Formulation of plant-based pesticides

Abstract

The increasing reliance on synthetic pesticides in modern agriculture is raising concerns regarding environmental contamination, biodiversity loss, pesticide resistance, and risks to human health. Because of this there is an increasing interest in botanical pesticides as a sustainable alternative to synthetic pesticides. Because of its warm Mediterranean climate, Malta faces this challenge in various crops, particularly in the production of brassica crops such as the cauliflower. which are economically important crops affected by caterpillar pests. This study evaluated the potential of Nicotiana glauca-based formulations as botanical insecticides through an integrated assessment of biological efficacy, toxicity, and residue persistence. The research focused on cauliflower (Brassica oleracea var. botrytis), one of Malta's most commonly cultivated brassica crops, and targeted two major pest species, the Small White Butterfly (Pieris rapae) and the Large White Butterfly (Pieris brassicae), both of which can cause substantial crop damage and economic losses to farmers. Three complementary approaches were employed: an in vivo caterpillar assay, a residue analysis in cauliflower tissues using UV-Vis spectrophotometry, and a brine shrimp lethality assay (BST) with probit analysis for LC₅₀ determination. The caterpillar study demonstrated that all treatments, including Nicotiana glauca (Ng) and its combination with garlic (T), significantly reduced survival over time. Although the synthetic insecticide (E) induced faster initial mortality, botanical treatments achieved comparable lethality within the experimental period. The BST assay confirmed dosedependent toxicity for all treatments, with strong linear probit-log dose relationships (R² = 0.88-0.99). The combined treatment (T) exhibited the highest toxicity (LC₅₀ = 19.82 µg/mL), followed by Ng (29.60 µg/mL), while nicotine showed the lowest toxicity (78.86 µg/mL). Statistical analysis revealed significant differences in both slopes and intercepts of doseresponse curves, indicating distinct toxicological profiles. Residue analysis showed that alkaloid-related compounds from Nicotiana glauca degraded rapidly in cauliflower tissues, with half-lives of approximately 1 day and DT₉₀ values around 3 days. In contrast, the synthetic insecticide exhibited significantly greater persistence (DT₉₀ ≈ 10 days). These findings indicate that botanical treatments provide strong biological activity while minimising long-term residue accumulation. The integration of results demonstrates that Nicotiana glauca-based formulations are effective and rapidly degrading bioinsecticides. However, the measurable toxicity of the control formulation highlights the importance of considering formulation effects. Overall, the study supports the potential of botanical pesticides as environmentally favourable alternatives to synthetic insecticides, while emphasising the need to balance efficacy, persistence, and formulation in their development.