Seasonal suitability of three rubber tree clones to Calacarus heveae (Acari, Eriophyidae)

The suitability of rubber tree clones to Calacarus heveae was inferred from the life cycle, reproduction and survivorship of this mite. The assays were performed under controlled conditions with leaflets detached from 6-year-old plants. The development of 20 C. heveae individuals on each of the clones GT 1, PB 235 and RRIM 600 was analysed. This experiment was performed four times during periods when C. heveae was abundant in the field: (P1) November–December 2005, (P2) January–February, (P3) March–April and (P4) May–June 2006. Accordingly, the leaflets used in each assay represented the physiological condition of the host plant during each period. This approach allowed us to evaluate the seasonal suitability of rubber tree clones to C. heveae. We observed seasonal differences in the suitability of rubber tree clones to mite attack. The mites reared on the PB235 had a shorter development period, the highest egg production and highest survivorship. This evidence showed that the PB 235 was the most suitable of those tested. We also observed that the leaflets used in the assays during periods P2 and P3 were the most favourable for the development of C. heveae. This finding emphasises the seasonal suitability of rubber tree leaflets. On the other hand, GT 1 showed higher resistance against C. heveae than did RRIM 600 and PB 235, primarily during the period from November to February. This result indicated that use of the GT 1 clone to control the mite might represent an alternative for growers.     

Behavioural and population responses to changing availability of <Emphasis Type="Italic">Artemia</Emphasis> prey by moulting black-necked grebes, <Emphasis Type="Italic">Podiceps nigricollis</Emphasis>

Chemical communication may inform about the location of prey, predators, co-specifics, and mate partners in zooplankton. In this study, we evaluated several life-history traits of the rotifer, Brachionus calyciflorus, exposed to conditioned media by a rotifer predator (Asplanchna brightwelli) and a cladocera competitor (Daphnia similis), quantifying population growth and life-table demography at two algal food levels (2.0 and 0.5 × 10⁶ cells ml⁻¹ of Chlorella pyrenoidosa). At both food levels, B. calyciflorus grown in predator-conditioned media had lower population abundance and slower population growth rate than controls. Conversely, the competitor-conditioned media treatments produced both higher rotifer population abundance and faster population growth rate than controls. Life-history parameters varied significantly depending on the presence of predator and competitor-conditioned media. The Asplanchna-conditioned media significantly decreased gross reproductive rate (GRR): 8–9 offsprings per female; net reproductive rate (R ₀): 6–7 offsprings per female; population growth rate (r): 0.34–0.37 day⁻¹; and increased generation time (T): 5.5–5.6 days. On the other hand, The Daphnia-conditioned media significantly increased the GRR (13–14 offsprings per female); net reproductive rate (8–9 offsprings per female); population growth rate (0.42–0.43 day⁻¹); and decreased generation time (4.9–5.0 days). However, the effects of food level on the life-history characteristic were not significant in both treatments. Maximum values of the population abundance and the population growth rate are significantly influenced by the predator densities and pre-culture time. This study suggests that rotifers use variable life-history strategies (low reproduction and high survivorship versus high reproduction and low survivorship) based on the presence of predators and competitors.     

Predator biodiversity increases the survivorship of juvenile predators

When predator biodiversity strengthens herbivore suppression, the pattern generally is attributed to interspecific complementarity. However, the relaxation of intraspecific interference within diverse communities has received less attention as an underlying factor, and most experiments to date span much less than one predator generation. Here, working with a community of aphid predators, we compared the survivorship of juvenile predators embedded within diverse versus single-species communities of adult predators. We found that greater predator diversity improved juvenile survivorship for three of four predator taxa (the lady beetles Hippodamia convergens and Coccinella septempunctata, and the bug Nabis alternatus; but not the small bug Geocoris bullatus), whereas survivorship was relatively low when juveniles foraged among only conspecific adults. When aphid densities differed they were lowest for the diverse treatment, and so resource availability could not explain differences in juvenile survivorship. Instead, feeding trials indicated that cannibalism generally posed a greater risk to juveniles than did intraguild predation (with Geocoris again the exception). Our results suggest that the dilution of intraspecific interference may play an important, and perhaps underappreciated, role in shaping predator diversity effects. Furthermore, relatively strong cannibalism but weak intraguild predation has the potential to project diversity effects forward into subsequent generations.     

