Speaking as someone who loves insects, actively participates in several entomological societies in my country and is currently also doing a PhD in biology, I can't say I fully agree with you here. The fear and demonization of insects is far from a modern phenomenon and is arguably much more driven by older and deeply entrenched cultural beliefs than any intentional modern propaganda. While I don't think that entomophobia is biologically/evolutionarily innate, it IS both ancient, widespread and not entirely irrational. At the end of the day, insects ARE one of the most significant vectors of disease transmission (both for animal and human diseases) and major agricultural pests. There's a reason why one of the biblical plagues of Egypt involved locust swarms (and another one involved flies) and it's not like that problem is exclusive to the ancient world - around 2020, East Africa experienced devastating loss of crops due massive locust swarms, leading to food insecurity for several million people. And while viral, fungal and bacterial plant diseases mostly look more like an abstract blight with an unknown source, insect pests could be much more directly and obviously connected with your crops dying and thus represented a more tangible and visible "enemy" (you can't see the tomato yellow leaf curl virus - but you can see a Colorado beetle). Insects also have a long history of being associated with death, rot and decay - think of fly maggots appearing on corpses and rotten food. As a result, they are one of the oldest religious, literary and artistic symbols of corruption and mortality, especially in western/christian tradition (in paintings like Bosschaert's Dead Frog With Flies, or the depictions of Beelzebub, demonic Lord of Flies). This also ties into classist ideas of the poor as infested with lice, fleas and bedbugs (as those parasites can more rapidly spread in cramped living conditions), marking these people as "unclean" - a trope that is especially common in 19th century literature, when the industrial revolution both created stark class divisions and forced the lower-classes into overcrowded and poorly-kept urban homes. A lot of aversion to insects also originates from the perception of arthropods as the ultimate "other" - unlike mammals (but similar to reptiles) they have few traits and behaviours that humans can readily anthropomorphize and relate to. Historically, they were often treated more like semi-living things than true animals, going as far back as Aristotle - the spontaneous generation theory literally posited that insects are so "thing-like" that they can spontaneously emerge from inanimate matter.
Yes, WW2 definitely saw an uptick in propaganda campaigns with negative depictions of insects, but their actual goal wasn't to make people hate insects, it was to eliminate insect-borne diseases (especially typhus and malaria) that were negatively impacting military troops. These campaigns were effectively identical to other health campaigns of the era, like those against venereal diseases, tuberculosis and malnutrition. The need to control insect vectors of typhus and malaria however did lead to the first creation of highly effective synthetic insecticides like DDT. The reason why 1950s saw such a boom in pro-pesticide fever isn't because the powers-that-be wanted the world to suddenly turn against insects, it's because that was the first time in history that effective (and seemingly safe) pesticides were broadly available. Pesticides were and are obviously a massive contributor to ecological degradation and species loss, but they were also a crucial part of the third agricultural revolution of the mid-20th century that ensured higher and more reliable crop yields. They are, unfortunately, still a core part of modern agriculture to this day - the previously mentioned locust swarm outbreak in 2020 was in large part a result of the COVID pandemic halting the delivery of insecticides to the region. Because some insect species genuinely do present a very real threat to food production, they were obviously often a target of various agricultural campaigns - such as the (ultimately disastrous) Four Pests campaign in China or the mass campaign against locusts in 1920s/1930s Soviet Union. The latter is also interesting because it reframed the locust as a foreign invader as a political tool to unite the still fractured country against a common enemy and justify mass mobilisation of troops into contested territories. During the cold war, Warsaw pact countries similarly launched a massive and ideologically driven propaganda campaign against the Colorado beetle under the belief that the USA intentionally introduced the species in order to destabilize potato production in the region (my grandparents were actually mobilized to pick Colorado beetles in a similar campaign in Yugoslavia). Yes, insects were used as a tool of political propaganda in all of these cases, but not because the promotion of the hate against insects was a goal unto itself, it's because insects already had widely held negative connotations that could be exploited for other propaganda purposes. And these negative connotations in many cases stemmed from people's actual lived experience of crop failures and disease.
(The 1950s boom of giant bug horror movies was also arguably more driven by anxieties surrounding the rapid progress of science, especially atomic energy, in the post-war era (the same thing that drove a surge in popularity of pulp sci-fi novels and more science-based silver age comics). Arthropods were commonly used not to intentionally fuel anti-insect propaganda, but because people already had pre-existing aversion to them (and because simply magnifying an actual animal was a cheap way to have mostly realistic looking giant monsters)).
Just so no one can misunderstand or misrepresent what I'm saying here: I strongly believe that the conservation of insect species is important and that widespread negative sentiment against them hinders that goal. I am not shilling for pesticide corporations or think that we should kill all insects, nor do I think insects should be equated with pests, vermin, or carriers of disease. The hate against insects is largely not based in fact and should not be condoned. Bugs are cool. What I am saying however, is that the fear and dislike of insects is a complex and multifaceted topic and putting the blame on some sort of intentional anti-insect conspiracy is reductive and ultimately unproductive.