Finite Rate Of Population Increase Research Articles

Cross-crop resistance of Spodoptera frugiperda selected on Bt maize to genetically-modified soybean expressing Cry1Ac and Cry1F proteins in Brazil

Spodoptera frugiperda is one of the main pests of maize and cotton in Brazil and has increased its occurrence on soybean. Field-evolved resistance of this species to Cry1 Bacillus thuringiensis (Bt) proteins expressed in maize has been characterized in Brazil, Argentina, Puerto Rico and southeastern U.S. Here, we conducted studies to evaluate the survival and development of S. frugiperda strains that are susceptible, selected for resistance to Bt-maize single (Cry1F) or pyramided (Cry1F/Cry1A.105/Cry2Ab2) events and F1 hybrids of the selected and susceptible strains (heterozygotes) on DAS-444Ø6-6 × DAS-81419-2 soybean with tolerance to 2,4-d, glyphosate and ammonium glufosinate herbicides (event DAS-444Ø6-6) and insect-resistant due to expression of Cry1Ac and Cry1F Bt proteins (event DAS-81419-2). Susceptible insects of S. frugiperda did not survive on Cry1Ac/Cry1F-soybean. However, homozygous-resistant and heterozygous insects were able to survive and emerge as fertile adults when fed on Cry1Ac/Cry1F-soybean, suggesting that the resistance is partially recessive. Life history studies revealed that homozygous-resistant insects had similar development, reproductive performance, net reproductive rate, intrinsic and finite rates of population increase on Cry1Ac/Cry1F-soybean and non-Bt soybean. In contrast, heterozygotes had their fertility life table parameters significantly reduced on Cry1Ac/Cry1F-soybean. Therefore, the selection of S. frugiperda for resistance to single and pyramided Bt maize can result in cross-crop resistance to DAS-444Ø6-6 × DAS-81419-2 soybean. The importance of these results to integrated pest management (IPM) and insect resistance management (IRM) programs is discussed.

Insecticidal activity and sublethal effects of Beauveria bassiana (Bals.-Criv.) Vuill. isolates and essential oils against Aphis gossypii Glover, 1877 (Hemiptera: Aphididae)

The cotton aphid, Aphis gossypii Glover, 1877, is a polyphagous species and one of the most important pests of cucumber crops in Iran. In this study, virulence of three Beauveria bassiana (Bals.-Criv.) Vuill isolates, IRAN 108, IRAN 429C and LRC 137, as well as insecticidal activity of two essential oils extracted from Matricaria chamomilla L. and Cuminum cyminum L. were evaluated against adult stage of A. gossypii under laboratory conditions. The data for life table were analyzed using the age-stage, two-sex life table theory. Results showed that all isolates were pathogenic on aphid, but their virulence was varied in different isolates. The lowest calculated LC50 was belonged to IRAN 429C (3.9 × 104conidia ml-1). The lowest LT50 was obtained at concentration of 108 and 107 conidia ml-1 for IRAN 429C (2.9 and 3.55 days, respectively). M. chamomilla essential oil had the lowest LC50 and LT50 values (19 µl l-1 air and 11.4 h), respectively. Longevity and population growth parameters, including the intrinsic rate of increase (rm), gross reproduction rate (GRR), net reproductive rate (R0), generation time (T) and finite rate of population increase (λ), were affected negatively by both agents. According to the results obtained in this study, both entomopathogenic fungi and essential oils could be used as an alternative to chemical insecticides in aphid IPM programs.

Fitness costs associated with thiamethoxam and imidacloprid resistance in three field populations of Diaphorina citri (Hemiptera: Liviidae) from Florida.

