Rate Of Natural Population Increase Research Articles

Temporal trends in the Colonisation of the Pacific: Palaeodemographic Insights

The colonisation of eastern parts of the Pacific Islands was the last phase in the preindustrial expansion of the human species. Given the scale and challenges of the endeavour it is unsurprising that scholars have long been interested in understanding the conditions that drove and supported the exploration and settlement of this vast region. There has been speculation as to the influence of demographic factors, either as drivers or in some way regulating the rate and success of human expansion, but testing this has proven challenging. This study evaluates two hypotheses of population dynamics: the adaptation/resilience hypothesis, which proposes that populations respond to localised environmental conditions and changes in subsistence strategy, technology, differences in pathogen loads, and other events that occur at different times in different places; and the temporal hypothesis, which proposes that populations respond to major events such as climate change that occur in a region at an absolute point in, or over an absolute period of, time (noting that the two hypotheses are not mutually exclusive). Applying new methods for estimating the rate of natural population increase from human skeletal remains, this study utilised 23 samples to evaluate trends in population increase following the human expansion into the region. The results indicate a trend in population growth following colonisation, with initially high population growth, followed by a significant decrease and subsequently an increase in growth rates. The lack of a temporal trend may represent a high degree of heterogeneity in the impacts of climate change on individual archipelagos and islands.

Energy budget in Alona guttata (Chydoridae: Aloninae) and toxicant-induced alterations

Although chydorids are the most diverse cladocerans in the world, there is still little information available related to their biology and even less with respect to their susceptibility to toxicants. Therefore, this work aimed to implement protocols with Alona guttata for acute, chronic, and sublethal toxicity tests, using the environmental concern toxicants deltamethrin (DM) and lead (Pb2+), which are commonly used due to agriculture and vector control or for the automotive industry, respectively. Once the results of LC50 (0.1160 ± 0.0107 μg/L for DM and 1.5797 ± 0.1605 mg/L for Pb2+) were obtained, sublethal concentrations (0.01 to 0.2 LC50) were used for the evaluation of biomarkers and chronic toxicity. Concentrations as low as 0.01 LC50 reduced Alona's survival and fecundity, negatively affecting demographic parameters, and decreased the energy reserves. A significant correlation was found between the natural rate of population increase and the caloric content, which demonstrates the suitability of these biomarkers as endpoints of early warning that allow inferring alterations at higher biological levels. Subsequently, this work could constitute the first report on the evaluation of the energy budget in a non-daphnid species, its alterations due to exposure to toxic substances and the correlation with demographic responses.

Detection of temporospatially localized growth in ancient Southeast Asia using human skeletal remains

Measures of population growth can provide significant insights into the health, adaptivity and resilience of ancient communities, particularly the way in which human populations respond to major changes, such as the transition to agriculture. To date, paleodemographic tools have facilitated the evaluation of long term, regional population growth, while identification of intraregional variability and short-term growth has been more challenging. This study reports on the application of a new method for estimating the rate of natural population increase (RNPI) from skeletal remains. We have applied the method to ancient Southeast Asian samples and, based on the LOESS fitting procedure, our preliminary results indicate a trend of temporal homogeneity and spatial heterogeneity. This trend is validated against the existing archaeological narrative for the region and, we argue, may indicate intraregional variability in population responses to major technological, economic and sociocultural events, consistent with the variable response observed at the regional level. Due to the critical importance of temporospatial specificity to a vast array of paleodemographic research questions, we have evaluated the precision, assumptions and limitations of this method in the context of other existing paleodemographic methods. Our RNPI measure, in isolation or in combination with existing methods, provides a promising tool that can be used to develop a deeper and more localized understanding of the conditions impacting on population dynamics and, conversely, community responses to change.

