How do insects choose flowers? A review of multi‐attribute flower choice and decoy effects in flower‐visiting insects

Abstract

1. Understanding why animals (including humans) choose one thing over another is one of the key questions underlying the fields of behavioural ecology, behavioural economics and psychology. Most traditional studies of food choice in animals focus on simple, single-attribute decision tasks. However, animals in the wild are often faced with multi-attribute choice tasks where options in the choice set vary across multiple dimensions. Multi-attribute decision-making is particularly relevant for flower-visiting insects faced with deciding between flowers that may differ in reward attributes such as sugar concentration, nectar volume and pollen composition as well as non-rewarding attributes such as colour, symmetry and odour. How do flower-visiting insects deal with complex multi-attribute decision tasks? 2. Here we review and synthesise research on the decision strategies used by flowervisiting insects when making multi-attribute decisions. In particular, we review how different types of foraging frameworks (classic optimal foraging theory, nutritional ecology, heuristics) conceptualise multi-attribute choice and we discuss how phenomena such as innate preferences, flower constancy and context dependence influence our understanding of flower choice. 3. We find that multi-attribute decision-making is a complex process that can be influenced by innate preferences, flower constancy, the composition of the choice set and economic reward value. We argue that to understand and predict flower choice in flower-visiting insects, we need to move beyond simplified choice sets towards a view of multi-attribute choice which integrates the role of non-rewarding attributes and which includes flower constancy, innate preferences and context dependence. We further caution that behavioural experiments need to consider the possibility of context dependence in the design and interpretation of preference experiments. 4. We conclude with a discussion of outstanding questions for future research. We also present a conceptual framework that incorporates the multiple dimensions of choice behaviour.

Climate Change–Induced Stress Reduce Quantity and Alter Composition of Nectar and Pollen From a Bee-Pollinated Species (Borago officinalis, Boraginaceae)

“…For example, a temperature increase of 8 • C (22-30 • C) reduced the amount of pollen produced by about 30-50% in Glycine max (Koti et al, 2005). According to the optimal foraging theory, reduced floral resource quantity per flower increases the visitation cost for pollinators, since they have to visit a greater number of flowers to obtain the same amount of resources (MacArthur and Pianka, 1966;Latty and Trueblood, 2020). The availability of floral resources is a major limiting factor for bee survival (Vaudo et al, 2015;Carvell et al, 2017;Abrahamczyk et al, 2020).…”

Growing and Flowering in a Changing Climate: Effects of Higher Temperatures and Drought Stress on the Bee-Pollinated Species Impatiens glandulifera Royle

“…In temperate regions, temperature rise and drought stresses are more likely to affect plants simultaneously during the Spring and Summer seasons, which are crucial periods for plant–pollinator interactions. Entomophilous plants attract pollinators with their floral traits and resources (nectar and pollen) to ensure pollination [ 4 , 5 ]. Bees rely exclusively on these floral resources as their food sources.…”

Warm Temperatures Reduce Flower Attractiveness and Bumblebee Foraging

“…The cost of foraging (e.g., ratio between energy use and energy intake during foraging, [67]) on plants grown at 26 • C might be higher than that of foraging on plants grown at 21 • C in our experiment as each bumblebee could collect maximum 50% less sugar at 26 • C despite spending the same amount of time per flower. Furthermore, pollinators, especially those depending on flower resources as their sole food source, are threatened when these resources decrease in response to a rise in temperature.…”

“…Shorter main flowering stems may also reduce the number of visits, since taller plants may be more attractive and visible to pollinators [17,65], although we did not observe more visits to the taller plants grown at 26 • C, which were not particularly more conspicuous than plants grown at 21 • C. Taken together, our results suggest that flowers from plants grown at 26 • C were less attractive to pollinators than flowers from plants grown at 21 • C, even though the changes in signals are contradictory (e.g., a larger floral area enhanced flower attractiveness at 21 • C, although the shorter plants grown at 21ºC are thought to be less attractive). When faced with complex choices with contradictory signals, bees tend to simplify the decision by ignoring some information and focusing on a single signal [66,67].…”