Pumpkin leaves are infected

Lesson to be learned.. if you see any discolouration on the leaves, always check on the underside.. high probability that they are infected with some insects that is leeching nutrients of the leaves.. I discovered this fact this morning. Was clearing dead leaves from the plants and when I was doing so for the pumpkins, I accidentally saw the underside is infected with yellow coloured creatures.. not sure what they are... I will have to use either garlic spray or one of those natural insecticide that I bought last month... can only wait till tomorrow morning to do so...... so sad!! I did not discover this earlier..... My pumpkins are almost bo-tak now :-((((