Abstract
Natural enemies of insect herbivores often use chemical cues from damaged plant tissue to find their prey. Recently, studies have explored plant mediated interactions between aboveground herbivores and belowground natural enemies. The current study explores these interactions using foliar feeding insects and soil dwelling entomopathogenic nematodes (EPNs) and specifically asks whether plant cues in the rhizosphere caused by leaf feeding herbivores affected EPN behavior.For my first of two experiments conducted for this thesis research, I used two-way choice tests to observe the response of EPNs in the rhizosphere to potato plants that were either fed upon by aphids or not, and the aphids were either viruliferous with Potato leaf roll virus (genus Polerovirus) (PLRV) or not. Thus, there were three treatments: (1) Untreated plant, (2) Plant fed upon by nonviruliferous aphids or (3) Plant fed upon by PLRV viruliferous aphids. Steinernema glaseri (Rhabditida: Steinernematidae) consistently moved toward plants which had been fed upon by nonviruliferous aphids over potatoes fed upon by viruliferous aphids. In dual choice tests using the same method, Heterorhabditis bacteriophora (Rhabditida: Heterorhabditidae) moved more towards both aphid-infested and untreated plants versus plants that had been fed upon by PLRV viruliferous aphids.
For the second experiment, I used six-way choice tests to observe the response of EPNs in the rhizosphere to potato plants sprayed with methyl jasmonate (MJ) + buffer (Tween 20 + ethanol), methyl salicylate (MS) + buffer, control (buffer), and three substrate-only (sand) arms. MJ and MS were used to simulate defense against chewing and piercing-sucking insect feeding types respectively (Filgueiras et al., 2016; Schwieger et al., 2014). This set of experiments was done to observe if a particular feeding type was more attractive to EPNs. Steinernema glaseri preferred plants treated with methyl salicylate. Heterorhabditis bacteriophora exhibited little to no preference or movement in the choice test arena when plants were the putative attractant.