Past and Present Risk: Exposure to Predator Chemical Cues Before and after Metamorphosis Influences Juvenile Wood Frog Behavior

Animals are exposed to different predators over their lifespan. This raises the question of whether exposure to predation risk in an early life stage affects the response to predators in subsequent life stages. In this study, we used wood frogs (Rana sylvatica) to test whether exposure to cues indicating predation risk from dragonfly larvae during the wood frog larval stage affected post‐metamorphic activity level and avoidance of garter snake chemical cues. Dragonfly larvae prey upon wood frogs only during the larval stage, whereas garter snakes prey upon wood frogs during both the larval stage and the post‐metamorphic stage. Exposure to predation risk from dragonflies during the larval stage caused post‐metamorphic wood frog juveniles to have greater terrestrial activity than juvenile wood frogs that were not exposed to larval‐stage predation risk from dragonflies. However, exposure to predation risk as larvae did not affect juvenile wood frog responses to chemical cues from garter snakes. Wood frogs exposed as larvae to predation risk from dragonfly larvae avoided garter snake chemical cues to the same extent as wood frog larvae not exposed to predation risk from dragonfly larvae. Our results demonstrate that while some general behaviors exhibit carry‐over effects from earlier life stages, behavioral responses to predators may remain independent of conditions experienced in earlier life stages.     

Within‐patch oviposition site shifts by spider mites in response to prior predation risks decrease predator patch exploitation

In egg‐laying animals with no post‐oviposition parental care, between‐ or within‐patch oviposition site selection can determine offspring survival. However, despite the accumulation of evidence supporting the substantial impact predators have on oviposition site selection, few studies have examined whether oviposition site shift within patches (“micro‐oviposition shift”) reduces predation risk to offspring. The benefits of prey micro‐oviposition shift are underestimated in environments where predators cannot disperse from prey patches. In this study, we examined micro‐oviposition shift by the herbivorous mite Tetranychus kanzawai in response to the predatory mite, Neoseiulus womersleyi, by testing its effects on predator patch exploitation in situations where predatory mites were free to disperse from prey patches. Adult T. kanzawai females construct three‐dimensional webs on leaf surfaces and usually lay eggs under the webs; however, females that have experienced predation risks, shift oviposition sites onto the webs even in the absence of current predation risks. We compared the predation of eggs on webs deposited by predator‐experienced females with those on leaf surfaces. Predatory mites left prey patches with more eggs unpredated when higher proportions of prey eggs were located on webs, and egg survival on webs was much higher than that on leaf surfaces. These results indicate that a micro‐oviposition shift by predator‐experienced T. kanzawai protects offspring from predation, suggesting adaptive learning and subsociality in this species. Conversely, fecundity and longevity of predator‐experienced T. kanzawai females were not reduced compared to those of predator‐naïve females; we could not detect any costs associated with the learned micro‐oviposition shift. Moreover, the previously experienced predation risks did not promote between‐patch dispersal of T. kanzawai females against subsequently encountered predators. Based on these results, the relationships of between‐patch oviposition site selection and micro‐oviposition shift are discussed.     

Are behavioural responses to predation cues linked across life cycle stages?

1. Prey organisms can perceive cues to predation hazard and adopt low‐risk behaviours to increase survival. Animals with complex life cycles, such as insects, can exhibit such anti‐predatory behaviours in multiple life stages. 2. Cues to predation risk may induce ovipositing females to choose habitats with low predation risk. Cues to predation risk may also induce larvae to adopt facultative behaviours that reduce risk of predation. 3. One hypothesis postulates that anti‐predation behaviours across adult and larval stages may be negatively associated because selection for effective anti‐predator behaviour in one stage leads to reduced selection for avoidance of predators in other stages. An alternative hypothesis suggests that selection by predation favours multi‐component defences, with both avoidance of oviposition and facultative adoption of low‐risk behaviours by larvae. 4. Laboratory and field experiments were used to determine whether defensive responses of adult and larval mosquitoes are positively or negatively associated. The study tested effects of waterborne cues from predatory Toxorhynchites theobaldi on oviposition choices and larval behaviours of three of its common prey: Culex mollis, Limatus durhamii and Aedes albopictus. 5. Culex mollis shows strong anti‐predator responses in both life stages, consistent with the hypothesis of a multi‐component behavioural defence. The other two species showed no detectable responses to waterborne predator cues in either adult or larval stages. Larvae of these unresponsive species were significantly more vulnerable to this predator than was C. mollis. 6. For these mosquitoes, species appear either to have been selected for multi‐component defences against predation or to act in ways that could be called predator‐naïve.     

