Mass breeding larvae of the critically endangered diving beetles Dytiscus sharpi sharpi and Dytiscus sharpi validus (Coleoptera: Dytiscidae)

For conservation purposes, and to supply critically endangered insects for laboratory use, a system for artificial breeding is crucial. However, in the case of carnivorous insects such as diving beetles, the larvae must be isolated because they are cannibalistic. We developed a method for mass breeding the larvae of two diving beetles, Dytiscus sharpi sharpi (Wehncke) and Dytiscus sharpi validus (Régimbart) (Coleoptera: Dytiscidae), which are designated critically endangered species in Japan. Ten to twenty larvae were raised in a small tank (35 cm × 25 cm × 10 cm; water depth 7 cm) with Rana ornativentris (Werner) tadpoles as prey. At low prey density, ~80 % of the larvae were cannibalized. At moderate prey density, 50–60 % were cannibalized. However, at high prey density, <3 % were cannibalized. Well-fed mass-bred adults were larger than individually bred and field-collected adults. This mass breeding method can be used for the conservation and breeding of these rare diving beetles in a manageable number of aquaria.     

Temperature-dependent regulation of reproduction in the diving beetle Dytiscus sharpi (Coleoptera: Dytiscidae)

The effects of temperature on the mating behavior, gonad development, germ cell maturation, and egg spawning of the predaceous diving beetle Dytiscus sharpi (Coleoptera; Dytiscidae), were investigated. By field observations, we found that mating behavior started in October and occurred more frequently from November to December. Under our laboratory breeding conditions, we observed almost the same seasonal variation in mating behavior. We found that temperatures lower than 20 degrees C were required to trigger mating behavior. We also found the same temperature threshold triggered gonadogenesis as well as spermatogenesis. Furthermore, for females, exposure to lower temperatures (<8 degrees C) during the winter was required for egg maturation and spawning in spring; that is, there was a second threshold for successful female reproduction. We conclude that the termination of summer reproductive diapause of D. sharpi is regulated in a temperature-dependent manner, thus effecting the adaptation of D. sharpi to southern warm habitats.     

Predaceous diving beetle, Dytiscus sharpi sharpi (Coleoptera: Dytiscidae) larvae avoid cannibalism by recognizing prey

Larvae of diving beetles such as the various Dytiscus species (Coleoptera: Dytiscidae) are carnivorous and usually prey on other aquatic animals. Cannibalism among larvae of Dytiscus sharpi sharpi (Wehncke) was observed to begin when they were starved for more than two days under artificial breeding conditions. However, the 2-day starved larvae did not show cannibalism in the presence of intact, motionless, frozen tadpoles, or frozen shrimps. The beetle larvae attacked and captured intact tadpoles faster (15 sec) than other motionless and frozen tadpoles (120 sec), indicating that prey movement was an important factor in stimulating feeding behavior in larvae. Prey density does not have an effect on larval cannibalism. In cases in which preys are present at lower densities than that of larvae, a group of beetle larvae frequently fed on single prey. This feeding behavior, therefore, provides direct evidence of self-other recognition at the species level. Using two traps in one aquarium that allows the larvae to detect only prey smell, one containing tadpoles and another empty, the beetle larvae were attracted to the trap with tadpoles at high frequency, but not to the empty trap. In another experiment, the beetle larvae were not attracted to the trap containing a beetle larva. These results suggest that the larvae of D. sharpi sharpi are capable of recognizing prey scent, which enables the promotion of foraging behavior and the prevention of cannibalism.     