Morphological studies on the Sulawesi macaques I: Phyletic analysis of body color

The body color of Sulawesi macaques was measured quantitatively and compared among the different monkeys. As a result, divergence models for extant Sulawesi macaques, withtonkeana as the starting point and fading as the sole direction of color change, were inferred as follows: (1) fading slightly on the upper half of the body—nigra, fading more on the proximal part of the body—nigrescens; (2) fading over the whole body—maura; (3) fading greatly on the legs—hecki; and (4) fading on the distal part of the body—ochreata, fading more over the whole body, including the proximal part of the body—brunnescens. The color changed progressively in the order of (1) through (4). The divergence model, excluding the position ofhecki (3), supports the speciation model ofFooden (1969). If the proto-Sulawesi macaques had a body color pattern similar to the livingnemestrina, darkening would have been necessary for the evolution of the Sulawesi macaques after their immigration, and it may have been acquired as an adaptation to the ground (forest floor) living nature of the Sulawesi macaques, together with influences deriving from the insularity and/or from the absence of predators.     

Life history of the predatory mites <Emphasis Type="Italic">Neoseiulus paspalivorus</Emphasis> and <Emphasis Type="Italic">Proctolaelaps bickleyi</Emphasis>, candidates for biological control of <Emphasis Type="Italic">Aceria guerreronis</Emphasis>

The eriophyoid mite Aceria guerreronis Keifer (Eriophyidae), commonly called the coconut mite, is a key pest of coconut fruits. Surveys conducted on coconut palms in Brazil revealed the predatory mites Neoseiulus paspalivorus DeLeon (Phytoseiidae) and Proctolaelaps bickleyi Bram (Ascidae) as the most commonly associated natural enemies of A. guerreronis on coconut fruits. However, virtually nothing is known about the life history of these two predators. We conducted laboratory experiments at 25 ± 0.1°C, 70–90% RH and 12:12 h L:D photoperiod to determine the life history characteristics of the two predatory mites when feeding on A. guerreronis and other potential food sources present on coconut fruits such as Steneotarsonemus furcatus DeLeon (Tarsonemidae), coconut pollen and the fungus Rhizopus cf. stolonifer Lind (Mucoraceae). In addition, the two-spotted spider mite Tetranychus urticae Koch (Tetranychidae) was tested for its suitability as prey. Both predators, N. paspalivorus and P. bickleyi, thrived on A. guerreronis as primary food source resulting in shorter developmental time (5.6 and 4.4 days, respectively), higher oviposition rate (1.7 and 7.0 eggs/female/day, respectively) and higher intrinsic rate of increase (0.232 and 0.489 per female/day, respectively) than on any other diet but were unable to develop or lay eggs when fed T. urticae. Coconut pollen and S. furcatus were adequate alternative food sources for N. paspalivorus and Rhizopus for P. bickleyi. We discuss the relevance of our findings for natural and biological control of the coconut mite A. guerreronis.     

Predators induce egg retention in prey

To prevent predation on their eggs, prey often avoid patches occupied by predators. As a result, they need to delay oviposition until they reach predator-free patches. Because many species allocate energy to egg production in a continuous fashion, it is not clear what kind of mechanism prey use to delay oviposition. We used females of the phytoseiid mite Neoseiulus cucumeris to study these mechanisms. Females were placed in patches with pollen, a food source they use for egg production, and they were exposed to another phytoseiid mite, Iphiseius degenerans, which is an intraguild predator of N. cucumeris juveniles. We found that the oviposition of N. cucumeris females on patches with the predator was lower than on patches without the predator. Cues left by the intraguild predator were not sufficient to elicit such behaviour. Females of N. cucumeris reduced oviposition when exposed to the predator by retaining the egg inside their body, resulting in a lower developmental rate once these eggs were laid. Hence, females are capable of retaining eggs, but the development of these eggs continues inside the mother’s body. In this way, females gain some time to search for less risky oviposition sites.     

