I was looking up something unrelated, and had an interesting idea. Besides scavenging from stores for insecticides, survivors should be able to manufacture DDT with the correct chemistry knowledge and a chemistry bench. A few other specialized tools might be needed as well, but they could be manufactured by the player. From what I’ve been reading DDT kills insects and arachnids, and a good chunk of the Arthropoda phylum in general. The precursors can be synthesized with simple laboratory equipment that a chemistry bench would have, and a few metal catalysts like copper, platinum, etc.
Ought to work well on giant bugs and spiders. Its not like the ecosystem isn’t already fucked in the long-term in the first place, and small scale usages won’t be nearly as deleterious to the food chain as mass dispersal on farms and in cities for pest control.
https://en.wikipedia.org/wiki/DDT
The first ingredient precursor, Chloral, is manufactured in a two stage process from hydrochloric acid, sulfuric acid and Acetaldehyde: https://en.wikipedia.org/wiki/Chloral
The Acetaldehyde can be made several ways, such as the partial dehydration of ethanol, or hydration of acetylene: https://en.wikipedia.org/wiki/Acetaldehyde#Production
The other ingredient, Chlorobenzene, is trickier, but can be done several ways, though it may require metal catalysts and some home made apparatus, like a miniature reaction vat or something: https://en.wikipedia.org/wiki/Benzene#Reactions
https://en.wikipedia.org/wiki/Chlorobenzene
