Suitability of stressed and vigorous plants to various insect herbivores

Abstract

2001. Suitability of stressed and vigorous plants to various insect herbivores. -Oikos 94: 228 -235.We conducted a controlled experiment to test the plant vigor and the plant stress hypotheses. The two hypotheses associate plant physiological conditions to insect feeding mode and performance. We exposed tomato, Lycopersicon esculentum, to different types of growing conditions: optimal (vigorous plants), resource based stress (water and/or nutrient deficit), and physical stress (punched hole in terminal leaflets). Plant performance, foliar nutritional value for insects and chemical defenses were analyzed after 14 d. These plants were offered to insects belonging to distinct feeding guilds: the silverleaf whitefly, Bemisia argentifolii, a phloem feeder; the leafminer, Liriomyza trifolii; and the corn earworm, Heliothis zea, a leaf chewing caterpillar. The experimental conditions generated a gradient of plant growth in the following order: optimal (vigorous)\control = hole punched \no fertilizer \no water \ no water and no fertilizer. The last two treatments resulted in plants with poor nutritional value (based on %water, C/N, %N) and higher levels of defensive compounds (i.e., peroxidase and total phenolics) compared with control and the vigorous plants. Hole-punching neither affected plant growth nor any of the phytochemicals measured. In a choice experiment adult whitefly ovipositioning was not affected by either vigor or punching but was reduced on the other plants (PB 0.01). Leafminer feeding and oviposition and corn earworm larval growth rates were higher on the vigorous plants and lower on the punched, no fertilizer, no water, and no water and no fertilizer host plants (P B0.01). Regardless of insect species or bioassay method, the results in the tomato system support the plant vigor hypothesis that predicts positive association between insect performance and plant growth. The results contradict the plant stress hypothesis that rank stressed plants as better hosts for insects. The mechanisms involved are a combination of poor nutritional value and chemical defenses. We demonstrate a negative association between plant growth and chemical defense. However, induced response triggered by hole-punching was not cost effective to the plants.

Evaluation of Different Integrated Pest Management Modules to Control Helicoverpa for Adaptation to Climate Change

“…Survival of insect is lower on stressed plants than irrigated plants (Showler and Moran, 2003) a scenario that was well shown in our study. This poor performance of bollworm may be due to reduced nitrogen availability (McMillin and Wagner, 1995) or elevated allelochemicals (Inbar et al, 2001) on stressed plants. High larval mortality of fall armyworm has also been reported on dry land soybean than on irrigated soybean (Huffman and Mueller, 1983).…”

Drought-stressed tomato plants trigger bottom-up effects on key mite pests

“…The "Plant stress hypothesis" assumes that the increase in free sugars and amino acids induced by drought stress increases the plant nutritional value, improving as consequence herbivore performance (White, 1984(White, , 2009. The "Plant VigorHypothesis" in contrast, states that the reduction in plant growth and the increase in some defense compounds induced by drought stress make the plant less suitable for herbivores (Inbar et al, 2001;Cornelissen et al, 2008). The resulting performance of phytophagous arthropods on drought-stressed plants will then depend on the balance of plant nutrients and defenses, which may vary from plant to plant, depending on the plant species and genotype and in response to the intensity and the mode of the imposition of stress (Huberty and Denno, 2004;White, 2009).…”

“…The resulting performance of phytophagous arthropods on drought-stressed plants will then depend on the balance of plant nutrients and defenses, which may vary from plant to plant, depending on the plant species and genotype and in response to the intensity and the mode of the imposition of stress (Huberty and Denno, 2004;White, 2009). For instance, different tomato cultivars and different drought stress levels have positive, negative or no-effect on the aphid Macrosiphum euphrobiae (Rivelli et al, 2013).Nevertheless, the consequences of water stressed plants are not equivalent for different feeding guilds, since in general they have positive responses for borers, negative responses for gallformers, and inconsistent responses for free-living species and leaf miners (Inbar et al, 2001;Huberty and Denno, 2004). Another important factor is the grade of specialization of the General Introduction │CHAPTER 1 23 herbivore, polyphagous species being expected to be more affected than specialists by droughtmediated alterations in plant defenses (Gutbrodt et al, 2011).…”

“…Nevertheless, the consequences of water stressed plants are not equivalent for different feeding guilds, since in general they have positive responses for borers, negative responses for gallformers, and inconsistent responses for free-living species and leaf miners (Inbar et al, 2001;Huberty and Denno, 2004). Another important factor is the grade of specialization of the General Introduction │CHAPTER 1 23 herbivore, polyphagous species being expected to be more affected than specialists by droughtmediated alterations in plant defenses (Gutbrodt et al, 2011).…”

“…Drought stress triggers both the mobilization of plant nutritional compounds (Bauer et al, 1997) and the induction of plant defenses (English-Loeb et al, 1997;Inbar et al, 2001;Hayat et al 2008) in tomato. Both scenarios are then possible in the case of drought-mediated tomato-mite interactions.…”