Instantaneous Rate Of Population Increase Research Articles

Resistance of landrace and commercial cowpea genotypes to Callosobruchus maculatus attack

In the northern and north-eastern regions of Brazil, the cultivation of cowpea (Vigna unguiculata L.) is socially and economically important. However, attack by weevils makes storage difficult. Landrace genotypes exhibit high genetic variability, which can confer resistance to pest attacks. In this study, the susceptibility of landrace genotypes of cowpea to the attack of the weevil (Callosobruchus maculatus (Fabr., 1775)) was assessed. A total of 13 genotypes were used (11 landraces and two commercial genotypes). Biological parameters (number of eggs; daily, accumulated, and final emergence; the instantaneous rate of population increase) of C. maculatus, and loss of cowpea seed mass were analysed. The treatments were composed of 30g of each genotype and 20 adult insects in an entirely randomised design with ten replicates. A principal component analysis and grouping analysis were performed due to the similarity between the genotypes, and three groups were described. Group 3 (‘BRS Pujante’, ‘Ligeiro’, and ‘Tardão’ genotypes) had the highest oviposition/number of eggs, daily emergence, number of emerging insects, and instantaneous rate of population increase. Group 2 (‘Azulão’, ‘Costela de Vaca’, and ‘Rabo de Tatu’ genotypes) showed intermediate values, and group 1 (‘Bala’, ‘Canapú’, ‘Corujinha’, ‘Manteiguinha’, ‘Moita’, ‘Seridó’, and ‘Sempre Verde’ genotypes) had the lowest values for all those variables. The commercial genotypes were grouped in groups 1 (‘Sempre Verde’) and 3 (‘BRS Pujante’) and showed similar behaviour to the landrace genotypes of those groups. This study demonstrated that the genotypes in group 3 are susceptible to the attack of C. maculatus, while those in group 1 showed antibiosis resistance. Utilization of insect-resistant genotypes can reduce cowpea infestation and synthetic insecticide application, leading to a positive economic impact.

Thresholds of population persistence for the Yangtze finless porpoise: implications for conservation managements.

The Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis), a critically endangered species, is the only cetacean species in the Yangtze River following the functional extinction of baiji (Lipotes vexillifer). To inform conservation actions, two important questions need to be addressed: what is the threshold value of survival rate, and what is the threshold value of population size? We calculate the instantaneous rate of population increase ( ) for the Yangtze finless porpoise for various combinations of the calf and the non-calf survival rates. We also test the probability of extinction for different minimum carrying capacities for 100 and 500 years using a stable population model. The threshold value of the non-calf survival rate is never lower than 0.869, but current estimates from field data have been far below this threshold. Our model based on extinction probability and carrying capacity suggests that the threshold for the population size to persist 100 years required 113 animals, and 472 animals are required to persist 500 years. Therefore, we recommend establishing an ex situ reserve network to guarantee the minimum 100-year carrying capacity. To ensure the long-term population viability, we suggest establishing two insitu reserve zones in two lakes and their surrounding reserves to meet a minimum 500-year carrying capacity. In addition, measures to avoid further habitat fragmentation should be priority.

Fertility Life Table, Population Parameters and Biotic Potential of Helicoverpa gelotopoeon (Dyar) (Lepidoptera: Noctuidae).

Helicoverpa gelotopoeon is an endemic pest of South America that affects soybean and other important crops. Life tables are a fundamental tool used to study insect populations, resulting in crucial information for integrated pest management programs. Therefore, the aim of this study was to evaluate the biotic potential and the construction of a life table of this species under laboratory conditions. The biological parameters that showed significant differences between male and female were pupal duration, longevity and life span, which were all longer in duration for males. The net reproductive rate (R0) was 95.49, the mean generation time (T) 37.53, and the instantaneous rate of population increase "r" 0.12. The population doubling time (DT) was 5.70 days, and the daily finite rate of increase (λ) 1.13. The maximum rate of population growth occurred in the day 33. Fecundity had two peaks: at days 35 and 37. Gross and net fecundity rate, and the average number of eggs laid per female per day were 565.87, 496.07, and 18.76 respectively. The biotic potential was 2.026 x 1018 individuals/female/year. The survivorship curve showed that mortality was high during incubation period and first larval instars, then it declined until the death of last adult. These results provide important information to develop management strategies of H. gelotopoeon in South America.

