Abstract
Abstract Calotropis procera is a xerophytic perennial milkweed shrub native to Asia and Africa, which currently is also widely distributed throughout the Brazilian Caatinga. C. procera is well defended against herbivores, especially with latex and toxic steroidal cardenolides. The goal of this study was to evaluate how patch size of this exotic host plant affect insect herbivory. Eight patches were selected containing a varied number of C. procera individuals (5, 8, 29, 31, 55, 79, 116, and 172 individuals/patch) in the Caatinga. Patches were divided into four categories according to the number of C. procera individuals: very small (5 and 8), small (29 and 31), intermediate (55 and 79), and large (116 and 172). The percentage of herbivory was greater in patch categories with more individuals. Among the herbivorous insects associated with C. procera, larvae of Danaus spp. (Lepidoptera: Nymphalidae) were commonly observed feeding on all patches. These herbivores present specialized behaviors to circumvent the presence of latex on the host leaves. Adult Danaus spp. females probably had higher probability to find large patches of C. procera, leaving a greater abundance of eggs and, consequently, increasing the herbivory by their larvae in these patches. In contrast to immigration tendency, emigration from large patches may be lower, because there is a higher probability of finding resources (e. g. suitable C. procera leaves) inside large patches compared with small patches. We conclude that patch size of the host plant C. procera is a major factor affecting herbivory.
Highlights
Calotropis procera is a xerophytic perennial milkweed shrub native to Asia and Africa, which currently is widely distributed throughout the Brazilian Caatinga
Plant density and patch size are important factors that can affect the abundance and diversity of insect herbivores (Root, 1973; Raupp and Denno, 1979; Kéry et al, 2001; Cassel-Lundhagen et al, 2008)
Several studies addressing the effects of host plant patch size on herbivore abundance have shown variable effects (e.g., Bach, 1988; Kareiva, 1983; Bukovinszky et al, 2010)
Summary
Calotropis procera is a xerophytic perennial milkweed shrub native to Asia and Africa, which currently is widely distributed throughout the Brazilian Caatinga. Plant density (the number of individuals of a given species that occurs within a given sample unit or study area) and patch size (the number of host plants or the geographical extent of the stand) are important factors that can affect the abundance and diversity of insect herbivores (Root, 1973; Raupp and Denno, 1979; Kéry et al, 2001; Cassel-Lundhagen et al, 2008). Several studies addressing the effects of host plant patch size on herbivore abundance have shown variable effects (e.g., Bach, 1988; Kareiva, 1983; Bukovinszky et al, 2010).
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