Ant Pristomyrmex Pungens Research Articles

Effects of a Native Ant, Pristomyrmex pungens (Hymenoptera: Formicidae) on the Population Dynamics and Spatial Distribution of the Invasive Mealybug Phenacoccus solenopsis (Hemiptera: Pseudococcidae)

The mealybug Phenacoccus solenopsis has been recently reported as a serious invasive insect pest in China. Earlier investigations suggest that some species of native ants may tend P solenopsis in the field, and affect the population number and spatial distribution of P solenopsis. To confirm this, we studied the relationship between P solenopsis and the native ant Pristomyrmex pungens on Dendranthema morifolium plants in a garden spot. We found there was a significant positive correlation between population numbers of P solenopsis and P pungens, and the less the distance from nest, the greater the quantity of P solenopsis. Additionally, the mean number of P solenopsis increased significantly in the presence of P pungens. P solenopsis and P pungens had strong crowding tendencies and these individuals were attracted to each other on all investigated dates except on August 6. Our results suggest the presence of P pungens has effects on the population numbers and spatial distribution of P solenopsis on D. morifolium plants, and this relationship between them may have an important effect on the population explosion and dispersal of the invasive mealybug.

Larvae of two ladybirds, Phymatosternus lewisii and Scymnus posticalis (Coleoptera: Coccinellidae), exploiting colonies of the brown citrus aphid Toxoptera citricidus (Homoptera: Aphididae) attended by the ant Pristomyrmex pungens (Hymenoptera: Formicidae)

The distribution of two small coccinellids, Phymatosternus lewisii and Scymnus posticalis, across colonies of the aphid Toxoptera citricidus in relation to ant-attendance of the colonies and ant species, behavioral interactions between the coccinellid larvae and ants, and the overlap in the larval distribution of the two coccinellids were examined in a citrus grove in Japan. P. lewisii larvae were found frequently in aphid colonies attended by the ant Pristomyrmex pungens but rarely in colonies attended by another ant, Lasius japonicus, and in ant-excluded colonies. A number of S. posticalis larvae were also recorded in P. pungens-attended colonies and some larvae in ant-excluded colonies. A few P. lewisii adults were noted only in P. pungens-attended colonies, whereas some S. posticalis adults were observed in ant-excluded colonies. In most encounters, P. pungens workers tapped P. lewisii larvae with their antennae but showed no aggressive behavior; otherwise, P. pungens workers ignored the larvae. P. pungens exhibited the same behavior when encountering S. posticalis larvae. The proportion of P. pungens-attended aphid colonies where the larvae of both coccinellids occurred did not significantly differ from the probability of both coccinellids occurring in the same colonies given their random distribution across the colonies. Thus, larvae of the two coccinellids exploited aphid colonies attended by a particular ant, P. pungens, and the larval distribution of the two species may be independent of each species.

Encounter-induced hostility to neighbors in the ant Pristomyrmex pungens

Field observations have demonstrated that internest hostility is negatively correlated with the distance between nests in the Japanese queenless ant, Pristomyrmex pungens. This runs counter to the “dear enemy” phenomenon. This result led us to hypothesize the existence of encounter-induced hostility in P. pungens. We created “neighbor(s)” and “stranger(s)” by an experimental method and tested the ant's ability to discriminate the neighbors from strangers. The results indicated that the ant could distinguish the neighbors from the strangers and displayed significantly stronger hostility toward the neighbors. The recognition of neighbors was quickly established after a few encounters and was maintained for at least 10 days after the most recent encounter. Nest mates without direct encounter experience with neighbors did not show hostile behavior toward neighbors. These findings suggest that information about neighbors (probably colony odor) is not transmitted to nest mates within the colonies. Aggressiveness toward the neighbors appears to be caused and maintained on the basis of individual memories from direct contact. It may be adaptive for a species that changes nest sites frequently to discriminate strangers from neighbors and selectively attack the latter.

Trail Pheromone of Myrmicine Ant Pristomyrmex pungens

The myrmicine ant Pristomyrmex pungens marks recruitment trails with poison gland secretions. The effective trail pheromone compound is 6-n-pentyl-2-pyrone. Poison gland components were identified by means of gas chromatographic coupled mass spectrometry. The biological activity was examined in trail-following experiments as well as in gas chromatographic coupled electroantennograms. In addition to 6-n-pentyl-2-pyrone, a number of monoterpenes were found in the poison gland secretion, i.e., α-pinene, camphene, β-pinene, myrcene, α-phellandrene, α-terpinene, and limonene. The terpenoid compounds increased the trail-following response only slightly when offered together with 6-n-pentyl-2-pyrone. In contrast to the latter component, synthetic monoterpenes elicited no orientation behavior in trail-following bioassays.

Reproductive Conflicts and Levels of Selection in the Ant Pristomyrmex pungens: Contextual Analysis and Partitioning of Covariance

Phenotypic selection on individual- and colony-level characters was examined in the myrmicine ant Pristomyrmex pungens by contextual analysis and partitioning of covariance. Pristomyrmex pungens has an extraordinary social system in which there are no queens and workers reproduce parthenogenetically. All workers can be reproductive and live only one year in this species. Thus, the annual colony growth rate measures the mean individual lifetime reproductive success. Within-colony individual variation in reproductive activity was estimated from individual ovarian development and revealed conflicting selection on worker dimorphism. Large workers are sporadically found in some colonies and had higher fitness on a within-colony level. However, large workers reduced a colony's fitness at the between-colony level. Therefore, large workers probably exist as a socially parasitic phenotype. Stabilizing and positive directional selection on the proportion of foragers appeared to be responsible for the evolutionary maintenance of cooperative breeding in this species. Cheaters that reproduce but never forage will be eliminated by colony-level selection. Overall, directional selection favored smaller colony size. Colony-level adaptation is important, because the mode of colony foundation, fission, is likely to enhance additive genetic variance of colonies and create the opportunity for a genetic response to colony-level selection.

