Why must one check schach for bugs – if the concern is that maybe a bug will fall into his food?
a) Wouldn’t this be a sfek sfeika?
b) Wouldn’t this be a miut which is eino matzui, or at least would depend on the degree of infestation?
c) Schach is exposed, so bugs can come in and fall down at any time, what is the difference?
d) Is there any earlier source for checking schach for bugs, or anything other than foods?
a) If the schach is full of bugs, it can be assumed that a bug will fall into the food, so that it is hard to apply a safek sefeika here.
c) After being stored for a year, there is a greater concern for bugs.
d) Not to my knowledge.
In general, the concern for bugs in Sechach is usually not great, and it depends on the moisture and storage method.
My advice is to place a white tablecloth on the table under the Sechach, shake around the Sechach, and check if bugs fall onto the table.
If the result is a clean table, clearly nothing more needs to be done.