Seed World

The Optics of Pest Insect Invasions

Light-based sensors could offer an early warning system for detecting pollen beetle infestations in oilseed rape crops.

Hi-tech optical sensors in fields could provide an effective means of monitoring beetle numbers arriving in oilseed rape (OSR) fields, according to a new study from Rothamsted Research.

Results from an optically sensed field were compared with those from fields baited with standard water traps and those where counting was done manually in the field. The optical sensors detected an increase in pollen beetles two days earlier than the water traps and four days earlier than the manual plant counts. In terms of early detection and the number of beetles recorded, this method proved to be the most efficient for pollen beetle monitoring.

“Understanding the dynamics of pest immigration into a crop field helps us find effective and timely management strategies,” said Professor Emily Bick of the University of Wisconsin-Madison who led the study, alongside scientists from Rothamsted Research, FaunaPhotonics A/S and the University of Copenhagen. “The pollen beetle is a significant pest of oilseed rape during budding stge. Many farmers in western Europe are now abandoning OSR as a crop because damage is so severe from pollen beetles, additional insect pests, and reduced availability of approved synthetic insecticides. Better surveillance of in-field pests could help us identify a way round the problem.”

Automated near-infrared optical sensors captured the signal of light backscattered by insects flying through a detector beam. Researchers were able to record insects in flight and identify each insect’s wing beat frequency, which often varies between species. For example, pollen beetles have a wing beat frequency of 120 Hz, so insects with frequencies ranging from 100 to 140 Hz were classified as pollen beetles. These sensors were continuously operated in fields in Denmark, while parallel experiments on the spatial distribution of pollen beetles in oilseed rape crops were conducted at Rothamsted (UK).

The release notes that in all fields in the study, pollen beetles were found in significant numbers and were shown to aggregate; beetle density was related to plant growth stage, with more beetles occurring on plants after the budding stage than before inflorescence development. 

“Our study suggests potential for precision agriculture to reduce insecticide use through targeting of pollen beetle aggregations — in other words treating only areas of the crop where pollen beetle density is high,” said Rothamsted’s Dr. Sam Cook who is the senior author of the study. “Optical sensing of pollen beetles gives us more efficient monitoring in both time and space, so it is a promising tool for early warning of insect pest immigration. 

“The aggregation pattern of pollen beetles following immigration could be utilized to precisely target control measures in oilseed rape crops.”

Pollen beetles typically aggregate first on the downwind edge of the field before spreading to the center. Early detection through sampling and monitoring should align with this migration pattern, enabling more effective control.

Cook suggested that a network of these or similar sensors at a crop or landscape scale could form the foundation of a pest map.

“A system that links the number of sensed insects immigrating into a field, the temperature, and the crop growth stage would better predict the risk of economic damage and provide an avenue for fully automated pest monitoring. Sensors might even be useful for tracking natural enemies to determine if an insecticide application is necessary considering biocontrol potential. Alternatively, pollinators may be identified in the field to avoid non-target insecticide effects on these beneficials, thereby contributing to both pesticide reduction and biodiversity protection goals for sustainable agriculture.”