The number of tadpoles consumed by the nymphs of the giant water bug <Emphasis Type="Italic">Kirkaldyia deyrolli</Emphasis> under laboratory conditions

Giant water bug Kirkaldyia (=Lethocerus) deyrolli (Belostomatidae: Heteroptera) nymphs consume many individuals of anuran larvae (tadpoles) before they reach adulthood. However, no quantitative data on the number of tadpoles consumed have been made available until now, despite the importance of this data for the conservation of this species. The number of tree frog, Hyla japonica (Hylidae: Anura), tadpoles consumed by nymphs of K. deyrolli was examined under laboratory conditions. The number increased according to the developmental stage of the nymphs; the fifth instar nymphs were the highest consumers. The total numbers consumed by the nymphs throughout development were 155.0 ± 12.8 (average ± SD) and 172.8 ± 9.6 for the males and the females, respectively. Thus, it might be important to maintain high densities of frogs in fields to conserve the population of K. deyrolli into the future.     

Young giant water bug nymphs prefer larger prey: changes in foraging behaviour with nymphal growth in Kirkaldyia deyrolli

Raptorial characteristics may evolve in predators because of their importance in obtaining food. The giant water bug, Kirkaldyia deyrolli, possesses a claw on the terminal segment of the raptorial foreleg that is crucial for capturing prey. Claw curvature has been previously shown to change during growth in this species, but the adaptive significance of this change has not yet been explored. Predation experiments have demonstrated that young nymphs with highly curved claws caught proportionally larger prey than older nymphs with less‐curved claws. Catching behaviours for a certain prey size differed significantly between young and older nymphs. The observation that nymphal growth affects prey‐catching behaviour in the giant water bug supports the hypothesis that predators can change catching behaviours based on changes in raptorial characteristics in order to maximize prey resources acquired at each developmental stage.     

Food shortage affects flight migration of the giant water bug Lethocerus deyrolli in the prewintering season

The endangered giant water bug Lethocerus deyrolli (Vuillefroy) is frequently attracted in large numbers to artificial lights in Japan. To examine factors enhancing flight migration for L. deyrolli, we carried out field work in western Hyogo Prefecture, central Japan, in September during the nonreproductive and prewintering season. The body weight of specimens collected under flight migration (flight bugs) was significantly less than that of those collected in ponds (pond bugs). A field experiment using open cages in a rice paddy field was carried out with two treatments, with and without a food supply. The remaining rate of L. deyrolli for the food present treatment was significantly higher than that for the food absent treatment for the first two days. These results suggest that L. deyrolli would fly in search of food when the food supply of the present habitat becomes unsuitable.     

The water system of traditional rice paddies as an important habitatof the giant water bug, <Emphasis Type="Italic">Lethocerus deyrollei</Emphasis> (Heteroptera: Belostomatidae)

The population dynamics of Lethocerus deyrollei, including the seasonal change in the habitat utilization, were studied in five types of waters, permanent and temporary pools, ditch, rice paddy and marsh in a Satoyama, the traditional landscape in Japan consisting of mixtures of coppice woodlands, farmlands, and settlements, in northern Osaka, from June, 1999 to December, 2001. A mark and recapture census was carried out with adults, and the stage and the number were recorded in nymphs. A total of 95 adults were numbered, and 48 (51%) were recaptured in all the five water types during the study period. Adults of the new generation appeared from late July, and disappeared before the winter in all types of waters. A total of three overwintered adults were recaptured in permanent and temporary pools, ditch, and paddy from between early April and early June. Densities of both L. deyrollei adults and their prey, tadpoles and frogs, were high in permanent and temporary pools, and ditch, in which water temperatures were high in the summer season. Third to fifth (final) instar nymphs were also observed in all water types with different densities in summer, while first and second instars were found only in permanent pool, ditch and paddy habitats in which water temperatures were high and oviposition substrata such as the rice plant, other hygrophytes and wooden stakes existed. These results show that the traditional water system of paddy in the Satoyama landscape as a whole provides an important habitat for L. deyrollei which is now under threat by changing agricultural practices like other native biota inhabiting the system.     

The movement of water into submerged prey during feeding by the aquatic bug Ranatra dispar (Heteroptera: Nepidae), the water stick insect

By the use of a fluorescent dye it was shown that, during feeding by an aquatic bug, water from the external environment passes into the prey's body though puncture holes from previous feeding sites. Such a phenomenon, resulting in the diluting of the prey's body contents, may be used as a physiological stimulus to detect the quality of the prey, leading to movement to another part of the prey's body or discarding the prey.     