Insecticide resistance is an increasing problem in citrus production. The Asian citrus psyllid, Diaphornia citri Kuwayama, is recognized as one of the most important citrus pests worldwide and it has developed resistance in areas where insecticides have been overused. The development of insecticide resistance is often associated with fitness costs that only become apparent in the absence of selection pressure. Here, the fitness costs associated with resistance to thiamethoxam and imidacloprid were investigated in three agricultural populations of D. citri as compared with susceptible laboratory colonies. Results showed that all field populations had greater resistance than laboratory susceptible colonies. For both thiamethoxam and imidacloprid, a Candidatus Liberibacter asiaticus-positive (CLas+) colony was more susceptible than the CLas- colony. Resistance ratios ranged from 7.65-16.11 for imidacloprid and 26.79-49.09 for thiamethoxam in field populations as compared with a susceptible, CLas- laboratory strain. Among three resistant field populations, a significantly reduced net reproductive rate and finite rate of population increase were observed in a population from Lake Wales, FL as compared to both susceptible strains. The fecundity of field populations from Lake Wales, FL was statistically lower than both laboratory susceptible populations. Certain changes in morphological characteristics were observed among resistant, as compared, with susceptible strains. Our data suggest fitness disadvantages associated with insecticide resistance in D. citri are related to both development and reproduction. The lower fitness of D. citri populations that exhibit resistance to neonicotinoid insecticides should promote recovery of sensitivity when those populations are no longer exposed to thiamethoxam and/or imidacloprid in the field. The results are congruent with a strategy of insecticide rotation for resistance management.

<p class="Body"><strong>Biology and fertility life table of <em>Oligonychus punicae</em> Hirst (Acari: Tetranychidae) associated with eucalyptus in a clonal minigarden</strong></p>

The mite Oligonychus punicae has potential for development in Eucalyptus spp. in clonal minigardens. However, there is no information on its biological and reproductive parameters on eucalyptus species. The objective of this study is to evaluate the biological and reproductive performance of O. punicae on different species of eucalyptus cultivated in a clonal minigarden. Development time, survival, longevity, fecundity and life table parameters of O. punicae were determined on six species of eucalyptus (Eucalyptus urophylla, Eucalyptus brassiana, Eucalyptus grandis, Eucalyptus tereticorinis, Eucalyptus pellita and Corymbia citriodora). All eggs of O. punicae originated females and completed the cycle in all hosts. Differences were observed in development, longevity, pre-oviposition, oviposition and post-oviposition, and fecundity of females of O. punicae when different eucalyptus species were used as hosts for O. punicae. The best performance of O. punicae was observed on E. tereticornis, while the worst performance was observed on C. citriodora, on which the net reproductive rates (R0) ranged from 5.09 to 44.85, the intrinsic rate of population increase (rm) ranged from 0.09 to 0.19, the finite rate of population increase (λ) ranged from 1.10 to 1.21, and the mean generation time (T) ranged from 0.09 to 0.19. These results suggest that E. tereticornis is an excellent host for O. punicae.

Rearing technique and demographic parameters of Tetrastichus giffardianus Silvestre (Hymenoptera: Eulophidae)

Tetrastichus giffardianus Silvestri (Hymenoptera: Eulophidae) is a gregarious koinobiont endoparasitoid of frugivorous dipterans. In recent years, T. giffardianus has been detected parasitizing Ceratitis capitata (Wiedemann) (Diptera: Tephritidae) in different Brazilian semiarid sites. Thus, T. giffardianus has potential to be used in the biological control of C. capitata in semi-arid conditions. However, one of the factors limiting the use of this parasitoid is the lack of detailed information on rearing methods and bioecological aspects. Therefore, the main objectives of this study were to demonstrate a rearing technique for T. giffardianus and to determine the increase in population under laboratory conditions. Specimens of T. giffardianus were obtained in the field through of the collection of fruits infested with C. capitata. The specimens obtained were used to adapt a rearing methodology for T. giffardianus under laboratory conditions. Information on demographic parameters for a T. giffardianus population was obtained using the same methodology. Based on the parameters evaluated, we found that the intrinsic rate of population increase of T. giffardianus was 0.34, the average time of one generation was 19.7 days, the population doubling time was 2.03 days and the finite rate of population increase (?) was 1.41. The demographic parameters obtained demonstrated that, with the rearing technique used, it is possible to maintain populations of T. giffardianus and enable them to multiply under laboratory conditions.