Provision of astigmatid mites as supplementary food increases the density of the predatory mite Amblyseius swirskii in greenhouse crops,but does not support the omnivorous pest,western flower thrips

Astigmatid mites can be used as prey for mass rearing of phytoseiid predators, but also as a supplemental food source to support predator populations in crops. Here we evaluated the potential of six species of astigmatid mites (living or frozen) as alternative food for the predatory mite Amblyseius swirskii Athias-Henriot in greenhouse crops. All prey mites tested were suitable for predator oviposition. In general, oviposition was greater when prey mites were reared on dog food with yeast than when they were reared on wheat bran with yeast. Amongst prey items provided as frozen diet, larvae of Thyreophagus entomophagus (Laboulbene), Acarus siro L. and Lepidoglyphus destructor (Schrank) that had been reared on dog food with yeast, resulted in the highest oviposition rates of A. swirskii. T. entomophagus larvae as frozen diet resulted in the shortest preimaginal developmental time of A. swirskii. On chrysanthemum plants, we found that the greatest increase in predator density occurred when living mites of T. entomophagous were used as a food source. This increase was greater than when predators were fed cattail pollen, a commonly used supplemental food. Effects on predators of providing living A. siro and L. destructor, or frozen larvae of T. entomophagous as food, were comparable with provision of pollen. Use of supplemental food in crops can be a risk if it is also consumed by omnivorous pests such as western flower thrips, Frankliniella occidentalis Pergande. However, we showed that both frozen and living mites of T. entomophagous were unsuitable for thrips oviposition. Hence, we believe that provision of prey mite species increases A. swirskii density, supporting biological control of thrips and other pests in greenhouse crops.

     

Consumption of introduced prey by native predators: Argentine ants and pit-building ant lions

When populations of native predators are subsidized by numerically dominant introduced species, the structure of food webs can be greatly altered. Surprisingly little is known, however, about the general factors that influence whether or not native predators consume introduced species. To learn more about this issue, we examined how native pit-building ant lions (Myrmeleon) are affected by Argentine ant (Linepithema humile) invasions in coastal southern California. Compared to areas without L. humile, invaded areas contained few native ant species and were deficient in medium-sized and large bodied native ants. Based on these differences, we predicted that Argentine ants would negatively affect ant lion larvae. Contrary to this expectation, observational surveys and laboratory growth rate experiments revealed that Myrmeleon were heavier, had longer mandibles, and grew more quickly when their main ant prey were Argentine ants rather than native ants. Moreover, a field transplant experiment indicated that growth rates and pupal weights were not statistically different for larval ant lions reared in invaded areas compared to those reared in uninvaded areas. Argentine ants were also highly susceptible to capture by larval Myrmeleon. The species-level traits that presumably make Argentine ant workers susceptible to capture by larval ant lions—small size and high activity levels—appear to be the same characteristics that make them unsuitable prey for vertebrate predators, such as horned lizards. These results underscore the difficulties in predicting whether or not numerically dominant introduced species serve as prey for native predators.     

A trophic cascade in a macrophyte-based food web at the land–water ecotone

Trophic cascades may purportedly be more common in aquatic than terrestrial food webs, but herbivory on freshwater vascular plants has historically been considered low. Water lilies are an exception, suffering severe grazing damage by leaf beetles. To test whether a central prediction of cascade models—that predator effects propagate downwards to plants—operates in a macrophyte-based food web, we experimentally manipulated predation pressure on a key herbivore of water lilies in the littoral zone of a lake in Michigan, USA. Field experiments comprised combinations of caging treatments to alter the number of predators (larvae of the ladybird beetle Coleomegilla maculata) that hunt the grazers of the macrophytes (larvae of the leaf beetles Galerucella nymphaeae) on the leaves of the water lily Nuphar advena. Predatory larvae of the ladybird beetles significantly reduced grazing damage to water-lily leaves by 35–43%. The predators reduced plant damage chiefly via density-mediated effects, when lower densities of grazers translated to significant declines in plant damage. Plant damage caused by the surviving herbivores was less than predicted from individual grazing rates under predator-free conditions. This suggests that trait-mediated effects may possibly also operate in this cascade. The observed strong effect of predators on a non-adjacent trophic level concurs with an essential component of the trophic cascade model, and the cascade occurred at the ecotone between aquatic and terrestrial habitats: Nuphar is an aquatic macrophyte with emergent and floating leaves, whereas both beetle species are semi-terrestrial and use the dry, emergent and floating leaves of the water lily as habitat. Also, the cascade is underpinned by freshwater macrophytes—a group for which trophic processes have often been underappreciated in the past.     