Light dependency of life trails,reproduction, locomotion,and predation in the polyphagous ladybird Hippodamia variegata

Light is regarded a key environmental cue influencing biological, physiological, and behavioral characteristics in insects. We compared the development, reproduction, locomotion, and predation ability of the predatory ladybird Hippodamia variegata (Goeze) (Coleoptera: Coccinellidae) under various photoperiods, light intensities, and light wavelengths. The results indicated long daylight, high light intensity, and particular colors light (blue, green, and yellow) could benefit H. variegata especially in shortening the period of immature development, increasing mating frequency (shorter mating and pre‐oviposition periods), higher fecundity, and a higher proportion of eggs hatched. Average locomotion speed and prey consumption rate of H. variegata increased with prolonged day length and increased light intensity. However, very high intensity of light could inhibit predation rates. Furthermore, green and yellow wavelength conditions increased locomotion speed of H. variegata, and the number of prey consumed increased with increased wavelength. The present study not only revealed significant influences of light conditions on the development and fertility of H. variegata, it also provided sufficient empirical data to improve the efficiency of mass rearing and field releases of this predatory ladybird by regulation of light conditions during biological control applications.     

A Single Hot Event Stimulates Adult Performance but Reduces Egg Survival in the Oriental Fruit Moth,Grapholitha molesta

Climate warming is expected to increase the exposure of insects to hot events (involving a few hours at extreme high temperatures). These events are unlikely to cause widespread mortality but may modify population dynamics via impacting life history traits such as adult fecundity and egg hatching. These effects and their potential impact on population predictions are still largely unknown. In this study, we simulated a single hot event (maximum of 38°C lasting for 4 h) of a magnitude increasingly found under field conditions and examined its effect in the oriental fruit moth, Grapholitha molesta. This hot event had no impact on the survival of G. molesta adults, copulation periods or male longevity. However, the event increased female lifespan and the length of the oviposition period, leading to a potential increase in lifetime fecundity and suggesting hormesis. In contrast, exposure of males to this event markedly reduced the net reproductive value. Male heat treatment delayed the onset of oviposition in the females they mated with, as well as causing a decrease in the duration of oviposition period and lifetime fecundity. Both male and female stress also reduced egg hatch. Our findings of hormetic effects on female performance but concurrent detrimental effects on egg hatch suggest that hot events have unpredictable consequences on the population dynamics of this pest species with implications for likely effects associated with climate warming.     

Life‐history parameters and predation capacity of Macrolophus pygmaeus and Nesidiocoris tenuis (Hemiptera: Miridae) on eggs of Plutella xylostella (Lepidoptera: Plutellidae)

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Interactions among morphotype,nutrition, and temperature impact fitness of an invasive fly