Resistance in lima bean to Aphis craccivora (Hemiptera: Aphididae)

The cowpea aphid (Aphis craccivora) can be an important pest on lima bean (Phaseolus lunatus L.). The objective of this work was to evaluate the effect of different genotypes of lima bean on the biology of A. craccivora and to identify possible sources of resistance to aphids under laboratory conditions. Two trials were set up, an antibiosis and a free-choice antixenosis test. Furthermore, the density of the trichomes on the leaf surface was determined for each genotype. Aphid life table parameters were similar in the antibiosis experiments for all of the genotypes tested. The calculated life table for the lima bean genotype used several parameters, namely Net Reproduction Rate (Ro) = 49.23; Time interval between each generation (T) = 10.24, Intrinsic rate of natural increase (rm) = 0.38; Finite rate of population increase (λ) = 1.46 and Time for population to duplicate (TD) = 1.82. The results of non-preference tests showed that genotype UFPI-887 exhibited antixenosis resistance when compared to genotypes UFPI-882 and UFPI-881. The trichome density average varied from 126.29 trichomes/mm2 in genotype UFPI-882 to 42.20 trichomes/mm2 in genotype UFPI-883. There was no correlation between trichome density in the leaves and no preference of A. craccivora for leaves of P. lunatus.

A comparison of sexual competitiveness and demographic traits of Anastrepha obliqua (Macquart) (Diptera: Tephritidae) among fruit-associated populations.

The control of Anastrepha obliqua includes the sterilization of mass-reared insects grown in isolation in a constantly controlled environment. Through time, laboratory mass-reared colonies may produce flies with lower field performance. To recover the genetic variation and aptitude of mass-reared populations, wild insects are introduced into mass-reared colonies. Our aim in this study was to determine whether the host species from two localities influence the life history traits of A. obliqua. We collected flies as larvae from infested fruits of Spondias purpurea, S. mombin, Mangifera indica cv. 'piña', and M. indica cv. 'coche' from two localities in Chiapas, Mexico. There were significant differences in the mating competitiveness of males collected from mango cv. 'coche' compared with mass-reared males. There were no differences in the mating propensity between flies from the two localities, even in the number of matings, when weight was considered as a covariable. The mass-reared strain showed the earliest age at first oviposition. The locality affected the longevity and oviposition period, and these influenced the birth rate, intrinsic rate of increase, finite rate of population increase, mean generation time, and doubling time. According to the demographic parameters, the population of S. mombin would allow artificial colonization in less time, considering that it has a high reproduction rate starting at an early age. Even in the propensity test, it had the highest number of matings. However, males with greater sexual competitiveness and longevity for colonization corresponded to those collected from S. purpurea.

Development, survival and reproduction of Stratiolaelaps scimitus (Acari: Laelapidae) on four diets

