Expressing concern over the escalating dengue cases in the country, Health Minister Zahid Maleque has said it appears that the city corporations are lacking in necessary measures to control mosquitoes. "We maintain a regular collaboration with the city corporations, providing them with valuable advice based on our ongoing research. I hope the city corporations will not relent in its efforts [to control mosquitoes]," he said while speaking at a discussion programme organised on the occasion of World Malaria Day in the capital yesterday.