Effect of application of a herbicide propyzamide into the soil by study of mineralization of glucose 14C(U) and distribution of radioactivity in various fractions of the soil (laboratory and open field tests)

The effects of the herbicide PROPYZAMIDE are studied in laboratory and field conditions. The modifications involved are characterized by measurement of 14C-glucose mineralization and radioactivity incorporation into the soil fractions. In laboratory conditions, temperature and moisture are kept stable and the experiment is performed during less than 24 hours. In these conditions, Kerb 50 (commercial formulation of propyzamide) and the emulsifier (material used in propyzamide formulation) exert little effect on 14CO2 evolution. In field conditions, propyzamide andKerb 50 are applied once at two different doses: at field rate (1,5 kg/ha) and twentyfold this rate. Essays are duplicated. The herbicide (propyzamide in Celanol and Kerb 50) and the emulsifiers alone (Celanol and the material used in propyzamide formulation) are applied on the soil surface (application date: 3.02.81). Two weeks later and then every month during four months, samples are taken to the depth of about 5 cm (Propyzamide migrates very slowly in the first centimeters of the soil). The characterization experiment is performed on 10 g soil samples by 14C-glucose incubation at 28 degrees C during two hours. 14CO2 evolved is measured after incubation and acidification with HCl. Then radioactivity distribution in the soil is counted after chemical fractionation of soil. This distribution is about 10-16.5% as 14CO2, 22-37% in the acid-soluble fraction, 10-25% in the alkali-soluble fraction and 15-45% in the human fraction (measured as 14CO2 evolved after combustion). This distribution is little modified by the herbicides or the emulsifiers but its evolution is significantly related to environmental conditions (temperature). Nevertheless a few modifications are observed. They can be due to the herbicide propyzamide itself but the emulsifiers and the degradation products of propyzamide can also influence the measurement (After forty days in the soil, 70-95% of the starting active ingredient have disappeared). They can also be a result of the initial effects of the products (modification of the microflora and of the environment).     

Reproductive conflict in animal societies: hierarchy length increases with colony size in queenless ponerine ants

Dominance interactions determine reproductive status in many animal societies, including many cooperatively breeding vertebrates and eusocial Hymenoptera without queen-worker dimorphism. Typically, the dominant individual monopolises reproduction, and subordinates behave like helpers. In Dinoponera queenless ants, workers are totipotent females and can potentially reproduce, yet only the top-ranking worker actually reproduces. Individual workers ranked immediately below the dominant breeder worker (gamergate) are hopeful reproductives. Whether or not a worker benefits from joining the hierarchy of high-ranking workers depends on the trade-off between the probability of becoming dominant and reproducing directly, and the colony-level cost of an additional lazy high ranker. Inclusive fitness models predict that the length of the dominance hierarchy depends on relatedness, colony size, and the linearity of the hierarchy. Here, we test the effect of colony size by comparing hierarchy length among three species that differ in colony size (Dinoponera australis: median=14 workers, quartiles=10 and 19 workers; D. gigantea: median=41, quartiles=33 and 74; D. quadriceps: median=78, quartiles=55 and 90). Although difficulties in defining where the hierarchy ends hamper comparisons, the results are in broad agreement with the predictions. Hierarchies are close to the predicted lengths and are longer in species with larger colonies (one, three and three workers in the three species in order from smallest to largest colony vs two, three and four predicted). These conclusions are further supported by determining Kokko and Lindström's λ index of skew, which is smaller (i.e. characteristic of a longer hierarchy) in species with larger colonies.     

Policing in queenless ponerine ants

Potential reproductive conflicts are common in insect societies. One process that can reduce or suppress conflict is policing. We review worker and "queen" policing in queenless ponerine ants. Queenless ants are an important model system for the study of intracolony reproductive conflict. Policing is widespread in queenless ants because workers are totipotent, so that additional potential conflicts occur in comparison to species where workers cannot mate, and these additional conflicts are frequently reduced by policing. Policing is more diverse than suggested by the examples known in other social insects. In almost all species of social Hymenoptera it can include preventing workers from reproducing by killing worker-laid eggs, but in queenless ants it can additionally include immobilisation or mutilation of workers attempting to reproduce by replacing the gamergate (i.e. mated worker with a queen-like role) or by becoming an extra gamergate. Policing by both workers and by the gamergate are important. Policing can be facultative. Depending on the age of the gamergate, workers can prevent her replacement by immobilising challenging workers or they can favour replacement by immobilising the gamergate. The initial definition of policing was inspired by species in which workers retain ovaries but cannot mate. We broaden the definition to include species, such as queenless ants, where females are totipotent, thereby including not only conflict over male production but also over gamergate replacement and gamergate number. Finally, we compare policing with punishment and dominance hierarchy. Policing is not always punishment and it does not necessarily entail dominance relationships.     

