It will be 90 degrees for 80% of the 15 weeks, for a total of 0.8*15=12 weeks.
It will be 100 degrees F for the remainder of the 15 weeks, or 15-12=<<15-12=3>>3 weeks.
During the 12 weeks when it averages 90 degrees F, he will eat 4 crickets per week for a total of 12*4=<<12*4=48>>48 crickets.
When it averages 100 degrees F, he eats twice as many crickets per week as when it averages 90 degrees F per week, for a total of 2*4=8 crickets per week.
During these 3 weeks, he will eat 8*3=<<8*3=24>>24 crickets.
Therefore, over the 15 weeks, he will eat a total of 48+24=<<48+24=72>>72 crickets.
#### 72