Rate of natural population increase as a paleodemographic measure of growth

The aim of this study was to provide a verifiable measure of population increase from age-at-death data. It was anticipated that the D0-14/D ratio would be a good predictor of the rate of natural increase (births minus deaths) due to its strong relationship with the total fertility rate. United Nations age-at-death data for 58 countries was used to calculate the rate of natural population increase and evaluate its relationship to the D0-14/D ratio. Additionally, the impact of migration on both the rate and the ratio was measured. A correlation of r = 0.863 (95% CI 0.777–0.917) between the D0-14/D ratio and rate of natural population increase was found. Linear regression provided a simple equation for calculating the rate of population increase. The rate of natural population increase accounts for the disparity (or lack of) between births and deaths, and provides a valuable measure for evaluating ancient population variability. While the rate does not factor in migration, we believe migration should be measured independently as it is not always of interest to bioarcheological research questions and has a negligible impact on the rate of natural increase and the D0-14/D ratio. Estimating the rate of natural population increase has the potential to provide significant insights into past populations and the human response to change.

An investigation of villages in the Republic of Ireland

Major growth and change have occurred in villages of under 500 population in the Republic of Ireland. There had been no data or research on these small places. This paper reports on an investigation of twenty-six villages, one in each county. There was a high rate of natural population increase and also substantial in-migration, which was mainly over short distances. Housing was found to be a major locational factor. Village expansion had far exceeded local employment opportunities and half those at work travelled to employment elsewhere, the extent of commuting varying greatly between places. Urban orientation had increased greatly, though most villages had retained a range of basic services and the usage patterns of each place were different. Residents were generally favourably disposed towards village development and life but they suggested a wide range of improvements, led by the great need for employment. With some functional shift from service centre towards place of residence, villages have become more integrated into the national settlement system and their place in it could be strengthened, but expansion seems unlikely to continue at the recent rate.

Laboratory selection of chlorpyrifos resistance in an Invasive Pest, Phenacoccus solenopsis (Homoptera: Pseudococcidae): Cross-resistance, stability and fitness cost

The cotton mealybug, Phenacoccus solenopsis is an important polyphagous sucking pest of ornamentals, horticultural and fiber crops worldwide. Some P. solenopsis populations have developed insecticide resistance. This study evaluated cross-resistance, stability of insecticide resistance and life history traits affected by chlorpyrifos resistance in P. solenopsis. After nine generations selected with chlorpyrifos, P. solenopsis exhibited a 539.76-fold resistance level compared to an unselected population (UNSEL Pop). Chlorpyrifos selected population (Chlor-SEL Pop) displayed moderate cross-resistance to profenofos, nitenpyram and high cross-resistance to lambda-cyhalothrin. Biological parameters of P. Solenopsis were affected by chlorpyrifos resistance. The Chlor-SEL Pop had a significant reduction in fitness (relative fitness=0.10), along with significant decreases in pupal weight, fecundity, egg hatching %, intrinsic rate of natural population increase, biotic potential, and mean relative growth rate. It is concluded that selection with chlorpyrifos had marked effect on resistance development in P. solenopsis and upon removal of selection pressure chlorpyrifos resistance declined significantly indicating unstable resistance. Development of resistance led to high fitness costs for the chlorpyrifos-selected strain. These findings should be helpful for better and more successful resistance management of P. solenopsis.

Fitness cost and realized heritability of resistance to spinosad in Chrysoperla carnea (Neuroptera: Chrysopidae).

The common green lacewing Chrysoperla carnea is a key biological control agent employed in integrated pest management (IPM) programs for managing various insect pests. Spinosad is used for the management of pests in ornamental plants, fruit trees, vegetable and field crops all over the world, including Pakistan. A field-collected population of C. carnea was selected with spinosad and fitness costs and realized heritability were investigated. After selection for five generations, C. carnea developed 12.65- and 73.37-fold resistance to spinosad compared to the field and UNSEL populations. The resistant population had a relative fitness of 1.47, with substantially higher emergence rate of healthy adults, fecundity and hatchability and shorter larval duration, pupal duration, and development time as compared to a susceptible laboratory population. Mean relative growth rate of larvae, intrinsic rate of natural population increase and biotic potential was higher for the spinosad-selected population compared to the susceptible laboratory population. Chrysoperla species are known to show resistance to insecticides which makes the predator compatible with most IPM systems. The realized heritability (h 2) value of spinosad resistance was 0.37 in spinosad-selected population of C. carnea.

