Abstract
The diet of entomophagous coccinellids is mainly based on aphids and other food sources such as pollen, nectar, or fungal spores. Knowledge of their foraging behavior on plants infected by powdery mildew and their survival on fungal spores is currently limited. In this study, we investigated the olfactory response of Coccinella septempunctata to odor emission of barley plants infected by powdery mildew and their survival on fungal spores in the presence or absence of aphids. Odors released by powdery-mildew infected plants were more attractive for ladybirds compared to those of uninfected controls. After 3 days, the survival rate of ladybirds feeding only on powdery-mildew spores was less than 50%, while for ladybirds feeding exclusively on Rhopalosiphum padi aphids, the survival rate was close to 90%. After 15 days, the highest survival rate (almost 80%) was observed for ladybirds feeding on plants with both aphids and powdery mildew. Molecular analyses confirmed the presence of fungal spores in ladybird guts when feeding either on powdery mildew or on a mixed diet. Our results provide new insights into foraging behavior of entomophagous coccinellids revealing the potential of powdery mildew to be utilized as important non-essential food in a mixed diet, but also its lethal effect if consumed alone.
Highlights
Coccinellids are a heterogeneous group of insects divided into three major categories according to their food preferences: zoophagous, phytophagous, and mycophagous (Giorgi et al 2009)
There was no difference in ladybird olfactory responses when they had a choice between the odor of powdery-mildew infected and aphid-infested barley plants (Wilcoxon test: Z = 0.243, P = 0.807, n = 22; Fig. 1c)
An observation of a high number of C. septempunctata ladybirds in barley fields infected by powdery mildew, but with extremely low aphid abundance, prompted us to investigate the mechanism of the high ladybird abundance implying the possibility of their survival on powdery mildew
Summary
Coccinellids are a heterogeneous group of insects divided into three major categories according to their food preferences: zoophagous (predating), phytophagous (plant eating), and mycophagous (fungus eating) (Giorgi et al 2009). Predatory ladybirds have evolved from mycophagous ladybirds that first were adapted for feeding on sooty molds, but accepted the insects that produce honeydew such as aphids (Leschen 2000). . Entomophagous coccinellid species regularly consume non-prey food such as pollen and nectar (Togni et al 2016), honeydew and plant parts (Giorgi et al 2009), and fruits and fungi (Triltsch 1997). These types of food are an important component of diets for many ladybirds as an additional source of energy and often necessary for the development (Lundgren 2009a). The importance of the presence of this type of non-prey food in ladybird diet and impact on their foraging behavior are poorly understood
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