Characteristics and Drivers of High-Altitude Ladybird Flight: Insights from Vertical-Looking Entomological Radar

Understanding the characteristics and drivers of dispersal is crucial for predicting population dynamics, particularly in range-shifting species. Studying long-distance dispersal in insects is challenging, but recent advances in entomological radar offer unique insights. We analysed 10 years of radar data collected at Rothamsted Research, U.K., to investigate characteristics (altitude, speed, seasonal and annual trends) and drivers (aphid abundance, air temperature, wind speed and rainfall) of high-altitude flight of the two most abundant U.K. ladybird species (native Coccinella septempunctata and invasive Harmonia axyridis). These species cannot be distinguished in the radar data since their reflectivity signals overlap, and they were therefore analysed together. However, their signals do not overlap with other, abundant insects so we are confident they constitute the overwhelming majority of the analysed data. The target species were detected up to ∼1100 m above ground level, where displacement speeds of up to ∼60 km/h were recorded, however most ladybirds were found between ∼150 and 500 m, and had a mean displacement of 30 km/h. Average flight time was estimated, using tethered flight experiments, to be 36.5 minutes, but flights of up to two hours were observed. Ladybirds are therefore potentially able to travel 18 km in a “typical” high-altitude flight, but up to 120 km if flying at higher altitudes, indicating a high capacity for long-distance dispersal. There were strong seasonal trends in ladybird abundance, with peaks corresponding to the highest temperatures of mid-summer, and warm air temperature was the key driver of ladybird flight. Climatic warming may therefore increase the potential for long-distance dispersal in these species. Low aphid abundance was a second significant factor, highlighting the important role of aphid population dynamics in ladybird dispersal. This research illustrates the utility of radar for studying high-altitude insect flight and has important implications for predicting long-distance dispersal.

明晰扩散的特征与驱动因子，对于预测种群动态至关重要，针对正发生分布范围迁移的物种而言尤为如此。对昆虫长距离扩散行为开展研究颇具挑战，但近年来昆虫雷达（entomological radar）技术的进步为相关研究提供了独特视角。本研究分析了英国洛桑研究所（Rothamsted Research）采集的10年雷达数据，旨在探究英国两种优势瓢虫——本土七星瓢虫（Coccinella septempunctata）与入侵性异色瓢虫（Harmonia axyridis）的高空飞行特征（飞行高度、速度、季节与年度变化趋势）及其驱动因子（蚜虫丰度、气温、风速与降雨量）。由于这两种瓢虫的雷达反射信号存在重叠，无法在雷达数据中直接区分，因此本研究将二者合并分析。但它们的信号与其他优势昆虫的信号并无重叠，故可确认所分析数据中的绝大多数目标均为这两种瓢虫。研究在距地面约1100米的高度检测到了目标瓢虫，此处记录到的飞行迁移速度可达约60公里/小时；但绝大多数瓢虫的飞行高度集中在约150至500米区间，平均迁移速度为30公里/小时。通过吊飞实验（tethered flight experiments）估算，目标瓢虫的平均飞行时长为36.5分钟，同时观测到最长飞行时长可达2小时。据此推算，单次典型高空飞行中，瓢虫的迁移距离可达18公里；若在更高海拔飞行，最远迁移距离可达120公里，这表明此类瓢虫具备极强的长距离扩散能力。瓢虫种群丰度呈现显著的季节变化趋势，丰度峰值与仲夏的最高温时段相吻合；而气温是影响瓢虫飞行行为的核心驱动因子。因此，气候变暖可能会提升这两种瓢虫的长距离扩散潜力。蚜虫丰度偏低是第二个显著影响因子，这凸显了蚜虫种群动态在瓢虫扩散过程中的重要作用。本研究验证了雷达技术在昆虫高空飞行研究中的应用价值，同时为长距离扩散行为的预测提供了重要参考依据。