Inter-colonial selection for the maintenance of cooperative breeding in the ant Pristomyrmex pungens: a laboratory experiment

The queenless ant Pristomyrmex pungens has an unusual social structure, in which all workers reproduce parthenogenetically and help others. Laboratory experiments manipulating the proportion of post-reproductive foragers in the colony at various rates suggested that colonies with 5–10% forager ratios had the maximum efficiency per-worker. This result suggests that the cooperative colonies may be maintained by colony-level natural selection. Non-cooperative mutants that oviposit but do not forage should increase in relative frequency in the colony in the short term. However, decreased colony productivity and the resulting competition among colonies might eliminate colonies dominated by such mutants in the long term. P. pungens has a viscous population without migration between colonies, which may facilitate this process.

Inter-colonial selection for the maintenance of cooperative breeding in the ant Pristomyrmex pungens : a laboratory experiment

Inter-colonial selection for the maintenance of cooperative breeding in the ant Pristomyrmex pungens : a laboratory experiment

Reproductive division of labour related to age in the Japanese queenless ant, Pristomyrmex pungens

In the ant Pristomyrmex pungens, only intranidal workers (which stay inside the nest) reproduce. This paper reports laboratory investigations into the factors differentiating intranidal and extranidal (foraging) workers. All workers begin life as intranidal workers, and later become extranidal workers. Taken over the whole lifespan of individuals, there is no non-reproductive caste in this species. All intranidal workers have active ovaries, but extranidal workers have resorbed ovaries. Thus, in P. pungens, reproductive division of labour has been reduced and is now related only to age rather than caste. Extranidal workers collected from the field, isolated from intranidal workers and fed to satiation in the laboratory, failed to recover ovarian activity, indicating that once a worker has become extranidal, she cannot return to laying eggs. All individuals thus both work and reproduce in this species in cooperative societies. Parthenogenetic, laying of diploid eggs by workers may be an evolutionary response to the risk of losing a queen in nomadic species such as P. pungens.

Obligate parthenogenesis and reproductive division of labor in the Japanese queenless ant Pristomyrmex pungens

Two types of workers were recognized in colonies of Pristomyrmex pungens: extranidal workers (which characteristically walk outside the nest) and intranidal workers (which characteristically stay inside the nest). The ovaries of extranidal workers showed little activity, whereas those of intranidal workers showed high activity and often contained mature oocytes. I therefore conclude that only the intranidal workers reproduce. A behavioral repertoire of 103 individuals was obtained and used to infer group subdivision using cluster analysis; in addition, principal component analysis was performed on the intranidal workers in this set. These data enabled objective separation of extranidal and intranidal workers. Intranidal workers were larger in size on average than extranidal workers; however, the distributions overlapped. Three tests for further subdivision within the group of intranidal workers indicated that such subdivision is weak, and it is also likely that all intranidal workers lay eggs. There was no significant correlation between body size and reproductive status. The number of mature oocytes per ant fitted a Poisson distribution, and the first two principal component factors scores of behavior showed significant correlation with head width. All extranidal workers had resorbed ovaries and also had yellow bodies (which indicated a history of oviposition). When and how the differentiation between the reproductive intranidal workers and the non-reproductive extranidal workers occurred is discussed. The best-supported hypothesis is that extranidal workers are old intranidal ones. Neither males nor inseminated workers were found in any smaples collected in the field or studied in the laboratory, which greatly strengthens earlier suggestions that Pristomyrmex pungens is the first-known ant to be obligately thelytokous. These findings indicate that Pristomyrmex pungens is no longer eusocial, although it has the highest form of social behavior of any thelytokous species; they also raise the question of whether or not there are factors promoting the loss of eusociality and sexuality in this species. Ecological factors are tentatively indicated, namely, the need to maintain large colonies in the face of a nomadic lifestyle involving frequent colony fragmentation.

The reproductive cycle of the queenless ant pristoMyrmex pungens

The life cycle of the myrmicine antPristomyrmex pungens was investigated. Colonies of this species are usually composed of several thousand small workers, although a few males (2–3 %) occasionally appear during June and July in mature colonies, and large workers with ocelli and abortive spermathecae (here termedergatoid queens) were observed extremely rarely. We found that the virgin small workers can lay eggs and that these develop into further small workers. Cerebral ganglion cells and oogonial cells had the diploid chromosome number (2 n=24), but the haploid number (n=12) was observed in oocytes at pachytene, and also in spermatocytes from the rare males. Males have functionally normal copulatory organs and their spermatogenesis is normal, but they probably do not mate, because small workers have no spermatheca and their copulatory organs are degenerative. These observations indicate that reproduction inP. pungens is carried out predominatly or, probably, wholly by the small workers and hence is thelytokous. We discuss the evolution of theP. pungens life cycle, pointing out the difficulty of applying the “queen” concept to this species or even in deciding whether or not it is “eusocial”. In view of the apparent genetic isolation between colonies, the mode of selection maintaining sociality in this case is probably interdemic group selection rather than kin selection.