Effect of the Botanical Insecticides on <i>Amegilla</i> Friese, 1897 (Hymenoptera: Apidae) Foraging on the Cowpea Flowers in Dang (Adamaoua, North-Cameroon)

Abstract

Synthetic pesticides present risks of pollution of the environment, humans and livestock and the alternative proposed today is to use botanical extracts in the fields against crop pests. But in North Cameroon, little information exists concerning the effect of these extracts on useful pollinating insects in general and no information exists in particular on foragers of the genus <i>Amegilla</i> Friese, 1897 (Apidae: Apinae: Anthophorini). The frequency and foraging activities of <i>Amegilla</i>, on newly blooming flowers of <i>Vigna unguiculata </i>(L.) Walp., 1843 (Fabales: Fabaceae) were recorded during five consecutive days in 2021 and 2022 planting campaigns. Plants were divided into untreated plots and plots treated using the synthetic insecticide Parastar (l p.c..ha<sup>-1</sup>) or 10%, 20% and 30% aqueous leaf extracts of <i>Calotropis procera</i> (Aiton) Aiton, 1811 (Gentianales: Apocynaceae), <i>Eucalyptus camaldulensis </i>Dehnh., 1832 (Myrtales: Myrtaceae) and <i>Tithonia diversifolia</i> (Hemsley) Gray, 1883 (Asterales: Asteraceae) respectively. Among 8,987 insects collected (48.9% in 2021), <i>Amegila calens</i> Le Peletier. 1841 with stockier foragers (2021 campaign: 2.2% of the total collection, entomophily F<sub><i>A. calens</i></sub>=4.5%; 2022 campaign: 0.7%, F<sub><i>A. calens</i></sub>=1.3%; pooled campaigns: 2.9%, F<sub><i>A. calens</i></sub>=2.9%) and <i>Amegilla</i> sp. with slender foragers (2021: 3.8%, F<sub><i>Amegilla </i>sp.</sub>=7.7%; 2022: no data) were recorded. Foragers started activity from 6 a.m. and stopped foraging before noon, with a peak of activity in 8 to 9 a.m. time slot for <i>A. calens </i>and 10 to 11 a.m. time slot for <i>Amegilla</i> sp.. During the five consecutive days from the first blooming day of the flowers, 598 visits (89.8% in 2021 and 10.2% in 2022) were recorded with a peak of visits during the 3<sup>rd</sup> day and then declined until it stopped during the 5<sup>th</sup> day. Treatments including the synthetic insecticide (which was the most repellent to the wild bees), did not significantly reduce the frequency of visits. But 20% aqueous extract of <i>Ca. procera</i> showed a significant increased of the mean duration of visits of the bees, compare to the results recorded in Parastar-treated plots. Therefore, the tested extracts, especially 20% aqueous leaves extract of <i>Ca. procera</i> may be recommended to control field insect pests and for preservation of foraging activities of <i>Amegilla </i>genus.