Relative nutritional value of ciliate protozoa and algae as food forDaphnia

The relative importance of autotrophic flagellates, desmids, cyanobacteria, and ciliates as food forDaphnia magna was examined using cohort life tables. Each cohort was fed a single food type at a given concentration, and comparisons among each type were made. Algal feeding treatments included three levels of young (7 to 14 days old)Chlamydomonas reinhardi (Chlorophyta, Chlamydomonadacae), two levels of senescent (> 14 days old)C. reinhardi, two levels ofCryptomonas sp. (Chlorophyta, Cryptomonadacae), two levels ofStaurastrum sp. (Chlorophyta, Desmidacae), four levels of young (7 to 15 days old) or senescent (> 15 days old)Microcystis aeruginosa (Cyanophyta, Chlorococcacae), and a no-food treatment. The ciliatesCyclidium sp. andParamecium caudatum were also presented at concentrations of 1 or 10² cells/ml, as well as mixtures ofC. reinhardi (10³/ml) andCyclidium (1/ml) orP. caudatum (1/ml).Daphnia growth, reproduction, and survivorship were highest whenC. reinhardi orCryptomonas were the food source, while those starved or fedM. aeruginosa had shorter survivorship and lower growth and reproduction.Daphnia grew and had high survivorship when fedP. caudatum, but even though eggs were produced, most were aborted after 2 or 3 days.Staurastrum andCyclidium produced intermediate growth and survivorship, but reproduction was seen only in the 10³ Staurastrum/ml treatment. Carbon and nitrogen content were general indicators of nutritional value. However, growth, reproduction, and survivorship were higher in some cohorts fed treatments containing relatively low levels of carbon and nitrogen. Other cohorts were short-lived and did not reproduce, despite being fed much higher levels of carbon and nitrogen. The results also suggest that green algae are nutritionally valuable forDaphnia, whereas cyanobacteria are not. As measured by life-table parameters, the nutritional value of ciliates was variable, with some being poor food sources. Thus, the potential of ciliates as a trophic link between microbial production and higher trophic levels may vary with the ciliate community structure. Our results suggest that ciliates alone were insufficient as a food source to supportDaphnia population growth.     

Non-prey food for subsistence of Amblyseius idaeus (Acari: Phytoseiidae) on cassava in Africa

The nutritional effects of pollen from cassava, oil palm, castor bean, Leucaena leucocephala and a phloem exudate from cassava were tested in the laboratory for their effect on survivorship and oviposition of Amblyseius idaeus (Denmark & Muma). Survival and longevity of even-aged females were enhanced on the aforementioned non-prey diets when compared with the control of no food. Castor bean pollen provided sufficient nutrition to induce an irregular and low ovipositional rate of A. idaeus over a five week interval. Oviposition ceased after 48 h in the presence of the other non-prey foods or free-water only. These studies suggest that A. idaeus is capable of switching or supplementing its diet with non-prey foods during periods when spider mite populations are low.     

Cannibalism and Interspecific Predation in a Phytoseiid Predator Guild from Cassava Fields in Africa: Evidence from the Laboratory

Interspecific predation and cannibalism are common types of interaction in phytoseiid predator guilds, but the extent and nature of these interactions have not been determined yet in phytoseiid guilds composed of African native and neotropical exotic phytoseiid predators found in cassava habitat in southern Africa. We determined in laboratory experiments the level of cannibalism and interspecific predation among the three phytoseiid mite species Euseius fustis, Iphiseius degenerans, and Typhlodromalus aripo in the absence of food and in the presence of limited or abundant quantities of two food types – Mononychellus tanajoa and maize pollen – commonly found on cassava in Africa. When confined without food, only two T. aripo females laid each two eggs within 5 days, and this species survived longer than I. degenerans and E. fustis. In the presence of con- or hetero-specific larvae or protonymphs, the three species fed more on the former than on the latter, and more on hetero-specifics than on con-specifics. Oviposition rates of the three species did not exceed 0.7 egg/female/day on con- and hetero-specific immatures. Typhlodromalus aripo and E. fustis survived longer on con-specific and hetero-specific larvae and on hetero-specific protonymphs than in the absence of any food, while T. aripo survived longer than the two other species on the same diets. Provision of limited quantity of food decreased interspecific predation rate by I. degenerans and T. aripo, but not by E. fustis, and increased oviposition rate and longevity of all three species. Provision of abundant food, however, eliminated cannibalism by all three species and further reduced interspecific predation rates, but their oviposition and longevity remained relatively unchanged compared with limited food provision. Potential consequences of cannibalism and interspecific predation among phytoseiid mites on cassava for the biological control of M. tanajoa are discussed.     

