Plants have a variety of defense mechanisms that are often induced following attacks by herbivores; this benefits those plants by decreasing performance or preference of herbivores that attack the plants later. We investigated the effects of previous exposure of plants to the safflower aphid, Uroleucon carthami, cotton bollworm, Helicoverpa armigera, and mechanical wounding on subsequent safflower aphid infestations using commercial safflower (Carthamus tinctorius) cultivars and wild safflower species (C. oxyacantha). The experiments were conducted in a greenhouse with two treatments: previously induced plants via direct herbivory or mechanical wounding, and control plants that had never experienced herbivory. To test the performance of safflower aphid on different plant treatments, five unwinged aphids were placed on each plant and allowed to reproduce for 14 days. Finally, the total numbers of aphids on each plant were counted and the percentage of produced winged individuals was calculated. The number of aphids on plants that were previously infested or injured was significantly lower than in control plants. Percentage of winged aphids was significantly higher on induced plants, which is an indicator for unsuitable conditions. Also, significant increase in total phenolic content and hydrogen peroxide was observed in induced plants, showing that the levels of these compounds were either treatment, cultivar and/or genotype × treatment dependent, highlighting the specificity of these interactions. Overall, among the safflower cultivars the lowest number of aphids and the highest percentage of winged aphid individuals were observed on Mahali-Isfahan cultivar and wild safflower, showing that this cultivar is more sensitive to herbivory and/or responds to it more than other cultivars. These findings could contribute to a better utilization of induced defense in the integrated pest management of safflower fields.

Organisms belonging to the green algal genera Desmodesmus and Scenedesmus are characterized by a high degree of flexibility allowing them to be true cosmopolitans and to withstand harsh conditions. The environmental conditions determine which phenotypes are being produced and one of the most dangerous situations for the algae is when the organisms are confronted with strong grazing pressure from numerous zooplankton organisms. An overview is given of several aspect of an induced defense in many non-spiny Scenedesmus and some spiny Desmodesmus that may form typical protective eight-celled colonies to avoid mortality from numerous grazers. The morphological response does seem to be linked with a herbivorous zooplankton chemical cue, rather than to a more general animal excretory product. The grazing activity of small sized grazers is reduced, but not of large Daphnia. However, arguments are given why grazing protection of colonial Scenedesmus is probably more efficient under natural than under carbon/light limited laboratory conditions. Finally, a life-history cycle of Desmodesmus and Scenedesmus is presented in which biological aspects such as the anti-grazer response and sexual reproduction are being included.