The Colorado potato beetle Leptinotarsa decemlineata (Say) (CPB) is one of the most relevant pests in potato cultivation. Even in organic potatoes, CPB are often managed using organically certified insecticides that may also affect non-target organisms and increase the risk of insecticide resistance. Applying transferred organic mulch to potatoes has been shown to reduce egg masses and larvae of CPB, however, the underlying mechanisms remain unclear. To assess effects of mulch on initial infestation of CPB, marked individuals were released in the field between plots with transferred organic mulch and plots with bare soil and counted after 12 h in 2021 and 2022. In 2022, one additional assessment was carried out 72 h after release and eggs and larvae where assessed after 10 days. More than 75% of CPB adults preferred the unmulched plots, a major reason for the reduction of eggs and larvae in mulched potatoes found in previous field trials. Barrier effects, olfactory disruption or disorientation could be responsible for the reduction.
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