温度和食物浓度对三品系萼花臂尾轮虫实验种群动态的影响

应用个体培养方法,研究了温度(20、25和30℃)和藻类食物浓度(1．5×10^6、3．0×10^6、6．0×10^6和9．0×10^6cells·ml^-1)对青岛、芜湖、广州三品系萼花臂尾轮虫种群动态的影响．结果表明,温度仅对轮虫的世代时间和种群内禀增长率有显著影响,而品系对所有生命表参数均无显著影响．轮虫种群的内禀增长率随培养温度的升高而增大,世代时间则随培养温度的升高而缩短．食物浓度仅对轮虫的生命期望值和平均寿命有显著影响,品系对轮虫的净生殖率、世代时间、生命期望值和平均寿命也有显著影响．三品系间,以广州品系轮虫的净生殖率、世代时间、生命期望值和平均寿命最大,芜湖品系最短．当食物浓度为3．0×10^6cells·ml^-1时,轮虫的生命期望值和平均寿命最长,9．0×10^6cells·ml^-1时最短．各品系轮虫的净生殖率、世代时间、总生殖率、生命期望值和平均寿命均随培养温度的升高而减小,广州品系的净生殖率除外．轮虫种群的内禀增长率和广州品系轮虫的总生殖率则随培养温度的升高而增大．青岛和广州品系轮虫的各生命表参数,均与食物浓度呈曲线相关,但芜湖品系仅世代时间、平均寿命和生命期望值随食物浓度的增大而缩短．     

Increased nondisjunction of chromosome 21 with age in human peripheral lymphocytes

Fluorescence in situ hybridization (FISH) on binucleated cells with chromosome-specific DNA probes provides a convenient way to visualize reciprocal segregation patterns in daughter nuclei, and overcomes most problems related to the artefactual loss or gain of chromosomes that flaw chromosome preparations. In this study, FISH was employed to evaluate age- and sex-effects on spontaneous malsegregation, nondisjunction and loss of chromosome 21 in human lymphocytes after the first division in culture. A total of 68 healthy nonsmokers and nondrinkers of alcohol (37 males and 31 females) were grouped by age as Group I (0-10 years), Group II (20-30 years), Group III (40-50 years) and Group IV (60-70 years), with at least seven subjects per group and sex. FISH with a pericentric chromosome 21 specific DNA probe was carried out on binucleated lymphocytes, cytokinesis-blocked by cytochalasin B (6 microg/ml for 26 h) at 44 h after initiation of cultures.Linear regression analyses demonstrated a significant age-related increase in the frequency of micronuclei without chromosome 21 (MN-21)(r=0.73, p<0.001 in females; r=0.69, p<0.001 in males) in all binucleated cells, with a steeper slope in females (0.1758) than in males (0. 1241). Analysis using the 2x2 chi-square (chi(2)) test on the frequencies of MN-21 showed significant age-related differences in both males and females, except males in Group III and Group IV (p>0. 05). A significant sex-related difference was found only in subjects over 60 years (p<0.05), with females having more MN-21 (12.57 per thousand vs. 8.43 per thousand) than males.Loss of chromosome 21, occurring at mean levels of 0.38 per thousand in all binucleated cells and 0.24 per thousand in binucleated cells containing four FISH signals, was shown not to be age- or sex-related. A positive age-related increase in nondisjunction of chromosome 21 was shown in males (r=0.50, p<0.01), females (r=0.61, p<0.001) and all subjects (r=0.55, p<0.001) by linear regression analysis. An age effect was found only between children and adults (p<0.01 for females, p<0.05     

Effect of cotton cultivar on performance of Aphis gossypii (Homoptera: Aphididae) in Iran

Cotton aphids, Aphis gossypii Glover (Homoptera: Aphididae), obtained from cotton, Gossypium hirsutum L., fields in the Gorgan region of northern Iran, were colonized on 'Varamin' cotton plants in a growth chamber. The development, survivorship, and life table parameters of the cotton aphid were evaluated at 27.5 +/- 1 degrees C, 65 +/- 10% RH, and aphotoperiod of 14:10 (L:D) h of artificial light on five commonly growing cotton cultivars: Varamin, 'Sealand' (relatively resistant cultivar), 'Bakhtegan', 'Sahel' (both relatively susceptible cultivars), and 'Siokra' [resistant to Bemisia tabaci (Gennadius)]. The developmental times of immature stages ranged from 4.6 d on Bakhtegan and Varamin to 6.3 d on Sealand, whereas the immature survival was 97.5 to 65% on Sahel and Siokra, respectively. On average, there were 28.7, 28.3, 23.5, 20.1, and 16.8 nymphs produced per female on Sahel, Bakhtegan, Varamin, Sealand, and Siokra, respectively. The intrinsic rate of natural increase (r(m)) for cotton aphids on Sahel was the highest, whereas the values for r(m) varied from 0.284 (nymphs per female per d) on Siokra to 0.368 on Sahel. Jackknife estimates of generation times (T), net reproductive rate (R(0)), doubling time (DT), and finite rate of increase (lambda) on these cultivars were as follows: 9.79-10.84 d for T, 9.23-23.81 nymphs per female for R(0), 2.17-3.19 d for DT, and 1.28-1.38 nymphs per female per d for lambda. Cotton aphid performance was at its highest on Sahel and lowest on Siokra.     