The effect of food consumption on sodium and water balance in the predaceous diving beetle,Dytiscus verticalis

Summary Sodium and water balance ofDytiscus verticalis in fresh water were investigated under three feeding regimes: unfed, and fed a diet either low or high in sodium chloride. Unfed sodium influx was 0.13 and sodium efflux was 0.74 moles/100 gwm·h. These values are low in comparison with most freshwater animals. The electrical potential difference across the integument in artificial soft water (ASW) was about 150 mV smaller than the potential necessary to maintain sodium balance in the absence of active transport. However, sodium influx did not show saturation kinetics over an external concentration range of 91 to 1725 M. Unfed beetles failed to arrest net sodium loss to baths that were initially distilled water or ASW, even when bath sodium concentrations reached 75–298 M. The long-term rate of net sodium loss ranged from 0.61 to 4.4 moles/100 gwm·h for four sets of animals. Beetles decreased sodium efflux during a period of fasting. During subsequent feeding, beetles fed a high sodium diet (HSD) increased sodium efflux while beetles fed a low sodium diet (LSD) maintained low rates of sodium efflux. HSD fed beetles increased body sodium and hemolymph sodium concentration, and expanded extracellular fluid, relative to LSD fed beetles. Thus beetles cannot achieve sodium balance in fresh water without dietary sodium input, although they are able to regulate sodium loss.Abbreviations gwm grams wet mass - ASW artificial soft water - DW distilled water - HSD high sodium diet - LSD low sodium diet - ECF extracellular fluid volume     

Preference of oviposition plant and hatchability of the diving beetle,Dytiscus sharpi (Coleoptera: Dytiscidae) in the laboratory

For the conservation of the diving beetle, Dytiscus sharpi (Wehncke) (Coleoptera: Dytiscidae), which is included in the Red List of Japan, it is critical to understand its ecological background. In the present study, oviposition preference and hatchability were investigated under laboratory conditions. Possible candidates of oviposition plants were observed in the natural breeding habitats of D. sharpi. Eight aquatic plants were identified, and Oenanthe javanica (Blume) was the major species present in March, when first instar larvae appeared. The number of eggs laid was investigated under the following conditions: (i) eight field plants were authentically recreated at a similar covering rate to that in the natural habitat; (ii) each of the eight plants was set at the same covering rate; (iii) a single plant taken from the field was placed separately. Significant oviposition preference for O. javanica was found when these eight aquatic plants were present in the same aquaria. In addition, hatchability in O. javanica was significantly higher than that in any of the other plants. These results suggest that O. javanica is an important aquatic plant for oviposition by D. sharpi.     

Beetle and plant density as cues initiating dispersal in two species of adult predaceous diving beetles

Dispersal can influence population dynamics, species distributions, and community assembly, but few studies have attempted to determine the factors that affect dispersal of insects in natural populations. Consequently, little is known about how proximate factors affect the dispersal behavior of individuals or populations, or how an organism’s behavior may change in light of such factors. Adult predaceous diving beetles are active dispersers and are important predators in isolated aquatic habitats. We conducted interrelated studies to determine how several factors affected dispersal in two common pond-inhabiting species in southern Alberta, Canada: Graphoderus occidentalis and Rhantus sericans. Specifically, we (1) experimentally tested the effect of plant and beetle densities on dispersal probabilities in ponds; (2) surveyed ponds and determined the relationships among beetle densities and plant densities and water depth; and (3) conducted laboratory trials to determine how beetle behavior changed in response to variation in plant densities, conspecific densities, food, and water depth. Our field experiment determined that both species exhibited density dependence, with higher beetle densities leading to higher dispersal probabilities. Low plant density also appeared to increase beetle dispersal. Consistent with our experimental results, densities of R. sericans in ponds were significantly related to plant density and varied also with water depth; G. occidentalis densities did not vary with either factor. In the laboratory, behavior varied with plant density only for R. sericans, which swam at low density but were sedentary at high density. Both species responded to depth, with high beetle densities eliciting beetles to spend more time in deeper water. The presence of food caused opposite responses for G. occidentalis between experiments. Behavioral changes in response to patch-level heterogeneity likely influence dispersal in natural populations and are expected to be important for observed patterns of individuals in nature. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Variation in prey-specific consumption rates and patterns of field co-occurrence for two larval predaceous diving beetles

