Lisa Filippi

Pre- and post-hatch trophic egg production in the subsocial burrower bug, Canthophorus niveimarginatus (Heteroptera: Cydnidae).

In recent years, three terrestrial bugs, Adomerus triguttulus and Sehirus cinctus (Cydnidae) and the closely related Parastrachia japonensis (Parastrachiidae), have been the focus of several fascinating studies because of the remarkable, extensive parental care they were found to display. This care includes egg and nymph guarding, production of trophic eggs, unfertilized, low cost eggs that are used as food by newly hatched nymphs, and progressive provisioning of the host seed. In this study, we have investigated yet a third related Asian cydnid, Canthophorus niveimarginatus, with regard to the possible occurrence of some or all of these complex traits in order to assess how widespread these maternal investment patterns are in this group of insects and to better understand the implications of their manifestations from an evolutionary context. Manipulative experiments were carried out in the lab to determine whether females provision nests. Observational and egg removal studies were carried out to determine whether trophic eggs are produced, and, if they are, their possible impact on nymphal success. The findings revealed that C. niveimarginatus does, in fact, progressively provision young, and this species also displays all of the other behaviors associated with extended parental care in subsocial insects. Moreover, unlike the other two related species, which place trophic eggs on the surface of the original egg mass, C. niveimarginatus produces both pre- and post-hatch trophic eggs. Nymphs deprived of access to post-hatch trophic eggs had significantly lower body weight and survival rate than those that fed on them. To our knowledge, this is the first time the production of both pre- and post-hatch trophic eggs has been demonstrated in insects outside the Hymenoptera. In this paper, we qualitatively and quantitatively demonstrate the provisioning behavior and patterns of trophic egg production in C. niveimarginatus. When and how trophic eggs are produced and delivered to young should have important correlations with the ecological and life history constraints under which a species has evolved. Thus, we also discuss the possible ecological and life history factors that favor the evolution of post-hatch trophic eggs.

Maternal-Care Behaviour in Adomerus variegatus (Hemiptera: Cydnidae)

Abstract Subsociality involving provisioning for offspring has been reported for one shield bug and three burrower bug species (Hemiptera: Pentatomoidea: Parastrachiidae and Cydnidae: Sehirinae). We present the first report of subsocial behaviour in the burrower bug Adomerus variegatus (Signoret), focusing on manifestations of maternal-care, specifically the production of trophic eggs, guarding of offspring, and progressive provisioning. In our study, each female produced an egg mass that included some trophic eggs. Prior to nymphal hatch, females remained in their nests and showed egg mass guarding behaviour. Mothers started provisioning behaviour a few hours after nymphal hatch. Each mother dragged a seed (larger than her body) with her proboscis to the nest as food for the nymphs. These findings suggest that A. variegatus shows maternal-care behaviours similar to those reported in some other pentatomoid species and that trophic egg production and nest provisioning have evolved as interrelated processes.

The Directional Homing Behaviour of the Subsocial Shield Bug, Parastrachia japonensis (Heteroptera: Cydnidae), under Different Photic Conditions

Abstract The female subsocial shield bug, Parastrachia japonensis, provisions its nymphs by foraging on the ground in the forest during the Japanese rainy season, and the bug uses homing navigation to drag a drupe back to its burrow by the shortest route during the day. To study whether or not this bug performs this provisioning behaviour under different photic conditions, we observed the homing behaviour and homing direction of bugs in the field around the clock and/or under various weather conditions. The bugs foraged the whole day during the busiest provisioning period, and the number of walking bugs was not affected by the different weather conditions. Such navigational behaviour, regardless of the time of the day and the weather conditions, is rare in insect navigation. To test whether the bug uses visual cues, we covered the compound eyes and ocelli with opaque or clear paint just before homing began. During the day and at night, and in all weather conditions, the homing direction of blind bugs, but not those with clear-painted eyes was disoriented, indicating that this species uses visual cues dominantly under all photic conditions.

