Effects of temperature and other environmental factors on the post‐diapause development of walnut husk fly Rhagoletis completa (Diptera: Tephritidae)

Abstract

To more effectively manage walnut husk fly Rhagoletis completa (Diptera: Tephritidae), in California walnut orchards, it is important to understand the factors that affect the timing of adult emergence. In the present study, we examine the effects of incubation temperature, pre‐chill and chill durations, latitude, cultivar and size on the post‐diapause development of R. completa puparia. The lower developmental threshold, upper developmental threshold and optimal temperature for puparial development are estimated to be 4, 34 and 26.6 °C, respectively. The thermal requirement for adult emergence after 120 days of chilling is estimated to be 2024 degree days. Percentage adult emergence declines at both higher and lower incubation temperatures. Chill duration at 5 °C for diapausing puparia has a nonlinear negative effect on the thermal requirement but no effect on percentage emergence. Insufficient chilling leads to poor synchronization of adult emergence. Greater pre‐chill duration at room temperature increases the thermal requirement and slightly decreased percentage emergence. Latitude has a negative effect on the thermal requirement. Puparia from northern California black walnut (Juglans hindsii) have a slightly greater thermal requirement than puparia from cultivated walnut (Julgans regia). There is no significant difference in puparial fresh weight or mean thermal requirement between males and females, although the positive correlation between thermal requirement and puparial fresh weight is stronger for females than males. The effects of temperature and other environmental factors on the post‐diapause development of R. completa are discussed in relation to observations from other Rhagoletis species.

The Effect of Winter Length on Duration of Dormancy and Survival of Rhagoletis completa (Diptera: Tephritidae) and Associated Parasitoids From Northeastern Mexico

“…Although the effect of winter length has been examined for several species in the genus Rhagoletis (Feder et al 1997; Rull et al 2016, 2017), until very recently it had not been specifically examined for R. completa . Emery and Mills (2019a) did not find significant differences in percent emergence among pupae exposed to various chill duration regimes ranging from 0 to 21 wk (0 to 3,600 chill hours). Here, R. completa pupae emerged as adults in similar proportions when exposed to chill periods of either 8, 12, 16, or 20 wk.…”

“…Males emerged in higher proportions under constant temperatures or a short winter length (4wk), than under longer winter lengths. This result does not appear to be explained by sex related size differences in R.completa , since both sexes are roughly the same size (Emery and Mils 2019a). In general, female arthropods have greater lipid content than males (Lease and Wolf 2011).…”

“…Such duration may have been arbitrarily established and adopted as a convention. Additionally, Emery and Mills (2019a) report that chill periods starting from 45 d (1,080 chill hours) produce good synchronization of adult emergence. In consequence, for artificial rearing or research purposes, R. completa can be handled in the laboratory by exposing pupae to artificial winters for periods starting at 45 d in duration.…”

“…The other cups were transferred to a conventional refrigerator (5 ± 1°C), (roughly corresponding to the average mean minimal winter temperatures of the collection site) in the dark for a winter period of different duration; 4, 8, 12, 16, and 20 wk (hereafter referred to as 4 wk, 8 wk, 12 wk, 16 wk, and 20 wk). Twenty weeks has been used as the optimal chill duration for dormancy studies on R. completa Northern populations (Emery and Mills 2019a). After each winter period, cups were returned to the lab, under similar conditions of the pre-winter period, for emergence.…”

“…Chen et al (2006) compared genetic composition and diapause length between Californian introduced and native R. completa populations, and Guillén et al (2011) compared diapause length of Swiss populations stemming from different Juglans regia cultivars. More recently, Emery and Mills (2019a) examined the effect of temperature and other environmental factors on post-diapause duration of Californian R. completa.…”