Freshwater predatory insects can exert strong effects on prey, although how multiple similar predators may coexist is not well understood. Larval predaceous diving beetles are often numerically and taxonomically abundant predators in lentic systems, but the proximate mechanisms that explain their high abundance remain unknown. Field surveys were conducted twice in June in ponds in Alberta, Canada to assess the associations between larvae of two genera (Graphoderus, Rhantus), their spatial locations, and correlations with potential prey. Both larvae were common and positively correlated within wetlands although neither varied with pond depth nor distance from edge. Laboratory trials indicated that Graphoderus consumed more prey (corixids) at the surface, whereas Rhantus killed benthic prey (chironomids) and corixids at an equal rate; damselflies were the least consumed prey. Predation also varied with depth, with both larvae feeding at higher rates in the shallowest environments compared to Graphoderus at an intermediate depth. Predator–prey correlations from ponds were mostly congruent with predation trials; Graphoderus was positively correlated with corixids, Rhantus was positively correlated with corixids and chironomids; beetles were uncorrelated with damselflies. Reliance on different prey in different microhabitats may be an important mechanism for the maintenance of high abundance of dytiscid larvae.     

Behavior and aquatic plants as factors affecting predation by three species of larval predaceous diving beetles (Coleoptera: Dytiscidae)

Predation among aquatic invertebrate predators can have important effects on patterns of exclusion and coexistence in aquatic habitats, especially if these predators also act as intraguild predators. Such patterns may be explained by variation in predator foraging mode and in the extent and overlap of habitat use. Predaceous diving beetles (Coleoptera: Dytiscidae) are abundant in isolated bodies of water and are effective predators on many aquatic organisms, including other dytiscids. The under-investigated role of hunting behavior and habitat use in altering outcomes of predation under different plant densities may offer insights into patterns of coexistence among larval dytiscids. I performed experiments that quantified behavior of larvae of three common genera of dytiscids that share common prey and then measured predation among genera in the presence or absence of aquatic plants. Behavioral analyses concluded that there were significant differences in foraging modes, with Dytiscus primarily exhibiting sit-and-wait tactics, Graphoderus engaging in active, open water searching, and Rhantus displaying combinations of these behaviors. Predation among larvae was common and occurred when predators were larger than the prey, with no indication of prey preference. Incidence of predation among generic combinations depended on the presence of plants and appeared to be related to behavioral differences among genera. The presence or absence of plants and differences in larval behavior may help to mitigate predation by reducing negative interactions in natural aquatic systems. These results have implications for IGP interactions and may be one of the explanations for the observed richness of this group of predators within aquatic habitats.     

Cracks or holes in the stems of oviposition plants provide the only exit for hatched larvae of diving beetles of the genera Dytiscus and Cybister

Diving beetles such as Dytiscus and Cybister species (Coleoptera: Dytiscidae) usually oviposit inside an aquatic plant stem beneath the surface of the water. The hatched larvae need to escape from the stem to intake oxygen from the air. To determine where larvae of these diving beetles hatch in the plant stem, the hatchability and escape rates in larvae of Dytiscus sharpi Wehncke, Cybister chinensis Motshulsky, Cybister lewisianus Sharp, and Cybister brevis Aubé were investigated under laboratory conditions. Hatchability of D. sharpi in the stem of Sagittaria trifolia L. (Alismataceae) was extremely low (8.2%). However, it was high (>90%) when late‐stage eggs (2–3 days before hatching) were isolated from the stem and kept in water. On the other hand, the hatchability of Cybister spp. was high (88–95%) in S. trifolia. Usually, Cybister spp. females bite a hole in the plant stem on oviposition. When the oviposition pore in the stem was plugged with glass wool, no larvae could escape from the stem, indicating that the oviposition pore was the only exit for hatched larvae of Cybister spp. In contrast, females of D. sharpi oviposited directly by making a crack in the stem of Oenanthe javanica (Blume) DC. (Apiaceae) without biting. Eggs grew to a length and diameter equal to the stem crack size 2–3 days before hatching. Dytiscus sharpi eggs isolated from O. javanica were artificially inserted into plant stems of O. javanica or S. trifolia (so‐called inserted egg model), and the hatchability and larval escape rates were determined. Larval escape strongly depended on the stem crack width of both O. javanica and S. trifolia, suggesting that the stem crack was an exit for hatched larvae of D. sharpi.     

