What control method is primarily ineffective against adult mosquitoes resting under structures?

The effectiveness of control methods against adult mosquitoes can vary significantly depending on the location and behavior of the mosquitoes. Aerial spraying involves applying insecticides from an aircraft over a large area to target adult mosquitoes that are active in flight. However, when mosquitoes are resting under structures, such as eaves, porches, or other sheltered areas, aerial spraying is generally less effective. This is because the insecticide may not adequately reach the areas where the mosquitoes are hiding.

In contrast, alternative approaches, like ground applications and larviciding, directly target areas where mosquitoes may breed or rest. Ground applications can focus on localized areas, including those under structures, ensuring that the insecticide is applied where it is most needed. Larviciding specifically targets the immature stages of mosquitoes in standing water, which does not directly address adult mosquitoes but is vital in reducing the overall population by preventing future generations. Insect growth regulators also focus on disrupting the life cycle of mosquitoes and can be effective at various life stages.

Thus, the primary reason aerial spraying is deemed ineffective against adult mosquitoes resting under structures is due to its inability to access sheltered areas where the mosquitoes are not easily reached during the application process.