The Powsner (1935) Q10 Equation
Drosophila melanogaster development is one of the cleanest examples of temperature-dependent developmental rate in any model organism. Powsner (1935) measured egg-to-adult times across the entire 12–32 °C range and fit an exponential equation that still serves as the working model today.
The equation
development_time_days = a × exp(-b × T)
with a ≈ 220 and b ≈ 0.13 for wild-type Canton-S. The Q10 — the factor by which the rate changes for a 10 °C shift — is approximately 2.5, which is typical for biochemical processes.
Anchor points
25 °C → ~9 days (the standard rearing condition)
22 °C → ~11 days (room temperature in many labs)
18 °C → ~18 days (used to "park" stocks and slow evolution of recessive lethals)
16 °C → ~28 days (cold storage; some balancer stocks are kept here)
What the model does NOT capture
Crowding, food quality, and humidity shift development by ±10–20%. Mutant lines with cell cycle, metabolic, or hormonal defects can shift it much further. Balancer chromosomes typically add 5–10%.
Virgin Collection — Temperature Matters
Virgin female collection is the bottleneck of any Drosophila genetics workflow. The principle: female flies become sexually receptive only after their cuticle hardens and their reproductive tract matures, which takes 8–16 hours after eclosion depending on temperature.
Standard windows
25 °C: collect every 8 hours (mornings only is risky — overnight you may get mated females)
22 °C: collect every 12 hours (a once-daily schedule is acceptable for many lines)
18 °C: collect every 16 hours (the easiest temperature for virgin work)
Best practice
Move stocks to 18 °C the day before you need to collect virgins. The wider window means you can do morning + evening collection and reliably get virgins, even from prolific stocks.
Visual cues for virgins
Newly eclosed females are pale, have a visible meconium (dark spot on the abdomen), and have not yet expanded their wings. The meconium disappears within 6 hours, so it is the most reliable visual marker.
