Abstract
Biological pest control depends on the ability of natural enemies to find herbivore-infested plants, which is often guided by herbivore-induced plant volatiles (HIPVs). While foraging behavior of natural enemies has been extensively studied under controlled conditions, little is known on how odor-guided foraging behavior is influenced by fluctuating weather conditions in the field.Here we investigated how HIPV-guided foraging of Cotesia glomerata parasitoids is influenced by prevailing weather conditions in the field. C. glomerata females were released in 5 m radius circles of cabbage plants infested with Pieris brassicae caterpillars, and host finding success and direction of foraging activity was assessed by recapturing parasitoids on the host-infested plants. Wind speed and direction, humidity, barometric pressure and temperature was recorded and related to parasitoid foraging activity. Parasitoid foraging behavior was studied in more detail by observing individually released parasitoids in 0.5 m circles with host-infested cabbages.Recapture rates and movement direction of parasitoids was influenced by an interaction between humidity, wind speed, temperature and change in barometric pressure. High humidity and low wind speed was generally positively associated with host finding success. Direct observations of parasitoid flight behavior confirmed the influence of humidity and wind speed. Successful host finding in upwind direction was only observed at wind speeds below 3 m/s.Our study highlights the complex ways in which weather variables moderate parasitoid foraging behavior under field conditions. Since unfavorable weather conditions result in a strong reduction in parasitoid foraging efficiency, weather conditions are an important factor in the effectiveness of parasitoids as biocontrol agents.
Highlights
Insect pests can cause considerable crop losses
Recapture rates decreased with decreasing humidity and increasing wind speed and temperature, while decreasing barometric pressure resulted in low recapture rates
In this study we show that herbivore-induced plant volatiles (HIPVs)-guided upwind flights of parasitoids over 0.5 and 5 m distance only occur during favourable weather conditions and that adverse weather conditions, such as low humidity or high wind speed, strongly reduce parasitoid foraging activity and foraging success
Summary
Economic costs that arise due to yield losses and expenses for crop protection were estimated to reach 18.8 billion US$ per year alone in the USA (Losey and Vaughan, 2006). These costs accrue despite the fact that the majority of potential pest species are successfully suppressed by naturally occurring predatory insects and parasitoids. Some studies suggest that parasitoid behaviour can be influenced by weather conditions, such as changes in barometric pressure and wind speed (Steinberg et al, 1992; Fink and Völkl, 1995; Messing et al, 1997). Further insight in the way how fluctuating weather conditions influence the foraging efficiency of natural enemies
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