150 Bulletin de la Société Royale Êntomologique d'Egypte 
The new investigator introduced a new constant, 
the critical cold-point into the formula. The cri¬ 
tical cold-point is that temperature at which 
the development time of the insect has increased to 
such an extent that the formation of a curva is im¬ 
possible. The new formula fo Munck runs : « The 
product of duration of development and the diffe¬ 
rence between the surrounding temperature and the 
critical cold-point is constant ». The time of develop¬ 
ment, forms in relation to the surrounding temperature 
an equilateral hyperbola. If we know for two tempe¬ 
rature points of this hyperbola the corresponding dura¬ 
tion of development, we may construct the whole hy¬ 
perbola, this means that we know for any other tem¬ 
perature point between the critical heat and cold- 
point the corresponding duration of development. 
Furthermore we are able to estimate the critical cold 
point fiom two known equations : 
t ( v — k ) = cons.t. 
I, (v, — k) = cons.t. 
t, ( v, 
t 
t, 
We may also infer from any duration of develop¬ 
ment known to us the corresponding urrounding 
temperature. This curva is valid only under optimal 
conditions. 
We will examine in the following lines the use¬ 
fulness of the Blunck-formula in practice by means of 
the seasonal history of Ceratitis capitata Wied. This 
fruit-fly is a multivoltine insect and therefore very fit 
for this examination. 
