On “intercolonial” cannibalism in Japanese paper wasps,Polistes chinensis antennalis Pérez andP. Jadwigae dalla torre (hymenoptera: Vespidae)

Summary Foundresses of two species of Japanese paper wasps,Polistes chinensis antennalis andP. jadwigae, attacked other colonies of the same species. A foundress ofP. chinensis antennalis visited two nests of the same species, and ate larvae from them, while two foundresses ofP. jadwigae each visited a nest of the same species, eating larvae and pupae even when the foundress of the attacked nest was on her nest. In addition, a foundress ofP. jadwigae distributed flesh balls thus obtained among their larvae. Discussion was made on the adaptive significance of the inter-colonial cannibalism. It was considered that, at first, it increases the foraging efficiency and secondly it plays a role in regulating population density.     

Extra molting,cannibalism and pupal diapause under unfavorable growth conditions in Atrophaneura alcinous (Lepidoptera: Papilionidae)

Atrophaneura alcinous adopt multiple strategies such as extra molting, cannibalism and pupal diapause under unfavorable growth conditions. The conditions under which these strategies are adopted have been separately verified, but their relationship has often been overlooked. We examined which strategy A. alcinous adopted and the relative advantages of strategies using four experimental groups under different food quantity and individual density conditions. Our results indicated that A. alcinous often extra‐molted, prolonged the larval period, and larval and pupal weights were lighter under food shortage. Cannibalism and disease often occurred under the high density and food shortage condition. We also showed that individuals cannibalized during the prepupal or pupal period were less likely to extra molt before they were killed. Extra molting tended to occur more frequently in females than in males under a shortage of food. In addition, we showed that, when food was insufficient, A. alcinous might initiate pupal diapause under low densities, but not under high densities. These results suggest that A. alcinous prolongs the larval period by engaging in extra molting during times of unfavorable food conditions. This strategy might decrease the risk of cannibalization because surrounding larvae who could potentially cannibalize others pupate before larvae who prolong the larval period pupate. Our results also suggest that diapausing pupae under a shortage of food can only survive when there are few surrounding conspecifics, due to a lower cannibalization risk. In conclusion, there is a complex interaction between extra molting, cannibalism and pupal diapause strategies.     

Construction of Nest Defensive Structure According to Offspring Value and Its Effect on Predator's Attack Decision in Paper Wasps

Various organisms are known to build nests with defensive structures to protect their offspring from predation, but our understanding of plasticity in the nest structure remains poor. In this study, we investigated whether a paper wasp, Polistes chinensis antennalis, adjusted the construction of nest defensive structure according to the value of their offspring, and we also analysed the effect of adjusting the construction of the structure on predator's decision to attack. P. chinensis antennalis foundresses start a colony and maintain her nest alone until the emergence of workers. During this stage, foundresses often construct a defensive structure on cocoon caps of pupae using nest materials (pulp), which prevents predation of pupae by conspecifics from other nests. The value of pupae to the foundress varies among those in a nest, where the value is higher in pupae that spun the cocoon (and initiated pupation) earlier than other pupae in the nest. From field observations, we found that foundresses constructed a larger pulp structure on the cocoons of pupae that cocooned earlier in the order of cocoon spinning, even after considering confounding factors. We also found that the probability of a pupa being attacked by conspecific intruders decreased with the size of pulp structure on the cocoon. This indicates that intruders avoid attacking cocoons with larger pulp structures. Our study indicates that foundresses adjust the construction of nest defensive structures according to their offspring value, and this allows them to protect the high‐value offspring efficiently and effectively.     

Social behavior of early emerging males of a Japanese paper wasp,Polistes chinensis antennalis (Hymenoptera: Vespidae)

Summary Five cases of the early emergence of males in a Japanese paper wasp,Polistes chinensis antennalis, in which male emerged together with the first group of workers, were described. In one case of the five where the queen disappeared before the emergence of male, worker(s) produced female offspring. The frequency of the nests where the early emergence of male was observed was 16.7% (5/30 nests). In two colonies, worker(s) and/or queen chased off males. But in an orphan nest where worker(s) produced female offspring, the dominance order among workers which was similar to that of colony without male was observed. The significance of the early emergence of male in the social evolution of wasps was discussed.     

Influence of Diet and Density on Laboratory Cannibalism Behaviors in Gypsy Moth Larvae (Lymantria dispar L.)