Population-level effects of abamectin, azadirachtin and fenpyroximate on the predatory mite Neoseiulus baraki.

The coconut production system, in which the coconut mite Aceria guerreronis is considered a key pest, provides an interesting model for integration of biological and chemical control. In Brazil, the most promising biological control agent for the coconut mite is the phytoseiid predator Neoseiulus baraki. However, acaricides are widely used to control the coconut mite, although they frequently produce unsatisfactory results. In this study, we evaluated the simultaneous direct effect of dry residue contact and contaminated prey ingestion of the main acaricides used on coconut palms (i.e., abamectin, azadirachtin and fenpyroximate) on life-history traits of N. baraki and their offspring. These acaricides are registered, recommended and widely used against A. guerreronis in Brazil, and they were tested at their label rates. The offspring of the exposed predators was also evaluated by estimating the instantaneous rate of population increase (r i ). Abamectin compromised female performance, whereas fenpyroximate did not affect the exposed females (F0). Nonetheless, fenpyroximate strongly compromised the offspring (F1) net reproductive rate (R0), intrinsic rate of population growth (r i ), and doubling time (DT). In contrast, fenpyroximate did not have such effects on the 2nd generation (F2) of predators with acaricide-exposed grandparents. Azadirachtin did not affect the predators, suggesting that this acaricide can be used in association with biological control by this predatory species. In contrast, the use of abamectin and fenpyroximate is likely to lead to adverse consequences in the biological control of A. guerreronis using N. baraki.

Comparative life history characteristics of the mite predator Neoseiulus cucumeris (Oudemans) (Acari: Phytoseiidae) on mite and pollen diets

ABSTRACTThe food diversification strategy that can offer suitable nutrients as a diet for the natural enemies may possibly help to decrease pest populations by boosting the efficiency of predators. Therefore, my objective was to evaluate the effects of plant and animal diets on biological parameters of the phytoseiid mite Neoseiulus cucumeris (Oudemans). This predator that is a natural enemy of mites was reared on plant pollens (maize (Zea mays L.), sweet pepper (Capsicum annuum L.), mungbean (Vigna radiata L.), cucumber (Cucumis sativus L.), tomato (Lycopersicon esculentum Mill.), and rose (Rosa multiflora Thunb.), offered alone, and in combination with the prey mite Tyrophagus putrescentiae (Schrank). Results showed that N. cucumeris fed, developed and reproduced better when it was provided with plant and animal diets together, compared to pollens offered alone. The predator showed the most efficient capability for completion of life parameters (development, survival, fecundity, oviposition, longevity and instantaneous rate of increase) with maize and mungbean ingested pollens in combination with T. putrescentiae. The least competency was observed on cucumber and rose pollens used separately. The lowest developmental time of the predator from neonate larva to adult emergence, the highest immature survivorship, higher fecundity, long oviposition period, and the highest adult female's life span were observed when offered maize pollens along with T. putrescentiae compared to other treatments. Accordingly, the instantaneous rate of population increase (ri) day−1 was surpassed by N. cucumeris for the combination of pollen and T. putrescentiae diets than pollens utilized alone. It is determined that N. cucumeris can reproduce and develop more successfully on a food complex consisting of pollen and animal diets than any single diet. These findings reveal that pollen can be used by N. cucumeris as a suitable alternative food in periods when prey in the field is sparse or absent. Moreover, such propensity of predators to feed on food from plant origin increases their survival during periods when prey is locally scarce, but natural enemies might occur at the expense of an ability to utilize food as efficiently as specialized predators to boost the management strategies of pest species in field's ecosystem.

