No abstract

Factors such as aggressiveness and adaptation to disturbed environments have been suggested as important characteristics of invasive ant species, but diet has rarely been considered. However, because invasive ants reach extraordinary densities at introduced locations, increased feeding efficiency or increased exploitation of new foods should be important in their success.Earlier studies suggest that honeydew produced by Homoptera (e.g., aphids, mealybugs, scale insects) may be important in the diet of the invasive ant species Solenopsis invicta.To determine if this is the case, we studied associations of S. invicta and Homoptera in east Texas and conducted a regional survey for such associations throughout the species' range in the southeast United States. In east Texas, we found that S. invicta tended Homoptera extensively and actively constructed shelters around them. The shelters housed a variety of Homoptera whose frequency differed according to either site location or season, presumably because of differences in host plant availability and temperature. Overall, we estimate that the honeydew produced in Homoptera shelters at study sites in east Texas could supply nearly one-half of the daily energetic requirements of an S. invicta colony. Of that, 70% may come from a single species of invasive Homoptera, the mealybug Antonina graminis. Homoptera shelters were also common at regional survey sites and A. graminis occurred in shelters at nine of 11 survey sites. A comparison of shelter densities at survey sites and in east Texas suggests that our results from east Texas could apply throughout the range of S. invicta in the southeast United States. Antonina graminis may be an exceptionally important nutritional resource for S. invicta in the southeast United States. While it remains largely unstudied, the tending of introduced or invasive Homoptera also appears important to other, and perhaps all, invasive ant species. Exploitative or mutually beneficial associations that occur between these insects may be an important, previously unrecognized factor promoting their success.

Factors such as aggressiveness and adaptation to disturbed environments have been suggested as important characteristics of invasive ant species, but diet has rarely been considered. However, because invasive ants reach extraordinary densities at introduced locations, increased feeding efficiency or increased exploitation of new foods should be important in their success. Earlier studies suggest that honeydew produced by Homoptera (e.g., aphids, mealybugs, scale insects) may be important in the diet of the invasive ant species Solenopsis invicta. To determine if this is the case, we studied associations of S. invicta and Homoptera in east Texas and conducted a regional survey for such associations throughout the species' range in the southeast United States. In east Texas, we found that S. invicta tended Homoptera extensively and actively constructed shelters around them. The shelters housed a variety of Homoptera whose frequency differed according to either site location or season, presumably because of differences in host plant availability and temperature. Overall, we estimate that the honeydew produced in Homoptera shelters at study sites in east Texas could supply nearly one‐half of the daily energetic requirements of an S. invicta colony. Of that, 70% may come from a single species of invasive Homoptera, the mealybug Antonina graminis. Homoptera shelters were also common at regional survey sites and A. graminis occurred in shelters at nine of 11 survey sites. A comparison of shelter densities at survey sites and in east Texas suggests that our results from east Texas could apply throughout the range of S. invicta in the southeast United States. Antonina graminis may be an exceptionally important nutritional resource for S. invicta in the southeast United States. While it remains largely unstudied, the tending of introduced or invasive Homoptera also appears important to other, and perhaps all, invasive ant species. Exploitative or mutually beneficial associations that occur between these insects may be an important, previously unrecognized factor promoting their success.

Sex-ratio conflict between queens and workers was explored in a study of colony sex ratios, relatedness, and population investment in the ant Pheidole desertorum. Colony reproductive broods consist of only females, only males, or have a sex ratio that is extremely male biased. Colonies producing females (female specialists) and colonies producing males (male specialists) occur at near equal frequency in the population. Most colonies apparently specialize in producing one reproductive sex throughout their life. Allozyme analyses show that relatedness does not differ within male-specialist and female-specialist colonies and they do not appear to differ in available resources. In the population, workers are nearly three times more closely related to females than males; however, the investment sex ratio is near equal (1.01, female/male), which is consistent with queen control. Selection should be strong on workers to increase investment in reproductive females, so why do workers in male-specialist colonies produce only (or nearly only) males? One hypothesis is that queens in male-specialist colonies prevent the occurrence of reproductive females, perhaps by producing worker-biased female eggs. An earlier simulation study of genetic evolution of sex ratios in social Hymenoptera (Pamilo 1982b) predicts that such mechanisms can result in the evolution of bimodal colony sex ratios and queen control. Results on P. desertorum are generally consistent with that study; however, information is not currently available to test some of the model's predictions and assumptions.

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