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Field assessment of the impact of farmers’ practices and cacao growing environment on mirid abundance and their damage under unshaded conditions in the southern Cameroon

Mahob, R. J., Dibog, L., Ndoumbè-Nkeng, M., Begoude Boyogueno, A. D., Fotso Toguem, Y. G., Nyassé, S., Bilong Bilong, C. F.
International journal of tropical insect science 2020 v.40 no.2 pp. 449-460
Sahlbergella singularis, branches, crop production, ecology, farmers, farms, forests, leaves, trees, Cameroon
Mirid populations and their damage on cacao production have been widely studied under shaded conditions worldwide. There is a lack of information on the mirid populations and their damage under unshaded conditions. To reach that goal, we assessed biweekly mirid abundance through visual counts of individuals and their damage via scoring dry leaves on branches and cankers on twigs and trunks of trees, in nine farms across three agrosystems in Cameroon during two consecutive years. It was found that all mirid individuals belonged to the species Sahlbergella singularis (Hemiptera: Miridae); their mean number was low (0.08 mirid tree⁻¹for year 1 and 0.23 mirid tree⁻¹ for year 2) and precisely lower in the Savannah zone (0.27 mirid tree⁻¹) than transition (0.63 mirid tree⁻¹) and forest zones (0.55 mirid tree⁻¹). The mirid damage varied significantly (p < 0.05) between plots, study areas and years; however, cankers were very high (average median score: 1.20) compared to dry leaves (0.51). Our study clearly showed a positive correlation between the abundance of mirids and their damage with, rα = 0.29 for cankers, and 0.56 for dry leaves; nevertheless it is suggested that the observed damage are not only caused by the in situ mirid populations, but by a synergistic action of exogenous factors, notably the ex situ mirids, the closed environment of the studied plots. This work reveals that the low abundance and high damage of mirids in the studied plots are not linked to cacao growing systems, but depend mainly on farmers’ practices. These new data contribute to the better understanding of mirid (S. singularis) ecology.