Host-Plant-Mediated Competition Via Induced Resistance: Interactions Between Pest Herbivores On Potatoes

Abstract

Plant-mediated competition among insect herbivores occurs when one species induces changes in plant chemistry, nutrition, or morphology that render plants resistant to attack by others. We explored plant-mediated interspecific interactions between the potato leafhopper (Empoasca fabae) and the Colorado potato beetle (Leptinotarsa decemlineata), two important pests on potatoes. Leafhoppers colonize fields in advance of beetles, and thus the possibility exists that previous feeding by leafhoppers induces changes in potato plants that have adverse consequences for beetles. The consequences of leafhopper-induced resistance for beetle performance were studied in the greenhouse, field cages, and in large open-field plots. Potato plants were exposed to four densities of leafhoppers (none, low, moderate, and high), and visible feeding symptoms were measured as percentage leaf curling, chlorosis, and necrosis. The oviposition preference, performance, and survivorship of Colorado potato beetles were then measured on the four categories of induced plants in field-cage and greenhouse settings. In open field plots, survival on the four categories of induced plants was determined by placing cohorts of beetle adults onto plants and measuring the densities of resulting eggs, larvae, and emerging Fl adults. Leafhopper-induced symptoms on potato plants were density dependent, with the percentage of curled, chlorotic, and necrotic leaves increasing with leafhopper density. Previous feeding by leafhoppers adversely affected oviposition and larval performance of beetles. Fewer egg masses were deposited on plants that incurred high levels of leafhopper feeding. Similarly, larval development was delayed and emerging adult beetles weighed less when fed induced foliage from the high leafhopper-density treatment. Beetles survived less well in the field on plants experiencing moderate and high levels of leafhopper feeding as evidenced by lower densities of eggs, larvae, and emerging F1 adults. Overall, leafhoppers and beetles competed through feeding-induced changes in plant quality. Notably, the asymmetric interaction took place at a large spatial scale in open field plots and had negative consequences that persisted to the next beetle generation. Ultimately, to establish an effective management strategy for crop pests such as leafhoppers, it is essential to consider the positive indirect effects of induced resistance along with the negative direct effects on crop yield.

Leafhopper-induced plant resistance enhances predation risk in a phytophagous beetle

“…Both herbivores are foliar-feeding insects that frequently co-occur on potato (Solanum tuberosum L.) plants in the mid-Atlantic US and together inXict the vast majority of damage (>90%) from herbivorous insects in potato Welds (G. Dively, unpublished data). The annual colonization sequence of these herbivores diVers, with sap-feeding leafhoppers initially colonizing plants in early June followed by leaf-chewing potato beetles in mid-July (Lynch et al 2006). As a result, leafhoppers colonize and initiate feeding on potato plants well in advance (5-6 weeks) of beetles.…”

Web-Mediated Interspecific Competition Among Spider Mites

“…Asymmetry is a common characteristic of interspecific competition among herbivores (HuntJoshi & Blossey 2005;Lynch et al 2006;Kaplan & Denno 2007). In this case, it appears that spidermites had greater influence on whitefly behavior than vice versa.…”

“…Changes in nutrient content and increases in allelochemical concentrations in plant host quality can affect survival, reproduction, behavior, and population dynamics of co-occurring or later arriving herbivores (Gianoli 2000;Wise & Weinberg 2002;Ferrenberg & Denno 2003;Hunt-Joshi & Blossey 2005;Lynch et al 2006). We propose that reduced whitefly oviposition on spidermite-treated leaves may have been a result of perceived and/or actually reduced host quality.…”

“…Negative interactions are most often thought of as competition, which can be direct (exploitation of a common limited food resource) or indirect (mediated by the host plants, even for spatially or temporally-separated competitors (Wise & Weiberg 2002;Hunt-Joshi & Blossey 2005;Lynch et al 2006). Many studies on competition conclude that previous feeding by one species induces nutritional and allelochemical changes in the plant that adversely affect the performance of another species feeding subsequently on the same host (Petersen & Sandström 2001;Awmack & Leather 2002;Bezemer et al 2003;Denno & Kaplan 2007).…”

Plant responses to multiple herbivory : phenotypic changes and their ecological consequences

“…Plant-mediated effects on the performance of herbivores that feed on the plant successively are often, but not always (Mayer et al 2002), negative when the herbivore species belong to the same feeding guild Agrawal 2000b;Lynch et al 2006;Kaplan and Denno 2007). However, facilitation of subsequently colonising herbivores has also been observed, for example when the herbivores belong to different feeding guilds ).…”