The gypsy moth (Lymantria dispar) is an insect folivore that feeds on a broad range of hosts, and undergoes intermittent outbreaks that cause extensive tree mortality. Like many other herbivorous insects, gypsy moth larvae consume a substrate that is low in nitrogen. Gypsy moth larvae have been known to cannibalize under crowded conditions in the laboratory. In this study, we assessed the influence of nitrogen and density on cannibalism behavior in gypsy moth larvae. Cannibalism rates increased with decreased nitrogen and increased density. There was no interaction between these two parameters. Developmental experiments confirmed that low dietary nitrogen is detrimental, in agreement with previous studies. In a second experiment, we assessed the influence of previous cannibalism experiences on subsequent cannibalism behavior. Gypsy moth larvae that had previously cannibalized other larvae subsequently exhibited higher cannibalism rates than those larvae that had not cannibalized. In conclusion, low nitrogen, high larval density, and previous cannibalism experience are important factors contributing to gypsy moth larval cannibalism. Future studies are needed to estimate benefits to larvae, and to more closely approximate field conditions.     

Growth-related changes in predation behavior in incipient colonies of the ponerine antEctatomma tuberculatum (Olivier)

Summary We traced the development in the laboratory of 18 young colonies of the arboricolous ponerine antEctatomma tuberculatum. Colony foundation is of the partially-claustral type. During the early stages, when the colony is entirely dependent on the queen's behavior, the growth of the colony in terms of number of workers produced over time was relatively predictable. Afterwards, divergence in colony growth in function of the time increases as fast as the number of workers influences the efficiency of colony provisioning.Comparative analysis indicated clear changes in the predation behavior of foundresses and workers as colonies developed. For any stage of colony growth, all individuals provisioned the nest with dead prey or sugar-rich substances in the same way. However, prey hunting involves two different strategies. Foundresses and nanitic workers (originating from colonies with 9–15 workers) foraged actively, catching prey as the result of random encounters. Post-nanitic foragers (originating from colonies with 20–30 workers) and those from nature colonies developed an ambush strategy. Workers in these colonies gained experience at catching and handling prey during a period when they acted as nest guards, and so tended to be more efficient hunters than poorly experienced foundresses or nanitic foragers. The change in strategy was also positively correlated with an increase in the size of workers as the colony matured. A stable maximum in workers size is apparently reached only after the appearance of efficiently hunting foragers, presumably in numbers sufficient to provide adequate quantity and quality of larval food. Such a correlation between worker size and colony growth, assumed general for all ants, has not been demonstrated for Ponerinae before this work.     

Behavioral ecology of Japanese paper wasps,Polistes spp. IV. Comparison of ethograms between queens and workers ofP. chinensis antennalis in the ergonomic stage

Behavioral catalogues, transition matrices between 2 consecutive behavioral acts, and the frequency distribution of time spent in each behavioral act were described for queens and workers of a Japanese paper wasp,Polistes chinensis antennalis in the ergonomic stage (the period from the emergence of the first worker to the emergenece of the first reproductive). The results were; (1) The whole behavior repertoire of queens was completely included in that of workers. Workers oviposited frequently in queen-right colonies. (2) The proportion of off-nest activities to the number of total acts for workers was higher than that for queens. The proportion of time spent off the nest in workers was 5 times as high as that in queens. (3) There was no significant difference in the proportion of number of oviposition to the total number of acts between queens and workers. The oviposition rate was 0.06 eggs/h for workers and 0.37 eggs/h for queens. Queens made more dominance behavior and workers more subordinated behavior. Queens made abdomen wagging more frequently than workers. (4) For behavioral acts common in both queens and workers, the mean duration of a specific act was approximately equal for both. The mean duration of unsuccessful flesh collection for workers was 3.4 times as longs as that for queens. Workers did not search for flesh in 10.1% of duration of flesh collections in the field. (5) The pattern of transitions between 2 consecutive behavioral acts in workers was similar to that in queens. (6) Alien workers approaching a nest with a load were more often accepted by the nest occupants than alien workers with no load. Alien workers with no load were not accepted as often as a legitimate nestmates with no load. The reproductive division of labor between queens and workers inP. chinesis antennalis was incomplete. This suggests worker-queen conflict in different reproductive strategies among colony members. Several behaviors were consistent with the view that they are the behavioral expression of this conflict.     

An experimental study of population regulation in the salamander,Notophthalmus viridescens dorsalis (Urodela: Salamandridae)

Summary The roles of density-dependent larval survival and cannibalism of larvae as potential mechanisms of population regulation in the newt (Notophthalmus viridescens dorsalis) were evaluated in laboratory and field experiments. In laboratory containers, adults cannibalized larvae and large larvae cannibalized smaller larvae. In artificial ponds, larval survival did not depend on initial larval density. No cannibalism could be demonstrated in the complex environment, although the experiment was powerful enough to detect an ecologically relevant difference in survival. Adult growth was negatively correlated with the final biomass of larval newts, suggesting that the two life stages competed for resources. Larval growth rates were negatively correlated with final larval density, suggesting that larvae competed with each other. The proportion of larvae that became sexually mature at age 7 months (paedomorphs and adults that skipped the eft stage) varied inversely with larval density. Therefore, the potential regulatory mechanisms identified in this study are competition within and between life stages.     