Fitness costs associated with low-level dimethoate resistance in Phytoseiulus macropilis

Phytoseiulus macropilis Banks (Acari: Phytoseiidae) is an effective predator of tetranychid mites, but there are no data on its response to pesticides. We investigated the resistance of the predatory mite P. macropilis to the acaricides abamectin and dimethoate, and we examined the fitness costs associated with resistance. Two populations were tested: one from conventional cultivation and another from an area not commercially exploited. After the application of acaricides to the predator, we determined the lethal effects of the acaricides, the instantaneous rate of population increase (r(i)), the predation on Tetranychus urticae Koch (Acari: Tetranychidae) and its ability to locate prey in an olfactometer. P. macropilis exhibited resistance to dimethoate only. The low level of resistance (9.4x) of the predator did not affect their ability to locate prey. However, the dimethoate resistant population was not as effective in contatining prey population when in lower density and exhibited a more pronounced decrease of r(i) in the presence of this acaricide, due to the reduced oviposition of the predator, a likely consequence of the different genetic background of this population.

Phosphine resistance in Rhyzopertha dominica (Fabricius) (Coleoptera: Bostrichidae) from different geographical populations in China

This study was carried out to determine the level of phosphine resistance in 16 Rhyzopertha dominica (Fabricius) populations that were collected from ten provinces and one municipality in China following the Food and Agriculture Organization’s (FAO) standard method. Results showed that the 50% lethal concentration (LC50) of phosphine to these R. dominica populations ranged from 0.017 to 4.272 mg/L. Of the 16 populations, 5 were of low resistance, 6 were moderately resistant, and 5 were high resistant. The instantaneous rate of population increase (ri) was correlated with phosphine resistance followed by the Exponential model (y = 0.037e -0.005X , R 2 = 0.937). The relationship between the types of grain storage

Physiological and behavioral resistance to esfenvalerate + fenitrothion in populations of the maize weevil, Sitophilus zeamais

The maize weevil, Sitophilus zeamais (Coleoptera: Curculionidae) is considered the main pest of stored maize in Brazil and its control is achieved mainly by insecticides. The massive and intensive use of these compounds may lead to selection of resistant populations and consequently compromise the control efficacy of this insect pest in Brazilian storage facilities. Therefore, we surveyed physiological and behavioral resistance to the insecticide mixture esfenvalerate + fenitrothion in 27 populations of S. zeamais collected in several Brazilian counties and Paraguay, and also investigated possible costs associated with this phenomenon. The insects were subjected to concentration-mortality bioassays to determine the lethal concentrations LC 50 and LC 95 . The populations were also subjected to two walking trials on surfaces fully-treated and partially-treated with dried insecticide residues for detection of behavioral resistance. We also determined the instantaneous rate of population increase (ri), and body mass of individuals of each population. The concentration-mortality bioassays indicated resistance ratios (at LC 50 ) ranging from 1.00 to 5.02x for the insecticide mixture esfenvalerate + fenitrothion compared with the susceptible standard population (Sete Lagoas). Although the resistance ratios were modest at LC 50 , they reached up to 232x at LC 95 (Votuporanga county, Sao Paulo, Brazil). The behavioral trait of walking in treated arena varied among populations and sex, but there was no significant avoidance to the insecticide mixture. There was no correlation between physiological and behavioral resistance, indicating that physiological resistance is independent of behavioral resistance in the populations tested. There was no significant difference in the instantaneous rate of increase (ri), and body mass among the insects. Therefore, we conclude that there was no fitness cost associated with the levels of resistance observed in the populations studied. Keywords : Insecticide resistance, Locomotion, Behavioral avoidance, Fitness cost, Rate of population growth

Assessing pest control using changes in instantaneous rate of population increase: Treated targets and stable fly populations case study

