TITLE:
Bioefficacy of Plectranthus kirbii Powder and Extracts on Stored Cowpea Pest Callosobruchus maculatus (Coleoptera: Chrysomelidae)
AUTHORS:
Jean Wini Goudoungou, Félicité Arindo, Katamssadan Haman Tofel, Raoul Barry Borkeum, Jean Pierre Abdou, Elias Nchiwan Nukenine
KEYWORDS:
Cowpea Beetle, Plant Extracts, Mortality, Damage, Viability
JOURNAL NAME:
Advances in Entomology,
Vol.10 No.3,
May
26,
2022
ABSTRACT: Cowpea seed constitutes an important source of proteins for populations
in Sub-Saharan Africa. But this food resource is heavily damaged by cowpea
beetle Callosobruchus maculatus. The control of that pest is mainly
carried out by using synthetic insecticides. Despite the efficacy of this
method, it caused environmental and health problems. Therefore, the search for
alternative methods is vivaciously needed. In this issue, the bio-efficacy of Plectranthus
kirbii extracts was assessed on C. maculatus regarding adult mortality, suppression of
population and grain damage as well as seed viability preservation and
repellency. The leaf powder and aqueous extracts of the plant were tested at 2,
4, 8 and 16 g/kg on bruchid adult for toxicity and damage bioassays. Repellency
test was carried out using the plant aqueous, methanolic and ethyl acetate
extracts at 0.5, 1, 2 and 4 mg/cm2. The seed viability was evaluated
using seeds preserved for three months at the single concentration of 16 g/kg
of each plant extract. Significant mortality of cowpea beetle was induced by
the plant aqueous extract and leaf powder. LC50 values decreased
with the increasing exposure period, and aqueous extract and leaf powder
recorded 33.42 and 9.48 g/kg respectively within 3 days whereas within 5 days,
the same extracts in the same order recorded LC50 of 1.31 and 8.73
g/kg respectively. These extracts significantly reduced damage by suppressing
almost completely the bruchid population growth. The non-infested grain
preserved recorded high grain viability compared to the infested ones. The
non-treated infested recorded the lowest germination rate (11.33%). The
repellency rate ranged from 38.75% to 83.75%. Ethyl acetate and methanolic
extracts were classified as the class III repellent product, while aqueous
extract ranged as class IV in repellency. Considering these findings, the
extracts of P. kirbii could favourably replace the synthetic insecticides used in the cowpea
protection during storage.