Resistance of Spodoptera litura (Lepidoptera: Noctuidae) to profenofos: Relative fitness and cross resistance

Profenofos, an acetylcholine esterase inhibitor insecticide, has been used for the management of various lepidopteron pests of many crops in Pakistan. In the present study, we investigated the impact of insecticide resistance on fitness cost in Spodoptera litura, and evaluated cross resistance to other insecticides. The effect of profenofos on different life history parameters including survival rate, female ratio, fecundity and hatchability, intrinsic rate of population increase and biotic potential was determined. Significant differences associated with fitness costs were revealed. A field collected S. litura strain was selected by exposure to profenofos in the laboratory (Profen-SEL) and after 14 generations of selection it developed a 52-fold resistance to this insecticide. The Profen-SEL strain showed high cross-resistance to chlorpyrifos (62-fold), but very low to no cross resistance to lambda-cyhalothrin (2.34-fold) or methomyl (0.80-fold), respectively. The resistant strain had a relative fitness of 0.38 with a low larval survival rate, longer larval duration, longer male pupal duration, longer development time, low emergence rate of healthy adults, fecundity and hatchability compared with an unselected strain. The intrinsic rate of natural population increase, mean relative growth rate and biotic potential were lower for the selected strain compared with an unselected strain. Development of resistance may cause fitness costs for the resistant strain. This study provided important information for understanding profenofos resistance and facilitating a better strategy for the management of resistance.

Increased fitness and realized heritability in emamectin benzoate-resistant Chrysoperla carnea (Neuroptera: Chrysopidae)

The common green lacewing Chrysoperla carnea is a key biological control agent employed in integrated pest management (IPM) programs for managing various insect pests. A field collected population of C. carnea was selected for emamectin benzoate resistance in the laboratory and fitness costs and realized heritability were investigated. After five generations of selection with emamectin benzoate, C. carnea developed a 318-fold resistance to the insecticide. The resistant population had a relative fitness of 1.49, with substantially higher emergence rate of healthy adults, fecundity and hatchability and shorter larval duration, pupal duration, and development time compared to the susceptible population. Mean population growth rates; such as the intrinsic rate of natural population increase and biotic potential were higher for the emamectin benzoate selected population compared to the susceptible population. The realized heritability (h(2)) value of emamectin benzoate resistance was 0.34 in emamectin benzoate selected population of C. carnea. Chrysoperla species which show resistance to insecticides makes them compatible with those IPM systems where emamectin benzoate is employed.

Comparative Demography of the Spider Mite,Oligonychus afrasiaticus,on four Date Palm Varieties in Southwestern Tunisia

The date palm mite, Oligonychus afrasiaticus (McGregor) (Acari: Tetranychidae), is a serious pest of palm date fruits. Life cycle, fecundity, and longevity of this mite were studied on fruits of four date palms, Phoenix dactylifera L. (Arecales: Arecaceae)(varieties: Deglet Noor, Alig, Kentichi, and Besser), under laboratory conditions at 27 = 1 °C, 60 ± 10% RH. Total development time of immature female was shorter on Deglet Noor fruits than on the other cultivars. O. afrasiaticus on Deglet Noor had the highest total fecundity per female, while low fecundity values occurred on Besser. The comparison of intrinsic rates of natural increase (rm), net reproductive rates (Ro), and the survival rates of immature stage of O. afrasiaticus on the host plants suggests that O. afrasiaticus performs better on Deglet Noor fruits. The mite feeding on Alig showed the lowest intrinsic rate of natural population increase (rm = 0.103 day 1). The estimation of difference in susceptibility of cultivars to O. afrasiaticus is crucial for developing efficient pest control programs. Indeed, less susceptible cultivars can either be left unsprayed or sprayed at low threshold.

