Gel Dots on a Grid: The Widest Spacing That Still Collapses a German Cockroach Population in a Kitchen

Gel bait is applied as small dots near harbourages, and tubes are sold with little guidance on how far apart the dots may sit. This study models 20 m of kitchen harbourage line, a mean nightly foraging distance that gives each dot 1.1 m of effective coverage, a starting population of 400 German cockroaches, and a nightly population projection including reproduction and secondary transfer through faeces and remains. At 1.1 m spacing, 19 dots using 1.9 g of gel costing USD 0.89 bring the population below 10 percent of its starting size in 21 days. At 1.6 m spacing the same point takes 38 days; at 2.2 m, 91 days; and at 3.0 m spacing the population never falls below 10 percent within 120 days, because the nightly fed fraction of 0.308 no longer outruns reproduction plus the untreated refuges. Denser grids than 1.1 m change nothing in the model, because coverage is already complete. The originated rule is to space gel dots at most 1.1 m apart along every harbourage line, including the second level of cabinets, and to treat dot count rather than gel weight as the quantity to check. This study is simulated, not measured. SIMULATED, NOT MEASURED.