Canopy compass in nocturnal homing of the subsocial shield bug, Parastrachia japonensis (Heteroptera: Parastrachiidae)

In contrast to an open environment where a specific celestial cue is predominantly used, visual contrast of canopies against the sky through the gap, known as canopy cues, is known to play a major role for visually guided insect navigators in woodland habitats. In this paper, we investigated whether a subsocial shield bug, Parastrachia japonensis, could gauge direction using canopy cues on a moonless night. The results show that they could perform the round trip foraging behaviour even in an experimental arena with only an artificial round gap opened in the ceiling of the arena and adjust their homing direction for a new azimuth when the gap was rotated. Thus, P. japonensis can use slightly brighter canopy cues as a compass reference but not complex landmarks during nocturnal homing behaviour.

Round-the-clock Homing Behavior of a Subsocial Shield Bug, Parastrachia japonensis (Heteroptera: Parastrachiidae), Using Path Integration

Abstract Females of the subsocial shield bug, Parastrachia japonensis (Parastrachiidae), are central-place foragers, collecting drupes for their young from nearby host trees by walking along the forest floor both during the day and at night. Because burrows are often some distance from the drupe-shedding tree, the bugs must repeatedly leave their burrows, search for drupes, and return to the burrows. After a bug leaves its burrow, it searches arduously until it encounters a drupe. When a drupe is obtained, the bug always takes the shortest route back to its burrow. It has been clarified that this bug utilizes path integration during diurnal provisioning excursions. In this paper, we examined nocturnal behavior and some parameters of the path integration utilized by P. japonensis. There were no observable differences between day and night in the patterns of foraging and direct-homing behavior. When the bug was displaced to another position during the day or night, it always walked straight toward the fictive burrow, the site where the burrow should be if it had been displaced along with the bug, and then displayed searching behavior in the vicinity of the fictive burrow. The distance of the straight run corresponded accurately with a straight line between the burrow and the place where the bug obtained the drupe. These results indicate that P. japonensis orients toward the burrow using path integration both during diurnal and nocturnal provisioning behavior.

Variation in the Start of Nest Abandonment in the Subsocial Shield Bug Parastrachia japonensis (Hemiptera: Parastrachiidae)

Abstract Females of the shield bug Parastrachia japonensis Scott (Hemiptera: Parastrachiidae) provision their nymph-containing nests with drupes of the single host tree, Schoepfia jasminodora Sieb. et Zucc (Olacaceae: Rosidae: Santales). We carried out several field experiments to examine the variation in the start of nest abandonment by using field cages set in a copse in Japan. First, in individual cages where female parents could freely provision their nests with drupes provided in abundance in a distant foraging cage, we observed when nymphs began abandoning the nests. Considerable variation was found in the beginning of nest abandonment among nests, with a tendency for it to be delayed in nests where the average number of drupes provided per nymph (average provisioning rate) was high. Second, we excluded females from nests when nymphs were in the second stadium. We then artificially supplied drupes at two levels of abundance to verify whether the delay in the start of nest abandonment was caused by an increase in the nymphal daily food availability. Nymphal nest abandonment started in direct response to the amount of artificially provided food. Finally, a field experiment to determine the ability of nymphs at various developmental stages to reach the foraging site from the nest site revealed that younger independent nymphs were rarely able to succeed. We discuss nymphal nest abandonment with regard to assessing the risk of starvation, attributable to a shortage of food provided by the female parent, and postindependence risk.

Guarding behaviour against intraspecific kleptoparasites in the subsocial shield bug, Parastrachia japonensis (Heteroptera: Parastrachiidae)

Females of the subsocial shield bug Parastrachia japonensis progressively provision nymphcontaining burrows with drupes of the host tree, Schoepfia jasminodora. Because an earlier study revealed that intraspecific kleptoparasitism, whereby females steal provisioned drupes from the burrows of other females, is quite prevalent, we investigated whether females have acquired any particular guarding behaviours against intraspecific kleptoparasites. A homed female showed two different behavioural phases: the first was a holding posture phase, assumed when the bug was still holding the newly provisioned drupe, and the second was an attending phase, which occurred when the female released the drupe and set it down in the nest. The nymphs gathered on the provisioned drupe as soon as the female began the holding behaviour, upon returning to the nest. The duration of the holding phase decreased gradually with the development of the nymphs. During the holding phase, the female displayed a distinctive guarding behaviour toward the intruding female, and as a result, had significantly greater success in repelling the intruder than during the attending phase, although the attending behaviour also significantly reduced the rate of kleptoparasitism compared to the control. These results suggest that holding and attending behaviours after homing are direct counter-strategies to intraspecific kleptoparasitism in P. japonensis.