On net reproductive rate and the timing of reproductive output

Abstract: Understanding the relationship between life-history patterns and population growth is central to demographic studies. Here we derive a new method for calculating the timing of reproductive output, from which the generation time and its variance can also be calculated. The method is based on the explicit computation of the net reproductive rate (R0) using a new graphical approach. Using nodding thistle, desert tortoise, creeping aven, and cat's ear as examples, we show how R0 and the timing of reproduction is calculated and interpreted, even in cases with complex life cycles. We show that the explicit R0 formula allows us to explore the effect of all reproductive pathways in the life cycle, something that cannot be done with traditional analysis of the population growth rate (lambda). Additionally, we compare a recently published method for determining population persistence conditions with the condition R0 > 1 and show how the latter is simpler and more easily interpreted biologically. Using our calculation of the timing of reproductive output, we illustrate how this demographic measure can be used to understand the effects of life-history traits on population growth and control.     

Life table demography and population growth of Brachionus variabilis Hempel, 1896 in relation to Chlorella vulgaris densities

We studied the life history variables and population growth characteristics of Brachionus variabilis, which was recorded for the first time from Mexico. The animals were fed Chlorella, using five concentrations (0.25, 0.5, 1, 2 and 4 × 10⁶ cells ml^–1) at 25 °C. Food density was observed to have significant effect on life expectancy, average lifespan, gross reproductive rate, net reproductive rate, generation time and population growth rate. The average lifespan ranged from 3 to 6 days depending on the food density. The net reproductive rate ranged from 2 to 7 neonates female^–1 d^–1. The rate of population increase per day varied from 0.14 to 0.35. The highest net reproductive rate and average lifespan and life expectancy were recorded at Chlorella concentrations of 1 × 10⁶ and 2 × 10⁶ cells ml^–1.     

镰形臂尾轮虫和尾突臂尾轮虫的生活史特征比较

应用单个体培养方法,以浓度为3.0×10⁶ cells·ml^-1的斜生栅藻为食物,在18 ℃、23 ℃、28 ℃和33 ℃的温度梯度下比较了镰形臂尾轮虫和尾突尾轮虫的生活史特征.结果表明：18 ℃和23 ℃下,尾突臂尾轮虫的生殖期和平均寿命均显著长于镰形臂尾轮虫,产卵量也显著大于镰形臂尾轮虫;28 ℃下,2种轮虫的各主要发育阶段历时、平均寿命和产卵量均无显著差异;33 ℃下,镰形臂尾轮虫的生殖期和生殖后期历时以及平均寿命均显著长于尾突臂尾轮虫,产卵量显著大于尾突臂尾轮虫.18 ℃下,尾突臂尾轮虫的生命期望、净生殖率和种群内禀增长率均显著大于镰形臂尾轮虫;23 ℃和28 ℃下,尾突臂尾轮虫的生命期望显著长于镰形臂尾轮虫,而其他种群增长参数间均无显著差异;33 ℃下,镰形臂尾轮虫的世代时间、生命期望、净生殖率和种群内禀增长率均极显著大于尾突臂尾轮虫.2种轮虫的主要发育阶段历时、平均寿命、产卵量、世代时间、生命期望、净生殖率和种群内禀增长率对温度变化的反应也存在差异.研究结果表明,尾突臂尾轮虫更能适应较低的环境温度,而镰形臂尾轮虫则相反.     

Influence of poplar clones on fertility life-table parameters of Chaitophorus leucomelas (Hemiptera: Aphididae)

The aphid Chaitophorus leucomelas Koch (Hemiptera: Aphididae) is one of the most important pests of poplar (Populus spp.) plantations in Iran. In this study, development, reproduction, and life history of the aphid were assessed on 11 poplar clones; belong to three species, Populus nigra L., Populus deltoides Bartram ex Marshall, and Populus. euramericana Guinier. The experiments were carried out under controlled conditions at 24 +/- 1 degrees C, 50-60% RH, and a photoperiod of 12:12 (L:D) h. The developmental time at immature stage ranged from 10 to 12 d. Nymphs reproduced per female were ranged from 49 to 98 nymphs on Populus deltoides var. missoriensis and P. deltoides 72/51, respectively. The intrinsic rate of natural increase (r(m)) varied from 0.176 to 0.264 d(-1) among poplar clones. The r(m) values of the aphids were adversely affected in P. euramericana 242 in comparison with P. nigra 56/72 and P. nigra 63/135. In addition, the jackknife estimates of net reproductive rate (R0) indicated the presence of resistance among poplar clones. R0 ranged from 16.48 on P. nigra var. betulifoli to 47.53 on P. nigra 63/135. Mean generation times (T) was last 17.56 d on P. euramericana 242 to 14.51 d on P. deltoides 69/55. However, doubling time (DT) was 3.87 d on P. euramericana var. grandis to 2.63 d on P. nigra 63/135. The finite rate of increase (lambda) was 1.192 on resistant clone (P. euramericana 242) and 1.302 on susceptible clone (P. nigra 63/135). These results indicate that variation in life-table parameters could be an important component of variation in resistance to C. leucomelas in poplar.     

