Which environmental factor can increase vector populations?

Stagnant water accumulation is a crucial environmental factor that can significantly increase vector populations, particularly for mosquitoes and other aquatic insects. Stagnant water provides an ideal breeding ground for these vectors, as it allows mosquitoes to lay their eggs and for the larvae to develop in a protected environment with limited water movement. The still water offers a stable habitat devoid of natural predators that would typically be present in flowing waters, facilitating a higher survival rate of the immature life stages.

In contrast, other options do not support the proliferation of vector populations as effectively. High temperature fluctuations can lead to stress on the organisms, potentially decreasing their populations. Low humidity levels can create an unsuitable environment for many vectors, leading to dehydration and reduced reproductive success. Fast-flowing rivers and streams generally do not support standing water environments necessary for the breeding of many vectors; instead, they tend to wash away eggs and larvae, making such conditions less conducive to vector population growth. Thus, stagnant water accumulation clearly stands out as a favorable condition for increasing vector populations.