<I>Rag1</I> Aphid Resistant Soybeans Alter the Movement and Distribution of Soybean Aphid (Hemiptera: Aphididae)

Abstract

Herbivorous insects often move and distribute according to the quality of the plant they are on, and this behavior could influence interactions with plants bred for herbivore resistance. However, when an insect is normally considered sedentary, less is known about the potential importance of movement. We performed experiments to determine if a resistant soybean variety alters the movement and distribution, both within and between plants, of the soybean aphid Aphis glycines Matsumura. We did this by counting apterous aphids on leaves of resistant and susceptible soybean plants across several days. In individual plant tests aphid distribution was different between susceptible and resistant soybeans. Most notably aphids on resistant plants were quickly found off the original leaf on which they were placed and were ultimately distributed throughout the resistant soybean. Aphids on susceptible plants, however, tended to stay on their initial leaf of placement. Follow up experiments indicated this was primarily because of the movement of individuals and not differential demography on various plant parts. In experiments where aphids were able to walk to an adjacent plant there appeared to be a net movement of aphids off resistant plants and on to susceptible plants. Aphid populations on susceptible plants were higher when the plant was adjacent to a resistant plant than when adjacent to another susceptible plant. The effect of resistant plants on aphid movement and distribution could lead to unintended side-effects such as greater spread of plant viruses or altered effectiveness of biological control agents.

Reduced wind strengthens top‐down control of an insect herbivore

“…Ladybeetles are mobile predators that actively search for prey (Forbes andGratton 2011, Meisner andIves 2013), whereas soybean aphids are sap-sucking herbivores and are relatively sedentary (Whalen and Harmon 2012). Thus, while foraging ladybeetles must struggle against the forces of drag and momentum on a moving substrate (Vogel 1994:50-80, 132-155), soybean aphids remain motionless and attached to the underside of leaves by their stylet.…”

The Use of Refuge in Host Plant Resistance Systems for the Control of Virulent Biotype Adaptation in the Soybean Aphid (Hemiptera: Aphididae)

“…Though block refuges maximize susceptible populations in sexual systems Gould 1998, Onstad et al 2011), it reduces the HPRÐ refuge interface, potentially limiting interplant movement of avirulent biotypes. Assuming aphids can use plant bridges within and between rows (Whalen and Harmon 2012), all HPR plants could neighbor a refuge with susceptible soybean proportions as low as 20%. In Fig.…”

“…Asexual fecundity is known to August 2014 WENGER ET AL. : A. glycines VIRULENCE MANAGEMENT be variable by Rag gene, as is the movement of avirulent aphids (Whalen and Harmon 2012). All plants within an R0S4 microcosm are susceptible, and are assumed to be of approximately equivalent suitability for feeding.…”

“…Soybean aphid biotypes are known to abandon plants to which they are avirulent (Whalen and Harmon 2012), which would beneÞt refuge-based control when avirulent aphids leave Rag soybean in favor of refuge plants. This movement may further alter the relative Þtness of soybean aphid biotypes, as they may be brought into direct competition for resources.…”

Temperature alters the interaction between a herbivore and a resistant host plant

“…This summation accounts for how many adults are on each plant and how long they lived. Previous research indicated that adult numbers on resistant and susceptible plants can differentiate over the course of hours to days (Whalen 2012). Therefore using the day 2 count allows us to take advantage of nymph data and use a time point we expect change to already be occurring.…”