Suitability of Aphis craccivora (Hemiptera: Aphididae) and Bemisia tabaci (Hemiptera: Aleyrodidae) biotype-B as prey for Chrysopa pallens (Neuroptera: Chrysopidae)

The suitability of Aphis craccivora Koch (Hemiptera: Aphididae) and Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae) biotype-B eggs and nymphs as prey for pre-imaginal development and survival, adult longevity, and fecundity of the lacewing, Chrysopa pallens (Rambur) (Neuroptera: Chrysopidae) was evaluated under laboratory conditions at 25±1°C, 50±10% RH and a photoperiod of 16 h L:8 h D. Survival of C. pallens from first instar to adult eclosion was significantly different between the larvae that fed on the two prey species. C. pallens fed on A. craccivora completed development from egg to adult emergence, but those fed on eggs and nymphs of B. tabaci could not complete development, resulting in abnormal pupae and no normal adults emerged. The net reproductive rate (R 0), intrinsic rate of natural population increase (r m ), finite rate of increase (λ), mean generation time (T), index of population trend (I), doubling time (DT), and gross reproductive of rate (GRR) of C. pallens that fed on A. craccivora were 201.9 eggs per female, 0.13/d, 1.1/d, 40.1 d, 68.5, 5.2 d, 203.1 eggs per female, respectively. These results could be useful for mass-rearing of C. pallens and for understanding its population dynamics in the field in relation to the availability of different prey species.

Life table and predation of Oligota pygmaea (Coleoptera: Staphylinidae) a major predator of the red spider mite, Oligonychus coffeae (Acarina: Tetranychidae) infesting tea

The staphylinid beetle, Oligota pygmaea (Solier) is an important predator of the red spider mite, Oligonychus coffeae (Nietner) infesting tea. Biology, life table and predatory efficiency of O. pygmaea were studied under laboratory conditions. Duration of developmental stages of O. pygmaea was 3.2, 5.7 and 12.5 d for eggs, larvae and pupae, respectively with an average of 23.0 d from egg to adult emergence. After a mean preovipostion period of 2.9 d, each female laid an average of 400.5 eggs in its life span. Adult O. pygmaea lived for an average of 54.1 d. Adult females lived for a longer period of 58.8 d compared to the longevity of 49.4 d of adult male. Studies revealed that its life table characterized by an intrinsic rate of natural population increase ( r) of 0.118 d, net reproductive rates ( R o ) of 243.693 eggs/female, gross reproduction rate (Σ m x ) of 245.313 eggs/female, generation time ( T) of 46.575 d, doubling time (DT) of 5.874 d and finite rate of increase ( λ) of 1.125 d. Seasonal abundance of O. pygmaea and its prey, O. coffeae was monitored by sampling 25 tea leaves randomly from each experimental block grown under the prevailing field conditions. O. pygmaea showed a typical pattern of population dynamics with a peak during January to March and low incidence during June to September. Peak in the population of O. pygmaea coincided with the abundance of O. coffeae in the tea fields. Weather factors such as high temperature, low relative humidity and low sunshine hours adversely affected the populations of O. pygmaea. The first to third instar larvae of O. pygmaea consumed 31.0–133.2 eggs of mites per day. Third instar larva of O. pygmaea consumed an average of 133.2 eggs, 46.4 hexapod larvae, 39.6 nymphs and 11.4 adults per day. Adult females consumed more number of red spider mites compared to the males.

