Warburgia Ugandensis and Croton Dichogamus: Possible Botanical Bullets Against Callosobruchus Maculatus

Botanical pesticides, derived from plant products have gained popularity over the conventional synthetic pesticides. These natural products often consist of several bioactive compounds, whereby the formulations may be effective against pests and perhaps reduce the chances of pests’ resistance (Reddy, 2020). Nevertheless, several challenges stem from the use of botanical pesticides, such as high variation in pest response due to differences in plant chemotypes and environmental conditions, short residual activity compared to many synthetic insecticides (which can translate into higher application rates), registration challenges (including demonstration of safety and efficacy for commercialization), making large quantities of botanical pesticides at consistent active ingredient concentrations, and low host specificity of some botanical products, which often requires the use of more products (Reddy, 2020).

2.0 Classification of Botanical Pesticide

Botanical pesticides are categorized into two generations.

2.1 First Generation Botanical pesticides

First-generation botanical pesticides are plant-extracted compounds, which have been employed in exterminating pests and were among the early products to receive commercialization.

2.1.1 Nicotine

Nicotine which comes from tobacco plants (Nicotiana spp.) has been in inclusion in insecticides for many years. It possesses the ability to function as a nerve toxin through the blocking of nicotinic acetylcholine receptors (Reddy, 2020). However, due to its high toxicity especially in mammals, its use has been banned in many countries as noted in the article by Le Foll et al. (2022).

2.1.2 Rotenone

Rotenone is formed from the roots of Derris and Lonchocarpus species and interrupts the process of cell respiration in insects (Reddy, 2020). Nonetheless, due to its poisonous effect on fish and controversy of a possible connection with Parkinson’s disease, its use has been deemed restricted in the recent years.

2.1.3 Essential plant oils

Different plant essential oils like clove, mint and citrus are insecticidal and repellent in nature. Their modes of action are complex and unknown in several cases but many of the oils are neurotoxins or affect the octopamine system in insects (Reddy, 2020).

2.1.4 Sabadilla

Sabadilla, which is derived from seeds of Schoenocaulon officinale contains chemicals that interfere with the nerve cell membrane physiology. It has been used against various pests but is less frequently used because of its higher cost and the problem of skin and respiratory sensitization to human beings (Reddy, 2020).

2.1.5 Pyrethrum

Pyrethrum is an extract obtained from the flowers of the Chrysanthemum cinerariaefolium plant and contains potent insecticidal ingredients known as pyrethrins. Pyrethrins act on the nervous system of insects, resulting in fast knockdown effect on the target insects (Reddy, 2020). Pyrethrum’s low toxicity against mammals and apparently long residual action have made it to be among the most effective botanical insecticides (Ngegba et al., 2022).

2.2 Second Generation Botanical pesticides

The second-generation botanical pesticides are relatively new and they have been found to have a specific mode of action and environmental benefits as compared to the first-generation ones.

2.2.1 Melia Extracts

The various limonoids from Melia azedarach, commonly called chinaberry, have insecticidal properties where the extracts from the plant are used. These compounds have been shown to function as anti-feedents, growth modifiers and toxins against several insect pests (Jaoko et al., 2020).

2.2.2 Synthetic Pyrethroids

Though not botanical in character, synthetic pyrethroids were developed using natural pyrethrins as their model. They are more stable and effective than the natural pyrethrins that are usually sought after in the management of pests; both in agriculture and in households (Hodo?an et al., 2023).

2.2.3 Neem Products (Azadirachtin)

Neem products include neem extracts containing azadirachtin and related compounds that exhibit diverse effects on insects, such as the suppression of feeding, inhibition of moulting, and the modulation of endocrine systems. Neem-based products have received much demand in places such as organic farming and integrated pest management because of its very low toxicity to mammals and its neutrality on the environment (Divekar, 2023).

3.0 Croton dichogamus

3.1 Description and Geographical distribution

Croton dichogamus, Pax, is a shrub or small tree species of the Euphorbiaceae family. The plant is an East African species, found ranging from Ethiopia to Somalia and south to United Republic of Tanzania. It is largely associated with dry bushland and woodland habitats and commonly grows on rocky slopes or soils that may be saturated with water for only a short period every morning. The stems have a smooth grey-brown barks which can be peeled off in small pieces. The shrub has simple, alternate leaves, which often appear to be silvery due to scales on the surface of the leave. The flowers are small and arranged in terminal racemes in male flowers while female flowers are also small and have terminal racemes (Matara et al., 2021a).