Plasticity of insect reproduction: testing models of flexible and fixed development in response to different growth rates

We tested alternative developmental hypotheses describing when during an insect oviposition cycle reproductive tactics are determined. Newly eclosed adult females of the grasshopper Romalea guttata were raised on eight different feeding treatments consisting of a low food diet, a high food diet, and changes from high to low food, or low to high food, at different times during the first oviposition cycle. When initial food availability was high, a decline in food availability >7 days after adult eclosion produced no significant increase in time to oviposition compared to constant high food. In contrast, when initial food availability was low, an increase in food availability as late as day 14 produced a significant decrease in time to oviposition compared to constant low food. Thus, time to oviposition is determined by feeding rate early in the oviposition cycle, but the time of this determination is later when food availability is lower. Masses of individual eggs were unaffected by these treatments. When initial food availability was high, a decrease in food availability on day 21 produced no significant change in numbers of eggs in a clutch compared to constant high food. In contrast, when initial food availability was low, an increase in food availability after day 7 produced no significant change in number of eggs in a clutch compared to constant low food. Changes in egg production resulted from oocyte resorption, which appeared to become unresponsive to food availability between day 14 and day 21. Our results refute the hypothesis that reproductive tactics are continuously flexible. Development toward oviposition seems to be structured so that reproductive tactics become independent of feeding late during the first oviposition cycle. Reproductive tactics become unresponsive to food at different times for groups initially receiving low or high food, suggesting that a particular developmental state, rather than some absolute time, marks the shift to development that is unresponsive to␣food. Plasticity in reproductive tactics appears to be␣controlled by hormones in a manner similar to the hormonal control of plasticity of metamorphosis in other insects. Received: 21 September 1997 / Accepted: 10 March 1998     

Effects of food limitation and temperature on cladocerans from a tropical Brazilian lake

Food limitation was tested in the laboratory by individual growth and reproduction of two cladoceran species, Ceriodaphnia richardi and Daphnia gessneri, from the shallow tropical Brazilian Lake Monte Alegre. The cladocerans were fed cultivated green alga Scenedesmus spinosus in concentrations of 0.20, 0.10, 0.05, and 0.025 mg C l⁻¹. Higher biomass and growth rates occurred in the two highest-food concentrations; the two lowest ones negatively affected clutch size and first reproduction. The threshold food concentration is lower than 0.025 mg C l⁻¹ and the incipient limiting level is a value between 0.10 and 0.20 mg C l⁻¹. The largest species, D. gessneri, was more sensitive to low food concentrations. The effects of low and high temperatures (19 and 27°C) were evaluated by life table experiments with three cladocerans from the lake—Daphnia ambigua, D. gessneri, and Moina micrura—with no food limitation (1 mg C l⁻¹ of S. spinosus). Higher population growth rates for the three species were found at 27°C; better performance in most life table parameters was observed for the former two species at the highest temperature, D. gessneri being the most sensitive to the lowest temperature. There are indications that temperature is an important abiotic factor that constrains populations of cladocerans for a short period in winter in the lake, when temperature decreases to 18–19°C. However, its influence cannot be separated from a biotic factor such as food, whose effect is stronger in the cool season, when concentrations are lower and contribution of inedible algae is relatively higher.     

