Did the bug screen come with your hatch or did you add that?
Not sure what you mean by "bug screen". The wire mesh in my photo has 1" x 2" openings, which I guess could serve as a partial bug screen only against unusually large invading locusts.... And it did not come with the hatch, I added it as a prevention against uninvited visitors like mice, chipmunks and squirrels.
I have a piece of "noseeum" mesh material, which I tailored to be laid upon the wire mesh for bug protection. Fortunately, in the 11 months of using the vent I never needed to deploy it, even though I have spent a few days in locales with very high bug pressure. Bugs just don't seem to appreciate the vent as an entrance.
A sidebar tidbit on ventilation literacy:
Screens suitable for prevention against midges and noseeums (~900-1000 holes per square inch) pose a huge airflow restriction since more than 70% of the total opening is occupied by solid material (mesh fibers), leaving less than 30% of the area available for airflow.
Most people do not realize this, and do not account for its effect while sizing their ventilation layouts...
This leads to dumb approaches - like using more than 1 fan, roof fans running starved for air while cranked high, resulting in accelerated wear, increased noise and power consumption, the latter impacting the sizing and utilization of the electric system. This adds to both the initial conversion cost and the cost of running the van.