Whorl-stage maize provides a microclimate refuge for predatory ladybeetles

Abstract

Ladybeetles are voracious predators and contribute to the in-field suppression of herbivorous pests, yet are especially vulnerable to variable climatic conditions. In this study, we surveyed the temporal dynamics of ladybeetles on maize plants (Zea mays L.) at different phenological stages within experimental plots (2010–2014) and commercial fields (2013–2014). Ladybeetle adults attained high abundance on whorl-stage maize, despite a relative scarcity of prey items (e.g., aphids, insect eggs). Field work in 2015 further revealed how ladybeetle abundance on whorl-stage maize was higher than on adjacent cotton plants – with > 88% of ladybeetle adults occurring within the maize whorl. Whorl-inhabiting adults were the most abundant at 12:00, when air temperature was the highest; abundance levels dropped at 6:00, 18:00 and 24:00 with declining ambient temperature. Within maize whorls, average temperature was 3.9 °C lower and presence of free water 50.1% higher than under ambient conditions. Hence, whorl-stage maize plants offer suitable micro-climatic conditions for foraging ladybeetles and could act as a refuge during seasonally hot or dry conditions in agro-ecosystems. Our work offers novel information on how crop diversification (i.e., addition of maize strips) can benefit in-field abundance and activity patterns of ladybeetles, and thereby eventually promote conservation biological control in agro-ecosystems of northern China.