War in Late Antiquity: A Social History (review)

Reviewed by: War in Late Antiquity: A Social History Bernard S. Bachrach War in Late Antiquity: A Social History. By A.D. Lee . Malden, Mass.: Blackwell Publishing, 2007. ISBN 978-0-631-22926. Maps. Tables. Figures. Glossary. Notes. Bibliographies. Indexes. Pp. xxv, 282. $34.95. Lee, associate professor of Classics (Nottingham), has written a useful study. He explores a limited spectrum of the "political, economic, social, and religious dimensions" of the military in the later Roman empire "from the mid-third to the early seventh century" (p. xii). The title is misleading. The focus is not on war but on the Roman army and largely on the eastern half of the empire, not the late antique era. For example, Lee fails to use the information in the western letter collections of Ausonius, Sidonius, Ruricius, Avitus, and Epiphanius in his "quantitative" study (Table 6.1). Cities such as Alexandria and Edessa, not to mention the "camp" at Dura-Europos receive more than six times the attention given to Britain and Gaul combined. Many of Lee's generalizations, often based on eastern information, lack applicability to the west, and, on the whole, differences between east and west over time are not given sufficient attention. The value of Lee's work lies in his effort to raise important questions about the impact of the military on society. Although stylistically his "index cards" sometimes bleed through, Lee gathers a large quantity of accurate information valuable to undergraduates and graduate students, who can use it as their needs require. The inclusion of a good bibliography enhances the value of the work. Lee, however, avoids a cogent discussion of the nature of social history. His problematic extension, without a compelling justification, of "A Social History" to treat political, economic, social, and religious matters results in a collection of largely unconnected essays. This is made more obvious by the lack of an overall conclusion which makes clear the importance of social history. Each of the seven chapters, dealing seriatim with Emperors, Military Loyalties, Infrastructure, Economic Impact, Experience of War, Soldiers and Society, [End Page 554] and Religion is of varying value. The essay on religion is the strongest, but it is necessary to emphasize that the text of Vegetius's De re Militari survives only in an edition made at Constantinople in 450. This affects the dating of the Christianization of the military sacramentum. The chapter on economy, potentially the most important, is also the most controversial. Lee attempts a "cost-benefit" analysis. While the lack of statistics potentially is crippling, Lee's unwillingness to work with the necessary basic economic concepts renders the exercise less fruitful than it might have been. Lee approaches the problem from the perspective of the imperial budget, which fundamentally ignores the way in which the primitive agricultural economy of late antique world is to be understood. The implication that the "costs of war" could bankrupt the central government and thus, as some scholars believe, caused its fall, smacks of a misleading hyper-inflation model and the vagaries of modern deficit spending. Ninety percent of the population in the late antique era lived in a rural context. Production stemmed directly from the size of the work force. Primary focus must be on the gross imperial product (GIP), i.e. the sum of goods and services produced. In simple terms, if war affected the demographic curve negatively, production declined. If war [famine, and pestilence] did not affect the demographic curve negatively, the population increased and production increased until the maximum carrying capacity of the land was reached. The natural rate of population increase is geometric under largely unstressed conditions. Strong evidence for the success of the late antique economy is the production of a large surplus of human and material resources. The fortification with massive stone walls of hundreds of urban centers, 100 in Gaul alone, between the later third and later fourth centuries bears witness to the availability of massive surplus resources resulting in the large scale production of military goods and services. The construction of thousands of lesser fortifications, e.g. castra and castella, provide additional evidence for such production. In a similar vein, the continuing increase in the size of...

Critique of early models of the demographic impact of HIV/AIDS in sub-Saharan Africa based on contemporary empirical data from Zimbabwe