Larval cannibalism and worker-induced separation of larvae in <Emphasis Type="Italic">Hypoponera</Emphasis> ants: a case of conflict over caste determination?

Reproductive altruism and cooperative brood care are key characteristics of eusocial insects and reasons for their ecological success. Yet, Hymenopteran societies are also the stage for a multitude of intracolonial conflicts. Recently, a conflict between adult and larval colony members over caste fate was described and evidence for overt conflict was uncovered in several bee species. In theory, diploid larvae of many Hymenopteran species should experience strong fitness benefits, if they would be able to change their developmental pathway towards the queen caste. However, larval self-determination potential is low in most advanced eusocial Hymenopterans, because workers often control larval food intake and queenworker caste dimorphisms are generally high. In the ant genus Hypoponera, larvae actively feed on food provided by workers and here we show extremely low queenworker size differences in these ants: the lowest in H. opacior, where fertile wingless (intermorphic) queens weigh on average only 13% more than workers. Thus, slightly better nutrition during development might change the fate of a Hypoponera larva from a completely sterile worker to a fertile queen. One possibility to obtain extra food for Hypoponera larvae with their well-developed mandibles would be to cannibalise adjacent larvae. Indeed, we observed frequently larval cannibalism in ant nests. Yet, adult workers apparently try to prohibit larval cannibalism by carefully separating larvae in the nest. Larvae, which were experimentally brought into close contact, were rapidly set apart. Workers further sorted larvae according to size and responded swiftly to decreasing food levels, by increasing inter-larval distance. Still, an experimental manipulation of the larval cannibalism rate in H. schauinslandi failed to provide conclusive evidence for the link between larval cannibalism and caste development. Hence, further experiments are needed to determine whether the widespread larval cannibalism in Hypoponera and the untypical brood distribution can be explained by an overt caste conflict. Received 18 December 2006; revised 2 August and 20 September 2007; accepted 21 September 2007.     

Hurrying Foragers Fail to Choose the Best Prey Item: Prey Choice in Paper Wasps Depredating Conspecific Nests

Animals frequently face situations where they must choose one prey item from a set of options. Animals are often considered to be able to choose the best prey item from multiple alternatives. However, time may be required to make accurate decisions, and under natural conditions, time is usually limited. Here, we examined whether animals fail to choose the most profitable prey item under time‐limited conditions. A queen (foundress) of a paper wasp Polistes chinensis antennalis starts a colony in spring and maintains the nest alone until the emergence of workers. At the stage, the foundress often depredates larvae in other conspecific nests. The intruder needs to finish choosing and extracting a single larva during the absence of the owner from the nest. Intruders preferred the fifth‐instar larvae, which are the largest and the most profitable prey among larvae. When the time spent in choosing was long, intruders were able to choose the fifth‐instar larvae with a higher probability. However, when the time spent in choosing was short, intruders sampled only a small fraction of larvae in a nest, and the probability of choosing the fifth‐instar larvae decreased. Furthermore, we found that intruders decreased the time spent in choosing under higher time constraints. These results suggest that under time‐limited conditions, intruders occasionally failed to choose the most profitable prey item because of incomplete information on the availability of options. These results also suggest a trade‐off between speed and accuracy of choosing the best item from a set of options.     

Growth rate and body weight of foundress-reared offspring in a paper wasp, <Emphasis Type="Italic">Polistes chinensis</Emphasis> (Hymenoptera,Vespidae): no influence of food quantity on the first offspring

Summary. Laboratory experiments with Polistes chinensis (Pérez) showed that growth rates and weights of the first-hatched offspring were not different between food-available and food-deficient conditions. In food-deficient colonies, some first-hatched offspring grew quickly, but their dry weights were not different from that of later offspring. The present results suggest that foundresses of P. chinensis may intensively feed some first-hatched larvae to produce the first workers quickly under food-deficient conditions. Since food availability of field foundresses of this species has been estimated as very low, it seems likely that they may produce the first offspring as early as possible by such feeding. On the other hand, heavier offspring were produced when extra food is available, especially in the latter half of the order of emergence. Foundresses of this species may change the amount of prey fed to each larva in response to food availability.     

