Team:KU Leuven/Project/Ecological/wetlab

In order to validate the BanAphids' model, we decided to investigate the effect of the two substances, E-beta-farnesene (EBF) and Methyl Salicylate (MeS) on aphids. Once we started our project, we noticed that we were not the only ones approaching this agricultural problem from this angle. Research groups like Rothamsted are currently investigating the use of EBF to repel aphids as well but in the form of GM crops. We also found that other areas of the industry were also interested in our project such as Biobest, worldwide leader in sustainable crop protection and pcfruit whose mission is to research prospects for biological fruit growing, new crop protection methods, etc. We were invited to perform our insect experiments at Biobest and pcfruit to validate the BanAphids model. We attempted to determine the working concentrations of our two substances in pure form and to examine the preference of aphids and their predators under different conditions and environments. With the data we have collected so far, we can observe that these two substances indeed do have an effect on aphids.

Aphids

Aphids are small, soft-bodied insects that feed on sap from leaves, twigs, or roots. Adult aphids exist in two forms, winged or wingless. They are most common in spring and summer. Under ideal temperatures, many aphid species can complete their life cycle in less than 2 weeks, and because of their prolific reproductive capacity, enormous populations of aphids can build up in a short time.
It is commonly known that when insects damage plants, these plants respond by emitting a range of volatile organic compounds (VOCs) (Blande et al., 2010). Damage caused by chewing herbivores releases a different profile of VOCs than damage by aphid feeding (piercing sucking insects) (Leitner et al., 2005). Blande et al. identified MeS as the most distinctive indicator of aphid feeding in the VOC emission profile. A significant increase in MeS VOC emission was detected from aphid infested plants as well as a significant time effect, meaning that MeS emission intensity increased with the length of the aphid infestation. The effect of aphid feeding on a plant’s MeS induction is immense, even though the feeding pressure due to aphids must exceed a threshold level before inducing volatile emissions. MeS comprises almost two-thirds of the total emission, even after 21 days of aphid feeding, compared to a negligible emission from control plants (Blande et al., 2010).
MeS is an important compound of a plant’s defence mechanisms acting both as an aphid repellent (Glinwood and Pettersson, 2000) and an attractor of natural predators and parasitoids of aphids (Zhu and Park, 2005). In field trials, MeS successfully reduced initial colonisation of cereals by bird cherry-oat aphids (Rhopalosiphum padi) migrants (Pettersson et al., 1994). R. padi alternate between a winter host, bird cherry Prunus padus tree and a summer host, cereals, by means of winged aphid migrants(Pettersson et al., 1994). With this and following studies, it has been shown that the principal mode of action against aphids is repellency, which is what we want to achieve with MeS and EBF. The behavioural response of aphids to these substances is increased mobility, reduced reproductive efficiency and increased mortality of adults. An aphid’s response however, appears to be dynamic, losing their negative response to MeS after three or four days of adult life (Glinwood and Pettersson, 1999).
A further study showed that application of MeS significantly reduced the mean aphid numbers in cereal crops by 25-50% (Ninkovic et al., 2003). The immigration and settling of R. padi in barley fields was delayed due to MeS application as well as a significant reduction in maximum aphid densities. Preference tests however showed that the effect of MeS on settling of R. padi on barley decreases with increasing plant age, demonstrating yet again the dynamicity of aphid behavioural responses (Ninkovic et al., 2003).