The instantaneous rate of population increase was used to assess the ability of attractive targets coated with permethrin to control stable fly populations on 3 dairy farms in south central Ontario, Canada. Two attractive targets were deployed over 10 wk in 2001 at each of 6 dairy farms. Three farms were outfitted with 2 untreated targets and 3 were outfitted with 2 targets treated with permethrin [Ectiban-impregnated Coroplast (Ectiban: Schering-Plough Canada Inc., Pointe-Claire, Québec, Canada; Coroplast: Great Pacific Enterprises Inc., Granby, Québec, Canada)]. Population growth rate was measured in terms of degree-days above a 10°C developmental threshold (rDD10). The rDD10 at the 3 treated dairy farms were significantly lower than rDD10 at the 3 neighboring untreated dairy farms (mean rDD10: treated=0.0088, untreated=0.013), but not in the previous year when targets were not installed (mean rDD10: treated=0.012, untreated=0.015). This supports a long-term approach to management that lowers population growth rates in those regions where stable fly numbers increase exponentially from spring until winter, by shortening the period of economic impact of this pest.

Ozone as a management alternative against phosphine-resistant insect pests of stored products

This study was carried out to assess ozone toxicity to 16 populations of Tribolium castaneum (Herbst), 11 populations of Rhyzopertha dominica (F.) and nine populations of Oryzaephilus surinamensis (L.) collected from six regions of Brazil. These populations were also used to test if there is cross-resistance to ozone and phosphine. The relationship between susceptibility to ozone and respiration rate, and associated fitness costs were also evaluated. The instantaneous population growth rate ( r i ), CO 2 production and mean insect body mass of each population were measured. Ozone toxicity was determined using time-response bioassays at the dosage rate of 150 ppm ozone in a continuous flow of 2 L min −1. All of the populations were susceptible to ozone and there was no cross-resistance to ozone and phosphine. The populations of each species differed in respiration rate and body mass, but there was no significant association between respiration rate or body mass and susceptibility to ozone, as was also the case for the instantaneous rate of population increase ( r i ). As none of the populations showed resistance to ozone, regardless of their susceptibility to phosphine, ozone is a potential alternative for phosphine resistance management in the insect species evaluated in this study.

Phosphine resistance, respiration rate and fitness consequences in stored‐product insects

Resistance to fumigants has been frequently reported in insect pests of stored products and is one of the obstacles in controlling these pests. The authors studied phosphine resistance and its physiological basis in adult insects of 12 populations of Tribolium castaneum (Herbst) (Tenebrionidae), ten populations of Rhyzopertha dominica (F.) (Bostrichidae) and eight populations of Oryzaephilus surinamensis L. (Silvanidae) from Brazil, and the possible existence of fitness costs associated with phosphine resistance in the absence of this fumigant. The bioassays for the detection of phosphine resistance followed the FAO standard method. The production of carbon dioxide and the instantaneous rate of population increase (r(i)) of each population of each species were correlated with their resistance ratios at the LC(50). The resistance ratio at LC(50) in T. castaneum ranged from 1.0- to 186.2-fold, in R. dominica from 2.0- to 71.0-fold and in O. surinamensis from 1.9- to 32.2-fold. Ten populations of T. castaneum, nine populations of R. dominica and seven populations of O. surinamensis were resistant to phosphine. In all three species there was significant association (P < 0.05) between respiration rate and phosphine resistance. The populations with lower carbon dioxide production showed a higher resistance ratio, suggesting that the lower respiration rate is the physiological basis of phosphine resistance by reducing the fumigant uptake in the resistant insects. Conversely, populations with higher r(i) showed lower resistance ratios, which could indicate a lower rate of reproduction of the resistant populations compared with susceptible populations. Thus, management strategies based on the interruption of phosphine fumigation may result in reestablishment of susceptibility, and shows good potential for more effective management of phosphine-resistant populations.