Precopulatory Sexual Cannibalism Causes Increase Egg Case Production,Hatching Success,and Female Attractiveness to Males

Precopulatory sexual cannibalism is an extreme form of sexual conflict that can entail significant costs to the cannibalized individual and a variety of costs and benefits to the cannibal itself. Characterizing these costs and benefits is fundamental to our understanding of how this behavior evolves. Using the spider Agelenopsis pennsylvanica, we tested the reproductive consequences of precopulatory sexual cannibalism by staging cannibalization events and comparing the performance of experimental cannibals against natural cannibals (i.e., those that cannibalized on their own) and non‐cannibals. We found two performance benefits associated with precopulatory sexual cannibalism: first, experimental cannibals were more likely to produce egg cases than non‐cannibals, and second, egg cases from experimental cannibals and natural cannibals were significantly more likely to hatch than those produced by non‐cannibals. We then tested whether males were more likely to approach the webs of experimental cannibals vs. non‐cannibalistic control females. Our data demonstrate that sexual cannibalism increases female attractiveness to males. Although this result seems counterintuitive, in fact, rates of precopulatory sexual cannibalism were much lower in females that had already cannibalized their first male: 38% of sexually naïve females engaged in precopulatory sexual cannibalism, whereas only 5% of females engaged in cannibalism a second time. Thus, males that approach cannibals receive two benefits: they are less likely to be cannibalized precopula, and they have the possibility of mating with females that have a higher probability of producing viable egg cases. Taken together, our data suggest that precopulatory sexual cannibalism affords females numerous benefits and may have a hand in shaping male mate choice decisions.     

Behavioral ecology of Japanese paper wasps,Polistes spp. III. Decision making byP. chinensis antennalis foundresses at the departure from nests

Analysis of the behavior of foundresses of a Japanese paper wasp,Polistes chinensis antennalis Pérez, was made to clarify the patterns of decision making. It was found that: (1) Foundresses postponed the next activity off the nest after being attacked by a foundress from another colony. (2) After a spiral flight, the frequency of subsequent spiral flights and patrol flights around the nest increased. (3) Following successful flesh collection, the frequency of flesh collection increased. (4) Following successful flesh collection, the time spent for a single trip of flesh collection increased. It was concluded thatP. chinensis antennalis foundresses solve their dilemma between the need of nest defence and resource gathering by decision making based on intraspecific attacks and the intake of the most difficult resource to obtain.     

Cooperative foundation of colonies by unrelated foundresses in the antPolyrhachis moesta

Summary Field studies ofPolyrhachis moesta revealed that colonies were facultatively founded by more than one queen, even though each established colony was inhabited by only one queen with her workers. In pleometrotic colonies, it was found that cofoundresses frequently exhibited cooperative behaviors, including trophallaxis. The results of DNA fingerprinting showed that multiple foundresses were not genetically to one another. It seems that they aggregate randomly and independently of their relatedness. A discussion of the reasons why foundresses ofP. moesta do not aggregate preferentially with genetically related females.     

Stay or move: how Bt‐susceptible Helicoverpa armigera neonates behave on Bt cotton plants

Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) larvae occasionally have been reported to survive at management threshold levels in fields of Bollgard II^® cotton, Gossypium hirsutum L. (Malvaceae). The pattern and degree of larval survival is not easily predicted but depends on the ability of first instars to establish on host plants. Experiments were conducted with Bacillus thuringiensis Berliner (Bt)‐susceptible and Bt‐resistant larvae of H. armigera to understand how physiologically Bt‐susceptible H. armigera survive on Bt cotton plants, and examine how their first meal influences survival rates. In assays using cotton plant parts, both strains of larvae displayed similar tendencies to drop‐off specific plant parts of Bt and non‐Bt cotton. However, significantly more Bt‐susceptible larvae dropped off young leaves, mature leaves, and squares of Bt cotton compared to non‐Bt cotton plants. Egg cannibalism significantly improved the survival of Bt‐susceptible H. armigera larvae on Bt cotton plants. Larvae were more likely to eat live aged eggs, than newly laid or dead eggs. Survival significantly improved when larvae cannibalized eggs before feeding on Bt leaves. The behavior of Bt‐susceptible larvae with respect to drop‐off and egg cannibalism may help enhance their survival on Bt cotton plants.     

Does the diapause experience of bumblebee queens Bombus terrestris affect colony characteristics?

