Effects Of Induced Responses Research Articles

Methyl jasmonate induced responses in four plant species and its effect on Spodoptera litura Fab. performance

Defensive proteins, such as polyphenol oxidase (PPO) and trypsin inhibitor (TI), are induced by herbivore wounding and exogenous methyl jasmonate application in various plant species. This study was conducted to measure induction of PPO and TI in radish, sweet pepper, tomato, and water spinach plants following herbivore wounding (I), methyl jasmonate application (M), and a combination of the two treatments (M + I). The effect of induced responses was also examined against third instar Spodoptera litura Fab. PPO activity was induced in radish by treatment I only; in sweet pepper, by treatments I and M; in tomato, by treatments I, M, and M + I; and in water spinach, by treatments M and M + I. The activity of TI was enhanced 1.2–1.4-fold in radish, sweet pepper, and tomato by M and M + I treatments, whereas in water spinach, it was enhanced 1.2-fold by all 3 treatments. The relative growth rate (RGR) of S. litura was reduced by 53% on radish plants following M treatment only. It was reduced by 37% and 42% on sweet paper plants following M and M + I treatment, respectively. RGR was significantly reduced on test tomato plants following I, M, and M + I treatments. The RGR of S. litura was unaffected on water spinach plants following any treatment. Collectively, the results of this study indicated that induction of plant defensive proteins in response to S. litura feeding or exogenous methyl jasmonate application varied among plant species, which further affected the induced plant resistance to the caterpillars.

Herbivore‐induced responses and patch heterogeneity affect abundance of arthropods on plants

Abstract. 1. Plants respond to herbivore damage by inducing defences that can affect the abundance of herbivores and predators. These tritrophic interactions may be influenced by heterogeneity in plant neighbourhood.2. In the present study, the effects of induced responses on the abundance of herbivores (flea beetles and aphids), omnivores (pirate bugs and thrips), and predators (lady beetles and spiders) on individual plants and their neighbours between and within patches composed of three tomato plants was investigated.3. Herbivore damage was manipulated to create homogeneous patches where either all or none of the plants had defences induced by herbivore damage, and heterogeneous patches where only one of the plants was induced.4. Arthropod abundance on plants at different scales was compared by testing between patch effects (patch level), for neighbourhood effects at the plant phenotype level (neighbourhood level), and between near and far plants (within patch position).5.At the patch level, plants in homogeneously induced patches contained fewer flea beetles and pirate bugs, but more lady beetles, compared with homogeneously non‐induced patches. There was no effect of patch type on the abundance of aphids, thrips, and spiders on plants.6.At the neighbourhood level, induced plants in heterogeneous patches contained more flea beetles and pirate bugs compared with induced plants in homogeneous patches, indicating that the abundance of some herbivores and omnivores on induced plants varied depending on the phenotype of the other plants within the patch. Within patch position, there was no evidence that the abundance of herbivores or predators on non‐induced plants was affected by proximity to an induced plant.7. Therefore, variation in plant neighbourhood generated by induced plant responses affected the abundance of three arthropods from three feeding guilds.

Induced defences in the neotropical tree Bauhinia brevipes (Vog.) to herbivory: effects of damage-induced changes on leaf quality and insect attack

Induced defences to herbivory are physical, nutritional, and allelochemical traits that change in plants following damage or stress, and that reduce the performance and/or preference of herbivores. The aim of this study was to verify the occurrence and effect of induced responses in Bauhinia brevipes (Vog.) (Leguminosae) which defend it against herbivores, through the manipulation of its leaves, and their effects on herbivore foraging behaviour. We selected 15 plants in the field, and three shoots per plant were subjected to one of three treatments: (1) damaged shoots (simulation of the main types of foliar herbivory and insect exclusion); (2) damaged control shoots (insect exclusion); and (3) control shoots (not manipulated). Water and nitrogen content, tannin concentration, levels of herbivory, and shoot growth rates were compared among treatments. Leaf quality varied among treatments. Damaged leaves showed higher tannin concentration, and lower water and nitrogen content compared to undamaged leaves. On the other hand, they experienced higher rates of herbivory than leaves on control shoots. Moreover, shoots that were experimentally induced showed a higher increase in final shoot length. These results suggest that simulated herbivory on B. brevipes reduced the nutritional quality of its leaves and increased the amount of secondary compounds, therefore altering insect herbivore attack and increasing shoot performance.

Within‐plant distribution of Rhopalosiphum padi on wheat seedlings is affected by induced responses

Cereal aphids have distinct patterns of occupation of plants, both in spatial and temporal terms (Dean, 1974). The preferred feeding site of the bird cherry-oat aphid, Rhopalosiphum padi (L.), on cereal seedlings is the stem base and lower leaves (Dean, 1974; Leather & Lehti, 1982), and this holds for both field and laboratory observations (Wiktelius, 1987). Previous works discussing this pattern of within-plant distribution have considered factors such as nutritional value of the tissues (Leather & Dixon, 1981; Weibull, 1987; Wiktelius, 1987; Wiktelius et al., 1990) and avoidance of extreme temperatures in the field (Wiktelius, 1987). Plant quality for herbivorous insects can decrease after feeding, due to induced responses of the plant (reviewed in Karban & Baldwin, 1997). Effects of induced responses on the within-plant distribution of the herbivore have also been reported (Edwards et al., 1991 and references therein). This work presents results suggesting that induced responses of wheat (Triticum aestivum L.) seedlings to aphid feeding play a role in shaping the within-plant distribution of R. padi. In particular, it compares the constitutive as well as the induced quality for the aphid of the stem (preferred site) and the third leaf (non-preferred site) of a three-leaf seedling.