Feeding preference of the rice stink bug on annual grasses and sedges

Adults of the rice stink bug, Oebalus pugnax (F.), preferred panicles of vasey grass, Paspalum urvillei Steud., over those of 11 species of other grasses and one species of sedge (Cyperus) associated with cultivated rice, Oryza sativa (L.). The number of feeding adults increased approximately 2 times from 1 h post-infestation (PI) to 6 h PI. The number of feeding females was greater than males at 1 h PI but no different at 6 h PI. Both sexes fed significantly (P<0.05) more on O. sativa panicles than on P. urvillei panicles at 6 h PI. Both sexes also fed significantly (P<0.05) more on 28 and 21 cm long O. sativa panicles than on 7 cm long panicles, but no such differences existed in feeding among P. urvillei panicles.

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Résumé Les adultes d'Oebalus pugnax F. ont préféré les panicules de Paspalum urivillei Stend à celles de 11 autres Graminées et 1 Cypéracée associées au riz cultivé, Oryza sativa L. Le nombre d'adultes s'alimentant a cru environ 2 fois de la lère (1P1) à la 6ème (6P1) heure ayant suivi l'infestation. Le nombre de femelles s'alimentant était supérieur à celui des mâles 1 heure après (1P1), mais ne présentait pas de différence 6 h après l'infestation (6P1). Les 2 sexes s'alimentaient significativement plus (P< 0.05) sur les panicules d'O. sativa que sur celles de P. urvillei 6 heures après l'infestation (6P1). Les 2 sexes se sont alimentés significativement plus (P< 0,05) sur des panicules d'O. sativa de 28 et 21 cm que sur ceux de 7 cm, mais aucune différence n'était observée dans l'alimentation sur les panicules de P. urvillei.

     

Odour-mediated responses of a predatory mirid bug and its prey, the two-spotted spider mite

It has been shown that many natural enemies of herbivorous arthropods use herbivore induced plant volatiles (HIPVs) to locate their prey. Herbivores can also exploit cues emitted by plants infested with heterospecifics or conspecifics. A study was conducted to test whether green bean HIPVs as well as odours emitted directly by spider mites influenced the orientation behaviour of the predatory mirid bug, Macrolophus caliginosus and its prey, Tetranychus urticae in a Y-tube olfactometer. Our results show that both spider mites and M. caliginosus preferred spider mite infested green bean plants to uninfested plants. For M. caliginosus this response was mediated by HIPVs whereas for T. urticae it was mediated through a composite response to both HIPVs and odours emitted directly by the conspecifics (and their associated products). The results may be of use in practical biocontrol situations, through e.g., plant breeding for improved HIPV production, conditioning of mass-reared predators to appropriate cues, and employment of “push–pull-strategies” by using HIPVs.     

Reproductive investment and somatic growth rates in longear sunfish

Synopsis Allocation of energy to current reproduction at the expense of other functions, such as growth, can limit future reproductive potential. This cost of reproduction is a central concept of life history theory but has been difficult to verify in comparative field studies. Three levels of comparison of growth rates and reproductive investments were evaluated within and among populations of longear sunfish,Lepomis megalotis. All three demonstrated high levels of reproductive investment associated with reduced somatic growth. Within populations of central longear sunfish there are precociously mature sneaker makes and later maturing parental makes; sneakers have greater gonadosomatic index (GSI) values and slower somatic growth rates than parental makes. Between subspecies of longear sunfish grown under common conditions, there are differences in age at maturity and in the level of physiological reproductive investment that are associated with distinct differences in growth rates. Between populations of central longear sunfish inhabiting different sites, there are differences in the level of reproductive investment that are also associated with differences in somatic growth. Each comparison produced evidence that trade-offs occur between these life history traits, supporting the hypothesis that there is a cost of reproduction among male sunfish and suggesting that differences in strategies of reproductive investment contribute to variation in somatic growth.     