How many gamergates is an ant queen worth?

Ant reproductives exhibit different morphological adaptations linked to dispersal and fertility. By reviewing the literature on taxa where workers can reproduce sexually (i.e. become gamergates) we show that (1) species with a single gamergate generally have lost the winged queen caste, whereas only half of the species with several gamergates have, and (2) single-gamergate species have smaller colonies than multiple-gamergate species. Comparison with "classical" ants without gamergates, where having one vs having several winged queens are two distinct syndromes, suggests that having one vs having several gamergates are not. Gamergate number does not affect the success of colony fission, but retention of the queen caste permits the option of independent foundation.     

Prospects for repellent in pest control: current developments and future challenges

The overall interest in environmentally safe pest control methods and the rise of insecticide resistance in pest populations have prompted medical and agricultural entomology research on insect repellents in recent years. However, conducting research on repellent is challenging for several reasons: (1) the different repellent phenomena are not well defined; (2) it is difficult to test for and quantify repellent; (3) the physiological mechanisms are poorly known; (4) the field efficacy appears to be highly variable. Here, we identified five different types of repellent: expellency, irritancy, deterrency, odor masking and visual masking, and described behavioral bioassays to differentiate between them. Although these categories are currently defined by their behavioral response to different stimuli, we suggest new definitions based on their mechanism of action. We put forward three main hypotheses on the physiological mechanism: (1) a dose effect that modifies the behavior, (2) a repellent mechanism with specific receptors, or (3) inhibition of the transduction of neural information.     

Reproduction versus work in queenless ants: when to join a hierarchy of hopeful reproductives?

Many animal societies contain few breeders and many helpers. In some species, individuals can become either helpers or breeders, and breeding is often restricted to high rankers in a dominance hierarchy. In social Hymenoptera with no morphological queen caste, all females have the potential to become dominant and reproduce. In our model, females involved in the hierarchy do not work and gain direct fitness if they become alpha following death of the current alpha, while females not in the hierarchy gain indirect fitness by working. Using an inclusive-fitness model combined with models of alpha replacement in slightly different types of near-linear hierarchies, we determined the critical rank (i.e., optimal hierarchy length) for which the gain in fitness by entering the hierarchy as a hopeful reproductive equals the cost caused by a reduced worker force. High relatedness decreases the hierarchy length by lowering the potential benefit of entering the hierarchy. In contrast, large colony size increases the hierarchy length because the cost of each non-working high ranker is relatively lower. The model predicts a hierarchy of five workers in the queenless ant Dinoponera quadriceps, close to empirical data which show that in a colony of about 100 females, the top 5 carry out 72.8% of the aggressive interactions. The model is also used to make several testable predictions about the effect on hierarchy length of (1) variation in colony size and (2) variation in worker reproductive options between species of the queenless ants genus Diacamma. Received: 16 March 1999 / Received in revised form: 30 June 1999 / Accepted: 11 July 1999     

Unequal resource allocation among colonies produced by fission in the ant Cataglyphis cursor

How organisms allocate limited resources to reproduction is critical to their fitness. The size and number of offspring produced have been the focus of many studies. Offspring size affects survival and growth and determines offspring number in the many species where there is a trade-off between size and number. Many social insects reproduce by colony fission, whereby young queens and accompanying workers split off from a colony to form new colonies. The size of a new colony (number of workers) is set at the time of the split, and this may allow fine tuning size to local conditions. Despite the prevalence of colony fission and the ecological importance of social insects, little is known of colony fission except in honey bees. We studied colony fission in the ant Cataglyphis cursor. For clarity, "colony" and "nest" refer to colonies before and after colony fission, respectively (i.e., each colony fissions into several nests). The reproductive effort of colonies was highly variable: Colonies that fissioned varied markedly in size, and many colonies that did not fission were as large as some of the fissioning colonies. The mother queen was replaced in half of the fissioning colonies, which produced 4.0 +/- 1.3 (mean +/- SD) nests of markedly varied size. Larger fissioning colonies produced larger nests but did not produce more nests, and resource allocation among nests was highly biased. When a colony produced several nests and the mother queen was not replaced, the nest containing the mother queen was larger than nests with a young queen. These results show that the pattern of resource allocation differs between C. cursor and honey bees. They also suggest that C. cursor may follow a bet-hedging strategy with regard to both the colony size at which fission occurs and the partitioning of resources among nests. In addition, colony fission may be influenced by the age and/or condition of the mother queen, and the fact that workers allocating resources among nests have incomplete knowledge of the size and number of nests produced. These results show that the process of colony fission is more diverse than currently acknowledged and that studies of additional species are needed.