A specialist pest can only feed and breed on the target crop. Each tick it tries to spread from every infested plant into its immediate neighbours: a healthy target-crop neighbour is infested easily, but a neighbouring plant of a different crop is not a host at all — the pest can only rarely "jump" past it to reach a host beyond, at a much lower rate. In a monoculture every neighbour is a host, so the pest radiates outward with almost no wasted movement. In a polyculture, non-host plants are scattered through the same target-crop area, so most of the pest's neighbours are dead ends — its effective search-and-spread rate collapses even though the pest itself hasn't changed at all.
- Field mode — monoculture plants only the target crop; polyculture keeps the same total number of target-crop plants but interspersed among 1–2 other crop types.
- Crop types — how many distinct species share the polyculture field (2 = target + one companion crop, 3 = target + two companion crops).
- Interspersion pattern — how the crops are arranged: a fine checkerboard mix, alternating rows, or a fully random mosaic.
- Target crop share — what fraction of the polyculture field's cells are the target crop; the field automatically grows to keep the absolute target-crop area identical to the monoculture field.
- Introduce pest — seeds one infested plant at the same relative position in both fields, so the comparison starts from identical conditions.
This is "associational resistance" from the resource-concentration hypothesis: diluting a host crop among non-hosts suppresses pest outbreaks without any pesticide, simply by making the field harder for a specialist to navigate.