Male flowers usually die after shedding pollen. But your defoliating zucchini plant may be happening because the female flowers are falling off before they can get pollinated. Your squash plant requires male and female flowers to reproduce and make fruit. So, if you only see male zucchini flowers, you won't get any squash. If female zucchini flowers keep dying without getting pollinated, you may need more bees. Increasing pollinators such as bees in your garden may help solve this problem. You can also try hand-pollinating the flowers by transferring pollen from the male to the female flowers if you can identify them.