December, ’18] 
RUST: ANASTREPHA FRATERCULUS 
465 
been seen to survive temperatures as low as — 7° C. By means of 
this resistance to unfavorable conditions all stages are able to with¬ 
stand the cool weather and resume their normal activities with the 
more favorable weather of early spring, when a new swarm, composed 
of both over-wintering females and those freshly emerged, is ready 
to attack the early apricots, thus completing the yearly cycle. 
Climatic Conditions 
Climatic conditions seem to be the decisive factor as to whether this 
insect will be severely destructive or only moderately so. If condi¬ 
tions have been favorable to a heavy crop of fruit, a good proportion 
of the same may, during the first part of the season, be free from 
attack, but from this very abundance of food results such a great and 
rapid increase of flies that the fruit maturing during the remainder of 
the season is apt to be very largely infested. Thus, a big peach crop 
gives rise to a swarm of fruit-flies which multiply rapidly in the many 
successive and suitable summer fruits, until oranges are sufficiently 
developed for oviposition in the autumn. These, being practically the 
only fruit left, receive the full attention of almost all the flies and a 
heavy infestation results. On the other hand, unfavorable weather 
conditions tend to check the increase of the fruit-fly, but sometimes 
they also result in curtailing the fruit crop as well, so that things are 
pretty evenly balanced and nearly all the fruit is again infested. 
However, if the unfavorable weather occurs early enough in the season, 
the flies may be severely checked without doing much damage to 
fruit-trees which have not bloomed as yet, and a good crop of com¬ 
paratively clean fruit results. 
Now, what climatic conditions may bring about these results? 
Naturally one thinks of cold. But a cold spell of sufficient duration 
and intensity is seldom encountered in the semi-tropics. Nor is it a 
condition to be desired from other points of view. During the present 
winter this locality has suffered from temperatures of from 0° C. to 
— 7° C., followed by warm sunshine, and at mid-day many specimens 
of A. fraterculus were observed as active as ever. Thus it appears that 
even a killing frost does not have much effect on the adults, and even 
less on larvae in oranges or upon pupae which may be safely protected 
in the soil. 
As to humidity. Where rains occur in the hot season, as here in 
Northern Argentina, they only stimulate plant growth and tend 
toward increasing the food supply of the flies and to the rapid develop¬ 
ment of the latter in all their stages. In fact it has been noted repeat¬ 
edly that during and after a rainy season, damage by the fruit-fly is 
generally more severe. 
