Regulation of ants' foraging to resource productivity

Abstract

We investigate the behavioural rule used by ant societies to adjust their foraging response to the honeydew productivity of aphids. When a scout finds a single food source, the decision to lay a recruitment trail is an all-or-none response based on the opportunity for this scout to ingest a desired volume acting as a threshold. Here, we demonstrate, through experimental and theoretical approaches, the generic value of this recruitment rule that remains valid when ants have to forage on multiple small sugar feeders to reach their desired volume. Moreover, our experiments show that when ants decide to recruit nest-mates they lay trail marks of equal intensity, whatever the number of food sources visited. A model based on the 'desired volume' rule of recruitment as well as on experimentally validated parameter values was built to investigate how ant societies adjust their foraging response to the honeydew productivity profile of aphids. Simulations predict that, with such recruiting rules, the percentage of recruiting ants is directly related to the total production of honeydew. Moreover, an optimal number of foragers exists that maximizes the strength of recruitment, this number being linearly related to the total production of honeydew by the aphid colony. The 'desired volume' recruitment rule that should be generic for all ant species is enough to explain how ants optimize trail recruitment and select aphid colonies or other liquid food resources according to their productivity profile.

Starvation drives a threshold triggering communication

“…Previous studies (Mailleux et al, 2000;Mailleux et al, 2003;Mailleux et al, 2005) provided evidence for the 'rule of thumb' used by foragers to assess the volume of single or multiple food sources in which the ability of scouts to ingest their own desired volume plays a key role. Ants' trail-laying behaviour is under the control of a threshold response (the desired volume) triggered by an internal stimulus (the ingested volume).…”

“…Starvation drives communication threshold volume acts as a response threshold that determines the proportion of trail-laying individuals among returning ants who will spread information about food discovery through the ant colony. Collective regulation of foraging results from the interplay between the distribution of these desired volume thresholds among colony members and the food volume available (Mailleux et al, 2003).…”

Factors affecting the biological control of California red scale Aonidiella aurantii (Hemiptera: Diaspididae) by Aphytis (Hymenoptera: Aphelinidae) in eastern Spain citrus: host size, ant activity, and adult parasitoid food sources

“…We considered the number of ants per honeydew source (absolute antattendance) as a measure of potential honeydew preference because ants respond more intensively to a more profitable source (see Mailleux et al, 2003). Also, the number of attending ants divided by the number of hemipterans per honeydew source (relative ant-attendance) was calculated because the effectiveness of ant protection varies with hemipteran density (Itioka and Inoue, 1996;Harmon and Andow, 2007).…”

“…Degen and Gersani (1989) reported that for weaver ants fresh matter honeydew collection is minimum during the hottest part of the day because of water evaporation from honeydew and maximum in the morning and night. Thus, considering that the number of foraging ants is directly related with the honeydew production (Mailleux et al, 2003) the maximum of fresh honeydew in combination with air temperature could be the reason why L. grandis is more active at the beginning of the night in citrus canopies. Although P. pallidula is not so strictly dependent on hemipteran honeydew because of its omnivorous diet (Detrain, 1990;Retana et al, 1992;Cerdá et al, 1997), its daily activity pattern on the canopies, where honeydew is the main food source, might also be attributed to a strategy for maximizing honeydew collection.…”

“…However, the temporal and spatial interspecific interactions as well as the feeding sources of ants on citrus canopies remain unclear. What it is known from other systems is that seasonal changes in honeydew demand (Sudd and Sudd, 1985) as well as the quantity and quality of honeydew (Völkl et al, 1999, Mailleux et al, 2003 may influence ant activity and behavior.…”