The interaction of water flow and nutrients on aquatic plant growth

A long-term experiment was conducted to compare the effects of flowing and still water on growth, and the relationship between water flow and nutrients, in Aponogeton elongatus, a submerged aquatic macrophyte. A. elongatus plants were grown for 23 weeks with three levels of nutrition (0, 0.5 and 1g Osmocote Plus® fertiliser pot^–1) in aquaria containing stirred or unstirred water. Fertilized plants grew much better than non-fertilized. The highest fertilizer level produced 29% wider leaves and 58% higher total dry weight in stirred water. Stirred water increased leaf area by 40% and tuber size by 81%, but only with the highest level of nutrition. These results suggest that this plant depends on its roots for mineral uptake, rather than from the open water, and the major limitation to growth in still water is the supply of dissolved inorganic carbon. It was the combined effects of nutrient availability and stirring that produced the strongest response in plant growth, morphology and composition. This study provides some explanation for the observations of others that these plants grow best in creeks or river systems with permanently flowing water.     

Effects of diet on longevity and fecundity of the spined stilt bug, Jalysus wickhami

We evaluated the suitability of selected food items for the adult spined stilt bug, Jalysus wickhami Van Duzee (Hemiptera: Berytidae), by providing one of seven diet treatments: (1) prepupae of the parasitoid, Cotesia congregata (Say) (Hymenoptera: Braconidae), on a leaf of tobacco (Nicotiana tabacum L., NC 2326) (Solanaceae); (2) C. congregata prepupae alone (i.e., no tobacco leaf); (3) eggs of the parasitoid's host, Manduca sexta (L.) (Lepidoptera: Sphingidae), on a tobacco leaf; (4) M. sexta eggs alone; (5) tobacco aphids, Myzus nicotianae Blackman (Homoptera: Aphididae), on a tobacco leaf; (6) a tobacco leaf alone; and (7) no prey and no tobacco. A tobacco leaf was necessary for the long-term survival of stilt bugs, but prey source did not affect longevity. Regardless of the prey type, stilt bugs with access to a tobacco leaf lived 21–23 days, while stilt bugs without access to tobacco lived less than 12 days. Animal prey provided a protein source required for egg deposition in J. wickhami, and prey species differed in their relative nutritive values. Female stilt bugs that fed on M. sexta eggs or on C. congregata prepupae were significantly more fecund (102 and 106 nymphs per female, respectively) than females that fed on tobacco aphids (24 nymphs per female). Results suggest that stilt bugs may feed on tobacco aphids and C. congregata prepupae when other prey are unavailable.     

Influence of prey on developmental performance, reproduction and prey consumption of Neoseiulus californicus (Acari: Phytoseiidae)

The Spical strain of the predatory mite Neoseiulus californicus (McGregor) is used as a biological control agent, but little is known about its preferred prey and host plants in Japan. Here we studied the development, reproduction and prey consumption of the Spical strain when fed on eggs of five different spider mite species deposited on both their laboratory-rearing plant and cherry, on which all five spider mite species developed well. The developmental periods of immature N. californicus females and males were significantly affected by the prey species they fed on, but not by the plants. No difference was found between males and females. The developmental period was shorter on eggs of two Tetranychus species than on eggs of Panonychus ulmi. Immature females had a higher predation rate than immature males. Preoviposition period, oviposition period and the number of eggs laid per female were not significantly affected by either the plants or the type of prey eggs. The postoviposition period and total adult longevity were shorter on eggs of P. ulmi than of the other four prey species, but there was no effect of plant substrate. The postoviposition period of the Spical strain was much longer than that of other N. californicus strains or other predatory mite species: the postoviposition period of the Spical strain was more than three times longer than the oviposition period, accounting for more than 75% of the total adult longevity. This suggests that the females need multiple mating to reach full egg load, but this remains to be tested. Total consumption by N. californicus adults was lower for eggs of P. ulmi than for eggs of the other four species, apparently because of the shorter postoviposition period when fed on eggs of P. ulmi. The intrinsic rates of natural increase (r _m) on the rearing plant did not differ among prey species, whereas those on cherry were significantly different: the value was higher on Tetranychus urticae eggs than on eggs of other species. Only when N. californicus fed on T. urticae eggs, the r _m-values were significantly different between the rearing plant and cherry (higher on cherry). Thus, the Spical strain of N. californicus could feed on eggs of all five spider mite species, deposited on a variety of plants with similar r _m-values, suggesting that it could be successfully used to control spider mites in orchards and various crop fields of Japan.     

