Response to photoperiod during diapause development in the spider mite Tetranychus urticae

Influence of abiotic factors on diapause termination and temperature requirements for postdiapause development in the European red mite, Panonychus ulmi (Acari: Tetranychidae)

The European red mite Panonychus ulmi (Koch) is widely distributed and it can severely affect pome fruit crops, particularly apple. Pest outbreaks are related to an overuse of non-selective pesticide treatments that lead to the development of resistance and the absence of natural enemies in the orchard. A key aspect to optimize the use of pesticide treatments in the context of IPM is to increase the knowledge on the biology and ecology of the pest to better predict population dynamics and outbreaks. For the European red mite, knowledge on the conditions that lead to diapause breaking by winter eggs is essential to model population dynamics. To increase this knowledge, winter eggs were collected during field surveys in northen Spain during three years and egg hatching was monitored under controlled temperature and photoperiod conditions in the laboratory. The "number of days exposed to cold temperatures" was the most significant factor that positively affected hatching of overwintering eggs. The time required for 50% of the egg population to hatch (T50%) was also negatively modulated by the duration of exposure to cold temperature. The temperature threshold for postdiapause eggs development collected from the field was estimated between 5 and 6 ºC in 2005 and 2007, respectively. Moreover, the degree-days required for post diapause development were estimated between 263.2 and 270.3, depending on the year of collection. Collectively, we provide additional information on the diapause termination and postdiapause development of the European red mite that may effectively contribute to optimize pest population models.

Relationship between body colour, feeding, and reproductive arrest under short-day development in Tetranychus pueraricola (Acari: Tetranychidae)

In Tetranychus spider mites (Acari: Tetranychidae), diapausing females have a conspicuous orange body colour, which is used as an indicator of diapause induction in many laboratory studies. However, to which extent body colour reflects reproductive activity is scarcely investigated. In this study, we investigated the relationship between body colour, reproductive arrest, and food intake in the inbred strain of T. pueraricola individually reared at 20 °C with a 10:14 h light: dark photoperiod. Our results showed that (1) body colour is a good indicator of reproductive arrest 11 days after adult emergence but does not completely reflect reproductive status at an earlier age; (2) even orange females intermittently feed, and the arrest of feeding comes after the change in body colour; and (3) reproducing females have a higher risk of death than non-reproducing females. These results suggest that measurement of diapause incidence by body colour alone may miss the variation in reproductive status in early adult life.

Eco-physiological phases of insect diapause

Insect diapause is a dynamic process consisting of several successive phases. The conception and naming of the phases is unsettled and, sometimes, ambiguous in the literature. In this paper, the ontogeny of diapause was reviewed and the most often used terms and the best substantiated phases were highlighted, explained and re-defined. The aim was to propose relatively simple and generally applicable terminological system. The phases of diapause induction, preparation, initiation, maintenance, termination and post-diapause quiescence were distinguished. The specific progression through diapause phases in each species, population (genotype), or even individual, is based on (thus far largely unknown) physiological processes, the actual expression of which is significantly modified by diverse environmental factors. Thus, such phases are eco-physiological in their nature.