Photoperiod‐independent diapause‐inducing thermal response of Trichogramma larvae: Pattern and mechanisms

Abstract It is well known that photoperiodic induction of insect diapause can be affected by temperature, whereas photoperiod‐independent diapause‐inducing thermal responses received much less attention of researchers. We studied the influence of a wide range (from 3 to 30°C) of constant and alternating temperatures on the rate of development, on pre‐adult survival and on the induction of pre‐pupal diapause in the egg parasitoid Trichogramma telengai . The progeny of females developed at 20°C and photoperiod of L:D = 18:6 or 12:12 was used in this study. The study showed that the pattern of the thermal response of T. telengai is an asymmetric inverted U‐shaped curve determined by two different mechanisms. The right part of the curve represents S‐shaped effect of temperature on the induction of diapause (the threshold for this response is 13–15°C depending on maternal photoperiod), whereas the left part represents an arrest of development caused by the direct effect of low temperature (with the threshold of about 5°C). We conclude that the effect of temperature on the induction of diapause in T. telengai is based on (or at least closely connected with) the thermal influence on the rate of metabolism and development. The results of this study can be used for the prediction of Trichogramma diapause incidence under natural conditions and for the development of the cold storage methods.