自然条件下福寿螺繁殖特性

为了弄清福寿螺在自然条件下的繁殖特性,在湖南省资兴市水稻田内进行了为期3年的人工养殖试验.结果表明:福寿螺在湘南自然条件下1年可发生不完全3代.第1代、第2代和第3代(越冬代)雌螺的平均性成熟期分别为59.3、45.4和213.0 d.雄螺的平均性成熟期比雌螺早4.3d.福寿螺的自然性比(♀∶♂)为1.54:1.每次交配持续时间平均为19.2h,但并非每次交配后都会产卵.田间福寿螺月产卵块数与月平均气温呈显著正相关(r=0.756).福寿螺卵块的平均孵化期(d)与日平均气温(℃)呈显著负相关(r=-0.980),其线性回归方程为y=-0.726x+23.064.福寿螺卵块的平均孵化期为20.7d,平均孵化率为44.1％.雌螺与雄螺的平均寿命分别为2.40和1.98 a.平均每头雌螺一生可产卵13764粒,可繁殖幼螺6070头.     

Costs and benefits of reproduction in predaceous ladybird: Effect of multiple matings on reproduction and offspring development

A few matings are sufficient for females to maximize their reproductive success, while male fitness usually increases with an increase in the number of matings. However, females of a majority of insects mate multiple times. This presents an evolutionary puzzle and brings an understanding that some benefits are associated with it. Therefore, to understand the costs and benefits of multiple matings, we performed an experimental study in a ladybird beetle, Anegleis cardoni and observed reproductive performance and longevity of adults as direct benefits and offspring development and survival as indirect benefits. This is the first time that the effect of multiple matings is being evaluated on offspring development and survival in a ladybird beetle. Results clearly reveal that females directly benefit from multiple matings in terms of increased lifetime fecundity and egg viability, but their longevity decreases with increased number of matings. Best-fit curves on lifetime fecundity and percent egg viability revealed that maximum fecundity and egg viability were both attained after 17 matings. Developmental duration of offspring decreased and their survival increased with an increase in number of matings. Developmental duration was shortest after 20 matings and longest after a single mating.     

Mating behavior of Aegla platensis (Crustacea, Anomura, Aeglidae) under laboratory conditions

The mating behavior of several decapod crustaceans has been extensively studied; however, this aspect of anomuran biology is still poorly known in some groups. Aeglids are the only anomurans inhabiting freshwaters, and the mating behavior of the species in this family is unknown. We provide the first account of the mating behavior of an aeglid, Aegla platensis, under laboratory conditions. The precopulatory phase was characterized by male agonistic display, male approach, and courtship. Males exhibited the agonistic display toward immature and mature females, but only physiologically mature females allowed males to approach. Male approach led to display of courtship behaviors (body vibration, thrust, body lifting, and abdomen flapping). During the copulatory phase, males and females touched each other with the antennae (antennae touch), and males positioned themselves beneath the females (supine position). Although sperm transfer was not directly observed, a “white mass” was detected among oocytes in the female abdominal chamber shortly after some copulations. Finally, in the postcopulatory phase, males guard females during the process of egg attachment. Despite their morphological similarities with other anomurans, the mating behavior of aeglids seems to be unique, and the freshwater environment appears to have an important role in driving these differences.     

