Again: the effect you're referring to here, food chain collapse, is already occurring, but on much larger and more indiscriminate scales. Meanwhile, there is scant real evidence that Anopheles is a critical component of the food chain. Here's the most fair treatment on the subject that I could find: https://archive.ph/h12qU

I've been following this subject since at least Olivia Judson's article was published back in 2003. Over the last 23 years, to the best of my knowledge, nobody has yet made a strong case that Anopheles was a necessary part of the ecosystem. If your alien species were unable to identify wheat as an important food source, one would question how they managed to figure out interstellar travel.

The most vocal arguments against are all of the kind we're seeing here: "we don't know what might happen" (a statement of the unintended consequences of science meddling with nature that goes back in fiction to at least Mary Shelley), "we should assume they're necessary" (and yet all other necessary critters seem to be optional), "something needs them, we just don't know what" (in 23 years, biologists have so far identified a single spider that maybe or maybe not depends on them).

And these are the arguments that condemn a million people a year to death.

I would be easily swayed by evidence of large-scale ecosystem destabilization if Anopheles were eradicated. To date, not only is there no such evidence, but there is some evidence to the contrary (species of mosquito have been introduced to island habitats where they went on to have significant effects on local animal populations).