Your worst enemy could be your best friend: predator contributions to invasion resistance and persistence of natives

Native predators are postulated to have an important role in biotic resistance of communities to invasion and community resilience. Effects of predators can be complex, and mechanisms by which predators affect invasion success and impact are understood for only a few well-studied communities. We tested experimentally whether a native predator limits an invasive species’ success and impact on a native competitor for a community of aquatic insect larvae in water-filled containers. The native mosquito Aedes triseriatus alone had no significant effect on abundance of the invasive mosquito Aedes albopictus. The native predatory midge Corethrella appendiculata, at low or high density, significantly reduced A. albopictus abundance. This effect was not caused by trait-mediated oviposition avoidance of containers with predators, but instead was a density-mediated effect caused by predator-induced mortality. The presence of this predator significantly reduced survivorship of the native species, but high predator density also significantly increased development rate of the native species when the invader was present, consistent with predator-mediated release from interspecific competition with the invader. Thus, a native predator can indirectly benefit its native prey when a superior competitor invades. This shows the importance of native predators as a component of biodiversity for both biotic resistance to invasion and resilience of a community perturbed by successful invasion.     

Life history characteristics of Frankliniella occidentalis on cucumber leaves with and without supplemental food

The development time, fecundity, longevity, and resultant intrinsic growth rate of the western flower thrips Frankliniella occidentalis (Pergande) [Thysanoptera: Thripidae] encaged on a cucumber leaf were compared among seven types of food supplied: six pollen species and a mixture of milk powder and yeast. The rationale was to find a food source that offers the least benefit for thrips and could therefore be considered as a food source for the preventative introduction of thrips predators. With the exception of the mixture of milk powder and yeast, all the food sources tested offered a nutritional benefit for the thrips. The addition of pollen increased fecundity and reduced development time, mainly during the larval stage. Betula pubescens and Corylus avellana pollen also increased adult longevity. The nutritional benefit of Pinus sylvestris pollen was greater than that of the other five pollen species, as manifested by its significantly greater positive effect on fecundity. The other pollen species could not be ranked in terms of nutritional benefit to F. occidentalis. The negative effect of the milk powder plus yeast mix on the life‐table parameters of F. occidentalis probably only occurs in an encaged situation where thrips cannot escape from the unfavorable environment. The crude estimate of the intrinsic growth rate of F. occidentalis increased from 0.163 on the plain cucumber leaf to 0.240 when P. sylvestris pollen was added to the leaf. The differences in intrinsic growth rate mainly reflect the differences in fecundity among the food sources. Thus, the peak oviposition rate may be used as a measure of the nutritional benefit F. occidentalis can obtain by feeding on supplemental food sources. The positive effect of a supplemental food source on thrips does not necessarily mean it is unsuitable for the preventative introduction of thrips predators, because the supplemental food can also affect the population dynamics of the predator and the predator–prey interaction and, hence, the outcome of biological control.     

Oviposition site selectivity of some stream-dwelling caddisflies

Population dynamics depends upon the spatial distribution of individuals in heterogeneous environments. The various processes surrounding insect oviposition are central to understanding their population dynamics because the choice of oviposition site ultimately influences the survivorship and spatial distribution of their progeny. Aquatic insects are often assumed to have non-selective oviposition habits, but empirical data are scarce and selective oviposition may be quite common. We quantitatively sampled egg masses of stream-dwelling caddisflies (Trichoptera) that specialise in egg-laying on hard substrata underwater, in order to characterise oviposition site selectivity and test for communal oviposition. In a field survey of two Scottish streams, we sampled egg masses of three species, Polycentropus flavomaculatus, Hydropsyche siltalai, Rhyacophila dorsalis, with the aim of testing whether egg mass abundance varied with current (riffles vs. pools), location within the channel (margins vs. centre) and rock exposure (emergent vs. fully submerged). In one stream, we captured adults landing on emergent rocks and assessed whether females were modified morphologically for swimming. The egg masses of two species (P. flavomaculatus, H. siltalai) occurred primarily on submerged rocks in pool margins, and adult females had legs modified for swimming. In contrast, egg masses of R. dorsalis were most abundant on the underside of emergent rocks in riffles, and females were not modified for swimming. Communal oviposition was evident for all three species, with most egg masses aggregated on the minority of potential rocks. How females locate oviposition sites and the consequences of these highly specialised oviposition behaviours to the survival and spatial distribution of larvae now require investigation. The effects of these behaviours on population dynamics are likely to differ from terrestrial herbivores because oviposition sites are not food resources for these aquatic species.     