Survival and reproduction in some algae under stress conditions

Pithophora oedogonia and Cladophora glomerata survived lowest 60 and 58%, respectively, in June when the pond diurnal water temperature (PDWT) increased to a maximum of 28 degrees C. The lowering of PDWT only by 1 degrees C in July improved survivability of both algae to their almost maximum level of 100 and 96%, respectively. Further lowering of PDWT to 17-22 degrees C in November initiated akinete formation in P. oedogonia. The process of akinete initiation, maturation and germination continued till April when PDWT increased to 20-24 degrees C, but not beyond that in May when PDWT was 21-26 degrees C. By this time, probably all akinetes have germinated in situ, and the alga was entirely vegetative. P. oedogonia population is not synchronous in nature, since during the 5-6-month reproductive season, some filaments were in active vegetative stage, some had akinete initiation, some had completed akinete formation, and some had akinetes germinating. C. glomerata grew dense vegetative in November and initiated (zoo)sporangial primordia formation (to some extent) in February (when PDWT was lowest, viz. 10-14 degrees C) till April. Meanwhile, no (zoo)-sporangial primordia either produced any zoospore or germinated into a germ tube; and all released their cytoplasmic content and died (along with some vegetative cells) with an increase in PDWT to 21-26 degrees C in May. Vaucheria geminata vegetative patches appeared on the soil surface, 2nd week of January by lowering of atmospheric diurnal temperature (ADT) to 9-16 degrees C in the 1st week. The alga started sexual reproduction by the 2nd week of March (when ADT increased to 20-23 degrees C) and completed the process of reproduction by the 1st week of April (when ADT increased to 24-26 degrees C) and died thereafter. P. oedogonia, C. glomerata and V. geminata survived better and longer in submerged conditions than air-exposed (which was true for P. oedogonia and C. glomerata aquatic habitat and also indicated that the soil alga V. geminata could survive to some extent if submerged in rain water). P. oedogonia formed akinetes and C. glomerata (zoo)sporangial primordia only in submerged condition and not when air-exposed on moist soil surface. V. geminata did not complete the life cycle both under submerged and air-exposed conditions. Vegetative survival in P. oedogonia, C. glomerata, V. geminata, Aphanothece pallida, Gloeocapsa atrata, Scytonema millei, Myxosarcina burmensis, Phormidium bohneri, Oscillatoria animalis, O. subbrevis, Lyngbya birgei, L. major, Microcoleus chthonoplastes and Rhizoclonium crassipellitum, reproduction in P. oedogonia, C. glomerata and V. geminata, cell division in A. pallida and G. atrata, heterocyst and false branch formation in S. millei, all, were adversely affected at approximately 28.5 degrees C for t12 h at light intensity of approximately 160 micromol m(-2) s(-1); high intensity does not ameliorate high temperature damage to any algae. The presence of liquid water, than its absence, outside the different algae moderated the severity of heat to some extent but not when the heat was severe.     

Flight muscle changes in male pine engraver beetles during reproduction: the effects of body size, mating status and breeding failure

Abstract. In a pattern that is typical for bark beetles, the lateralis medius flight muscle of male pine engravers, Ips pini Say (Coleoptera: Scolytidae), was found to decrease four-fold in volume (from mean ± SE = 1.36 ± 0.06 × 10^?2 mm³ to 0.34 ± 0.06 × 10^?2 mm³) within five days of the initiation of breeding galleries, and then to regenerate gradually to functional capacity during subsequent weeks. Although there was considerable variation in the timing and extent of flight muscle regeneration in males, this variation was not a consequence of differences between small (length < 4.0 mm) and large (length ≥ 4.0 mm) males. Two subsequent experiments revealed that male pine engravers can control the timing of flight muscle regeneration. In the first experiment, the flight muscles of males that were denied mates degenerated within 5 days of gallery initiation, but then showed complete regeneration 5 days later. In the second experiment, mated males that were removed from their breeding galleries (to simulate breeding failure) also showed extensive muscle degeneration 5 days after gallery initiation, but then regenerated their flight muscles to functional capacity by the tenth day. The ability of males to regenerate their flight muscles in response to conditions at the gallery is probably adaptive because it allows them to fly in search of new breeding opportunities when they are unable to attract mates or when breeding attempts fail.     

