Abstract
The circadian activity of adults of Smicronyx guineanus Voss (Coleoptera: Curculionidae) was studied in semi-field conditions. Pairs of weevils were observed on a 24-h cycle starting from 0800 to the following day at 0600 hrs for 21 days in cages containing Striga hermonthica (Del.) Benth (Scrophulariaceae) plants parasitising sorghum. Each female and male was observed every second hour. Occurrences of the vatious behaviours exhibited by the weevil were recorded. In decreasing frequency, the weevils were observed to be standing still, feeding, mating, walking, moving and foraging. In addition, the difference in time spent on the different parts of the host plant—classified into four groups: A- stem, leaves and bud; B- corolla; C- calyx; and D- sorghum, petiole, soil, capsule and cage—was highly significant (P = 0.0001,10 couples/days, n = 21 days). The weevil adults spent 46.8% of their time on the Striga inflorescence (bud, corolla and calyx). Striga plants were also stratified with respect to distance from the base and categories were designated as upper, central and lower parts. Smicronyx adults spent 85.2% of their time in the upper stratum, 9.8% in the central stratum and 5% of their occurrences were in the lower third of the Striga shoot. They were more active during daytime, suggesting that the best period of day to sample the weevils in the field is from 0700 to 1100 or from 1600 to 1800 hrs.
Résumé
L’activité journalière des adultes de Smicronyx a été étudiée dans des conditions seminaturelles. Des couples de charançons ont été observés pendant 24 h à partir de 8 h le matin jusqu’au lendemain à 6 h et ceci a été répété 21 fois (21 jours) en 1992 et 1993 dans des cages contenant des plantes de Striga hermonthica parasitant des plantes de sorgho. Chaque femelle et mâle a été observé toutes les deux heures. Les différentes exhibitions de comportement des charançons ont été notées. Dans Tordre décroissant, les charançons ont été observés à rester immobile, à se nourrir, à s’accoupler, à marcher, à se mouvoir et à prospecter. En plus, la différence de temps passé sur les parties de la plante hôte a été hautement significative. Ces parties de la plante de Striga et autres ont été groupées en quatre: groupe A = tige, feuille et bouton floral; groupe B = corolle; groupe C = calyx; groupe D = sorgho, pétiole, sol, capsule et paroi de la cage. Les charançons adultes ont passé 46,8% de leur temps sur les inflorescences du Striga (bouton floral, corolle et calyx). Les plantes de Striga ont été stratifiées à partir de la base et les catégories étant les parties supérieure, centrale et inférieure. Les adultes de Smicronyx ont été observés 85,2% de leur temps sur la partie supérieure, 9,8% sur la partie centrale et 5% de leur apparition ont été sur la partie inférieure des pieds de Striga. Ils ont été plus actifs pendant le jour, suggérant que la meilleure période du jour pour les échantillonner dans les champs se situerait de 7 h à 11 h le matin et de 16 h à 18 h dans l’après-midi.
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Traor’, D., Vincent, C. & Stewart, R.K. Circadian Activity of Smicronyx guineanus Voss, A Potential Biocontrol Agent of striga hermonthica (Del.) Benth. Int J Trop Insect Sci 18, 205–210 (1998). https://doi.org/10.1017/S1742758400023419
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DOI: https://doi.org/10.1017/S1742758400023419