Larvae respond to differences in light intensity. Young (first-instar) larvae are negatively phototropic and move away from light and downward in the breeding site. Last (third) instar larvae react more positively to light and move outward to lighter and drier areas to begin pupation.
The ability of larvae to detect light is primarily due to photosensitive cells located in a cluster in a pocket internally and anteriorly between the dorsal wing-like cephalopharyngeal sclerites.
The rate of larval development through the three instars depends on temperature within the range suitable for survival. Larvae can survive at –2°C (28°F) for several days. Below 10°C (50°F) the larvae will not pupate. Given a choice, young larvae seek areas with a temperature of 30–37°C (86–98°F). As larvae become older they move to areas of lower temperatures and prefer to pupate at 15°C (59°F).
These temperatures are the preferred ones. However, larvae can survive in a wide range of temperatures. The precise lethal temperature is not known and would vary with the stage of development of the larva. However, the lethal temperature is about 46°C (115°F). The threshold for larval development is about 8°C (46°F).
Although there are variations in the reported time of development of larvae at different temperatures the following are typical:
|
°C
|
°F
|
Days to pupation
|
|
16
|
61
|
11–26
|
|
18
|
64
|
10–14
|
|
20
|
68
|
8–10
|
|
25
|
77
|
7–8
|
|
30
|
86
|
5–6
|
|
35
|
95
|
3–4
|
|
| 