Invasive animals depend on finding a balanced nutritional intake to colonize, survive, and reproduce in new environments. This can be especially challenging during situations of fluctuating cold temperatures and food scarcity, but phenotypic plasticity may offer an adaptive advantage during these periods. We examined how lifespan, fecundity, pre‐oviposition periods, and body nutrient contents were affected by dietary protein and carbohydrate (P:C) ratios at variable low temperatures in two morphs (winter morphs WM and summer morphs SM) of an invasive fly, Drosophila suzukii. The experimental conditions simulated early spring after overwintering and autumn, crucial periods for survival. At lower temperatures, post‐overwintering WM lived longer on carbohydrate‐only diets and had higher fecundity on low‐protein diets, but there was no difference in lifespan or fecundity among diets for SM. As temperatures increased, low‐protein diets resulted in higher fecundity without compromising lifespan, while high‐protein diets reduced lifespan and fecundity for both WM and SM. Both SM and WM receiving high‐protein diets had lower sugar, lipid, and glycogen (but similar protein) body contents compared to flies receiving low‐protein and carbohydrate‐only diets. This suggests that flies spend energy excreting excess dietary protein, thereby affecting lifespan and fecundity. Despite having to recover from nutrient depletion after an overwintering period, WM exhibited longer lifespan and higher fecundity than SM in favorable diets and temperatures. WM exposed to favorable low‐protein diet had higher body sugar, lipid, and protein body contents than SM, which is possibly linked to better performance. Although protein is essential for oogenesis, WM and SM flies receiving low‐protein diets did not have shorter pre‐oviposition periods compared to flies on carbohydrate‐only diets. Finding adequate carbohydrate sources to compensate protein intake is essential for the successful persistence of D. suzukii WM and SM populations during suboptimal temperatures.     

Temperature effects on reproduction and adult lifespan of the smaller fruit tortrix,Grapholita lobarzewskii

The effects of temperature on adult lifespan, reproduction, and oviposition behaviour of Grapholita lobarzewskii Nowicki (Lepidoptera: Tortricidae) were studied under controlled and semi‐field conditions to improve the basis for phenological forecasting. The average female lifespan ranged from 18.9 days at 25.1 °C to 65.3 days at 11.0 °C. For adult female ageing, a lower thermal threshold (THR) of 8.6 °C and a thermal constant (K) of 298 degree days (dd) were established. At constant temperatures, fecundity ranged from 0.3 eggs per female at 11.0 °C to 107 eggs per female at 21.2 °C. The highest fecundity of 127 eggs per female was observed at fluctuating temperatures. Oviposition lasted on average 350 dd, but 50% of the eggs were laid within the first 100 dd after adult emergence. Grapholita lobarzewskii had a distinct circadian rhythm for oviposition. Females began to lay eggs at ca. 16:00 hours and ceased at 24:00 hours with the peak occurring generally at 19:00 hours. Females reacted very sensitively to sudden temperature changes. A temperature drop of 3.1 °C could cause a 1‐day interruption of oviposition.     

COMPARISON OF INTRASPECIFIC COMPETITION BETWEEN ERUPTIVE AND LATENT AUCHENORRHYCHA (HOMOPTERA) SPECIES ON RICE: SOGATELLA FURCIFERA (DELPHACIDAE) VERSUS RECILIA DORSALIS (DELTOCEPHALIDAE)*

Abstract A comparison of the effects of intraspecific competition between the white‐backed planthopper (WBPH) Sogatella furcifera (Horvath) and the zigzag leaihopper (ZLH) Recilia dorsalis (Motschulsky), as representatives of eruptive and latent Auchenorrhycha (Homoptera) species on rice, was carried out in the laboratory. Crowding during the nymphal stage extended the duration of development of WBPH but not of ZLH. The nymphal survival rate of WBPH, sex ratio, preoviposition period and fecundity of both species were however not affected. The brachypterous percentage of WBPH and nymphal survival of ZLH were significantly reduced under high nymphal density. Crowding during the adult stage reduced fecundity and longevity significantly of both species. Fecundity and longevity were further reduced when combined with high densities during the nymphal stage. Age‐specific life table analysis showed that the integrated effect of crowding on ZLH is stronger than on WBPH. The mechanism of eruptive and latent species' response to crowding during nymph and adult stages is not clearly expressed as a significant difference in fecundity. It is better described as the variation in the intrinsic rate of increase (r_m). Therefore the construction of an age‐specific life table is helpful, and perhaps necessary, to understand these effects. The results showed that the main ecological characteristics of ZLH, as a latent species were its longer immature period, lower total fecundity and decreased and retailed rate of oviposition, hence the lower r_m, as compared with WBPH.     