Effects of cadmium, mercury and lead on the survival and instantaneous rate of increase of Paronychiurus kimi (Lee) (Collembola)

The invertebrate springtail species Paronychiurus kimi (Lee) was selected for use in toxicity testing because it is more ecologically relevant to Korean soils than Folsomia candida Willem, which is the standard animal for toxicity tests. Responses of P. kimi to cadmium, mercury and lead were evaluated in artificial soils following the standardized ISO protocol. Although, reproduction of P. kimi was not as high as that of F. candida, 30 adults produced at least 200 juveniles over 28 days. For each of the three heavy metals, LC 50 and EC 50 for reproduction and NOEC and LOEC for the effect on reproduction and instantaneous rate of population increase ( r i ) were also estimated. The 7 days LC 50 was 532, 3.9 and 1322 mg/kg dry soil for cadmium, mercury and lead, respectively. As exposure time increased from 7 to 28 days, the LC 50 values decreased for cadmium but not or only slightly for mercury and lead. The 28 days EC 50 was 60.0 for cadmium, 0.23 for mercury and 428 mg/kg for lead. Significant changes in r i of P. kimi were closely followed by the changes in the sublethal endpoint measured (reproduction) and populations were heading toward extinction ( r i = 0) at concentration of 129, 2.0 and 1312 mg/kg dry soil for cadmium, mercury and lead, respectively. P. kimi was found to be more sensitive to all heavy metals tested than F. candida, confirming its suitability as a bioindicator species for soil toxicological testing in Korea.

Effect of eggplant transformed withoryzacystatingene onMyzus persicaeandMacrosiphum euphorbiae

Abstract: The effect of a genetically modified eggplant line expressingoryzacystatinonMyzus persicae(Sulzer) andMacrosiphum euphorbiae(Thomas) was examined. The transgenic eggplant reduced the net reproductive rate (R0), the instantaneous rate of population increase (r), and the finite rate of population increase (λ) of both aphids species compared with a control eggplant line. The mean generation time (T) of the aphids was unaffected by the transgenic plants. Age‐specific mortality rates ofM. persicaeandM. euphorbiaewere higher on transgenic plants. These results indicate that expression oforyzacystatinin eggplant has a negative impact on population growth and mortality rates ofM. persicaeandM. euphorbiaeand could be a source of plant resistance for pest management of these aphids.

The demography of the lizard Tropidurus torquatus (Squamata, Tropiduridae) in a highly seasonal Neotropical savanna

The demography of the lizard Tropidurus torquatus (Squamata, Tropiduridae) in a highly seasonal Neotropical savanna. The demography of a population of Tropidurus torquatus was studied from March 1996 until December 1998, in the Cerrado biome of central Brazil, using the method of capture and recapture. Population size, number of incoming individuals in the population, and age structure varied seasonally, reflecting the reproductive cycle of the species. The instantaneous rate of population increase did not differ from zero throughout the study. In general, the permanence rates of juveniles and adults were low, indicating a large turnover of individuals in the population, with a maximum life expectancy of three years. The sex-ratio among adults was biased toward females. Since no bias was observed among juveniles and there was no difference in adult permanence between sexes, we suggest that the biased adult sex-ratio resulted from a lower permanence of males during a short ontogenetic period, when secondary sexual characteristics develop. When compared to T. itambere, the studied population of T. torquatus attained a higher density and a greater female bias in the sex-ratio. In general, the studied population presented characteristics that, according to life history theory, should be associated with early age at maturity and polygyny: short life expectancy, high population turn over, and female biased sex-ratios.

Comparison of instantaneous rate of population increase and critical-effect estimates in Folsomia candida exposed to four toxicants

The instantaneous rate of population increase ( r i) integrates several life cycle variables into one accessible statistic and has been proposed as a more practical alternative than assembling full life tables in the study of population-level responses to toxicant exposure. In this study the sensitivity of instantaneous rate of population increase is compared to critical-effect estimates for populations exposed to four toxicants with different modes of action. Populations of the Collembolan Folsomia candida were exposed to cadmium, copper, pyrene, and chlorpyrifos in artificial soil following the standardized ISO (International Organization for Standardization, Geneva, 1999) protocol. We calculated r i values and LC 50, EC 50juvenile, and NOEC values for each chemical. Comparison of the relative toxocity of the four chemicals indicated that chlorpyrifos had the lowest values and was thus the most toxic, followed by pyrene, cadmium, and copper. Significant changes in r i were seen to follow closely changes in the sublethal parameter measured (juvenile production) and showed populations in decline at concentrations as low as 40% of the LC 50. The study showed r i to be a good measure of population response, and we conclude that the statistic gives a better understanding of effects on a population than through the sole use of traditional critical-effect estimates.

