Trichogrammatids: Adaptation to stresses

Abstract

Mass-reared trichogrammatids species require to be fortified with adequate levels of tolerance to the common physical and chemical stresses encountered in the target crop ecosystems. Past studies on the effects of the two physical factors temperature and humidity on the biology of Trichogramma have shown that temperature below 15 or above 35 °C tends to cause mostly negative effects on their survival and/or performance. It is possible to identify higher temperature tolerant strains among native species focused surveys as undertaken recently in East Africa. The other approach being successfully pursued at NBAII is to develop such strains by exposing the colonies to incremental levels of rearing temperature across generations. For instance, the temperature-tolerant strains recorded significantly higher parasitism than the laboratory strain up to 40 °C. Greater progress has been made in India in developing insecticide-tolerant strains in the last two decades. The first attempt led to endosulfan tolerant strain (T. chilonis commercially named as Endogram). Most recently, multiple insecticide strain (MITS-TC) has been developed against endosulfan, monocrotophos and fenvalerate. The available information on the genetics of stress tolerant Trichogramma species is limited and needs to be enriched by more holistic studies. Future research on stress tolerant strain development should include studies of heat shock protein (HSP), the genes and alleles responsible for stress tolerance and the mode of inheritance, besides seeking out for suitable mutants and assessing the role of endosymbionts on the stress tolerance and other fitness attributes.