Fitness and feeding are affected in the two-spotted stinkbug,Perillus bioculatus,by the cysteine proteinase inhibitor,oryzacystatin I

Plant resistance to insect pests based on recombinant proteinase inhibitors (Pis) could interfere with natural enemies of target pests, as their own proteolytic systems may also be sensitive to large spectrum PIs. Oryzacystatin I (OCI) is a potential insect pest resistance factor currently engineered into a variety of crop plants, including potato Solanum tuberosum. Potential for OCI interfering with female reproduction in Perillus bioculatus, a stinkbug predator of Colorado potato beetle, Leptinotarsa decemlineata, was studied by chronic feeding for 18 days on prey loaded with 1–16 μg OCI/day. Mortality of treated females was negligible, but fertility was reduced by up to 50%. Additional dose-dependent effects in reproducing females included delayed oviposition, reduced fecundity, lower egg mass size, and reduced egg eclosion incidence. Females fed for 18 days on OCI at ≤4 μg/day returned to normal oviposition when switched to prey without OCI after 18 days of treatment, but negative effects persisted for at least 10 days at higher doses. Affected reproduction in P. bioculatus is consistent with the use of OCI-sensitive digestive proteinases by this stinkbug. However, azocaseinase activity in whole body extracts of OCI-fed females increased about twofold indicating compensation, and OCI-sensitive proteinases were still present in extracts. When timed for delay to trigger attack on Colorado potato beetle larvae under controlled conditions, stinkbugs feeding on OCI appeared consistently hungrier than controls fed at similar rate, suggesting that predation by stinkbugs exposed to OCI-recombinant foliage would be higher than normal. Arch. Insect Biochem. Physiol. 38:74–83, 1998. © 1998 Wiley-Liss, Inc.     

Coccinellid interactions mediated by vegetation heterogeneity

Environmental heterogeneity can have profound effects on agroecosystem function and it is important for improving ecosystem services such as biological control. Promoting system diversity via non‐crop plants is one method for increasing habitat heterogeneity within farmscapes. Non‐crop plants provide access to refuges and alternative food resources provide multiple benefits to enhance populations of arthropod predators. In this study, we examined the effects of small‐scale spatial structure on life‐stage specific interactions between the native coccinellid, Hippodamia convergensGuérin‐Méneville, and the exotic Harmonia axyridis (Pallas) (both Coleoptera: Coccinellidae), which overlap in spatial distribution in many crop systems. Squash [Cucurbita pepo L. (Cucurbitaceae)] and non‐crop mugwort [Artemisia vulgaris L. (Asteraceae)] plants with and without aphids were used as a model of spatial heterogeneity in micro‐ and mesocosm experiments. In response to factorial treatment combinations, we evaluated oviposition behavior, egg predation, larval survival, and larval predator‐prey and predator‐predator interactions. Adult H. convergens displayed higher foraging activity on aphids when exposed to complex habitats containing a non‐crop plant. In the presence of the exotic coccinellid, H. convergens preferred to deposit eggs on the non‐crop plant. Furthermore, a combination of spatial heterogeneity and prey availability reduced larval intraguild predation and cannibalism, and improved reproductive output of H. convergens by reducing intra‐ and interspecific egg predation. Our results provide evidence that life‐stage‐specific intraguild interactions are mediated by access to non‐crop plants. Thus, the introduction or maintenance of non‐crop plants has the potential to enhance coexistence of multiple natural enemies and improve top‐down control of pests.     

Effect of cannibalism on predation,oviposition and longevity of the predacious mite,Agistemus exsertus Gonzalez (Acari: Stigmaeidae)

Cannibalism (intraspecific predation) on conspecific eggs was investigated in the predatory stigmaeid mite, Agistemus exsertus Gonzalez in the absence of eggs of Tetranychus urticae Koch (no-choice tests) and presence of three densities of prey eggs simultaneously (choice tests) in the laboratory. Data show that cannibalism occurs in immatures and adult females of the predator, which successfully developed and reproduced on conspecific eggs as an alternative prey in the absence of prey eggs. In no-choice tests, cannibalism rate on conspecific eggs by A. exsertus stages was significantly lower than the predation rate on T. urticae eggs. The predatory mite exhibited a marked decline in oviposition rate when preyed on conspecific eggs compared with feeding on prey eggs. The developmental duration and longevity of A. exsertus females were significantly longer 1.9 and 1.7 times, respectively, when fed on conspecific eggs than feeding on T. urticae eggs. The propensity of the predator towards cannibalism depends on the prey density, when T. urticae eggs and conspecific eggs are present simultaneously. Provision of increased densities of prey eggs significantly decreased cannibalism and predation by A. exsertus stages, which fed generally less on conspecific eggs than on T. urticae eggs in choice tests. The oviposition rate of the predator increased significantly, as the egg density of the prey increased. The developmental period and longevity of A. exsertus females showed significantly gradual shortness with increasing egg density of the prey.     

