Longitudinal Assessment of *Aphidius colemani* Parasitoid Efficacy for Aphid Management in Smallholder Cabbage Systems of the Amathole District

{ "background": "Smallholder cabbage production in South Africa is severely constrained by aphid infestations, leading to significant yield losses and over-reliance on synthetic pesticides. The potential of the parasitoid wasp Aphidius colemani as a biological control agent within these specific agro-ecological and socio-economic contexts remains poorly quantified.", "purpose and objectives": "This longitudinal study aimed to assess the field efficacy and seasonal persistence of inoculative releases of A. colemani for aphid suppression in smallholder cabbage systems, and to evaluate its impact on crop yield and marketable produce.", "methodology": "A repeated-measures on-farm experiment was conducted across multiple growing seasons. Aphid density and parasitism rates were monitored weekly on treated and control plots. Yield and quality data were recorded at harvest. Efficacy was analysed using a generalised linear mixed model: $\\log(E(Y{it})) = \\beta0 + \\beta1 Ti + \\beta2 t + \\beta3 (Ti \\times t) + ui + \\epsilon{it}$, where $Y{it}$ is aphid count, $Ti$ is treatment, $t$ is time, $ui$ is a random farm effect, and robust standard errors were used for inference.", "findings": "Parasitoid releases significantly reduced peak aphid densities by an average of 68% (95% CI: 61, 74) compared to control plots. Parasitism rates exceeded 40% for six to eight weeks post-release. A corresponding 31% increase in marketable yield was observed in treatment plots.", "conclusion": "Inoculative biological control with A. colemani is a viable and effective component for integrated pest management in smallholder cabbage production, providing sustained aphid suppression across seasons.", "recommendations": "Extension programmes should promote the seasonal integration of A. colemani within IPM strategies. Further research should investigate cost-effective