Notes on predators and their effect on the survivorship of the endangered giant water bug, <Emphasis Type="Italic">Kirkaldyia (</Emphasis>= <Emphasis Type="Italic">Lethocerus) deyrolli</Emphasis> (Heteroptera,Belostomatidae), in Japanese rice fields

A field research was carried out in Hyogo Prefecture, Japan in order to establish the role of the water-scorpion, Laccotrephes japonensis Scott as predator of nymphs of the endangered giant water bug, Kirkaldyia (= Lethocerus) deyrolli. To assess the impact of this predator, a field experiment was set up with (Control) and without L. japonensis (Removed). The survival rate of K. deyrolli in Removed treatment was higher than in the Control. Our experimental results showed that L. japonensis is an important predator for K. deyrolli nymphs in the field. Handling editor: S. Wellekens     

Zooplankton-induced unicell-colony transformation in Scenedesmus acutus and its effect on growth of herbivore Daphnia

The effects of colonial ecomorphs of the green alga Scenedesmus acutus on growth of Daphnia cucullata and D. pulex were examined. In ecologically relevant densities (up to 200 animals l^-1) the relatively small D. cucullata did not induce colony formation in Scenedesmus acutus, whereas the larger congener D. pulex significantly promoted colony formation. Both clearance rate and population growth rate (r) were significantly lower in D. cucullata when fed colonial Scenedesmus then when fed unicellular food. However, for D. pulex no effects of food type were observed. These results show that large Daphnia may influence its food in such a way that smaller congeners and competitors are negatively affected.     

Foliar sprays with ABA promote growth of Ilex paraguariensis by alleviating diurnal water stress

Stomatal closure, relative water content (RWC) and vegetative growth were monitored in Ilex paraguariensis plants grown under well-watered conditions with a photosynthetic photon flux density (PPFD) varying from 100% to 1.5%, and sprayed weekly with either distilled water (control) or 1.89 mM abscisic acid (ABA). ABA treatments caused stomatal closure, ranging from 62% to 73%. These treatments also increased RWC in the early evening from 82% to 92% and 88% to 94% in mature and immature leaves, respectively. Such alleviation of the water stress was correlated with increases in leaf area, leaf dry weight (DW), shoot length and shoot DW. On day 35 from the beginning of the experiment, the increases in DW of both leaves and shoots were 1.5-fold at the 1.5% PPFD and 3-fold (for leaves) and 4.5-fold (for shoots) under 100% PPFD. In water-sprayed control plants grown under 1.5% PPFD shoot length also increased significantly, although these shoots contained more ABA (assessed by capillary gas chromatography–mass spectrometry) than those of plants grown under 100% PPFD. These results show that ABA sprayed on to leaves promotes growth in I. paraguariensis plants by alleviating diurnal water stress.     

Nestling diet variation in an insular Mediterranean population of blue tits Parus caeruleus: effects of years,territories and individuals

Mediterranean evergreen forests of Corsica are characterized by relatively high species diversity of arthropods with low population densities. Food is never superabundant for Corsican blue tits Parus caeruleus. This study focused on the composition of the food of blue tit nestlings and especially on two main components, caterpillars and spiders. The nestling diet was studied for two years using 8-mm cameras that automatically took photographs of adult birds with food. The diet was composed of c. 50% caterpillars and c. 30% spiders. There were between-year and between-individual differences in these proportions. In both years of the study the proportion of caterpillars declined during the course of the breeding season. Individual and time effects on prey sizes were also observed. Pairs and individuals were fairly constant in the proportions of prey over the feeding period. Different food items were not brought in runs. These findings suggest that strong food limitation exists on Corsica, which can considerably influence life-history traits of the blue tit.     

Factors affecting the survival and growth of bacteria introduced into lake water

The populations of Pseudomonas sp. B4, Escherichia coli, Klebsiella pneumoniae, Micrococcus flavus, and Rhizobium leguminosarum biovar phaseoli declined rapidly in lake water. The initially rapid decline of the two pseudomonads and R. phaseoli was followed by a period of slow loss of viability, but viable cells of the other species were not found after 10 days. The rapid initial phase of decline was not a result of Bdellovibrio spp., bacteriophages, or toxins in the water since Bdellovibrio spp. were not present and passage of the lake water through filters that should not have removed bacteriophages or soluble toxins led to the elimination of the rapid phase of decline. The addition of 250 g of cycloheximide and 30 g of nystatin per ml eliminated viable protozoa form the lake water, and the population of Pseudomonas sp. B4 did not fall and the decline of E. coli and K. pneumoniae was delayed or slowed under these conditions. Pseudomonas sp. L2 proliferated rapidly in lake water amended with glucose, phosphate, and NH₄NO₃, but its numbers subsequently fell abruptly; however, in water amended with cycloheximide and nystatin, which killed indigenous protozoa, the population density was higher and the fall in numbers was delayed. Of the nutrients, the chief response was to carbon, but when glucose was added, phosphorus and nitrogen stimulated growth further. Removing other bacteria by filtering the lake water before inoculation with Pseudomonas sp. L2 suggested that competition reduced the extent of response of the pseudomonad to added nutrients. We suggest that the decline in lake water of bacteria that are resistant to starvation may be a result of protozoan grazing and that the extent of growth of introduced species may be limited by the supply of available carbon and sometimes of nitrogen and phosphorus, and by predation by indigenous protozoa.     