竹盲走螨对竹裂爪螨的捕食功能

在实验室模拟条件下,系统研究了竹盲走螨对竹裂爪螨的控制作用.结果表明,在25±0.5 ℃条件下,竹盲走螨对竹裂爪螨各螨态的功能反应均属HollingⅡ型.在同一温度条件下,雌竹盲走螨成螨对竹裂爪螨各螨态的处置时间依次为卵<幼螨<前若螨<后若螨<雌成螨.竹裂爪螨卵、幼螨、若螨、雌成螨共存时,竹盲走螨嗜食卵、幼螨和前若螨（Q>1）,但其对卵与幼螨及幼螨与前若螨无偏嗜现象.当竹裂爪螨密度低于9头时,竹盲走螨的产卵量随密度增加而增加;9～15头时,其日平均产卵量保持在每雌2粒左右;超过15头以后,产卵量反而下降,说明猎物密度过高对捕食者生存、繁殖存在干扰作用.     

Influence of ultraviolet-B radiation on growth,prevalence of deformities,and susceptibility to predation in Cascades frog (<Emphasis Type="Italic">Rana cascadae</Emphasis>) larvae

Ambient levels of ultraviolet-B radiation (UVB) have a variety of detrimental effects on aquatic organisms. These include death and effects on growth, development, physiology, and behavior. Amphibians show all of these effects. However, the effects vary with species, life history stage, and ecological context. Little is known about the implications of the detrimental effects of UVB on ecological dynamics. Our study was designed to test how UVB may affect predator–prey interactions, an important ecological dynamic. Specifically, we tested the effect of UVB on the susceptibility of Cascades frog (Rana cascadae) larvae to predation by rough-skinned newts (Taricha granulosa). We also further examined the sublethal effects of UVB on growth and development in Cascades frog larvae. We found no direct effect of UVB exposure on survival. However, UVB-exposed frog larvae displayed decreased growth and increased prevalence of deformities. UVB also caused increased susceptibility to predation, but there was a significant treatment–block interaction. UVB increased susceptibility to predation in two out of five blocks of Cascades frogs. The other three blocks did not show an effect of UVB on susceptibility to predation. Our study suggests that UVB can alter susceptibility to predation in at least one amphibian species. UVB-induced alteration of predator–prey interactions could potentially lead to changes at the population, community, and ecosystem levels. Handling editor: K. Martens     

Under pressure: Short- and long-term response to predation varies in two populations of a live-bearing fish

The non-lethal effects of predation can significantly influence animal behavior and population composition. Research has often centered around prey response to predator exposure in the short term, but fewer studies have highlighted the effects of long-term predator exposures. In addition, studies of responses to predation risk are not always calibrated against the ecological history of predation risk in specific populations. We address these gaps by examining the effects of both long- and short-term predator exposure on the behavior of individuals from populations that have different ecological histories of predation risk. We exposed individuals from high-predation and low-predation populations of the live-bearing freshwater poeciliid, Heterandria formosa, to predators to assess changes in male reproductive behavior toward females. We also assessed longer-term reproductive responses by exposing male and female H. formosa to predators at a random time of day, every day, for 30 days. In the presence of a predator, in the short term, males changed the frequency of their behaviors and females varied in their concentration of cortisol, demonstrating immediate responses to the perceived risk. The magnitude of these changes was larger in the population without a long history of predator exposure. However, we found that males and females did not change their reproductive output when exposed to predators over longer periods of time, suggesting that individuals acclimatize to the level of predation risk they experience. These results also suggest that short-term variation in behavior or stress hormone responses should not be used as proxies for long-term responses or fitness effects. Future work should assess both short-term behavior and long-term responses while simultaneously considering the ecological history of populations.     

