to toxic residues, especially on leafy vegetables that are harvested regularly [11,17,18], killing natural enemies of A. craccivora and leading to pest resurgence and the need for further pesticide application [14,19]. Intercropping cowpea with cereals such as maize, sorghum, and millet has been used as a strategy in the management of cowpea insect pests including A. craccivora, although intercropping alone does not completely control the pest [4,20,21].…”

“…Several species of Metarhizium have been identified as being pathogenic to A. craccivora, both in laboratory and in field conditions [30,31]. Furthermore, use of EPF-based biopesticides, notably Metarhizium anisopliae ICIPE 62, has been recently demonstrated to suppress aphid populations in cowpea under field conditions [17]. Several EPF-based biopesticide products for management of some aphids species are available in Europe and America, but are less common in Africa, and none have been registered for use against A. craccivora [17,32].…”