Abstract
Insect herbivores can increase the suitability of host plants for conspecifics by inducing susceptibility. Induced susceptibility can be separated into feeding facilitation, whereby herbivore feeding increases performance of conspecifics regardless of the genotype of the herbivore or plant, and obviation of resistance, whereby feeding by a virulent herbivore increases performance of avirulent conspecifics on resistant plants. Both forms occur between Aphis glycines (Hemiptera: Aphididae) and soybean. In natural and agricultural settings, A. glycines populations can colonize plants for brief periods before emigrating or being removed due to predation or insecticides. It is unclear if induced susceptibility lasts beyond the period when A. glycines are present on the plant. We measured the duration of induced susceptibility in the A. glycines-soybean system within a growth chamber by removing inducer populations after 24 h. We used an A. glycines-resistant soybean infested with an inducer population of either virulent, avirulent, or no aphids. Response populations of either virulent or avirulent aphids were added at three post-infestation times (24, 120, 216 h) and their densities measured 11 days after infestation. Feeding facilitation was lost within 24 h of the removal of avirulent inducer populations, and obviation of resistance diminished over time and was completely lost within 216 h of the removal of the virulent inducer populations. We discuss how these results support a hypothesis that virulence in A. glycines is due to effector proteins secreted by feeding aphids. We suggest that the duration of induced susceptibility may impact the durability of A. glycines resistance in soybean.
Highlights
Insect herbivores can directly or indirectly alter the suitability of a host plant for both conspecifics and heterospecifics (Karban and Myers 1989)
Induced susceptibility can be separated into feeding facilitation, whereby herbivore feeding increases performance of conspecifics regardless of the genotype of the herbivore or plant, and obviation of resistance, whereby feeding by a virulent herbivore increases performance of avirulent conspecifics on resistant plants
Feeding facilitation was lost within 24 h of the removal of avirulent inducer populations, and obviation of resistance diminished over time and was completely lost within 216 h of the removal
Summary
Insect herbivores can directly or indirectly alter the suitability of a host plant for both conspecifics and heterospecifics (Karban and Myers 1989) Such alterations of host plants can be categorized as either negative (e.g., induced resistance) or positive (e.g., induced susceptibility) for subsequent herbivores (Karban and Myers 1989; Price et al 2011). These herbivore-induced effects in plants may affect initial herbivore survival, fecundity, and/or preference for the host plant, and they may affect subsequent conspecific or heterospecific herbivore populations (Karban and Baldwin 1997; Price et al 2011). Some potential causes of induced effects include physical contact, chemical cues, plant viruses, insect endosymbionts, or insect proteins (Schoonhoven et al 2005; Oliver et al 2010; Casteel and Jander 2013; Pitino and Hogenhout 2013)
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