Although it is well known that insects are sensitive to temperature, how they will be affected by ongoing global warming remains uncertain because these responses are multifaceted and ecologically complex. We reviewed the effects of climate warming on 31 globally important phytophagous (plant‐eating) insect pests to determine whether general trends in their responses to warming were detectable. We included four response categories (range expansion, life history, population dynamics, and trophic interactions) in this assessment. For the majority of these species, we identified at least one response to warming that affects the severity of the threat they pose as pests. Among these insect species, 41% showed responses expected to lead to increased pest damage, whereas only 4% exhibited responses consistent with reduced effects; notably, most of these species (55%) demonstrated mixed responses. This means that the severity of a given insect pest may both increase and decrease with ongoing climate warming. Overall, our analysis indicated that anticipating the effects of climate warming on phytophagous insect pests is far from straightforward. Rather, efforts to mitigate the undesirable effects of warming on insect pests must include a better understanding of how individual species will respond, and the complex ecological mechanisms underlying their responses.
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A hypothesis is put forward that the long-lasting inducible responses of trees to herbivores, particularly lepidopteran defoliators, may not be active defensive responses, but a by-product of mechanisms which rearrange the plant carbon/nutrient balance in response to nutrient stress caused by defoliation. When defoliation removes the foliage nutrients of trees growing in nutrient-poor soils, it increases nutrient stress wich in turn results in a high production of carbon-based allelochemicals. The excess of carbon that cannot be diverted to growth due to nutrient stress is diverted to the production of plant secondary metabolites. The level of carbon-based secondary substances decays gradually depending on the rate at which nutrient stress is relaxed after defoliation. In nutrient-poor soils and in plant species with slow compensatory nutrient uptake rates the responses induced by defoliation can have relaxation times of several years. The changes in leaf nitrogen and phenolic content of mountain birch support this nutrient stress hypothesis. Defoliation reduces leaf nitrogen content while phenolic content increases. These responses of mountain birch to defoliation are relaxed within 3-4 years.
JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.Wiley is collaborating with JSTOR to digitize, preserve and extend access to Ecology Abstract. The long-term increase in foliage resistance of white birch subjected to artificial defoliation, which has been previously documented, may be a defensive response against leaf predators, or it may be a passive deterioration in foliage quality due to lost nutrients. We tested these hypotheses by two experiments in which foliage quality was assayed by the growth response of a geometrid caterpillar that is the tree's major herbivore in our area. Fertilization of the soil around defoliated trees did not eliminate the change in foliage quality caused by mechanical damage, contrary to the prediction of the nutrient-stress hypothesis. Another result consistent with the defensive hypothesis was that insect damage was a more effective inducer of changes in birch foliage than mechanical damage was. Artificial defoliation was an effective inducer in a nutrient-poor but not in a nutrientrich site; this result can be explained by either of the two hypotheses.
Abstract. 1. The parasitic wasp family Ichneumonidae (Hymenoptera) is of great interest because it has been claimed that its species richness does not increase with decreasing latitude. 2. No extensive studies of the family have been conducted in South American localities. 3. Arthropods were sampled using 27 Malaise traps in the Allpahuayo–Mishana National Reserve (56 000 ha) in the north‐eastern Peruvian Amazonian lowland rainforest. The total duration of the sampling programme was 185 Malaise trap months. 4. Altogether, 88 species were collected. This is one of the highest local pimpline and rhyssine species numbers ever recorded. A comparison with results from Mesoamerica revealed that at equal numbers of individuals sampled, the number of Pimplinae and Rhyssinae species in Peruvian Amazonia is at least twofold compared with lowland locations in Mesoamerica and somewhat higher than in the most species‐rich Costa Rican higher altitude localities. 5. Non‐parametric methods of estimating species richness were applied. These suggest that additional sampling would yield a considerable number of new Pimplinae and/or Rhyssinae species.
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