Early mathematical models varied in their predictions of the impact of HIV/AIDS on population growth from minimal impact to reductions in growth, in pessimistic scenarios, from positive to negative values over a period of 25 years. Models predicting negative rates of natural increase forecast little effect on the dependency ratio. Twenty years later, HIV prevalence in small towns, estates, and rural villages in eastern Zimbabwe, has peaked within the intermediate range predicted by the early models, but the demographic impact has been more acute than was predicted. Despite concurrent declines in fertility, fueled in part by HIV infections (total fertility is now 8% lower than expected without an epidemic), and a doubling of the crude death rate because of HIV/AIDS, the rate of natural population increase between 1998 and 2005 remained positive in each socioeconomic stratum. In the worst-affected areas (towns with HIV prevalence of 33%), HIV/AIDS reduced growth by two-thirds from 2.9% to 1.0%. The dependency ratio fell from 1.21 at the onset of the HIV epidemic to 0.78, the impact of HIV-associated adult mortality being outweighed by fertility decline. With the benefit of hindsight, the more pessimistic early models overestimated the demographic impact of HIV epidemics by overextrapolating initial HIV growth rates or not allowing for heterogeneity in key parameters such as transmissibility and sexual risk behavior. Data collected since the late 1980s show that there was a mismatch between the observed growth in the HIV epidemic and assumptions made about viral transmission.

Change in phenotypic plasticity of a morphological defence in Daphnia galeata (Crustacea: Cladocera) in a selection experiment

Some water fleas Daphnia change their head morphology to reduce predation risk in response to chemical substances (kairomones) released from larvae of the invertebrate predator Chaoborus (Insecta: Diptera). We tested for evidence of the costs associated with elongation of the head spine in Daphnia galeata and the consequences of these costs on the inducibility of head spine elongation in predictable and unpredictable environments. We exposed D. galeata in outdoor experimental ponds to conditions under which predation pressure by Chaoborus larvae and the concentration of kairomones from this predator were controlled for about 70 days. In the laboratory, we then used Daphnia clones collected from the outdoor ponds to investigate the inducibility of head spine formation in response to Chaoborus kairomones. The inducibility of head spine formation increased in D. galeata from the ponds that had contained both predators and kairomones, whereas in water fleas from the ponds containing only kairomones the plasticity (inducibility) of head spine formation decreased compared with that in the control ponds. These results suggest that the production of a defensive head spine, its phenotypic plasticity, or both entail some costs. Contrary to our predictions, exposure to Chaoborus kairomones in the laboratory resulted in head lengths that were not significantly different among any of the clones from the three outdoor treatments. We found no evidence for costs associated with head spine elongation in terms of fecundity, time to maturity, or intrinsic rate of natural population increase. Average within-clone partial correlations calculated for head length and intrinsic rate of natural population increase, corrected for body length, were not significantly negative, indicating no cost of defence. This was probably because food conditions in the laboratory were so good that the costs of defence could not be detected. Furthermore, community-level changes, such as changes in food conditions caused by manipulation of the predation regime in the outdoor ponds, might have worked as selection pressures and confounded the results.

Predation and Life Table of Feltiella acarisuga (Diptera: Cecidomyiidae) Preying on Eggs of Tetranychus urticae (Acari: Tetranychidae)

Feltiella acarisuga (Vallot) is a common gall midge that feeds on many species of spider mites. Predation and all major biological and life table parameters of F. acarisuga were determined using eggs of the twospotted spider mite, Tetranychus urticae (Koch), as prey under laboratory conditions (26.7°C, 85% RH, and 14:10 [L:D] h). First-, second-, and third-instar F. acarisuga larvae consumed an average of 37.8, 60.4, and 87.2 T. urticae eggs per day, respectively. Larvae consumed a total of 185.4 eggs each from first to third instars, and female larvae consumed 201.2 spider mite eggs, 18.6% more than male larvae. Developmental time of F. acarisuga was 2.6, 7.8, and 7.0 d for eggs, larvae, and pupae, respectively, with an average of 17.4 d from oviposition to adult emergence. Female immatures developed slightly slower (≈1 d) than males. Adult longevities of F. acarisuga averaged 13.0 d. After an average of 1.1-d preoviposition period, each female laid an average of 33.3 eggs during her lifespan. The intrinsic rate of natural population increase (r), net reproductive rates (Ro), gross reproductive rate (Σmx), generation time (T), doubling time (DT), and the finite rate of increase (&lgr;) of F. acarisuga were estimated by life table analysis at 0.1155/d, 15.25 eggs per female, 21.69 eggs per female, 23.6 d, 6.0 d, and 1.1225/d, respectively. Because the r value of F. acarisuga is relatively lower than that of T. urticae, frequent release of F. acarisuga may be necessary to suppress populations of T. urticae.

