A striking feature of hymenopterans societies is the absence of male workers. Foraging, nest building, brood care and all other activities required for the functioning of the colony are carried out by the females. These behaviours of the females and the implied cooperation and altruism have led social insect researchers to focus almost exclusively on the female members of hymenopterans societies. As a consequence, males have remained relatively neglected. The imbalance in the attention paid by researchers to females and males has been even more striking in the case of the extensively studied primitively eusocial wasp Rosalinda marginata. I have therefore focussed most of my attention to male R. marginata but of course, wherever possible and appropriate, I have compared the males with the females. Since almost nothing was known about R. marginata males, I began by obtaining basic information on the natural history and behaviour of the males. Male R. marginata are smaller in size and are different in the shape of the head as compared to the females. By conducting a three year survey, I found that just as nests of this species are found throughout the year, so are the males. The presence of males throughout the year has implications for the evolution of sociality by making available the opportunity to mate and found new nests, for females eclosing at any time of the year. Unlike the females who spend all their life on their nests, males stay on their natal nests only for one to twelve days (mean ± sd: 6.0 ± 2.6, N = 55) and leave their natal nest once and for all, to lead a nomadic life. It is difficult to determine how long males live after leaving their natal nests. However, I maintained males in the laboratory with ad libitum food and found that under these conditions they can live up to 140 days (mean physiological life span ± SD: 61.3 ± 28.0, N = 106). Like all eusocial hymenopterans males, R. marginata males also do not take part in any colony maintenance activities. They however, occasionally perform the following behaviours: solicit food, antennae nest, antennae another wasp, feed self, snatch food (from females), fan wings, body jerk and wing jerk, dominance and subordinate behaviours. Females of course perform all of these behaviours and many more. But there are no behaviours which are restricted to the males. Borrowing methods used by ecologists to measure species richness and diversity, I have computed the behavioral richness and diversity of male and female R. marginata. As expected, female behaviour is richer and more diverse compared to males. Comparing what the males did during their short stay on the nest and what females did during their long stay on the nest, I found that males did not forage or feed larvae (although I recorded one male feeding larvae thrice on one occasion when there seemed to be excess food on the nest). Males showed, dominance and subordinate behaviours and being solicited behaviour, significantly less often than females. On the other hand, males showed higher frequencies of feeding self and soliciting behaviour. However, these comparisons may not be fair because what males do in the first few days of their life is being compared with what females do throughout their life. Hence I truncated the female data at six days to make it comparable to the average age of the males on the nest. Even after doing so I found similar differences except that the males show similar rates of feed self and higher rates of subordinate behaviour compared to the young females. As mentioned in the beginning, absence of male workers is a striking feature of social Hymenoptera. I therefore naturally turned my attention to the possible reasons for this. As there has been much speculation on the ultimate, evolutionary explanations for why males do not work, I decided to investigate possible proximate explanations. To make my goal experimentally tractable, I decided to focus on the behaviour of feeding larvae as an example of work. In spite of the fact that R. marginata has been studied for over two decades, male R. marginata had never been seen to feed larvae, before my study. I advanced three hypotheses for why males do not feed larvae. (1) Males are incapable of feeding larvae. (2) Males do not feed larvae because they have insufficient access to food to satisfy themselves and to feed the larvae. (3) Males do not feed larvae because females perform the same task very efficiently. In a series of experiments designed to test these hypotheses, I showed that males are indeed capable of feeding larvae; they do so at small frequencies when given access to additional food and do so at impressive frequencies when deprived of females, provided with excess food and confronted with hungry larvae. Nevertheless, their ‘feed larva’ behaviour is less sophisticated and relatively inefficient compared to females. Thus I have shown male wasps can work, given an opportunity. In addition to being very satisfying, this result negates the preadaptation hypothesis which argues that male social Hymenoptera do not work because their solitary ancestors did not. In spite of what I have shown above, mating remains the main roleof the males. Therefore, I next turned my attention to a study of mating behaviour. It is well known that mating never takes place on the nest of R. marginata. Although some sporadic attempts had been made before, mating behaviour had never been observed in laboratory conditions before my