Finding indications of lag time, saturation and trading inflow in the emergence record of exotic agricultural insect pests in Japan

Agricultural imports are the primary pathway for the introduction of exotic insect pests. The invasion records of exotic insect pests are also influenced by the lag time before detection and saturation caused by the limited species pool of potential invaders. We compiled an exhaustive list of exotic insect species in mainland Japan and tried to evaluate the connection between the commodity types of agricultural imports and insect types of agricultural pests, in addition to the effects of lag time and saturation. We found that lag time was prominent when all pest types were merged into one group, whilst saturation always existed when we divided the records into the four agricultural pest types. Saturation was especially prominent in stored product pests because this group contained many cosmopolitan insect pests that could have easily inhabited the newly built mills throughout Japan in the 1950s. We suspect that the saturation effect was masked by admixture amongst pests with different saturation patterns. Our findings indicate that all commodities, i.e. flowers, fruits, vegetables, cereal and timber, contributed to the invasion of pest insects as potential pathways. However, it was unclear if certain items had comparatively greater significance in this process.