Fig 4 - uploaded by Claudio Bidau
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a. Pepsis formosa (Pompilidae). B. Scaphura nigra (Tettigoniidae). For color version, see Plate Xii.
Source publication
I analyzed chapter VIII of William Henry Hudson's "The Naturalist in La Plata", a popular book published in 1895. Herein the famous naturalist ornithologist and writer relates many observations made by him in his youth in a region of Buenos Aires, Argentina, accounts of a large number of natural phenomena especially pertaining to animal life. Chapt...
Citations
... Chromacris colorata (Serville 1938) is an Orthoptera considered a potential pest although might not be as specific (Marino-Pérez et al. 2011). Nymphs of the genus have gregarious habits and feed in large groups, often entirely consuming the host plant; solanaceous plants are preferred perhaps because their toxicity is associated with defense (Bidau 2012, Despland 2020. C. colorata is distributed from northeastern Mexico to Central America, including the Natural Reserve El Cielo, Sierra Madre Oriental, and Tamaulipas highland plateau (Mathieu 1970, Sánchez-Soto et al. 2019. ...
... T. eques, R. microptera) whereas others (e.g. Chromacris species) exhibit an unusual ontogenetic shift, switching to crypsis with flash-colouration as adults: the body is cryptic, but in flight the colourful hindwings appear [23,[28][29][30][31][32][33]]-see Fig 1. Adults appears to combine low contrast with background vegetation and disruptive patterns, such that they are difficult for humans to detect on vegetation [29]. Several possible scenarios could underlie this unusual ontogenetic colour change: the simplest involves an ontogenetic change in host plant use that impacts effectiveness of chemical defense (1)-indeed, several Orthopteran species are aposematic as nymphs feeding on toxic plants but become cryptic as adults when they change their diet [3]. ...
... C. psittacus adults shows no evidence of specialized defensive secretions but do regurgitate when handled (personal observation). The species is thought to be distasteful to predators [23,28,29,45]; distastefulness is more likely derived from gut-contents than from sequestered compounds [46,47], although this has not been tested. ...
... T. eques, R. microptera, native to the United States) whereas others (the Tropidacris and Chromacris spp of South America) mature into flighted adults with flash colouration. Little is known about the diet-breadth or distastefulness of the species with the latter strategy [28,43], but this table suggests that flight could be an important factor in adult defensive strategies. In general, romaleid defensive strategies appear very effective, as field studies record never witnessing even predation attempts [8,11,25,28]. ...
Traits of chemically-defended animals can change as an individual grows and matures, and both theoretical and empirical evidence favour a direction of change from crypsis to aposematism. This study examines the suite of traits involved in an unusual opposite shift from aposematism to crypsis in a neotropical toxic-plant-feeding Romaleid grasshopper, Chromacris psittacus (Gerstaecker, 1873). Field surveys, behavioural observations and a rearing experiment compare host plant choice, aggregation, locomotion and thermoregulation between life history stages. Results showed that both nymphs and adults fed exclusively on a narrow range of Solanaceae plants, suggesting that the shift in defensive syndrome is not due to a change in chemical defense. Instead, nymphal aposematism appears linked to aggregation in response to plant-based selection pressures. Slow nymphal development suggests a cost to feeding on toxic plant compounds, and grouping could mitigate this cost. Grouping also increases conspicuousness, and hence can favour warning colourating in chemically-defended insects. The role of diet breadth in aposematism is poorly understood, and these results suggest how constraints imposed by feeding on toxic plants can generate bottom-up selection pressures shaping the adaptive suites of traits of chemically-defended animals.
