دانلود رایگان مقاله پیامدهای بالقوه برای کنترل بیولوژیک آفت حشرات

Abstract

Nectar-producing plants are increasingly used in agroecosystems to provide biological control agents (BCAs) such as predatory insects and parasitoids with necessary sugars to fulfil their nutritional requirements. However, it has recently been shown that nectar is commonly infested by microorganisms which may change the chemistry of the nectar and therefore its attractiveness and nutritional suitability for insects. The aim of this study was to investigate the impact of nectar-inhabiting microorganisms on nectar chemistry of three co-flowering plant species that are commonly used to provide BCAs with sugar resources (Borago officinalis L., Centaurea cyanus L. and Symphytum officinale L.). First, we assessed the abundance and visitation rate of flower-visiting insects on these plant species. Further, we identified the culturable microbes inhabiting the floral nectar and assessed changes in pH, total sugar concentration, main nectar sugars and amino acids. Flowers of all three plant species were found to be visited by a wide range of insects, with B. officinalis being the most attractive plant species for BCAs. Nectar microbial community structure differed significantly between plant species, irrespective of experimental field site. Microbial contamination affected both sugar and amino acid concentration and composition. Especially, sucrose and the fructan sugars 1-kestose and neokestose were found at significantly lower concentrations in contaminated nectar. Further, microbial contamination resulted in a significant increase of alanine and glycine, and a decrease in threonine and valine. Further research is needed to investigate the precise impact of these changes on the efficacy of biological control agents to control pest insects.

Potential implications of nectar-inhabiting microbes on BCA efficacy

We have shown that nectar microbes are able to alter nectar chemistry substantially, which in turn may affect BCA efficacy. It can therefore be expected that nectarinhabiting microorganisms play an important role in the interactions between nectar-producing plants, BCAs and pest insects. However, it remains to be investigated whether these microbe-mediated effects are either beneficiary or detrimental to the BCAs. It has been shown before that activity of specific nectar microbes may increase the palatability of nectar for pollinators (Herrera, Pozo, & Medrano, 2013; Schaeffer, Philips, Duryea, Andicoechea, & Irwin, 2014). Nevertheless, it has also been shown that particular microbes may decrease nectar attractiveness for pollinators (Vannette, Gauthier, & Fukami, 2013; Good, Gauthier, Vannette, & Fukami, 2014). Given the fact that BCAs may have a strong preference for certain sugars, or only show a feeding response when a given concentration isreached (Makatiani, Le, Olson, Wäckers, & Takasu, 2014), it can be assumed that nectars depleted in certain sugar types or sugar concentration may be less efficient to support BCAs. However, further research is needed to draw strong conclusions in this regard. Further, since amino acids are an important nitrogen source for pollinators and BCAs (Nicolson & Thornburg, 2007), any change in amino acid content can be expected to have an impact on BCA activity. In general, insects require amino acids for growth, development, and egg production. Several parasitoid species can obtain these amino acids from their larval stage, but for optimum egg production, many species should ingest them as adults, through host feeding, nectar consumption or other resources (Panizzi & Parra, 2012). Our results revealed that nectar-inhabiting microorganisms have a significant impact on the concentration of at least two essential amino acids, including threonine and valine (both decreased), while alanine and glycine both increased. However, the exact role of the different microorganisms in affecting BCA behaviour and efficacy remains unclear so far. We therefore suggest that future studies should focus on (i) the feeding behaviour of BCAs, (ii) the impact of individual microbes on the feeding behaviour of the BCAs and (iii) the impact of microbial contamination on the behaviour of the pest insects. We are convinced that a better understanding ofthe ecological role of nectar-dwelling microorganisms will lead to enhanced biological control in agricultural cropping systems.