.The development, survival and reproduction of Stratiolaelaps scimitus (Acari: Laelapidae) were determined on four diets (Ephestia kuehniella eggs, Artemia sp. cysts, Typha orientalis pollen, and Tyrophagus curvipenis) in the laboratory at 25 ± 1°C, 80 ± 5% RH, 24 h D: 0 h L. E. kuehniella eggs and T. curvipenis were very suitable for the overall development of S. scimitus to adulthood, with over 90% survival rates. Shrimp cysts were not suitable, with 11.1% survival to adults, and T. orientalis pollen were intermediate, with 50% survival to adults. S. scimitus immature development was the fastest on T. curvipenis (9.67 ± 0.18 days), and it was also very fast on E. kuehniella eggs, but relatively slow on T. orientalis pollen (18.26 ± 0.68 days) and the slowest on Artemia cysts (21.36 ± 1.23 days). The female pre-ovipositional period (APOP) averaged less than 3 days on E. kuehniella eggs but over 3 days on T. curvipenis, but mated and unmated females had a similar APOP, regardless of diet. Neither diet nor mating had significant effects on the total pre-ovipositional period from birth to oviposition (around 13 days). The oviposition period averaged 1 to 2 days longer for mated females than unmated ones, regardless of diet, which had no significant effects. Mated females produced 50% more eggs than unmated females when feeding on E. kuehniella eggs, but 69% more than unmated females when feeding on T. curvipenis; the effects of mating were significant, and the effects of diet were different depending on mating status of the predators: fecundity was higher on E. kuehniella eggs (20.21 ± 1.16) than on T. curvipenis (17.07 ± 0.49) only for unmated females. Most life table parameters (intrinsic rate of population increase r, finite rate of population increase λ, and net reproductive rate R0) were not significantly affected by diet and mating. However, the mean generation time T was shorter in unmated females than in mated ones, and more so when feeding on T. curvipenis. T. curvipenis is easy to rear, so it is considered a very promising diet for S. scimitus as it does not damage plants nor cause allergenic reactions in workers or users. Since T. curvipenis is common on plants, future studies should explore the combined use of foliar predators (e.g. Phytoseiidae) and soil predators for the biocontrol of greenhouse pests (e.g. thrips) using a shared non-pest prey such as T. curvipenis.

Landscape Effects on Reproduction of Euschistus servus (Hemiptera: Pentatomidae), a Mobile, Polyphagous, Multivoltine Arthropod Herbivore.

Landscape factors can significantly influence arthropod populations. The economically important brown stink bug, Euschistus servus (Say) (Hemiptera: Pentatomidae), is a native mobile, polyphagous and multivoltine pest of many crops in southeastern United States and understanding the relative influence of local and landscape factors on their reproduction may facilitate population management. Finite rate of population increase (λ) was estimated in four major crop hosts-maize, peanut, cotton, and soybean-over 3 yr in 16 landscapes of southern Georgia. A geographic information system (GIS) was used to characterize the surrounding landscape structure. LASSO regression was used to identify the subset of local and landscape characteristics and predator densities that account for variation in λ. The percentage area of maize, peanut and woodland and pasture in the landscape and the connectivity of cropland had no influence on E. servus λ. The best model for explaining variation in λ included only four predictor variables: whether or not the sampled field was a soybean field, mean natural enemy density in the field, percentage area of cotton in the landscape and the percentage area of soybean in the landscape. Soybean was the single most important variable for determining E. servus λ, with much greater reproduction in soybean fields than in other crop species. Penalized regression and post-selection inference provide conservative estimates of the landscape-scale determinants of E. servus reproduction and indicate that a relatively simple set of in-field and landscape variables influences reproduction in this species.

The influence of temperature on life history traits of Diadegma mollipla (Hymenoptera: Ichneumonidae), an African parasitoid of the diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae)

The use of Diadegma mollipla (Holmgren) as a biocontrol agent for diamondback moth (DBM)—a notorious pest of crucifers—can potentially be improved with increased scientific knowledge of the D. mollipla’s life history. This study investigated the influence of temperature on the life history traits of D. mollipla parasitizing DBM under laboratory conditions with 20 female D. mollipla for each of five constant temperatures i.e., 15, 20, 25, 30 and 35 °C. Data analysis using curvilinear regression models showed that D. mollipla’s highest intrinsic and finite rates of population increase, net reproductive rate, survival of immatures, daily fertility, shortest immature development and doubling times were achieved between 26 and 30 °C. Thus the results of this study provide evidence to that D. mollipla does not thrive well outside the 26–30 °C temperature range. These results provide baseline information for guiding the use of D. mollipla in the biological control of the destructive DBM pest.

