Sensor-Based Insecticide Spraying to Control Cereal Aphids and Preserve Lady Beetles

Lady beetles (Coccinella septempunctata) are one of the most effective predators of aphids (Sitobion avenae). Therefore, the development of plant protection technologies that do not lead to their eradication within the field is necessary. With a sensor-controlled field sprayer, which determined in real-time the plant biomass of a heterogeneous winter wheat field and, based on these measurements, also controlled the amount of applied insecticide, a variable rate spraying program was implemented. The insecticide savings totaled 13.4% when compared to that of uniform spraying. An application of a high dosage led to a rapid die-off of aphids. However, this same scenario did not occur in the areas that received a low dosage of insecticide. There, the aphids remained alive. It was observed that lady beetles colonized at first in these low dosage areas, where aphids were still present. Eventually 3 wk after insecticide application, aphids and lady beetles did not exist in the areas that received low insecticide dosages in the field. There, at this latter time the crop was mature. Now the aphids occurred in the high biomass areas, which were still green and not fully mature. The same scenario occurred for the lady beetles; as presence absence sampling indicated that they followed their prey. The time-dependent spatial variability of aphid and lady beetle occurrence were confirmed by GLIMMIX analysis which indicated a significant effect of the space time interaction on their joint occurrence.