Insecticides should only be used as a last resort when needed to control insect pests in a lawn. Most are toxic to people and pets and some are not very effective against soil-borne pests.
You might try treating your lawn with beneficial nematodes again. Nematodes which attack insects are safe and effective for controlling grubs (beetle larvae) and caterpillars (moth larvae) in lawns. These beneficial nematodes are very perishable and should be purchased from a company that provides fresh stock. Use the product as soon as it arrives or store it in a refrigerator and use it as soon as you can. Soil temperature should be about 70 degrees F or above when nematodes are applied to a lawn. Nematodes become inactive when the soil temperature is below 60 degrees F. Because nematodes are killed by light and heat, it’s best to apply them in the evening, especially when temperatures are high. Soil should be moist but not soggy when the nematodes are applied. Carefully follow the directions on the product label. Several irrigations may be needed to keep soil moist during the first two weeks after application.
By V. Lazaneo, Urban Horticulture Advisor, Emeritus, UC Cooperative Extension, August 2012