Onion Insect Management: Seed Maggots and Onion Thrips

I am new to Onion Cultivation, Please Guide me on the Insecticides to be used on onions and at what stages. The Onion Cultivation is at Sri Lanka (The Country near to India in Indian Ocean)

(a) What are the possible insect attack on onions while cultivation.

(b) What are the Best Products to use on Onion Thrips and Onion Maggots.

© How to Choose the Insecticide Products for Onion.

(d) Is there one product for Both Onion Thrips and Onion Maggots.

(e) When will Onion Maggots come and when will Onion thrips Come.

(f) Are Onion Maggots and Thrips the only Insects for Onion Cultivation or are there more.

(g) what are the Powder type Insecticide for Onion Insect Control

Please Guide and Help