The effects of drought stress and type of fertiliser on generalist and specialist herbivores and their natural enemies

Abstract

Abiotic stresses such as drought and nutrient availability can affect invertebrate herbivores feeding on plants, and potentially cascade up to impact their predators and parasitoids. Although these two factors separately been the subject of many studies, there are few tests of their combined effects in the context of pest species and their natural enemies on cultivated plants. Climate change models predict an increase in the frequency and severity of droughts, while the type and amount of fertiliser applied to crops is more under the control of growers. Understanding how these two abiotic factors may interact is key to utilising the potential of natural enemies to control pests under a future climate. To address this, a range of drought and fertiliser type treatments were applied to a model Brassica system in a factorial design, and the performance of two ubiquitous aphid species and their parasitoids was assessed. One aphid species was a specialist on Brassicas (Brevicoryne brassicae, with parasitoid Diaeretiella rapae) and the second a generalist aphid species (Myzus persicae, with parasitoid Aphidius colemani). The performance of both aphid species responded in a similar way to the treatments, and was maximised on plants growing in organic fertilisers under medium levels of drought stress. The strongest effects of drought and fertiliser cascaded up to affect parasitoids. Parasitoid performance responded in a broadly similar way to their aphid host performance in relation to fertiliser type. Some of the smaller effects of fertiliser treatments on aphid performance were not found for parasitoid performance. Aphid performance was greatest on plants under medium drought stress, but the parasitoids only responded consistently to the high drought stress treatment, on which their performance was reduced. Interactions between the drought and fertiliser did not have a large effect on aphid or parasitoid performance, compared with the strong main effects found for each treatment. These results are discussed in the context of previous and future research on the impacts of abiotic stresses on invertebrate herbivores and their natural enemies.

Plant defences for enhanced integrated pest management in tomato

“…potassium and nitrogen) and/or (bio)fertilisers for optimising the defence mechanisms of the plants (Larbat et al, 2016). Because of bottom‐up effects, modified defence volatiles and altered plant metabolism can affect tritrophic interactions (Coqueret et al, 2017; Denno et al, 2002; Han, Lavoir, Le Bot, Amiens‐Desneux, & Desneux, 2014; Shehzad, Gulzar, Staley, & Tariq, 2020). Salinity stress increases the osmotic potential, thus decreasing plant water availability, leaf dietary quality (Manaa et al, 2011; Romero‐Aranda, Soria, & Cuartero, 2001; Teklić et al, 2020) and also water availability to the larvae of herbivores.…”

Effect of Nitrogen Fertilization on the Density of the Corn Leafhopper and Its Impact on Both Disease Incidence and Natural Parasitism

“…Nitrogen (N) is a macronutrient in plants, but its excess has diverse negative environmental effects. Concerning crop pests, fertilization may in uence the plant's nutritional quality, increasing the population of herbivorous insects (Waring and Cobb 1992;Cook and Denno 1994) and could also affect the recruitment of their natural enemies (Chen et al 2010;Fallahpour et al 2019;Shehzad et al 2020). In the current scenario, the challenge is to increase yields while reducing the environmental impacts (Foley et al 2011).…”

“…In Argentina, the eggs of the vector are parasitized by 16 different species, including Mymaridae, Trichogrammatidae, Aphelinidae, and Eulophidae (Hymenoptera: Chalcidoidea) (Luft Albarracín et al 2017). It is widely recognized that plant quality can affect both the herbivore abundance and the tri-trophic levels (Tariq et al 2012;Shehzad et al 2020). In particular, parasitoids respond to volatile cues that indicate the presence of hosts (Turlings et al 1990;Coll Aráoz et al 2020).…”

Agro‐ecology and biodiversity in the Annals of Applied Biology

“…The combined effects of nutrient supply and climate change can alter interactions between herbivores and natural enemies. Shehzad, Gulzar, Staley, and Tariq (2021) assessed the effects of fertiliser type and drought treatments on two aphid species and their parasitoids on a Brassica crop system in Pakistan. Aphid performance was maximised on plants growing in organic fertiliser under medium levels of drought stress, while parasitoid performance was reduced under high drought stress.…”