Influence of adult diet on fitness and reproductive traits of the egg parasitoid Anagrus virlai (Hymenoptera: Mymaridae), a potential biocontrol agent against the corn leafhopper

Dalbulus maidis is the most important leafhopper pest of maize in the Americas. Anagrus virlai is an egg parasitoid commonly associated with the corn leafhopper. We evaluated whether the performance of A. virlai is dependent on different diets provided during 24 hr or throughout adult female lifetime. Additionally, functional response of A. virlai on D. maidis eggs using maize leaves containing honeydew plus honey was described. A. virlai is a mostly pro-ovigenic autogenic species whose females are able to parasitize eggs immediately after emergence. We found that wasps oviposit the majority of their eggs in the first day of their adult life. Realized lifetime fecundity and lifetime potential fecundity did not differ significantly among treatments, but longevity and egg production increased when honey was added to diet. Data were consistent with an intermediate functional response between type II and III, but closer to type II, indicating a high parasitism rate at low host densities and a decrease in the oviposition rate at high host densities, due to a possible egg limitation. Our results suggest that carbohydrate food sources (honeydew and honey) might not be the factor limiting reproductive success during the first 24 hr. Food supply, however, might influence egg maturation and survivorship of wasps, thus potentially enhancing biological pest control when hosts are scarce in the course of the first few days of adulthood.     

Feeding interactions and foraging of juvenile fish and shrimp in the estuaries of Peter the Great Bay in the summer-fall period

The feeding interrelations and foraging of juvenile fish and shrimp were investigated in estuaries of Peter the Great Bay in summer and fall 2006 and 2007. In total 3483 specimens were analyzed. The trophic spectra of 34 fish species and 3 shrimp species were described for the first time. Three trophic groups were singled out depending on differences in diet compositions: (i) detritophages (3 species of bitterlings—Acanthorhodeus sp., A. chankaensis and Rhodeus sericeus, redlip mullet Liza haematocheila and two species of shrimp-Palaemon macrodactylus and Crangon cf. septemspinosa); (ii) predators (lookup Culter alburnus and Amur catfish Silurus asotus); (iii) euryphages (28 fish species and the shrimp Palaemon paucidens). The detritus food chain was found to be the primary one in estuaries of Peter the Great Bay. Most of the species had two peaks of feeding activity each day. Values of daily feeding rations were determined for 21 fish species; these varied from 1.6% to 8.0% of body weight. Similarity in diet composition was significant only for 10% of the species, which shows a low level of competition for food in the community.     

The pollen beetle, Meligethes aeneus, changes egg production rate to match host quality

Motivation-based models dominate current theory concerning host plant selection for oviposition by herbivorous insects. A female searching for a host plant will be more likely to accept a host which is of inferior quality for her offspring if motivation is high, e.g. a large eggload or long time since last oviposition. This implies that insects will accumulate eggs if exposed to hosts of low acceptability and after a time lay eggs on such hosts. An alternative strategy for insects when exposed to less acceptable hosts is to stop producing, instead of accumulating, eggs. Thus, resources would be saved until a more acceptable host is found. If this hypothesis is true, a herbivorous insect would cease egg production when exposed to hosts of low acceptability and resume egg production when exposed to hosts of high acceptability. Previous exposure should not affect oviposition rate when an insect encounters a new host of a different quality. In an earlier study pollen beetles, Meligethes aeneus (F.) (Coleoptera: Nitidulidae), did not accumulate eggs in the absence of high quality hosts. In this study we monitored the daily oviposition rate of female pollen beetles on hosts plants of low (Sinapis alba L.), intermediate (Brassica nigra Koch) or high (B. napus L.) acceptability over a 5-day period. Individuals were then switched to an oviposition resource of a different acceptability. Beetles moved from high- to low-acceptability plants reduced their oviposition rate considerably. In the opposite case, low to high acceptability, the rate of oviposition increased markedly after the switch. When M. aeneus were moved from the high-acceptability host to that of intermediate acceptability oviposition rate was modified accordingly. However, when moved to the intermediate host from a host of low acceptability oviposition on B. nigra was much less than would normally be expected. A possible mechanism for this finding is discussed. M. aeneus, by adjusting oviposition rate to host acceptability, maximizes the average host quality for offspring, even at the cost of a lower egg-laying rate. Received: 5 October 1998 / Accepted: 20 April 1999