Fitness landscapes and life‐table response experiments predict the importance of local areas to population dynamics

AbstractAnimal resource requirements differ among life‐history stages, and thus, habitat is most appropriately thought of as specific to a particular life stage. Accordingly, different habitats may vary in their significance as functions of (1) the sensitivity of population growth to the life stage for which the habitat is most important, (2) spatial association of each habitat to other habitats, and (3) the abundance of the habitat in question. We used an analogy to a life‐table response experiment to develop spatial models linking key habitats to rates of population increase in Greater Sage‐grouse. We parameterized models linking demographic rates to vegetation and physical attributes of habitats, including spatial association of some habitats to others, using a decade‐long study of Greater Sage‐grouse in central Nevada. We modeled the contribution of each pixel in the landscape to regional λ (finite rate of population increase) using functional relationships between demographic rates and the attributes of that pixel, and the sensitivity of λ to each demographic rate. We incorporated the following demographic rates into our model: female nesting success, survival of chicks from hatching to 45 d, and adult female annual survival. We also incorporated the probability a site was used for nesting. Chick survival (62%) and nest site selection (21%) explained most of the variance in lambda. We found that only ~8% of all habitat for Greater Sage‐grouse contributed to λ > 1. Habitat supporting population growth occurred in mid‐high elevation areas with moderate slopes, and a high percent cover of sagebrush, and in nesting areas close to late‐brood habitat. Our models indicate that a relatively small proportion of habitat available to Greater Sage‐grouse in central Nevada is responsible for maintenance of the population in our study system. We suggest that the general approach we describe here can be used to improve understanding of habitats most likely to regulate populations in other systems, providing an important tool in ecology and conservation.

Entomopathogenic potential of fungi isolated from intertidal environments against the cabbage aphid Brevicoryne brassicae (Hemiptera: aphididae)

ABSTRACTThe use of biopesticides formulated from entomopathogenic fungi is a strategy utilised in integrated pest management programmes. The microorganisms used in these biopesticides are isolated from terrestrial organisms and ecosystems. However, bioprospecting in marine environments may lead to the discovery of promising fungi for pest control. In this study, marine fungi were identified and evaluated for the control of Brevicoryne brassicae. The effects of the most virulent isolate so identified on the mortality of aphids were compared to the effects of bioinsecticides that were formulated from fungal strains of Beauveria bassiana (Bovemax®) and Metarhizium anisopliae (Methamax®). Moreover, lethal and sublethal effects of this isolate on B. brassicae biological parameters were also examined. The isolates were identified as Aspergillus versicolor, Aspergillus sydowii (isolates 1 and 2), Penicillium dipodomyicola, and Trichoderma harzianum. The fungal strain A. versicolor was the most virulent fungal species, causing 85.9% mortality in B. brassicae at 24 h. The mortality rate caused by A. versicolor was similar to that caused by Bovemax® and Methamax® at concentrations of 105 conidia mL−1, and superior to that caused by Methamax® at a concentration of 109 conidia mL−1. The exposure of B. brassicae to CL25 (0.32 × 103) of A. versicolor did not affect the net reproductive rate (Ro), average generation time (T), intrinsic rate of population growth (rm), and finite rate of population increase (λ). This is the first study to demonstrate that A. versicolor isolated from a marine environment is a promising candidate for the biological control of agricultural pests.

Life History of Cochliomyia macellaria (Fabricius, 1775) (Diptera, Calliphoridae), a Blowfly of Medical and Forensic Importance.

