UC Riverside

Liometopum apiculatum Mayr, L. luctuosum Wheeler, and L. occidentale Emery are found in western North America and are referred to as velvety tree ants. They are usually associated with trees, but in recent years both L. luctuosum and L. occidentale have been reported as urban pests causing structural damage. Very little is known about the biology of these species.

Liometopum occidentale foragers readily consumed sucrose, glucose and honey sucanat solutions. Solid protein baits containing anchovy were retrieved by workers. In the early summer, foragers consumed more of the same types of foods during the day and at night. Even though workers are polymorphic, they all consumed about 0.25 mg of a 25% sucrose solution, providing a mechanism of determining foraging activity by measuring sugar water removal from monitoring stations. Baits containing 25% sucrose would be effective if suitable toxicants can be identified.

Liometopum luctuosum is restricted to the coniferous forests in the mountains in the southern range of its distribution, suggesting that it may be less xeric adapted than L. occidentale. When exposed the various temperatures and relative humidities, L. luctuosum workers survived significantly longer than L. occidentale. Furthermore, L. luctuosum lost significantly more water over 24 h than did L. occidentale at 25.6 and 33.0°C. The cuticular permeability (CP) of L. luctuosum was 17.8 and 19.1, while CP of L. occidentale was 17.0 and 19.8 at 25.3° and 33°C. The similarity of the CPs and the comparison of the effect of saturation deficit on survival indicated that water loss alone through the cuticle was probably not the major factor affecting survival. The CPs of both species suggests they are adapted for xeric conditions; but, also capable of surviving in mesic climates.

Liometopum occidentale nests are quite inaccessible making it extremely difficult to examine entire colonies and determine colony structure. A segment of the mitochondrial (mtDNA) COI gene was used to determine that L. occidentale nest contain either one queen or multiple maternally related queens. Observations of the behaviors displayed by workers from colonies separated in an urban landscape showed that there is a slight but significant correlation between geographic distance and their level of aggression.