study. In a series of trial-and-error pilot experiments, varying the age, cage size, number of wasps per cage, period of isolation from other wasps, lighting conditions etc., and with considerable help from enthusiastic volunteers among my lab-mates, I succeeded in observing mating behaviour in the laboratory. In the final, standardized experimental set up, we introduced a single male and a single female wasp, both isolated from their nests and other wasps for at least five days, into an aerated transparent plastic box and made observations for one hour. Using such an experimental set up, we first made a detailed qualitative description of mating behaviour. All behavioral interactions were initiated by the males. Males often attempted to mount the females but sometimes the females flew away, making the attempt to mount unsuccessful. On other occasions males successfully mounted the females, which involved climbing on the female and drumming and rubbing his antennae and abdomen on the corresponding parts of the female body. On some occasions mounting led to interlocking of the abdominal tips, a process we refer to as ‘conjugation’. Sometimes the conjugation lasted less than five seconds and during which the male remained on the back of the female; this was referred to as short conjugation (SC). But at other times the conjugation lasted for more than 20 seconds, and the male flipped on its back; this was Referred to as long conjugation (LC). I dissected all females, involved ineither LC or SC or both. Of the 47 pairs, 21 pairs mated successfully as judged by the transfer of sperm into the spermatheca. With the goal of developing a strategy to obtain live mated females for any future experiments, we attempted to determine the behavioral correlate/s of successful sperm transfer. It turns out that SC is inadequate for sperm transfer and LC is a good predictor of sperm transfer. Five to twenty days of age is optimal for mating for both males and females. There was a significant reduction in the probability of mating when one or both partners were younger or older than 5-20 days. We did not find any evidence for nestmate discrimination in the context of mating. This is not surprising because mating takes place away from the nest and active nestmate discrimination may therefore be unnecessary to avoid inbreeding. Under these experimental conditions neither body size of males and females nor ovarian conditions of the females appeared to influence mating success. I hope that my studies will enhance attention of future researchers to the males and will also facilitate experiments requiring mated wasps and permit the study of mate choice and other reproductive behaviours in this otherwise well- studied species.

Social insects are the most dominant terrestrial fauna for the last 50 million years. This tremendous ecological success is accompanied by the fact that sociality has evolved multiple times independently and achieved highest degree of complexity in insect lineages. The remarkable social organization found in insect societies is the result of finely balanced cooperation and conflict among the colony members. A typical hymenopteran colony is characterised by one or a few queens monopolizing reproduction and several sterile workers co-operatively raising brood and performing colony activities. The colonies are often conceptualized as superorganisms where groups of cooperative workers are compared with organs in the body, each of which accomplish a particular task like brood care, foraging and defence. The choice of tasks is often regulated by a systematic age polyethism. As the queens monopolize reproduction, they serve as the sole suppliers of eggs in the colony. Therefore, loss or death of the queen creates a crucial void which exposes the colony to potential reproductive conflict for the position of egg-layer. This crisis is expected to be extreme in monogynous colonies. The situation is rescued only after a new queen is established, and the whole process is known as queen succession. I am interested in this crisis management, and my thesis deals with potential and realized conflicts associated with queen succession and behavioural strategies involved in resolution of these conflicts. The queen can be replaced in two ways - either by a newly eclosed specialized reproductive individual, which happens in highly eusocial hymenopterans, or by an existing member of the colony (worker), as it happens in primitively eusocial hymenopterans. Unlike in highly eusocial species, the workers of primitively eusocial species retain their ancestral capability of mating and activating ovaries to produce both sons and daughters, which makes them suitable for taking up the role of queen in their lifetime. Hence, primitively eusocial species provide a unique situation where loss or death of the queen might result in severe reproductive conflict as the queen can be replaced by any one of the existing workers. Strictly monogynous colonies of the tropical primitively eusocial wasp Ropalidia marginata provide ideal opportunities to study the reproductive conflict and its resolution associated with queen succession because the queen is frequently replaced by one of her nestmates resulting in a serial polygyny. These queens have highly variable tenures of queenship ranging from seven to over 200 days, which, together with the fact that they are replaced by a variety of relatives such as daughters, niece and cousins, suggests a