The life history traits of blow fly Cochliomyia macellaria (Fabricius, 1775) was studied under semi-controlled laboratory conditions at 29.14°C temperature, 72.53% relative humidity, and 12-h photoperiod. The raw data were analyzed based on the age-stage, two-sex life table, considering the development rates among individuals of both sexes. Cochliomyia macellaria survival rate was 0.43 (♂) and 0.40 (♀), while life expectancy was 17.9 (♂) and 20.9 (♀) days, for adult males and females, respectively. The total fecundity was 681.15 eggs/female, with an average of 3.65 batches/female and 199 eggs/batch. The intrinsic rate of increase (r) was 0.327days-1, the finite rate of population increase (λ) was 3.35days-1, the mean generation time (T) was 17.15days, and the net reproduction rate (R 0 ) was 272.46 offspring/individual. The population parameters found here corroborates that C. macellaria population act as a r selected species under laboratory conditions. Additionally, development data and accumulated degree days (ADD) for each stage of C. macellaria are provided and its implications for the forensic use are discussed.

Temperature‐dependent phenology and growth potential of the Andean potato tuber moth, Symmetrischema tangolias (Gyen) (Lep., Gelechiidae)

AbstractThe Andean potato tuber moth, Symmetrischema tangolias (Gyen) [Lepidoptera, Gelechiidae], is an economically important pest of potato (Solanum tuberosum L.) in the mid‐elevated Andean region and an invasive pest of partially global importance. Determination of the pest's population life table parameters is essential for understanding population development and growth under a variety of climates and as part of a pest risk analysis. The development, mortality and reproduction were studied in two pest populations (from Peru and Ecuador) in which cohorts of each life stage were exposed to different constant temperatures ranging from 10°C to 28°C. Using the Insect Life Cycle Modeling software, nonlinear equations were fitted to the data and an overall phenology model established to simulate life table parameters based on temperature. The temperature‐dependent development curve was statistically well described for eggs by Ratkowsky's model and for larvae and pupae by Taylor's model. Variability in development time among individuals independent of temperature was significantly described by a log‐logistic model. Temperature effects on immature mortality were described using different nonlinear models. Optimal temperature for survival was between 14° and 17°C. Temperature effects on adult senescence and oviposition time were described by simple exponential models; within‐group variability was described by a Weibull distribution function. Fecundity per female due to temperature followed a nonlinear model indicating maximum reproduction at ~17°C. The established model revealed good convergence with historical life tables established at fluctuating temperatures. The results confirm that S. tangolias is more adapted to cooler temperature than the common potato tuber moth, Phthorimaea operculella (Zeller). S. tangolias develops at temperatures within the range of 8–28.8°C with a maximum finite rate of population increase (=1.053) at 21°C. The established process‐based physiological model can be used globally to simulate life table parameters for S. tangolias based on temperature and should prove helpful for evaluating the potential establishment risk and in adjusting pest management programmes.

Better Together: Association With 'Candidatus Liberibacter Asiaticus' Increases the Reproductive Fitness of Its Insect Vector, Diaphorina citri (Hemiptera: Liviidae).

The duration of the evolutionary association between a pathogen and vector can be inferred based on the strength of their mutualistic interactions. A well-adapted pathogen is likely to confer some benefit or, at a minimum, exhibit low pathogenicity toward its host vector. Coevolution of the two toward a mutually beneficial association appears to have occurred between the citrus greening disease pathogen, Candidatus Liberibacter asiaticus (Las), and its insect vector, the Asian citrus psyllid, Diaphorina citri (Kuwayama). To better understand the dynamics facilitating transmission, we evaluated the effects of Las infection on the fitness of its vector. Diaphorina citri harboring Las were more fecund than their uninfected counterparts; however, their nymphal development rate and adult survival were comparatively reduced. The finite rate of population increase and net reproductive rate were both greater among Las-infected D. citri as compared with uninfected counterparts, indicating that overall population fitness of infected psyllids was improved given the greater number of offspring produced. Previous reports of transovarial transmission, in conjunction with increased fecundity and population growth rates of Las-positive D. citri found in the current investigation, suggest a long evolutionary relationship between pathogen and vector. The survival of Las-infected adult D. citri was lower compared with uninfected D. citri, which suggests that there may be a fitness trade-off in response to Las infection. A beneficial effect of a plant pathogen on vector fitness may indicate that the pathogen developed a relationship with the insect before secondarily moving to plants.

