Role of crop border and host patch size on retention of electronically tagged walking adult Colorado potato beetle

Tagged Colorado potato beetles, Leptinotarsa  decemlineata (Say), were released on potato plants, Solanum tuberosum L., and tracked using a portable harmonic radar to determine the impact of host plant spatial distribution on the tendency of the insect pest to remain on the colonized host plant or host patch. The long residency time of beetles on the host plant initially colonized was confirmed. Continuous tracking over a period of 6h in small potato plots of the walking path of beetles leaving the initial host plant revealed that all types of mixed borders tested (bare ground, timothy and woodland) acted as a strong barrier and retained beetles within the plot. Additional tests where tagged CPB were released in potato patches surrounded by bare ground borders showed a strong influence of the border on walking path direction. The distribution of turning angles was clearly not uniform. Patch size had no or little effect on the role of mixed crop borders at limiting beetle departure.  The relative distribution between small (16 m²), medium (64 m²) and large size (256 m²) patches of potato of the total numbers of tagged beetles retained detected by radar four days after initial release remained similar to the distribution at release time in most patches. Mixed borders played a key role at retaining walking potato beetles in the host patch regardless of its size.  However, the 72% rate of beetle departure that occurred in spite of a strong mixed crop border barrier effect suggests that beetles left by flight and that, therefore, the effect of the border on beetle retention is largely limited to dispersal by walking. Based on these results, the manipulation of crop borders and patch size seem to have limited potential for the management of Colorado potato beetle dispersal between host patches.