Effects of photoperiod on the induction of egg diapause in the Senegalese grasshopper Oedaleus senegalensis (Krauss, 1877) (Orthoptera, Acridoidea)
1995
Diop, T. (Centre AGRHYMET/CILSS, Niamey (Niger). Dept. de Formation en Protection des Vegetaux)
In the present study photoperiod appeared to be a factor inducing egg diapause in the Senegalese grasshopper Oedalus senegalensis (Krauss, 1877). When reared under constant photoperiods this species exhibits a long day type response. The maximum diapause rate was achieved at photoperiods equal to or less than 14/24 h. Conversely, the minimum diapause rate was obtained with photoperiods close or equal to 14/24 h. The critical photoperiod determining 50 percent egg diapause in situated between 12 and 13 h of photophase. These correspond to the range of photoperiods experienced by the insects in nature. In other experiments, transfers of laboratory reared populations and naturally collected populations are done from 12/24 h to 11/24 h for the two populations and from 11/24 h to 14/24 h for only naturally collected populations. Results have shown that the last larval stage and the immature adult stage are sensitive to photoperiod, whereas this is apparently not the case in the mature insects. However the last larval stage seems to be more sensitive. During the sensitive stages the insects react to variations in photoperiod. These results help to explain the observations made on O. senegalensis in the field.
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