Population dynamics of feral horses (Equus caballus) in an exotic coniferous plantation in Australia

Context Understanding population dynamics of invasive species is crucial for the development of management strategies. Feral horses (Equus caballus) are a growing problem in the Tuan–Toolara State Forest (TTSF), a coniferous plantation in south-eastern Queensland, Australia. Aim The population dynamics of the TTSF feral horses was not known. Therefore, the study was designed to characterise the major vital parameters of this population and, using these data, develop a long-term management plan. Methods The study was conducted over 3 years (2011–14) involving 522 individually identified horses. Foaling rates were used to calculate fecundity. Body fat distribution was estimated using body condition score (BCS), which reflects the nutritional, metabolic and general health of individual animals. Multi state mark–capture population models were used to estimate age-specific survival, and the Leslie age-structured projection matrix model was used to determine the annual rate at which the population increased. Key results The mean annual fecundity was low (0.23 ± 0.07 s.d.). The mean BCS of the population was mid-range (2.55 ± 0.51 s.d.) with adult females having lower scores than other age and gender groups. Survival estimates were consistently high (0.92–0.95) across all age groups. The average annual finite rate of population increase (λ) for the 3 years of the study was 1.09. Sensitivity analysis demonstrated that the population growth rate was almost seven times more sensitive to changes in adult survival compared with juvenile survival, and almost twice as sensitive to changes in fecundity. Key conclusions Population dynamics of the TTSF feral horses were comparable to other feral horse populations similarly challenged by environmental nutritional limitations. Implications Defining population dynamics of the TTSF feral horses permits the formulation of management goals that can be audited and adapted as required. The most effective strategy for controlling population growth in the TTSF would involve the continuing removal of substantial numbers of adult females or manipulation of survival and/or fecundity. As selective removal will likely alter the adult sex ratio and age structure of the population, ongoing assessment is necessary to minimise adverse welfare outcomes.

Estimating Finite Rate of Population Increase for Sharks Based on Vital Parameters.

The vital parameter data for 62 stocks, covering 38 species, collected from the literature, including parameters of age, growth, and reproduction, were log-transformed and analyzed using multivariate analyses. Three groups were identified and empirical equations were developed for each to describe the relationships between the predicted finite rates of population increase (λ’) and the vital parameters, maximum age (Tmax), age at maturity (Tm), annual fecundity (f/Rc)), size at birth (Lb), size at maturity (Lm), and asymptotic length (L∞). Group (1) included species with slow growth rates (0.034 yr-1 < k < 0.103 yr-1) and extended longevity (26 yr < Tmax < 81 yr), e.g., shortfin mako Isurus oxyrinchus, dusky shark Carcharhinus obscurus, etc.; Group (2) included species with fast growth rates (0.103 yr-1 < k < 0.358 yr-1) and short longevity (9 yr < Tmax < 26 yr), e.g., starspotted smoothhound Mustelus manazo, gray smoothhound M. californicus, etc.; Group (3) included late maturing species (Lm/L∞ ≧ 0.75) with moderate longevity (Tmax < 29 yr), e.g., pelagic thresher Alopias pelagicus, sevengill shark Notorynchus cepedianus. The empirical equation for all data pooled was also developed. The λ’ values estimated by these empirical equations showed good agreement with those calculated using conventional demographic analysis. The predictability was further validated by an independent data set of three species. The empirical equations developed in this study not only reduce the uncertainties in estimation but also account for the difference in life history among groups. This method therefore provides an efficient and effective approach to the implementation of precautionary shark management measures.

Demography and Consumption of Spodoptera litura (Lepidoptera: Noctuidae) Reared on Cabbage and Taro.

