The passage talks about two generations of water bugs. The first hatches during the spring and reproduces in the summer. The second hatches in the summer and reproduces in the spring, so-called "overwintering" generation.
The passage then tells us that the wing form is environmentally determined by the temperature to which developing eggs are exposed prior to being laid. Eggs maintained in warm environment always produce bugs with normal wings, whereas exposure to cold produces micropterous individuals.
Eggs laid by the overwintering adults are formed in early autumn and early spring. Those eggs formed in autumn are exposed to cold winter temperatures, and thus produce micropterous adults in the summer generation. Those formed during the spring are never exposed to cold temperatures, and thus yield individuals with normals wings (lines 58-64). Further evidence that bugs of the overwintering generation brought into the lab during cold months produce only macropterous (fully-developed wings) offspring confirms this theory.
eggs formed in autumn -> cold temperatures - > micropterous wings eggs formed in spring -> warm temperatures - > macropterous wings
These facts allow us to infer that if the winter months are unusually warm, the eggs formed by the overwintering generation of water bugs in autumn are less likely to get exposed to cold temperatures and are thus more likely to produce more macropterous bugs.
Does this make sense?
Let me know if you have any further questions.
Julie-VSeptember 3, 2019
It does make sense, thank you so much for the detailed explanation!