The impact of changing irrigation practices in rice fields on frog populations of the Kanto Plain, central Japan

Rice fields are important substitute wetlands for frogs. Traditionally, rice fields in Japan were supplied with water and drained via shallow earth ditches (old-style). In the last 30 years, however, more than 80% of rice fields have been converted to a new irrigation system in which water is typically supplied through underground pipes via taps and is drained into deep, concrete-sided ditches (new-style). We compared the occurrence of frogs in paired areas of old- and new-style rice fields at six locations in Ibaraki Pref., central Japan, from May to August 1995. The Japanese tree frog (Hyla japonica) did not differ in abundance between the two types of rice fields, but the Japanese brown frog (Rana japonica) and the Tokyo daruma pond frog (Rana porosa porosa) preferred the old-style rice fields. These findings suggest that the status ofRana species has been adversely affected by the conversion of rice fields to the new irrigation system. Modification of the deep, U-shaped concrete ditches and the water management regime during the spawning season is needed to safeguard these species.     

Behavioral responses in prey location of the predatory stink bug, Eocanthecona furcellata, to chemical cues in the larvae of Spodoptera litura

Behavioral responses of the predatory stink bug Eocanthecona furcellata (Wolff) (Heteroptera: Pentatomidae) towards Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae) larvae were observed in olfactometers. In single-and dual-tube olfactometers, adult bugs were observed to approach and stretch their proboscis toward the odor source. These types of behavior were also observed toward the control odor source in the dual-tube olfactometer. However, the frequency of these phases toward the control odor was significantly lower than that toward the odors from intact or dead larvae. The solvent extracts of larvae elicited these similar behavioral phases significantly more frequently and for significantly longer duration than the control. In a linear track olfactometer, E. furcellata nymphs were observed to be attracted to the fraction eluted with hexane from silica gel chromatography but proboscis-protruding behavior was not observed. The other fraction, 15%-ether-in-hexane from silica gel chromatography, elicited the proboscis-protruding behavior by a simple behavioral assay using a Pasteur pipette. These findings therefore indicate the presence of at least two different chemical cues in prey location.     

Plant-mediated interactions between the rice water weevil and fall armyworm in rice

Greenhouse studies were conducted to investigate plant-mediated interactions between an above-ground and a below-ground herbivore when sharing a common host plant, rice (Oryza sativa L). Two common pests of rice were used: the rice water weevil (RWW), Lissorhoptrus oryzophilus Kuschel, as the root herbivore, and the fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith) as the foliage-feeding herbivore. Rice water weevil larval performance was assessed by measuring larval density and average weight in response to different levels of defoliation by FAW larvae. The reciprocal experiment was done to evaluate FAW performance (growth rate) in response to RWW feeding. Severe defoliation by FAW decreased RWW densities by 32% and reduced larval weights by 48% compared to larvae on roots of non-defoliated plants. Effects in the converse experiments were not as strong. FAW growth rates were reduced 9–37% when feeding on rice leaves from plants damaged by RWW compared to larvae feed leaves from the no damage treatment. These reciprocal negative effects show that RWW and FAW are potential competitors when sharing a rice plant. Because RWW and FAW did not interact directly, competition was plant-mediated.     

Habits and relative population densities of some hydrophilids in California rice fields

Populations of the hydrophilids Berosus styliferus Horn, Hydrophilus triangularis Say, and Tropisternus lateralis (Fabricius) were observed in northern California rice paddies. Relative adult and larval density for each species was determined using aquatic light traps adjacent to the water margin, and at 5 m and 30 m distances from the levee. Egg cases were monitored by recording numbers per unit area.The seasonal patterns of abundance indicate each species has a univoltine life cycle. All stages of B. styliferus and H. triangularis are more abundant nearer the levees. T. lateralis adults are commonly found at the levees during the first 10 weeks post-flood, whereas T. lateralis larvae and egg cases are most numerous at the 30 m distance.Colonication of the paddies occurs through water connections, flight, and adult overwintering.