Factors Affecting Egg Hatch of the Tadpole Shrimp Triops newberryi, a Potential Biological Control Agent of Immature Mosquitoes

The tadpole shrimp (TPS), Triops newberryi (Packard) (Notostraca: Triopsidae), is a potential biological control agent for immature mosquitoes breeding in ephemeral habitats. Studies were initiated in the laboratory to investigate the effects of some ecological and physiological factors on egg hatch. When subjected to successive hydrations, most of the hatch occurred in the first hydration with additional hatches noted in the second and third hydrations. In each hydration, most of the eggs hatched in 12 to 48 h. Temperature had a marked effect on egg hatch. Preconditioning treatment of eggs in soil at extreme temperatures lowered egg hatch in succeeding hydrations. Temperature during hydration also influenced egg hatch, with maximum hatch at 29°C. Length of photoperiod was another ecological factor affecting egg hatch; darkness during the hydration period reduced egg hatch. As a simulation of incomplete hydration commonly encountered in arid regions associated with light precipitation and scarce irrigation water, TPS eggs in soil were wetted and flooded for short time periods. These treatments enhanced egg hatch during succeeding full hydrations. The presence of soil during preconditioning and hatching did not affect egg hatch. High water salinity reduced or prevented egg hatch. Preconditioning treatment at high water salinity lowered egg hatch during succeeding hydrations with distilled water. Maximum egg hatch occurred at pH 7; preconditioning treatment at pH 3 lowered and at pH 11 eliminated egg hatch during succeeding hydrations with distilled water. TPS eggs from dead gravids (unlaid eggs) did not hatch after proper preconditioning and hydration.