A. Ann Sorensen

Control of food influx by temporal subcastes in the fire ant, Solenopsis invicta

SummaryTemporal subcastes in the fire ant, Solenopsis invicta Buren were selectively starved to determine if foragers could assess the nutritional status of their nestmates and respond accordingly. We found that starved foragers increase the honey entering the colony (Fig. 1). When nurses are starved more oil and liquid egg yolk enters the colony (Figs. 2, 3) and when both reserves and nurses are starved, more egg yolk powder is brought in by the foragers (Fig. 4). When queens are starved, more liquid egg yolk and oil enters the colony (Figs. 2, 3). Starved larvae increase the oil in the colony (Fig. 2) and when held with nurses for 24h before feeding, increase the egg yolk powder brought in and receive significantly more of it than other subcaste members (Fig. 5). We conclude that foragers can respond to the nutritional needs of their nestmates. Based on our behavioural observations, the quantity of food brought in by the foragers is regulated via discriminatory solicitation by reserves in response to the nutritional needs of the nurses.

The influence of oral secretions from larvae on levels of proteinases in colony members of Solenopsis invicta Buren (Hymenoptera: Formicidae)

Abstract The role of larvae in the digestion of protein in colonies of the red imported fire ant, Solenopsis invicta Buren was examined. Proteinase activity was significantly higher in the midguts of workers tending larvae compared to workers maintained without larvae. Food type (honey, egg yolk or soybean oil) influenced proteolytic activity in isolated workers but not in workers maintained with larvae. Proteinase activity in the labial glands and midguts of larvae maintained with or without workers was not significantly different. The total protein concentration in larval oral secretions was approximately 60–70% of that in the haemolymph. However, the percentage of free amino acids in the oral secretions was 2 to 3 times greater than that in the haemolymph.

Behaviour of worker subcastes in the fire ant, Solenopsis invicta, in response to proteinaceous food

ABSTRACT. The effects of division of labour on response behaviour to food in the red imported fire ant, Solenopsis invicta Buren, were examined to determine if caste members differ in amount of food taken, in rate of food transfer, or in internal distribution of food; and to see if food availability, time, or temporal subcaste pairing affect feeding behaviour. To measure differences in behaviour we fed radioiodinated albumin mixed with egg yolk to colonies containing larvae, queens, and (a) foragers and nurses, or (b) foragers and reserves, or (c) nurses and reserves. Samples were taken over a 72‐h period and radioactivity in the head, thorax and abdomen of each worker was determined. There were significant differences between nurses, foragers and reserves in quantity of food consumed, rate of transfer, and internal distribution of radioactivity. These differences were related to their respective roles of foraging, food storage and transfer, and brood tending. The quantity of food taken per subcaste was dependent on the total amount of food in the colony, with transfer rates differing between subcastes as the quantity of food in the colony increased. The rate at which protein was transferred between subcastes was slower in the reserves than that in either foragers or nurses. Therefore, reserves may serve as a temporary store of protein for the colony.

Trophallaxis by temporal subcastes in the fire ant, Solenopsis invicta, in response to honey

ABSTRACT. Trophallactic behaviour of temporal subcastes in Solenopsis invicta Buren colonies was studied in two separate experiments. First, radiolabeled honey was presented to small colonies containing larvae, queens and marked workers; radioactivity in the head, thorax and abdomen of each ant was measured after 0.25, 1, 6, 12, 24, 48 and 72 h. The quantity of honey per subcaste was dependent on the total amount of honey collected. As more honey entered the colony, the quantity in foragers, queens and reserves increased more rapidly than that in nurses or larvae. The internal distribution of radioactivity in the head, thorax or abdomen indicated that differences between subcaste members in either the rate of food exchange or digestion existed. In a second experiment behavioural observations were made on marked workers in colonies before and after the presentation of honey. Reserves spent significantly more time engaged in trophallaxis than either foragers or nurses, both as active donors and active receivers. Based on number of encounters, nurses were more likely to receive honey while reserves and foragers were more likely to donate honey. The duration of encounters involving nurses tended to be shorter than those involving reserves or foragers.

INSTRUMENTAL INSEMINATION OF THE FIRE ANT, SOLENOPSIS INVICTA

Colonies containing ♂♂ and alate virgin ♀♀ were collected from the field and maintained in greenhouse facilities. The alate virgin ♀♀ were induced to fly, anesthetized with CO2 and inseminated with either a mixture of sperm extracted from the ♂ seminal vesicles and accessory gland contents or sperm alone. Coconut milk was used as a sperm diluent for each insemination. Flight and sexual maturity were used as criteria for successful inseminations. Of the females we artificially inseminated 65% produced workers. This technique was developed for use with the fire ant and may be modified for use with other ant species.

The biological half life and distribution of 125Iodide and radioiodinated protein in the imported fire ant, Solenopsis invicta.

The radioisotope 125Iodide, a gamma emittor, was used in two different forms, as 125I mixed with egg yolk and as 125I covalently attached to egg albumin and mixed with egg yolk, to study food flow in the imported fire ant, Solenopsis invicta Buren. The biological half life of 125I‐albumin in egg yolk powder was determined to be 96 hr in isolated workers, 108 hr in individuals held with small groups of unlabelled workers, and 1,008 hr in workers held in colonies exposed to labelled food for 48 hr. In contrast, the biological half life of free 125I mixed with egg yolk powder was 22 hr, 20 hr, and 40 hr, respectively.