Population level effects of cadmium and the insecticide imidacloprid to the parasitoid, Aphidius ervi after exposure through its host, the pea aphid, Acyrthosiphon pisum (Harris)

Abstract The objective of this study was to assess the influence of toxic substances with different modes of action on a two-species system: an aphid-specific parasitoid, Aphidius ervi Haliday, feeding on the pea aphid, Acyrthosiphon pisum (Harris). The instantaneous rate of population increase ( r i ) was used as a measure of population level toxic effect in this study. The toxicants evaluated were imidacloprid, a nonpersistent neurotoxic insecticide, and cadmium, a chronic pollutant with a tendency to accumulate. We evaluated the effects of cadmium and imidacloprid on A. pisum and A. ervi because both toxicants can occur together in polluted areas where crops are grown. Cadmium (200 or 400 mg kg −1 dry weight soil) and imidacloprid (4 or 40 g a.i. ha −1 ) were applied to soil contained in plastic pots in which broad bean plants, Vicia faba L., were grown. Results of this study indicated that cadmium at the concentrations tested, reduced population growth rate of the pea aphid. Imidacloprid also reduced aphid growth rate, but only at the highest concentration tested (40 g a.i. ha −1 ). Combinations of cadmium and imidacloprid had the greatest impact on aphid growth rate. Imidacloprid alone had no effect on population growth rate of the parasitoid. However, cadmium alone or in combination with imidacloprid had a negative impact on A. ervi by reducing population growth rate 77%. These results indicate that negative impacts on parasitoids may occur in areas where cadmium contamination is present and imidacloprid is used to control aphids.

Demography of the Red Form of Myzus nicotianae (Homoptera: Aphididae) on Burley Tobacco

Life tables were constructed for the tobacco aphid, Myzus nicotianae Blackman, in the laboratory using three varieties of burley tobacco commercially available in Kentucky. Daily mortality and fecundity schedules were established to estimate net reproductive rate and instantaneous rate of population increase on each variety. The number of days to first reproduction, longevity, mortality, and fecundity were similar on each variety. Net reproductive rate, instantaneous rate of population increase, mean generation time, and doubling time of the populations were the same for each variety, indicating that population growth of the aphid on the three varieties did not differ significantly.

Laboratory Life Table Studies of the Blackfaced Leafhopper (Homoptera: Cicadellidae) on Johnsongrass and Corn

Laboratory life tables were constructed for Graminella nigrifrons (Forbes) using Johnsongrass and corn as hosts. Daily mortality and fecundity schedules were established to estimate net reproductive rate and instantaneous rate of population increase on each host. Nymphal mortality on Johnsongrass was greatest in the fifth instar. In general, nymphal mortality was higher on corn and was greatest in the second, third, and fourth instars. Net reproductive rate and instantaneous rate of population increase were higher on Johnsongrass than on corn. This was attributed to higher probabilities of survival to the midpoint of any stage or age interval and higher numbers of female eggs per female per week on Johnsongrass. Mean generation time was essentially the same for each host.

Differences in the Life Tables of Tropical and Temperate Milkweed Bugs, Genus Oncopeltus (Hemiptera:Lygaeidae)

The life tables of Oncopeltus fasciatus from a temperate locality (Ithaca, New York) and O. unifasciatellus from a tropical locality (Cali, Columbia) are compared. When reared under controlled conditions approximating those they experience during the summer in their natural environments, the two species exhibit remarkably similar rates of development and mortality. The temperate species, however, which begins ovipositing sooner and produces more eggs, has a higher instantaneous rate of population increase (r). These results extend some theories advanced to explain latitudinal differences in the clutch size of birds.