Mating behavior of bucks and does in goat operations under range conditions

The objectives of this study were to characterize the mating capacity of bucks under range condition and assess the effect of mating frequency on flock fertility. Two adjacent flocks of crossbred goats (Criolloxdairy breeds; n=70 does, 5 bucks and 141 does, 4 bucks) were used in this study. The mating period was 16 and 20 days for each flock, respectively, in January and February, 1996. Mating activity of bucks and does was recorded day and night during the first 11 days of the breeding period. The combined data of both flocks showed a strong relationship between number of goats in estrus and the average services of bucks (r=0.95; P<0.01). With an excess of estrous does, bucks on average copulated 9.1 times daily during the first 11 days of the mating period. Considering both flocks combined, does copulated on average 4+/-1.8 times through the estrus period, and they did so with an average of 2.2+/-1.3 different bucks. Sexual activity of bucks was greatest from sunset to midday. Number of services from different bucks did not affect pregnancy rate (81.4% for goats serviced by 1-2 bucks and 77.8% for goats serviced by 3-4 different bucks; chi(2)=0.25; P7 services, respectively; chi(2)=0.67; P0.05). Mean+/-S.D. daily liveweight loss of bucks during the entire mating period was 547+/-197 g. It was concluded that, with buck percentages higher than 3%, the number of ejaculations of bucks is linearly and positively related to number of females in estrus. Also, these findings indicate that neither number of copulations nor number of services from different bucks affected kidding rates.     

Phylogeny and classification of diving beetles in the tribe Cybistrini (Coleoptera, Dytiscidae, Dytiscinae)

Phylogenetic relationships among members of the diving beetle tribe Cybistrini (Coleoptera: Dytiscidae) were inferred from analysis of 47 adult and larval morphological characters and sequences from portions of the genes cytochrome oxidase I (COI) and II (COII), histone III (H3) and wingless. Thirty‐three species of Cybistrini were included, representing all genus‐groups except Regimbartina Chatanay and Megadytes (Bifurcitus) Brinck, and most historically recognized species groups and subgenera used in the tribe. Outgroups include six species from other tribes within Dytiscinae and Lancetinae. Analyses included parsimony analysis of the combined data, likelihood analysis of combined molecular data and partitioned Bayesian analysis of the combined data. Results indicate that Cybistrini is well supported as a monophyletic group. Within the tribe, all currently recognized genus groups were found to be monophyletic with the exception of Onychohydrus Schaum, which is paraphyletic with respect to Austrodytes Watts in the parsimony analysis, but monophyletic in the likelihood and Bayesian analyses, and Cybister sensu stricto, which is paraphyletic with respect to C. (Melanectes) Brinck and C. (Scaphinectes) Ádám in the parsimony analysis or only the latter in the likelihood and Bayesian analyses. Results also suggest that some, but not all, historically recognized species groups or subgenera in the large genus Cybister Curtis are monophyletic, and this is discussed and compared. To improve the classification, the name Sternhydrus Brinck is elevated from subgenus to genus rank ( new status ). Four subgenera in the genus Cybister are recognized: C. (Melanectes) Brinck, C. (Megadytoides) Brinck ( resurrected ), C. (Neocybister) Miller, Bergsten and Whiting ( new subgenus ) and C. (Cybister) Curtis. The following new synonyms are established: Trochalus Dejean ( new synonym ), and ScaphinectesÁdám = Cybister (Cybister) ( new synonym ). The Neotropical species Cybister parvus Trémouilles (not examined) apparently does not fit any historical or currently recognized genus‐group diagnosis in Cybistrini, so it is retained in Cybister but incertae sedis with respect to subgenus. In addition to classification, the evolution of the unique character combinations present in cybistrines are discussed. A key to the adults of genera and subgenera is presented.