Spodoptera litura (F.) causes considerable economic damage to multiple agro-crops annually in many countries. In this study, the demography of S. litura reared on cabbage and taro was investigated using the age-stage, two-sex life table at 25±1°C, 60±10% relative humidity, and a photoperiod of 12: 12 (L:D) h. Our results showed that the net reproductive rate, intrinsic rate, and finite rate of population increase on cabbage (1893.1 offspring, 0.2374 d(−1), and 1.2679 d(−1)) were all not significantly different from those on taro (1361.0 offspring, 0.2298 d(−1), and 1.2584 d(−1)). The net consumption rate on cabbage (439.1 cm2) was, however, three times higher than that on taro (141.7 cm2). According to the population parameters, both cabbage and taro are suitable host plants for S. litura. When both the population growth rate and the consumption rate were taken into consideration, the finite consumption rate on cabbage (ω=3.8054) was significantly higher than that on taro (ω=1.3184). In Taiwan, taro and cabbage are commonly planted in adjacent farm plots, with taro being grown from March to November and cabbage from October to April. Because of the overlapping growth periods of the two crops, S. litura can easily propagate throughout the year by switching between the adjacent crops during the overlap periods. Pest management strategies for controlling S. litura must be thoroughly reevaluated based on ecological characteristics, including its life table and consumption rate on its major host plants.

Reproductive parameters of Tetranychus urticae (Acari: Tetranychidae) affected by neonicotinoid insecticides.

Two-spotted spider mite is a major pest of many agricultural and ornamental crops worldwide. Some reports have indicated that application of neonicotinoid insecticides may lead to increased fecundity of this pest. If this is found to be true, the use of these pesticides may cause an outbreak of spider mite populations. Sublethal effects of three neonicotinoids, namely thiacloprid, acetamiprid and thiamethoxam were studied on T. urticae adults at field recommended doses. The experiments were carried out using bean leaf pieces in plastic Petri dishes. The adult mites were treated using two methods: (1) drench application and (2) spraying of leaves with Potter Spray Tower. Our results indicated that all neonicotinoids tested increased T. urticae population. In both treatment methods, acetamiprid treated mites had the highest intrinsic rate of population increase (rm) and finite rate of population increase (λ); and the lowest mean generation time (T) and doubling time among the treatments. If similar results are obtained from greenhouse and field trials, the use of these insecticides requires necessary precautions such as avoiding repeated use of neonicotinoid insecticide for controlling insect pests.

Effects of Competition and Predation by Native Mosquitoes on the North American Invasion of Aedes japonicus japonicus (Diptera: Culicidae).

The success and effects of a biological invasion can be dependent on species interactions with resident competitors and predators. Indirect interactions between competition and predation, such as keystone predation, can influence both invasion success and the impact of an invasive species on resident competitors. The invasive mosquito Aedes japonicus japonicus (Theobald) has been established within the North American range of the indigenous competitor Aedes triseriatus (Say) and indigenous mosquito predator Toxorhynchites rutilus (Coquillett). The effects of Tx. rutilus predation on competition between Ae. j. japonicus and Ae. triseriatus were tested in laboratory microcosms. Consistent with a prior study, there was minimal evidence of competitive asymmetry between Ae. j. japonicus and Ae. triseriatus, with similar effects of intraspecific versus interspecific interactions on both species. Tx. rutilus predation caused high mortality of both Ae. j. japonicus and Ae. triseriatus, and minimized the effects of density-dependent competition. Ae. japonicus females that survived predation had larger adult body sizes than those in treatments without predators. Ae. triseriatus females that survived Tx. rutilus predation were larger and developed quicker than individuals in treatments without predators. Intraspecific competition and predation negatively affected the finite rate of population increase for Ae. j. japonicus, but only affected individual fitness correlates for Ae. triseriatus, indicating that the overall population performance of the invader is more sensitive to these interactions than the native species. Based on these results, we predict that predation is likely to be an important barrier to the establishment and spread of Ae. j. japonicus in tree holes in North America.