J Ethol (2005) 23:133–138 © Japan Ethological Society and Springer-Verlag Tokyo 2005 DOI 10.1007/s10164-004-0138-y Springer-VerlagTokyohttp://www.springer.de101640289-07711439-5444Journal of EthologyJ EtholLifeSciences13810.1007/s10164-004-0138-y Egg cannibalism in Ascia monuste in the field; opportunistic, preferential and very frequent ARTICLE Received: November 10, 2003 / Accepted: November 14, 2004 / Published online: February 25, 2005 Helen C. H. Barros-Bellanda • Fernando S. Zucoloto H.C.H. Barros-Bellanda · F.S. Zucoloto (*) Department of Biology (FFCL-RP), University of São Paulo (USP), Av. Bandeirantes, 3900, 14049-901 Ribeirão Preto, São Paulo, Brazil e-mail: zucoloto@ffclrp.usp.br Abstract Newly hatched caterpillars of the specialist her- bivorous species Ascia monuste (Lepidoptera, Pieridae) feed on egg chorion before ingesting plant material. They also ingest their exoskeletons and perform egg cannibalism in both the field and the laboratory. Females lay eggs on plants which already have conspecifics (eggs and/or cater- pillars) leading to the observation of cannibalism in the field. Two favorable conditions are required for such an occurrence: (1) eggs laid close together on the same leaf, and (2) the finding by older caterpillars of eggs on the same plant. Oviposition preference experiments in cages showed that females do not avoid laying on plants with eggs. How- ever, they do avoid laying eggs on plants predated by cat- erpillars. All instars perform cannibalism in the field and, in addition to this, the ingested eggs are healthy and cannibal- ism occurs in the presence of abundant food. The ingestion of eggs from their own clutch was more intense when the clutch was large. Contact with eggs is also important for cannibalism. Caterpillars ingested healthy eggs during three successive days. According to the results, it is possible to state that egg cannibalism in A. monuste is opportunistic, preferential and highly frequent and that there is a toler- ance to a diet based on animal protein in this species. Since A. monuste obtains nutrients from both animal and vegeta- ble resources, it is probably better to consider it as oppor- tunistic omnivorous. Key words Ascia monuste · Cannibalism · Egg- distribution · Opportunistic omnivory · Pieridae Introduction Intraspecific predation, the process of both killing and eat- ing an individual of the same species, is a significant and widespread process. It is a major factor in the biology of many species which can influence population structure, life history, competition for mates and resources, and behavior (Polis 1981). Cannibalism is usually restricted to relatively vulnerable life phases, such as those of pupae, newly hatched larvae and eggs (Dong and Polis 1992; Hodek and Honek 1996; Dixon 2000), and it has been regarded as a behavior that is more usual in the following, among others: predatory and generalist insects (Bernays 1998), situations with few and/ or with low quality resources, confined spaces, high quantity of vulnerable conspecifics, or presence of weak individuals (Polis 1981; Michaud 2003). Cannibalism can originate, for example, from the low nutrient content of vegetable tissues and/or from the influ- ence of competition. This behavior can improve the insects’ performance or, alternatively, it may not have a positive effect on it. However, it could also harm such animals, since herbivores do not have adequate morphology or physiology for the digestion of animal matter (Whitman et al. 1994). Many species of larval Lepidoptera frequently engage in cannibalism (Schweitzer 1979; Joyner and Gould 1985; Pierce 1995; Reed et al. 1996; Boots 1998). Ascia monuste (Godart) (Lepidoptera, Pieridae) cater- pillars are specialized feeders on plants of the Brassicaceae family. Newly hatched caterpillars (NHC) feed on egg chorion before ingesting plant material and such behavior leads to a positive effect on the insects’ performance, gen- erating a confirmed nutritional advantage for those individ- uals (Barros-Bellanda and Zucoloto 2001). In addition, it has been observed that caterpillars ingest their own exosk- eleton and also that they perform egg cannibalism in both field conditions and the laboratory. Egg cannibalism seems to be a frequent behavior by the caterpillars in this species in the field. It is believed that cannibalism occurs: (1) because females frequently lay large numbers of eggs in the field, i.e. more than 60 eggs (H.C.H. Barros-Bellanda, personal observation), (2) because females sometimes lay eggs on plants which already have caterpillars and other eggs, (3) because 90% of the newly hatched caterpillars ingest their egg chorion (Barros-