Predation and Life Table of <I>Feltiella acarisuga</I> (Diptera: Cecidomyiidae) Preying on Eggs of <I>Tetranychus urticae</I> (Acari: Tetranychidae)

Feltiella acarisuga (Vallot) is a common gall midge that feeds on many species of spider mites. Predation and all major biological and life table parameters of F. acarisuga were determined using eggs of the twospotted spider mite, Tetranychus urticae (Koch), as prey under laboratory conditions (26.7 degrees C, 85% RH, and 14:10 [L:D] h). First-, second-, and third-instar F. acarisuga larvae consumed an average of 37.8, 60.4, and 87.2 T. urticae eggs per day, respectively. Larvae consumed a total of 185.4 eggs each from first to third instars, and female larvae consumed 201.2 spider mite eggs, 18.6% more than male larvae. Developmental time of F. acarisuga was 2.6, 7.8, and 7.0 d for eggs, larvae, and pupae, respectively, with an average of 17.4 d from oviposition to adult emergence. Female immatures developed slightly slower ( approximately 1 d) than males. Adult longevities of F. acarisuga averaged 13.0 d. After an average of 1.1-d preoviposition period, each female laid an average of 33.3 eggs during her lifespan. The intrinsic rate of natural population increase (r), net reproductive rates (R(o)), gross reproductive rate (Sigmam(x)), generation time (T), doubling time (DT), and the finite rate of increase (lambda) of F. acarisuga were estimated by life table analysis at 0.1155/d, 15.25 eggs per female, 21.69 eggs per female, 23.6 d, 6.0 d, and 1.1225/d, respectively. Because the r value of F. acarisuga is relatively lower than that of T. urticae, frequent release of F. acarisuga may be necessary to suppress populations of T. urticae.

Life history of Eretmocerus melanoscutus (Hymenoptera: Aphelinidae) parasitizing nymphs of Bemisia tabaci Biotype B (Homoptera: Aleyrodidae)

Abstract Eretmocerus melanoscutus Zolnerowich and Rose was originally imported from Thailand, and has been released in southern Texas, Arizona and California for biological control of Bemisia tabaci (Gennadius) biotype ‘B.’ Studies were conducted to determine biological parameters of E. melanoscutus , and evaluate its potential as a biological control agent of B. tabaci under laboratory conditions [26.7 ± 2 °C, 50–75% RH and a photoperiod of 14:10 (L:D) h]. E. melanoscutus successfully oviposited under all nymphal instars of B. tabaci on cabbage with the exception of late fourth instars. The females oviposited least under first instars (25.6 ± 3.2 eggs) and most under third instars (122.7 ± 9.6 eggs), followed by similar numbers of eggs under the second (95.6 ± 8.5 eggs) and early fourth instars (85.6 ± 6.9 eggs). Regardless of host stage parasitized, 93.4% adults emerged. Parasitoid development averaged 16.8 d from oviposition to adult emergence. Each female laid an average of 122.4 (±13.1) eggs during her lifespan or 11.2 ± 0.6 eggs per day. Mean longevity of adult females and males on plants with whitefly nymphs was 9.8 ± 0.9 and 13.2 ± 1.4 d, respectively. Of the offspring, 53.9% were females. The intrinsic rate of natural population increase ( r m ), net reproductive rate ( R o ), generation time ( T ), doubling time (DT), and the finite rate of increase ( λ ) of E. melanoscutus were estimated by life table analysis at 0.2175/d, 61.42 offspring, 19.0 d, 3.2 d, and 1.2429/d, respectively. These values are higher than those reported for B. tabaci on any host plant, indicating that E. melanoscutus has a great potential as a biological control agent of B. tabaci .