Rainbow Darter (Etheostoma caeruleum,Storer, 1845) predation on early ontogenetic stages of Lake Sturgeon (Acipenser fulvescens,Rafinesque, 1817)

Previous molecular diet analysis identified lake sturgeon (Acipenser fulvescens, Rafinesque, 1817) DNA in the gastrointestinal tracts of stream-resident rainbow darters (Etheostoma caeruleum, Storer, 1845) during the egg incubation, free embryo, and larval drift stages. The objectives of this experimental study were to: (a) quantify levels of predation by rainbow darters on lake sturgeon at the egg and free-embryo stages; and (b) evaluate whether predation varied as a function of substrate size and rainbow darter body size. We conducted experimental trials in 23-L polycarbonate tanks 0.41 m (L) × 0.33 m (W) × 0.30 m (D) with a standardized benthic area of 0.14 m². The tanks were randomly assigned one of two different substrate size classes: large rock (51.35 mm ± 0.91 mm) or small rock (27.68 mm ± 0.57 mm). We stocked individual rainbow darter, which were deprived of feed for 48 hr, with lake sturgeon (133 individuals/m²) in each of 12 replicates per ontogenetic stage and substrate type. The number of surviving lake sturgeon was quantified following a 24-hr predation exposure period. We used a generalized linear model with a binomial distribution to assess the influence of ontogenetic stage, substrate size, and rainbow darter body size on proportional lake sturgeon survival. Predation on lake sturgeon occurred at both egg (6.25 ± 1.16 individuals, mean ± 2SE) and free embryo (3.08 ± 1.08 individuals, mean ± 2SE) stages. Egg proportional survival was generally lower than at the free embryo stage in both substrate sizes; however, free embryo proportional survival was greater in small substrate trials. Rainbow darter total length did not affect the probability of lake sturgeon survival at either developmental stage. Results demonstrate that rainbow darters prey on early ontogenetic stages of lake sturgeon, corroborating previous results based on genetic diet analysis. Results fill a major knowledge gap concerning the vulnerability of pre-drift sturgeon to predation by an abundant river resident species that was previously discounted as a predator for early ontogenetic stages of lake sturgeon due to its small body size.     

Consumption,developmental and reproductive attributes of two con-generic ladybird predators under variable prey supply

Availability of aphid prey in habitat is often heterogeneous in space and time and its deprivation causes severe effects on life attributes of ladybird predators. Sometimes ladybirds locate high prey biomass while on certain occasions prey biomass may be either medium/low or altogether absent. Present study has been designed in view of three prey biomass conditions in nature, viz. low, medium and high, selecting Coccinella septempunctata and Coccinella transversalis as experimental ladybirds. Results revealed that consumption, developmental and reproductive attributes of both ladybirds changed in response to prey availability. On high prey biomass larvae had higher consumption and growth rates, developed faster and had low mortality, while emerging adults were large in size, had high consumption rates and utilized prey biomass maximally on production of eggs, self maintenance and survival. In contrast low prey biomass reduced chances of larval survival and emerging adults were small in size, had poor prey consumption rates, low fecundity, egg fertility and short life span. Females exhibited triangular fecundity and egg fertility functions and plateau shaped prey consumption rate function with age, indicating towards their highest reproductive performance during middle age on three prey biomasses; being highest on high prey biomass. On three prey biomasses, females had higher body biomass conversion efficiency during pre- and post-oviposition periods and higher egg biomass conversion efficiency during oviposition period; being highest on high prey biomass. Thus middle aged ladybirds reared on high prey biomass may suppress pest populations better than those reared on low/medium prey biomass.     