1. Bumblebee colonies show much variation in the number of workers, drones, and queens produced. Because this variation prevails even when colonies are kept under identical conditions, it does not seem to be caused by extrinsic factors but rather by differences between founding queens. 2. The most likely factor that could cause differences between queens is diapause. Although colonies are raised under standardised conditions, the queens often experience diapause of different length. If there are costs associated with diapause that influence post‐diapause reproduction, the diapause history of the queens could affect colony characteristics. 3. Here, several colony characteristics are compared: number of first and second brood workers; total number of workers, drones, and queens; energy spent on sexuals; sex ratio; rate of worker production; time to emergence of first reproductive; and colony lifetime. Colonies were used where the queens experienced a diapause treatment of 0 (nondiapause queens), 2, and 4 months. 4. Although no proof was found for the existence of costs associated with diapause, the colony characteristics of nondiapause queens were significantly different from those of diapause queens. Colonies of nondiapause queens produced the lowest number of workers but the highest number of young queens. 5. It is argued that these nondiapause colonies are more time‐constrained than diapause colonies because nondiapause colonies produce two generations within the same season and should therefore be more efficient in producing sexual offspring. 6. Moreover, nondiapause colonies should rear a more female‐biased sex ratio because they can be certain of the presence of males produced by other (diapause) colonies.     

Copulation duration in the spiderPhilodromus vulgaris (Hentz) (Araneae: Philodromidae) and its influence on the evolution of host transfer behavior during cannibalism byMantispa uhleri banks (Neuroptera: Mantispidae)

Matings and acts of cannibalism were observed in the crab spiderPhilodromus vulgaris, some of which were carrying a first-instar larva of the mantispidMantispa uhleri. Larval mantispids did not transfer during the copulation of their spider hosts but did switch from spider to spider during cannibalism. Twenty-three of 27 total cannibalisms in which the cannibalized spider carried a larva resulted in larval transfers, for a transfer rate of 85%. Copulation times inP. vulgaris were found to be extremely short in comparison to lycosids such asSchizocosa ocreata, whose long copulation time supports the larval transfer ofClimaciella brunnea. The time required for larval transfer during cannibalism inP. vulgaris was measured. Cannibalisms were much longer than copulations but larvae transferred to the cannibalizing spider in a comparatively short period of time.     

核型多角体病毒感染对棉铃虫幼虫同类相残行为的影响

在室内研究核型多角体病毒（HaSNPV）感染对棉铃虫Helicoverpa armigera（Htibner）幼虫同类相残行为的影响。结果显示：感病棉铃虫随感病程度的加重,越容易被健康棉铃虫残食,而自然死亡的感病棉铃虫、冻死的感病棉铃虫和冻死的健康棉铃虫三者被健康棉铃虫残食的百分率无显著差异。表明感病棉铃虫和病虫尸体更易于被健康棉铃虫残食,是由于棉铃虫体力减弱而失去反击能力,不是由于病毒本身的影响。以健康棉铃虫、感病棉铃虫为残食者,冻死的病虫为被残食者,相残率无显著差异,表明病毒并未改变棉铃虫残食同类的天性。残食病虫的健康棉铃虫的化蛹率和羽化率均低于正常的健康棉铃虫,残食者为相残行为付出了很高的代价。     

The effect of larval age range on survival of twoTribolium castaneum strains in mixed cultures,through pupal cannibalism

The effect of larval age range on survival of two Tribolium castaneum strains in mixed cultures was studied in an experimental situation in which other selective forces were reduced to a minimum. Increasing the difference in larval age setween the strains by one day resulted in a reduction of survival of the faster-developing mutant strain, because more of its earlier pupae were cannibalized by the larvae. General aspects of the effects of pupal cannibalism by larvae on the outcome of intra-specific competition (sensu lato) in Tribolium are discussed.     

Geographic Variation in Air Temperature Leads to Intraspecific Variability in the Behavior and Productivity of a Eusocial Insect

In primitively eusocial insects, air temperature is the environmental factor that primarily affects colony cycle. Several studies demonstrated interspecific differences in the adaptation of eusocial insects to local air temperature. Nevertheless, studies on intraspecific adaptations are rare. In this study, we investigate the influence of air temperature on local adaptations in behavior and colony productivity of Polistes biglumis foundresses living in warm and cold temperate zones. We hypothesized that foundresses from warm temperate zones would show a higher activity level compared to those from cold temperate zones before brood emergence, based on differences in air temperature between the two zones. After brood emergence, we expected a reduced foundress activity level in the warm climate zone, due to workers’ help. In contrast, foundresses living in the cold-climate zone, which do not produce workers, were expected to remain active throughout the nesting season. We also hypothesized that colony productivity was higher in warm-climate colonies. As expected, warm-climate foundresses reduced their activity level after brood emergence and, with their relatively large number of workers, continued egg production throughout the nesting season. Further studies are necessary to assess if these intraspecific differences are attributable to phenotypic plasticity or genetic divergence.