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Short-day induced reproductive diapause makes supplementary lighting indispensable to the use of thrips predator Orius majusculus (Reuter) for biological control in greenhouses during the winter. In order to reduce energy costs, strains with a shorter critical day-length and the ability to avert diapause under low-intensity supplementary lighting, are desirable. With this in mind, a southern strain of O . majusculus from a locality (37.0°N, 30.5°E) in Antalya, Turkey was investigated. Its response to the photoperiod was studied at day-lengths of 11.5, 12, 12.5, 13.5, 14.5 and 16 h, at 26 ± 1 °C, 60 ± 10% r.h. and 2400 lux. The duration of nymphal development and developmental time were longer in both sexes at the short day-length, 11.5 h, than at other day-lengths. Significant but inconsistent effects of the photoperiod were found on the incubation period, generation time, egg hatch rate and nymph survival. The pre-oviposition period and longevity tended to be longer at the short day-length. Fecundity was also affected, being lower at 12 h, than at 14.5 and 16 h. The sex ratio was not influenced by the photoperiod. The critical day-length was between 11.5 and 12 h, and all females entered reproductive diapause at 11.5 h, while only 25% did so at 12 h, and none at 14.5 and 16 h. The effect of light intensity was determined at 10, 25, 50, 100, 200 and 2400 lux, at 26 ± 1 °C, 60 ± 10% r.h. and a day-length of 12.5 h. The duration of nymphal development, developmental time and generation time were longer in both females and males at 200 lux than at other light intensities. The incubation period, egg hatch rate, pre-oviposition period, longevity, fecundity and sex ratio were not affected by the light intensities that were tested. An inconsistent influence was found on nymph survival. The oviposition period was longer at 2400 lux than at lower light intensities. The light intensities did not affect diapause incidence. In conclusion, O. majusculus from Antalya have a shorter critical day-length than the northern strains and therefore would require shorter supplementary lighting if used as a biological control in greenhouses. Diapause would be averted under a supplementary light of 10 lux and over with little or no effects on biological characteristics. |
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