Bottom-up Effects on Tri-trophic Interactions: Plant Fertilization Enhances the Fitness of a Primary Parasitoid Mediated by Its Herbivore Host

Abstract

Plants play a pivotal role in interactions involving herbivores and their natural enemies. Variation in plant primary and secondary metabolites not only affects herbivores but, directly and indirectly, also their natural enemies. Here, we used a commercial NPK fertilizer to test the impact of three fertilizer, namely 50, 100, and 200 ppm nitrogen, and one control (i.e., water) treatments, on the weight of the nymphs of the whitefly Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae). Subsequently, the whitefly parasitoid Eretmocerus mundus Mercet (Hymenoptera: Aphelinidae) was reared on the different groups of whitefly nymphs and upon parasitoid emergence, the number of oocytes was determined as a measure of reproductive capacity. Trials were done on tomato and tobacco plants. The level of nitrogen concentration in tobacco leaves was directly correlated with the fertilizer applications, thus confirming the effect of our fertilizer treatments. Both in tomato and tobacco plants, healthy as well as parasitized whitefly nymphs, were heaviest in the 200 ppm nitrogen treatment. The highest number of oocytes per female parasitoid was recorded in the 200 ppm nitrogen treatment in tomato (31% more oocytes as compared with the control) and in the 100 and 200 ppm nitrogen treatments in tobacco (200% more oocytes). We suggest that the increase in oocytes was the result of the enhanced size (food quantity) and/or nutritional quality of the whitefly host. The practical implications of these results for the mass rearing of whitefly parasitoids and for biological pest control are discussed.

Conservation of Non-Pest Whiteflies and Natural Enemies of the Cabbage Whitefly Aleyrodes proletella on Perennial Plants for Use in Non-Crop Habitats

“…Soil analyses at both locations revealed that the soil in Hannover lacked nitrogen (N), potassium (K), and magnesium (Mg) resulting in generally larger and more vital plants in Sarstedt. Therefore, the plants in Sarstedt represented a qualitatively and quantitatively better nutritional source and thus may have benefited both, A. lonicerae and its parasitoid E. tricolor [ 36 ]. Next to plant nutrition, local differences in climatic parameters (e.g., on average 7°C warmer and in total 87 mm more precipitation in Hannover compared to Sarstedt during the entire experimental period), vegetation or additional food sources are further potential factors that could have influenced the abundances and colonization with herbivores and natural enemies at the two locations.…”

Ecology and biology of the parasitoid Trechnites insidiosus and its potential for biological control of pear psyllids

“…48 It is also well known that using high levels of fertilizers on plants has an indirect positive impact on phytophagous insect fitness traits, 97,98 as well on upper trophic level species. 99 Therefore, reducing excessive plant growth and avoiding intensive fertilizers could help manage C. pyri on pear trees. 3 Then, orchard management could focus on improving the survival and population growth of the set of natural enemies of pear psylla.…”

Silicon fertilisation affects morphological and immune defences of an insect pest and enhances plant compensatory growth

“…bottom-up effects) (Singer and Stireman 2005;Vidal and Murphy 2018). Changes in performance and fitness can impact the anti-predator defences of insect herbivores, which in turn can affect their vulnerability to natural enemies such as predators and parasitoids (top-down forces) (Forkner and Hunter 2000;Pekas and Wäckers 2020). For example, feeding on high-quality host plants can enhance insect immune defences such as encapsulation and melanisation of invaders (i.e.…”