Biology, life table and predation of Feltiella acarisuga (Diptera: Cecidomyiidae) feeding on Tetranychus cinnabarinus eggs (Acari: Tetranychidae)

Abstract Feltiella acarisuga (Vallot) is a common predatory gall midge, which feeds on many species of spider mites. All major life history and life table parameters of F. acarisuga were determined using the carmine spider mite, Tetranychus cinnabarinus (Boisduval) eggs as prey under laboratory conditions [26.7 ± 2 °C, 75 ± 5% RH, and a photoperiod of l4:10 (L:D) h]. Developmental times of F. acarisuga were 2.6, 7.1, and 6.7 d for eggs, larvae, and pupae, respectively, with an average of 16.4 d from egg to adult emergence. Female immatures development took ≈1 d longer than male immatures did. Adult F. acarisuga lived an average of 12.8 d, and the female adults (13.3 d) lived significantly longer than male adults did (11.9 d). After an average of 1.5 d preoviposition period, each female laid an average of 27.3 eggs in its life span with an average of 2.1 eggs per day and an average of 2.8 eggs on each of its oviposition day. The raw data were analyzed using an age-stage, two-sex life table method that takes into consideration of the variable developmental rates among individuals and between sexes. The intrinsic rate of natural population increase (r), net reproductive rates (Ro), gross reproductive rate ( ∑ m x ) , generation time (T), and doubling time (DT), and the finite rate of increase (λ) of F. acarisuga were estimated using the age-stage, two-sex (male and female) life table analysis as 0.122 d−1, 16.19 eggs per female, 20.81 eggs per female, 22.81 d, 1.1298 d, and 5.7 d−1, respectively. Each of the first, second, and third instar larvae of F. acarisuga consumed an average of 35.5, 54.0 and 86.9 T. cinnabarinus eggs per day, respectively. Larvae of F. acarisuga could consume an average of 175.4, T. cinnabarinus eggs, and female larvae consumed 14% more spider mite eggs (187.6 eggs) than male larvae (165.1 eggs). The significance of other life table parameters related to the population and the potential of using F. acarisuga as a biological control agent are discussed.

Life history and life table analysis of the whitefly predator Delphastus catalinae (Coleoptera: Coccinellidae) on collards

The ladybeetle, Delphastus catalinae (Horn), is one of the most commonly used predacious natural enemies being commercially reared for controlling whiteflies, including Bemisia tabaci (Gennadius) biotype B (=B. argentifolii Bellows & Perring), on various ornamental and vegetable crops under greenhouse conditions. The development, survivorship, and fecundity of D. catalinae feeding on B. tabaci biotype B on collard plants were determined in the laboratory, and the age-specific life table parameters were analyzed based on the life history data. Developmental time was 4.0, 1.9, 1.1, 1.4, 5.2, and 5.3 days for eggs, first, second, third, fourth instars, and pupae, respectively, with an average of 18.9 days from oviposition to adult emergence for both sexes, 19.0 days for females, and 18.8 days for males. Adult longevities averaged 146.6 days for both sexes, 122.6 days for females, and 170.5 days for males. After an average 4.9 days preoviposition period, females laid a mean of 5.6 eggs per day over a 97.0-day period. Net reproductive rate (R0) and gross reproductive rate (ΣMmx) were estimated by life table analysis at 276.8 and 325.1, respectively. Generation time (T) and doubling time (DT) were 35.6 and 4.8 days respectively, and the intrinsic rate of natural population increase (rm) was estimated at 0.158, or l= 1.171 for the finite rate of increase. The rm value of D. catalinae is similar to or higher than those of the whitefly feeding on most vegetable and ornamental crops, indicating that the ladybeetle is capable of regulating populations of B. tabaci biotype B and other whiteflies under greenhouse conditions.