Methods for independently manipulating palatability and color in small insect prey

Abstract

Understanding how the psychology of predators shapes the defenses of colorful aposematic prey has been a rich area of inquiry, with emphasis on hypothesis-driven experiments that independently manipulate color and palatability in prey to examine predator responses. Most of these studies focus on avian predators, despite calls to consider more taxonomically diverse predators. This taxonomic bias leaves gaps in our knowledge about the generalizability of current theory. Here we have adapted tools that have been successfully used with bird predators and scaled them down and tested them with smaller predators (Habronattus jumping spiders) and small insect prey (termites, milkweed bug nymphs, pinhead crickets, fruit flies). Specifically, we test (1) the application of denatonium benzoate (DB) to the surface of live termites, crickets, and fruit flies, and (2) the effectiveness of manipulating the palatability of milkweed bug nymphs through diet. We also test the effectiveness of combining these palatability manipulations with various color manipulations. Across several experiments, we confirm that our palatability manipulations are not detectable to the spiders before they attack (i.e., they do not produce aversive odors that spiders avoid), and show that unpalatable prey are indeed quickly rejected and spiders do not habituate to the taste with experience. We also investigate limitations of these techniques by assessing possible unintended effects on prey behavior and the risk of contact contamination when using DBtreated prey in experiments. While similar tools have been used to manipulate color and palatability with avian predators and relatively large insect prey, we show how these techniques can be effectively adapted for use with small invertebrate predators and prey.

Alternative responses by two species of jumping spiders to unpalatability and toxicity in prey

“…However, more work is needed to assess whether the same general findings from this study will hold up when examining other types of unpalatable prey. For example, Winsor et al (2020) recently showed that Habronattus pyrrithrix (Chamberlin, 1924) will taste and reject prey treated with the odorless bittering agent, Bitrex (denatonium benzoate). It would be useful to examine whether Phidippus would be more willing to accept Bitrex-treated prey (compared with Habronattus), as we would predict based on our findings in the present study.…”

Lack of neophobic responses to color in a jumping spider that uses color cues when foraging (Habronattus pyrrithrix)

“…We collected termites (Reticulitermes flavipes) from the Natural Area Teaching Lab at the University of Florida, Gainesville, FL, USA and maintained them in the lab for the duration of the project. We artificially colored them by painting their dorsal abdomens using enamel paint following methods previously used to study jumping spider prey color preferences [32,36,38,39] (Fig 1). For this experiment, we used three colors: blue, green and red, that were similar in brightness.…”

“…Prior research has shown that enamel paint on termites does not affect their movement rates when compared to unpainted termites [38]. We chose to use termites as prey in this study because they are palatable prey items that are readily attacked and consumed by the spiders, their colors are easy to manipulate, and they have been used successfully as prey in several previous studies with Habronattus jumping spiders [32,36,38,39].…”

“…Because our study is the first to examine color neophobia in any jumping spider, it is too soon to say how generalizable our findings may be. Future work could manipulate the size of colorful prey choices (perhaps using smaller termites or small hemipterans or flies, e.g., [32]) or other aspects of prey riskiness. In addition, manipulating other factors that affect the motivation of predators (e.g., hunger level, previous experience with defended prey, etc.)…”

“…Habronattus is a diverse genus with members that are common in a variety of habitat types across North America [30]; as such they are likely to encounter a variety of colorful and chemically-defended prey items in the field. The chemical defenses of many insects are unpalatable and/or toxic to Habronattus [e.g., [31][32][33], so it is not surprising that these spiders attend to color when foraging. What has been surprising is how similar their responses to color are to those of birds; multiple recent studies have shown that Habronattus and other jumping spiders have similar patterns of innate and learned color biases to birds [31,[34][35][36][37], similar patterns of color learning and generalization [31,35], and similar color aversions that are triggered by noxious odors [38,39].…”