Submitted to: Annals of the Entomological Society of America
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/13/2001
Publication Date: 9/1/2001
Citation: Leopold, R.A., Wang, W., Berkebile, D.R., Freeman, T.P. 2001. Cryopreservation of embryos of the new world screwworm, Cochliomyia hominivorax (Diptera: Calliphoridae). Annals of the Entomological Society of America. 94(5):695-701. Interpretive Summary: The screwworm, Cochliomyia hominivorax is a highly destructive ectoparasite of mammals and has been eradicated from the U.S. and most of Central America by using the sterile insect release method. This insect continues to be reared under factory-like conditions in southern Mexico and is released in areas of the Caribbean and Panama to guard against reinfestation of the U.S. To cut rearing costs of ongoing research and sterile release programs funded by the USDA, a long-term storage method was developed using cryogenic technology. This protocol allows embryos of this insect to be stored indefinitely in liquid nitrogen. When needed, research colonies and back-up strains maintained for the mass-rearing programs can be reestablished, thus saving the costs associated with the continuous culture of this insect.
Technical Abstract: A method for cryopreserving embryos of the screwworm, Cochliomyia hominivorax, was developed for the long-term storage of the strains used in research projects and for colonies maintained as back-up to the production strains that are mass-reared for the sterile insect release programs. This protocol, when combined with a previous procedure that was designed to render screwworm embryos permeable to water loss and the influx of cryoprotectants, yields rates of about 53% hatching, 22% pupation and 75% adult emergence. These yields are all lower than control levels, but by the next generation the progeny of the cryopreserved flies are near or equal to control levels and are available in sufficient numbers to reestablish laboratory colonies. Important to the success of this study was identifying the optimum embryonic stage for treatment, formulating an incubation regime which allowed consistent retrieval of embryos at the optimum stage, establishing the correct dehydration time for the pre-vitrification step and developing a recovery system after liquid nitrogen storage of the embryos.