Mixed Signal Prey

[Macedonio Heninger]

Figure1. How the simplest cases of predator eavesdropping (A) differ from prey targeting (B) is clear. In predator eavesdropping, a distant predator detects a signaling prey, and subsequently approaches, whereas in prey targeting, the predator has already detected a tight group of prey, is close to it, and now selects one individual to attack. However, other situations may be more of a blend of both processes. In (C), predator eavesdropping on a group, a distant predator approaches a group as a whole after detecting the signaling of some of its members. Hence, the signaling of some group members influences the predation risk of others; see section Signaling in Mixed-Species Groups and Aggregations for a discussion of this situation. In (D), prey targeting in a signaling group, the predator is close to or inside a group in which multiple individuals are signaling. In the widely dispersed group shown in this panel, the predator must travel a long distance to attack one prey, close to the distances traveled in predator eavesdropping. In section The Cocktail Party Effect: Is There an Auditory Analog of the Confusion Effect?, we ask if a situation such as (D) might result in a confusion effect, as occurs in the simpler case of prey targeting.

Copyright 2019 Goodale, Ruxton and Beauchamp. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

All articles published by MDPI are made immediately available worldwide under an open access license. No special permission is required to reuse all or part of the article published by MDPI, including figures and tables. For articles published under an open access Creative Common CC BY license, any part of the article may be reused without permission provided that the original article is clearly cited. For more information, please refer to

Feature papers represent the most advanced research with significant potential for high impact in the field. A Feature Paper should be a substantial original Article that involves several techniques or approaches, provides an outlook for future research directions and describes possible research applications.

Abstract: Simple SummaryBiological control of insect pests is the main alternative to the extensive application of chemicals. Mass rearing of biocontrol agents requires the development of a cost-effective diet. We evaluated the potential of using a mixed diet consisting of one low-quality (the grain moth eggs) and one high-quality (the green peach aphid) prey species as food for females of a predatory ladybird Cheilomenes propinqua. The fecundity of females fed only on the grain moth eggs was very low. Daily consumption of two aphids increased the proportion of egg-laying females and daily consumption of 10 aphids resulted in an increase in their mean fecundity. Thus, the use of a mixed diet can be considered a promising technique for mass rearing of C. propinqua, although the economic feasibility of this method would most probably require the improvement of aphid rearing system. The fecundity of C. propinqua females used for biological control of pests in greenhouses by preventing colonization and supplied with the grain moth eggs will be low but the appearance of pests will cause a proportional increase in the mean fecundity of ladybirds. AbstractIt is known that food has a double impact on females of predatory ladybirds: qualitative signal effect (the onset of oogenesis) and quantitative nutritional effect (the increase in oogenesis intensity). We compared the patterns of these effects by feeding Cheilomenes propinqua females on mixed diets: unlimited low-quality prey (eggs of the grain moth Sitotroga cerealella) and limited high-quality prey (the green peach aphid Myzus persicae: 0, 2, 10, and 50 aphids per day). About half of the females fed only on the grain moth eggs oviposited and their fecundity was very low. Daily consumption of 2 aphids increased the proportion of egg-laying females whereas only consumption of 10 aphids increased their mean fecundity. Thus, the threshold of the signal effect was lower than that of the nutritional effect. As applied to mass rearing, we conclude that the addition of high-quality prey to low-quality food causes a substantial increase in egg production, although the economic feasibility of this method is not clear. Regarding biological control of pests by preventing colonization, we conclude that the fecundity of C. propinqua females supplied with the grain moth eggs in the absence of aphids will be low but the appearance of pests will cause a proportional increase in the mean fecundity of ladybirds. Keywords: reproduction; oogenesis; fecundity; resorption; diapause; food; biological control; Cheilomenes propinqua; Sitotroga cerealella; Myzus persicae

The site is secure.

The ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Toxic prey that signal their defences to predators using conspicuous warning signals are called 'aposematic'. Predators learn about the toxic content of aposematic prey and reduce their attacks on them. However, through regulating their toxin intake, predators will include aposematic prey in their diets when the benefits of gaining the nutrients they contain outweigh the costs of ingesting the prey's toxins. Predators face a problem when managing their toxin intake: prey sharing the same warning signal often vary in their toxicities. Given that predators should avoid uncertainty when managing their toxin intake, we tested whether European starlings (Sturnus vulgaris) preferred to eat fixed-defence prey (where all prey contained a 2% quinine solution) to mixed-defence prey (where half the prey contained a 4% quinine solution and the other half contained only water). Our results support the idea that predators should be more 'risk-averse' when foraging on variably defended prey and suggest that variation in toxicity levels could be a form of defence.

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

Aposematic organisms defend themselves through various means to increase their unprofitability to predators which they advertise with conspicuous warning signals. Predators learn to avoid aposematic prey through associative learning that leads to lower predation. However, when these visual signals become unreliable (e.g., through automimicry or Batesian mimicry), predators may switch from using visual signals to taste sampling prey to choose among them. In this experiment, we tested this possibility in a field experiment where we released a total of 4800 mealworm prey in two clusters consisting of either: (i) undefended prey (injected with water) and (ii) model-mimics (injected with either quinine sulphate [models] or water [mimics]). Prey were deployed at 12 sites, with the mimic frequency of the model-mimics ranging between 0 and 1 (at 0.2 intervals). We found that taste rejection peaked at moderate mimic frequencies (0.4 and 0.6), supporting the idea that taste sampling and rejection of prey is related to signal reliability and predator uncertainty. This is the first time that taste-rejection has been shown to be related to the reliability of prey signals in a mimetic prey system.

Generally, prey within clusters were at least 1 m from other prey within the cluster and clusters were normally situated on adjacent areas on the same tree or on neighbouring trees. The reason the sub-sites were the same between days was for two main reasons. First, the predators needed to learn about the prey and the reliability of their colour signals. This is because the birds would need to become educated about the sites and prey properties. If the location of the prey changed every day, uneducated birds would have been more likely to attack the prey which would reduce the relationship between mimic frequency and taste sampling. Initially, birds would have been less educated about prey and learned about the variability in prey defences from their sampling behaviour. Therefore, clustering of prey and use of the same areas would have aided birds in learning where the prey were if they wanted to interact with them. Second, it logistically made the experiment simpler and it was easier to test for spatial autocorrelation within sites and among sites. If we changed the site every day, it would have been more difficult to account for spatial autocorrelation.

This experiment was approved by the Animal Ethics Experimental Committee of Guangxi University and the Animal Ethics Committee of the Department of Zoology at Kyoto University. The experiment complied with all laws of the countries in which it was conducted and adhered to the Animal Behavior Society/Association for the Study of Animal Behaviour regulations for the use of animals in research. This experiment also adhered to the ARRIVE guidelines.

Our experiment time was designed to minimize the effects of time of day, time of year, study site, and the effect of biases predators might have had for or against particular colours (Table S1). However, the abundance and diversity of predators might influence the attack rate and taste rejection rate22,23. Therefore, before starting the daily trials, we conducted a 5-min bird point-count to determine the assemblage of potential predators24, recording the species identity of all birds detected (seen or heard, except those in flight). The bird count was performed at the centre of a 50 m diameter circle of the study site. Bird counts were performed during the 4-day experimental stage [see21,25 for further details of bird count methods].

3a8082e126