Seed Yield Improvement in Vigna unguiculata (L.) (Fabaceae): Efficiency of Pollinators and Impact of Aqueous Leaf Extract of Three Plant Species in North Cameroon

Abstract

Aims: Because of the problems in agroecosystems following the anarchic use of synthetic insecticides, studies propose an alternative, the use of botanical biopesticides against pests.
 Study Design: The present study was conducted to evaluate (1) the potential of leaf extract of Calotropis procera (Gentianales: Apocynaceae), Eucalyptus camaldulensis (Myrtales: Myrtaceae) and Tithonia diversifolia (Asterales: Asteraceae) against insects and (2) impact of Apis mellifera (Hymenoptera: Apidae) on Vigna unguiculata (Fabales: Fabaceae) seed yield in North Cameroon.
 Place and Duration of Study: A field study was set up in 2021 in North Cameroon, during the rainy season. Fourthy four plots of 4x3.5 m each were distributed according to a randomized complete block design model comprising four untreated, four treated using parastar (40EC 535/10/IN, 20 g/l imidaclopride and 20 g/l lamda-cyhalothrine), and 36 plots treated using 10%, 20% and 30% aqueous leaf extracts separately sprayed against Aphis craccivora (Hemiptera: Aphididae).
 Methodology: Four groups of flowers were randomly selected: (1) free, (2) protected from insects, (3) free exclusively to Ap. mellifera and (4) protected against insects.
 Results: A total of 10,984 captured flower insects belonged to three orders (Hemiptera, Hymenoptera and Lepidoptera), three families (Aphididae, Apidae and Nymphalidae) and seven species [one (14.3%) sap-sucking Aphis craccivora (Hemiptera: Aphididae), four (57.1%) pollinators Hymenoptera Apidae [Amegilla calens, Amegilla sp., Apis mellifera and Xylocopa olivacea] and two (28.6%) Lepidoptera Nymphalidae [Danaus plexippus and Hypolimnas misippus]. A total of 7,425 insects associated with V. unguiculara corresponded to four orders [Hemiptera (56.7%), Coleoptera (41.5%), Heteroptera and Orthoptera with 0.9% respectively], nine families [Aphididae (45.3%), Chrysomelidae (38.7%), Pyrrhocoridae (4.8%), Coreidae (3.8%), Cicadellidae (2.8%), Coccinellidae (1.9%), Alydidae, Tenebrionidae and Tettigoniidae with 0.9% respectively], 11 genera and 11 species.
 Conclusion: Apis mellifera was the major pollinator and Aphis crassivora the major pest. The seed yield was improved by 30% extract of plants without impact on pollinators.

Impact of Plant Extracts on the Pollination Activity of <i>Apis mellifera</i> Linnaeus, 1758 (Hymenoptera: Apidae) on Flowers of Cowpea Variety Feekem, in Dang (Adamaoua, Cameroon)

“…In African countries, the cowpea production is limited by several factors [5], among which the shortage of agricultural land, the low soil fertility, the poor management of pollinating insects, the pressure from insect pests in the fields and the post-harvest looses in warehouses, are frequently reported [5,11]. Fields and warehouses pests control is mainly based on the spraying of approved synthetic insecticides [12,13], which have proven their harmful effect to humans, livestock, the environment in general and the beneficial insects in particular [14]. Many plants species depend on the pollination by insect [15,16].…”

“…Hence the preservation of pollinating insects, particularly Ap. mellifera, in cultivated plots, is nowadays recommended [14]. In Cameroon, the use of synthetic pesticides improves farmers' potential yield, but handling them with inexperienced hands increases the risk of human contamination and environmental pollution, and also reduces any prospect of sustainable agricultural development [24].…”

“…In Cameroon, the use of synthetic pesticides improves farmers' potential yield, but handling them with inexperienced hands increases the risk of human contamination and environmental pollution, and also reduces any prospect of sustainable agricultural development [24]. These products exterminate not only the target insect pests in treated fields, but also negatively affect the behavior of non-target organisms such as useful insects [14,25,26], destroy pollinating insects [27], directly contaminate the environment, plant production, farmers and livestock [24,28], and indirectly contaminate the consumer due to the presence of toxic pesticide residues in fruits and vegetables [29,30]. Due to the confirmed toxicity of synthetic pesticides which results in the high toxicity of synthetic chemicals, of the degradation products, and their strong persistence in the environment [31,32], it is nowadays imperative to consider the use of control methods that respect the environment, beneficial insects and consumers.…”

“…A. Gray, 1883 (Asterales: Asteraceae) [11,14]. Floricultural entomofauna of V. unguiculata is well documented in cowpea producing countries in general and more particularly in Benin [34], in Ghana [35], in Nigeria [36], and in Cameroon [19,23,37].…”

“…mellifera are frequently recorded on the cowpea flowers. In Cameroon, although many natural additives based on plant extracts have proven effective against harmful insects [11,14,38], their effects on pollinating insects in particular Ap. mellifera remains less known and it is necessary to carry out studies in the Adamaoua Region (Cameroon) on the effect of local plants on the foraging behavior of Ap.…”