Efficacy of Metarhizium Anisopliae Based-Biopesticide for Biocontrol of Spodoptera Frugiperda in Maize Production in Migori and Homabay Counties, Kenya
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Date
2025-06
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Kenyatta University
Abstract
Maize is an important staple food crop for majority of individuals in Sub-Saharan Africa, particularly in East Africa, where it is cultivated on over 25 million hectares of land. However, its production in Kenya faces significant challenges from both abiotic and biotic factors, resulting in more than 50% crop losses. One of the most serious biotic threats is the invasion of Fall armyworm (FAW), scientifically known as Spodoptera frugiperda. This pest inflicts extensive damage in all stages of maize growth, jeopardizing sustainable production and food security. Although conventional chemical insecticides are highly relied on for management of FAW, they pose serious risks and deleterious effects on the environment and biodiversity. Therefore, there is a pressing need to promote the development of innovative and sustainable approaches for managing FAW. One promising alternative is the use of microorganisms in pest management, as they offer effective control with minimal or no negative environmental impact. A virulent isolate of Metarhizium anisopliae ICIPE 41 (Metschnikoff) Sorokin, obtained from the fungal culture collection germplasm housed at the International Centre of Insect Physiology and Ecology (icipe), and its different formulations were evaluated under the laboratory and field conditions. Initially, the study assessed the sub-lethal effects of these formulations on second instar larvae of S. frugiperda and on some associated parasitoids (Cotesia icipe, Telenomus remus and Trichogramma chilonis) of the FAW. Also, the compatibility of the fungal isolate with FAW sex pheromone (Falltrack®) was evaluated. Out of the four M. anisopliae ICIPE 41 formulations screened for pathogenicity against S. frugiperda, three formulations, namely canola oil, olive oil and corn oil, induced significantly higher mortalities, ranging from 70.4% to 76.1%. Post-treatment mortality at 50% lethal time (LT50) ranged from 2.0 to 8.1 days. In contrast, the M. anisopliae ICIPE 41 formulations exhibited significantly lower mortality rates on the FAW parasitoids, ranging from 2.5% to 21.3%. The findings also showed that M. anisopliae ICIPE 41 was highly compatible with the FAW sex pheromone at eight days post-exposure with viability count ranging from 97% to 100%. The most effective formulation which caused high mortality in FAW larvae while being less toxic to the parasitoids was further evaluated under field conditions. For the field trials, evaluation of pathogenicity and conidial persistence of M. anisopliae ICIPE 41 corn oil formulation was carried out weekly for one month after application on maize leaves. Larval mortality resulting from exposure to the formulated fungal isolate was significantly higher than that of commercial detain biopesticide at both field sites, recording 80.1% and 81.6% mortality, respectively. Conidial germination rates on days 14, 21 and 28 showed a gradual decline at both Migori and Mbita sites, with mortality rates of 87%, 74% and 61% at Migori and 88%, 72% and 61% at Mbita, respectively. There was a significant number of Cotesia icipe parasitoids (56%) that emerged from field-collected dead larvae. Notably, corn oil formulation of M. anisopliae ICIPE 41 significantly enhanced maize yield compared to Mazao Achieve® and the control, indicating its potential as a viable biocontrol option. In conclusion, this study identified the corn oil-based formulation of Metarhizium anisopliae ICIPE 41 to be pathogenic to second instar larvae of S. frugiperda while exhibiting minimal negative effects on associated parasitoids. It therefore recommends the potential integration of locally developed delta traps, baited with FAW sex pheromone, with this fungal formulation as a lure and infect mechanism for effective field-level pest management.
Description
A Thesis Submitted in Fulfillment of the Requirements for the Award of the Degree of Master of Science (Microbiology) in the School of Pure and Applied Sciences of Kenyatta University, June 2025.
Supervisor
1. Ezekiel Mugendi Njeru
2. Leonidah Omosa Kerubo
3. Komivi Senyo Akutse