Diapause induction in Eotetranychus smithi (Acari: Tetranychidae): effect of average temperature, but not of thermoperiod

Abstract

Facultative diapause of Eotetranychus smithi appears to occur at the egg stage and is induced by temperatures ≤17.5 °C, independent of photoperiod. However, the effect of thermoperiod on the induction of diapause remains unclear. To answer this question, we exposed female E. smithi to various thermoperiods under constant light conditions. First, we found that the deposition order of eggs affected the incidence of diapause: the first eggs (exclusively males) tended to avert diapause compared with the second and third eggs (most of them are females), possibly because of the sex of the eggs. Next, the incidence of diapause of the second eggs decreased with shortening of the cryophase, which was associated with an increase of the average temperature, and it showed clear long‐day‐type thermoperiodic response curves. However, this species does not sense the ratio of day (thermophase) to night (cryophase) of a given thermoperiod. Short thermoperiods did not increase the incidence of diapause, but rather precluded the entry into diapause. We detected no sign of the involvement of the circadian system in diapause induction in the thermoperiodic Nanda–Hamner protocol. We conclude that diapause induction of E. smithi does not involve the circadian system, and thus does not show thermoperiodism. Diapause induction under the various thermoperiodic conditions tested in the present study appears to be derived from the temperature itself. E. smithi is an exceptional species that relies on temperature alone to induce diapause.

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

“…The experiment with equal physiological duration of exposures showed a typical S-shaped pattern of thermal response (Figure 4), which was observed in some previous studies with Trichogramma wasps (Sorokina & Maslennikova, 1986;Zaslavski & Umarova, 1990) and some other insects (e.g. Carton & Claret, 1982;Claret & Carton, 1980;Denlinger, 1979;Takano et al, 2021;Tan et al, 2016), but in none of these studies was the left In combination, the results of our study suggest that despite superficial similarity, inverted U-shaped patterns of thermal and photoperiodic inductions of diapause are essentially different. The authors of different models of photoperiodic response agree that the left and right thresholds are based on the same mechanism (Saunders, 2011(Saunders, , 2013(Saunders, , 2021Saunders et al, 2002).…”

“…The experiment with equal physiological duration of exposures showed a typical S‐shaped pattern of thermal response (Figure 4), which was observed in some previous studies with Trichogramma wasps (Sorokina & Maslennikova, 1986; Zaslavski & Umarova, 1990) and some other insects (e.g. Carton & Claret, 1982; Claret & Carton, 1980; Denlinger, 1979; Takano et al., 2021; Tan et al., 2016), but in none of these studies was the left (lower) temperature threshold determined. It should be emphasized that although in nature the lower threshold of the diapause‐inducing thermal response does not have any adaptive value, it is very important for long‐term cold storage under mass rearing conditions.…”

“…Nevertheless, two main types of the patterns of thermal responses can be distinguished: S‐shaped curves with diapause‐inducing and diapause‐averting temperature ranges and a transition zone in between, as for example in above‐mentioned C. bowringi (Tan et al., 2016), tropical flesh flies (Denlinger, 1979), L. boulardi (Carton & Claret, 1982; Claret & Carton, 1980), some Trichogramma species (Sorokina & Maslennikova, 1986; Zaslavski & Umarova, 1990) and the spider mite Eotetranychus smithi (Takano et al., 2021) and U‐shaped curves with a maximum incidence of diapause observed at a certain ‘optimal’ temperature, as for example in Sarcophaga inzi , S. exuberans (Denlinger, 1979) and several Trichogramma species (Garcia et al., 2002; Ma & Chen, 2006; Sorokina & Maslennikova, 1987; Sorokina & Potemkina, 2015).…”