Induction of diapause in Colladonus montanus reductus (Van Duze) Public Deposited

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  • Experiments conducted in the greenhouse showed that the leafhopper, Colladonus montanus reductus (Van Duzee), is a long-day insect. This conclusion is based on the production of diapausing eggs when the leafhoppers were kept under short days (ten hours) during the nymphal stage and the adult pre-oviposition period. Continuous development of generations occurred when insects were kept under long days (16 hours) during the nymphal stages and the adult pre-oviposition period. The effect of short days during the nymphal stages could be reversed if the nymphs were transferred to long days as they became adults; few diapausing eggs were produced under these conditions. The effect of long days during the nymphal stages was only slightly altered if the nymphs were transferred to short days as they became adults; very few, if any, diapausing eggs were produced. Embryos in diapause appeared to be in the anatrepsis stage of development; segmentation was taking place insofar as buds of future legs and mouthparts could be seen. Females deposited the majority of their eggs in the leaves of Trifolium subterraneum L., regardless of the combinations of photo-periods that they had experienced during their life cycles. Very few, if any, eggs were laid in the basal portions of the plants by adults that spent all of their life cycle under the 16-hour photoperiod. Females that spent part or all of their life cycle under the ten-hour photoperiod laid significantly greater percentages of their eggs in the basal portions of the plants than females that spent all of their life cycle under the 16-hour photoperiod. I suggested that diapausing eggs laid in the basal portions of the plants would be better protected from injury and dessication during the winter. In general, adult leafhoppers that were reared as nymphs under eight-hour or ten-hour photoperiods were somewhat lighter in color than adults reared under a 16-hour photoperiod. Males were usually black and females were usually brown, although the color variation was such that the darkest females were about as dark as the color of the lightest males. The sexual dichromatism was much more striking than the seasonal dichromatism. Adults reared as nymphs under ten-hour and 16-hour photo-periods did not vary significantly in length when each sex was compared separately in one of the experiments. In another experiment, females reared under an eight-hour photoperiod were significantly shorter than females reared under a 16-hour photoperiod. Similarly, males reared under the eight-hour photoperiods were significantly shorter. I suggested that the significant difference in the latter experiment was due to the poor vigor of the plants that the nymphs fed on under the eight-hour photoperiod, rather than to a direct influence of the photoperiod on the leafhoppers.
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