An experimental study of the relative humidity preference and survival of the Argentine ant, Linepithema humile (Hymenoptera, Formicidae): comparisons with a native Iridomyrmex species in South Australia

Abstract

The Argentine ant, Linepithema humile (Mayr), is a widespread invasive ant species that commonly displaces native ants and other ground-dwelling invertebrates in its introduced range. Previous studies have documented a relationship between the spread of Argentine ants and abiotic conditions (particularly water availability) in invaded areas, suggesting that the invasion success of Argentine ants may be related to specific abiotic factors. This study describes the relative humidity preferences and survival of Argentine ants and a dominant native ant, Iridomyrmex 'rufoniger' sp. group, in the laboratory. In a preference experiment, Argentine ant workers showed a significantly greater propensity than Iridomyrmex to locate themselves in containers with the highest relative humidity. A series of survival trials revealed that the survival of both species was related to the relative humidities within experimental containers. The survival of Argentine ant colonies was reduced in comparison with those of Iridomyrmex sp. after 4 h, however by 24 h both species displayed similar levels of survival in all relative humidity conditions. These findings confirm a relationship between the level of available moisture and the distribution and survival of Argentine ants, and may help to account for the current distribution and invasion success of Argentine ants in Australia. Figure 2. Relative humidity (%) preferences of workers of Argentine ants and Iridomyrmex sp. over 24 h (Silica gel = 7 %, MgCl 2 = 33 %, NaCl = 75 %, KCl = 80 %, K 2 Cr 2 O 7 = > 90 % RH). Error bars show 95 % Confidence Interval of Mean

Hygropreference and brood care in the honeybee (Apis mellifera)

“…Our results diverge from similar studies conducted on some ground dwelling ant species in that honeybee workers show a preference for a humidity of approximately 75% RH and not for an extremely high humidity (90% RH, Walters and Mackay, 2003;Roces and Kleineidam, 2000;North, 1991;Potts et al, 1984). The amount of water required to saturate the brood nest at 35 8C is approximately 1.1 ml and this volume could evaporate from the abundant sources of moisture (e.g.…”

“…discontinuous gradients, absence of brood in the connecting tubes) prevent the movement of bees between chambers and the expression of a strong preference. However, using similar designs, strong hygropreference was shown for many ant species with most of the workers gathering in the chamber with the highest humidity (North, 1991;Walters and Mackay, 2003). Rather than an experimental artefact, the weak preference observed could therefore correspond to a real biological phenomenon if honeybees can actively regulate humidity in their nest.…”

“…Humidity based decision-making has been shown in leaf-cutting ants of the genus Atta Ribeiro and Navas, 2006), four species of fire ants from the genus Solenopsis (Potts et al, 1984), the wood ant Formica rufa (North, 1991), the meat ant Iridomyrmex sp. and the Argentine ant, Linepithema humile (Walters and Mackay, 2003). These studies have shown that ants prefer humidities of greater than 90% RH, and Atta sexdens and Solenopsis sp.…”

“…Gradients of RH (as in Roces and Kleineidam, 2000;Walters and Mackay, 2003) were established in a set of five linearly arranged 500 ml plastic screw cap jars, interconnected with transparent tubing (length 5 cm, diameter 2 cm) and containing mesh covered stands to prevent workers from contacting the salt solution or silica gel (Fig. 1).…”

Traits related to biological invasion: A note on the applicability of risk assessment tools across taxa

“…Invasive insects more active at higher soil temperatures than natives (Human et al 1998) O Humidity Invasive insects prefer high humidity, whereas natives do not (Walters and Mackay 2003);…”