Effects of photoperiod and temperature on the termination of diapause in the univoltine seed wasp Eurytoma plotnikovi

Abstract

Mummified pistachios containing fully grown diapause larvae of Eurytoma plotnikovi Nikol'skaya (Hym., Eurytomidae) were collected in early August and late September in coastal northern Greece and subjected to various photoperiod and temperature treatments, then maintained at 19 or 26°C and a long‐day (LD 16:8 h), a changing, or a short‐day (LD 10:14 h) photoperiod until pupation. In larvae of early August (beginning of diapause) subjected for 20 weeks to 19°C under a long, a changing, or a short photophase, followed by 19°C and a long photophase, 50% of the larvae pupated after 24, 18 and 13 weeks respectively. After exposure for 20 or even 12 weeks to a short photophase and low temperatures (10 or 4°C), pupation occurred after only 7–8 weeks and was more synchronous. The ranges of temperature for diapause development and post‐diapause morphogenesis overlap. After exposure for 12 weeks to short days and low temperature, larvae of late September pupated much sooner under long days than under short days and sooner at 26° than at 19°C. E.plotnikovi depends on both temperature and photoperiod for diapause development, low temperature having a strong favourable effect on the earlier part and long day on the later part of diapause. In a few larvae of another pistachio seed wasp, Megastigmus pistaciae Walker, after a long enough period of low temperatures, diapause was terminated normally at 26°C and long days, or at 19°C and long or short days.

Time of Diapause Termination in the Pistachio Seed Wasp Eurytomα plotnikovi (Hymenoptera: Eurytomidae) ίη Northem Greece and Under Certain Photoperiods and Temperatures

“…Even by the 14th day under the above laboratory condition only 64 to 75% of the larvae pupated. Subsequent work already publish ed, with larvae from the same orchard, has shown that after larvae are exposed to short days and low temperature, as was the case with larvae of the present experiment, pupation takes place much sooner under long days than under short days (Tzanakakis et al 1992). We do not know whether the delayed termination of diapause in the caged fruits was due to differences in photoperiod, in temperature, or in both from those on the trees.…”

“…The present work preceded that by Tzanakakis et al (1992), which was carried out with larvae taken two years later from the same trees. There fore, the photoperiod and temperature combin ations we used were not planned to complement that work.…”

“…To detect possible differences in pupal development on the last day of observations, the pupae were arbitrarily classified as totally white, with red eyes, with black eyes, and with black body. For monthly temperatures and natural dayleneths in the orchard area see Tzanakakis et al (1992).…”

“…In the Thessaloniki area of coastal northern Greece, larval growth is completed and diapause starts in mid to late summer. Laboratory work with larvae from that area showed that diapause development depends on both temperature and photoperiod, low temperature having a strong favorable effect on the earlier part, and long day on the later part of diapause (Tzanakakis et al 1992). The time of year diapause in E. plotnikovi is terminated in nature has not been determined in any part of this insect's area of distribution.…”

Diapause completion in the almond seed wasp, Eurytoma amygdali (Hymenoptera: Eurytomidae) following early low temperature treatment

“…This wasp has at least two diapause stages or phases. In the laboratory, larvae collected in early August completed the first stage more rapidly under a short-day and low temperature conditions, and the second stage more rapidly under a long-day and high (26°C) to mildly high (19°C) temperature conditions (Tzanakakis et al, 1992).…”