Sublethal effect of beta‐cypermethrin on development and fertility of the Asian multicoloured ladybird beetle Harmonia axyridis

The Asian multicoloured ladybird beetle, Harmonia axyridis, is utilized as a major natural enemy of aphids in the field, greenhouses and orchards. However, it has been looked as invasive predator distributing in worldwide. To refine integrated pest management (IPM) against aphids, it is important to evaluate the effects of insecticides on physiology and behaviour of the high adapted predators. Beta‐cypermethrin, a broad‐spectrum insecticide, not only kills aphids at lethal concentrations but also affects natural enemy of aphids. In our study, the age‐stage, two‐sex life table was used to evaluating sublethal effects of beta‐cypermethrin on the predatory ladybird beetle H. axyridis. In the parent generation, the pre‐oviposition period of H. axyridis was significantly shortened (8.93 days) after exposure to LC₅ beta‐cypermethrin (5% lethal concentration) as compared with control (10.06 days). However, the oviposition period was significantly longer (46.17 days instead of 43.90 days), and fecundity (eggs per female) was significantly increased by 49.64% when compared with control. In the F₁ generation, the length of the juvenile stage was not affected, but the oviposition period increased significantly (38.19 days compared to 31.39 days in the control). This positive effect was translated to the fecundity that increased significantly by 62.27% as compared with control. According to the life‐table analysis, the intrinsic rate of increase (r_m) was significantly higher in treatment (0.140 per day) than that in the control (0.123 per day). In addition, the net reproductive rate (R₀) increased significantly by 91.53%. These results would be useful in assessing the overall effects of beta‐cypermethrin on H. axyridis and even for discussing the ecological mechanism of the unexpected extension of H. axyridis during IPM programme.     

Impact of Chaoborus predation upon the structure and dynamics of a crustacean zooplankton community

Summary During ice-free seasons of 1975, 1977 and 1978, replicated experimental alteration of spring densities of predatory Chaoborus larvae inside 20–27 m³ enclosures in a fishless oligotrophic lake had relatively small, but significant, short-term effects upon prey species abundances. Enhancement of predator densities generally had greater numerical effects relative to controls than did complete removal of predators. With the exceptions Diaphanosoma and Bosmina under artificially elevated Chaoborus densities, numerical effects on prey species did not persist for more than a few weeks after midsummer in these 3 years. During cooler 1976, however, much larger Chaoborus effects in May and June persisted into September. Low temperatures and small initial population densities slowed population growth and tended to increase the proportion of each species' recruitment lost to Chaoborus predation. As water temperatures increased during 3 of 4 summers, rapid juvenile development and compensating increase in adult fertility generally permitted most prey species to escape regulation by these large, univoltine and semivoltine predators. With growing prey population size, declining food levels suppressed crustacean fecundity in July and August, thereby permitting predatory losses to climb again to substantial fractions of the reduced prey recruitment. Nevertheless, prey densities in predator-free and control or predator-enhanced enclosures differed little from July through September (except in 1976). Thus, summer population growth of most prey species seemed more limited by food shortages than by predators per se. Growth of individual zooplankters was affected by food availability during critical periods in July and August in all years, and Chaoborus predation seemed to influence the timing of this food limitation in at least 2 of the 4 years     

Predation and reproduction of the generalist predator Nabis pseudoferus preying on Tuta absoluta

The damsel bug, Nabis pseudoferus Remane (Hemiptera: Namidae), is a generalist predator of small arthropods, including key insect pests of vegetable crops. In this study, we characterized the predation and development of various N. pseudoferus life stages when preying on the eggs and first- and fourth-instar nymphs of the invasive South American tomato pinworm, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae). These findings were compared to those of the bug’s common prey, cotton aphid, Aphis gossypii Glover (Hemiptera: Aphididae). Of the life stages tested, females showed the highest predation rate on all tested prey, due to their high longevity, large body, and great energy requirements for reproduction. The predator’s oviposition rate was clearly influenced by prey type, and was highest when feeding on fourth instars of T. absoluta. Considering the zoophytophagy of most of the life stages of other mirid species of tomato, and the lower propensity of N. pseudoferus to feed on plants, these results show that this species can be considered as a key indigenous natural enemy for sustainable pest control packages against T. absoluta in newly invaded areas.