Influence of induced resistance in soybean on the development and nutrition of the soybean looper and the Mexican bean beetle

Abstract

Standard gravimetric technique was used to assess the effect of induced resistance in soybean on the consumption and utilization of food by the Mexican bean beetle (MBB), Epilachna varivestis, and the soybean looper (SBL), Pseudoplusia includens. Induced resistance had significant retarding effects on the development and growth of both SBL and MBB. SBL fed leaves of previously injured soybean plants had a 8.5% longer developmental time through the entire larval stage and a 10.4% lower pupal weight than larvae fed leaves from uninjured plants. MBB fed on leaves from previously injured plants through the first three instars had a 9.1 % longer developmental time and a 16.5% lower final weight than those fed on leaves from uninjured plants. Induced resistance showed no significant effect on total food consumed by either SBL or MBB. Nutritional indices including relative consumption rate (RCR), relative growth rate (RGR), efficiency of conversion of ingested food (ECI), approximate digestibility (AD), and efficiency of conversion of digested food (ECD) were calculated on dry weight measurements. In general, induced resistance had greater impacts on the performance of MBB than on that of SBL. Résumé Influence de la résistance induite chez le soja sur le développement et l'alimentation de Pseudoplusia includens et Epilachna varivestis Une technique gravimétrique uniforme a été utilisée pour mesurer l'effet de la résistance induite du soja et la consommation et l'utilisation d'aliments par E. varivestis (Coléop.: Coccinellidae) et P. includens (Lepid.: Noctuidae). La résistance induite a significativement retardé la croissance et le développement des 2 insectes. La consommation de feuilles déjà abîmées a prolongé de 8.5% la durée du développement de P. includens et a réduit de 10.4% le poids des chrysalides. La consommation de feuilles de soja abîmées pendant les 3 premiers stades d'E. varivestis a prolongé le développement de 9.1% et a réduit de 16.5% le poids des nymphes. La résistance induite n'a pas provoqué une modification significative de la quantité de feuilles de soja abîmées chez les 2 insectes. Les indices de nutrition, comprenant le taux de consommation relative (RCR), le taux de croissance relative (RGR), l'efficacité de transformation de l'aliment ingéré (ECI), la digestibilité approchée (AD) et l'efficacité de conversion de l'aliment digéré (ECD), ont été calculés à partir des poids secs. En général, la résistance induite a eu des effets plus nets sur les performances d'E. varivestis que de P. includens.

Bioassay versus chemical assay: measuring the impact of induced and constitutive resistance on herbivores in the field

“…Induced resistance in soybeans has been measured in previous studies both by bioassay and by tracking increases in various substances, including PIs, after damage (e.g., Kraemer et al 1987;Lin and Kogan 1990;Bi et al 1994;Botella et al 1996;Underwood 1998). In this study we focus on cystein PIs because they are known to inhibit the digestive enzymes of several beetle species (Hines et al 1991;Zhao et al 1996), and thus might be likely to affect Mexican bean beetles.…”

“…Much is now understood, especially for a few species such as tobacco, tomato and soybeans, about how plant chemistry can change after herbivore attack [see Karban and Baldwin (1997) for review]. Many studies have also demonstrated that previously damaged plants can lower insect preference and performance in the laboratory and field (e.g., Edwards et al 1985;Haukioja and Neuvonen 1985;Karban 1986;Lin and Kogan 1990;Bi et al 1994;Underwood 2000), and that chemicals that change after damage can inhibit insect digestion or lower performance in the laboratory (e.g., Johnson et al 1989;Bi et al 1994;Zhao et al 1996). A smaller number of theoretical and field studies indicate conditions that should favor the evolution of induced versus constitutive resistance (Adler and Karban 1994;Astrom and Lundberg 1994;Zangerl and Rutledge 1996), and suggest that induced resistance should have important consequences for herbivore populations (Rhoades 1985;EdelsteinKeshet and Rausher 1989;Underwood 1999), and for the predators of herbivores (Thaler 1999).…”

“…PIs in particular have received a large amount of attention as a potential mechanism for induced resistance in plants (Ryan 1990). It is well documented that damage to soybeans results in increased resistance to herbivores, in the form of insect preference for undamaged plants, and reduced growth and increased development time of insects on damaged plants in the laboratory (Lin and Kogan 1990;Kogan and Fischer 1991;Underwood 2000). However, much less is known about whether induced resistance in soybeans has consequences for herbivores in the field (but see Iannone 1989), and more particularly, how specific compounds such as PIs might be related to any such consequences.…”

Cross-Resistance and resistance longevity as induced by bean leaf beetle, <italic>Cerotoma trifurcata</italic> and soybean looper, <italic>Pseudoplusia includens</italic> herbivory on soybean.

“…Induction enhances soybean resistance to insects and pathogens (Lin and Kogan 1990, Dann et al, 1998, Thaler 1999. Induced responses produce volatiles that act as a direct defense against the herbivores (Karban and Baldwin 1997) and as an attractant to parasitoids in the form of indirect defense (Turlings et al 1995, Dicke andLoon 2000).…”

“…From the perspective of herbivore population dynamics, induced resistance is any change in a plant resulting from damage that imparts a negative effect on herbivores (Karban and Baldwin 1997). Insect herbivory has been shown to induce resistance in soybean plants (Lin et al, 1990b, Fischer et al, 1990, Lin and Kogan 1990) against the soybean looper, Pseudoplusia includens and the Mexican bean beetle, Epilachna varivestis.…”