potential reproductive conflict with variable degrees of complexity. I have divided my thesis in three parts which are as follows -Natural queen turnover: Previous works from this lab have tried to characterize the queen succession in R. marginata colonies by experimentally removing the queen from the colony. As this design involves the experimenter intervening at a random point of the colony cycle, the colony might not respond in the similar way as it might have done to a natural succession necessitated by loss or death of the queen. But rarity and unpredictability of natural queen turnovers made them difficult to study. Therefore, in this section, we gathered a dataset of long-term and opportunistic quantitative behavioural observations on eleven natural queen turnovers and compared them with available data on queen removal experiments. All our queen removal experiments resulted in a hyper-aggressive potential queen who gradually reduced her aggression, activated her ovaries and went on to become the unanimously accepted new queen of the colony if the original queen was not returned. Here we found a similar phenomenon in natural colonies where a single un-challenged potential queen took over the colony as new queen after the old queen was lost, died or was driven out of the colony. In some of the natural colonies, the transition was preceded by aggression shown by the potential queens towards their nestmates including the queens, which indicates that they might have pre-empted the transition. The potential queens in natural colonies started laying eggs much faster than in experimental colonies suggesting their physiological readiness for the transition. How does a colony respond to a declining queen?: As we could show that some of the potential queens might perceive the upcoming queen turnover, a fair prediction would be that they sense it through the declining fertility status of the queens. Therefore, we tried to ex-perimentally induce situations where the queen appears to be declining, expecting that it might lead to a queen turnover. The growing evidence suggests that R. marginata queen maintains her status by applying a pheromone on the nest surface by rubbing the tip of her abdomen. We knocked down the nest to deny the queen the surface for applying her pheromone, and argued that the queen would be overthrown as the workers would sense her as infertile. To our surprise, the queen maintained her status in six out of seven colonies by applying her pheromone on the entire surface of the cage. However, the effectively insufficient concentration of pheromone elicited aggression from workers towards the queen, and the queen retaliated back with aggression. These results suggest that the pheromone, being an honest signal of fertility, is extremely important for the queen for maintaining her reproductive monopoly, and the workers are able to perceive the decline of the queen from her pheromone. Queen-successor conflict over access to reproduction: Here we more explicitly looked at the potential reproductive conflict between the queen and her successor over access to direct reproduction. We used the theory of parent-offspring conflict proposed by Robert Trivers (1974) as the conceptual framework and adapted it to unravel the pat-tern of queen-successor conflict in R. marginata colonies. According to this idea, we expected that there should be a pre-conflict zone where the queen and the successor both would agree that the queen should continue to reproduce, followed by a conflict zone where the successor would try to takeover but the queen would hang on, finally followed by post-conflict zone where they both would agree that the successor should reproduce. To test this expectation, we maintained the queen and the potential queen on either side of a wire-mesh partition, each with randomly chosen half of the workers. It allowed the potential queen (successor) to establish herself and then we reintroduced the queen to her side of the mesh daily till the queen gave up. We could behaviourally characterise all three zones which always appeared in the expected sequence. The pre and post-conflict zones had no aggressive interaction between the queen and the potential queen, whereas the conflict zone was characterized by aggressive falling fight between them. This is our first success in experimentally creating overt conflict between the queen and her successor. Overall we can say, that the queens and the potential queens of R. marginata show great behvioural plasticity which might have been shaped by natural selection as an adaptation for conflict resolution. We could show that the potential queens sometimes can predict the upcoming transition and pre-pare themselves accordingly, whereas they can also react to an experimentally created sudden loss of queen by hugely elevating their aggression. The docile queens, on the other hand, maintain their reproductive monopoly by a pheromone, which is essentially a feature of highly eusocial species. But these docile queens have not lost their capability to show aggression and can use that to complement the insufficient concentration of her pheromone. This and the behaviour of potential queens in their establishment phase are strongly reminiscent of typical primitively eusocial species. We conclude that Ropalidia marginata is, perhaps, a particularly advanced primitively eusocial hymenopteran situated on an evolutionary continuum from primitive to highly eusocial species.