Life tables and development of Bemisia argentifolii (Homoptera: Aleyrodidae) at different temperatures

The life history of Bemisia argentifolii Bellows & Perring (Homoptera: Aleyrodidae) on tomato (Lycopersicum spp.) was studied based on the age-stage, two-sex life table at 15, 20, 25, 28, 30, and 35 degrees C. The intrinsic rate of increase (r) at these temperatures is -0.0176, 0.0667, 0.1469, 0.1611, 0.1745, and 0.0989 d(-1), respectively. The relationship among the gross reproductive rate (GRR), the net reproductive rate (R0), and the preadult survivorship (l(a)) is consistent with GRR > l(a) x GRR > R0 for all results at different temperatures. The mean generation time is 81.9, 48.6, 28.4, 25.3, 22.1, and 18.2 d, respectively. The developmental rate of the egg stage at different temperatures fit a linear equation with a thermal summation 89.2 degree-days and a developmental threshold of 11.4 degrees C. The developmental rates of the nymphal stage fit the model of Stinner et al. and the parameters of C, Rmax, k1 and k2 were 0.085, 0.0833, 5.298, and -0.263, respectively.     

Life tables of Habrobracon hebetor (Hymenoptera: Braconidae) parasitizing Anagasta kuehniella and Plodia interpunctella (Lepidoptera: Pyralidae): effect of host density

The reproductive performance of the parasitoid Habrobracon hebetor (Say) (Hymenoptera: Braconidae) against the moths Anagasta kuehniella Zeller and Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae) was studied in the laboratory. The analysis was based on the comparison of parasitoid's life table parameters related to those of its hosts at various conditions of host density (daily supply of 1, 5, 15, and 30 full-grown host larvae). The estimated parameters were the intrinsic rate of natural increase (rm), the net reproductive rate (R0), the mean generation time (G), the finite capacity of increase (lambda), the gross reproductive rate (GRR), the doubling time (DT), the reproductive value (Vx), and the life expectancy (ex). The rm of H. hebetor proved to be significantly higher than those of its hosts at all host densities. When only one host per day was supplied, the wasp had the lowest reproductive potential, whereas it was maximized when 15 hosts per day were exposed. Maximum values of R0 and GRR were obtained at densities > or =15 host larvae per day. Any increase in host supply above this threshold did not cause significant changes in life table parameters. Variation of rm as a function of host density can be described by the linear regression. Sex ratio of wasp progeny (females/total) ranged from 0.36 to 0.42, irrespective of host density or species. Newly emerged adults recorded maximum ex and Vx. The results of this study can be used to improve mass rearing programs and inoculative release applications of H. hebetor against moth pests of stored products.     

Relative fitness of near isogenic lines for melanic and typical forms of the oriental armyworm, Mythimna separata (Walker)

Melanism in the oriental armyworm Mythimna separata (Walker) is characterized by a black color in adults instead of the normal body color of off-white. Because inheritance of melanism in this moth follows Mendel's law, with the melanic allele (t) recessive to the normal allele (T) at a single autosomal locus, a backcrossing procedure was used to develop near isogenic lines (NILs) for melanic (NILs-tt) and typical forms (NILs-TT) of this moth. Melanic males (tt) and typical females (TT) were crossed in the laboratory, their progeny (F(1)) were interbred, and F(2) melanic males were backcrossed to typical female offspring of the parallel line. This cycle was repeated five times to create NILs for melanic and typical forms of this moth. The effects of the melanic allele on relative fitness were evaluated in terms of developmental and reproductive characteristics. Life tables of the NILs were constructed to determine net reproductive rate (R(0)). Results indicated that NILs-tt possessed apparent developmental and reproductive advantages, including shorter immature development time, higher larval and pupal survival, a shorter adult preoviposition period, and more eggs laid per female compared with the NILs-TT.     

Temperature tolerance of the diamondback moth, Plutella xylostella (Lepidoptera: Yponomeutidae) in tropical and temperate regions of Asia

Temperature tolerance was investigated in nine populations of Plutella xylostella Linnaeus from tropical and temperate regions of Asia. At all rearing temperatures between 15 and 35 degrees C, no clear differences were observed in female egg production or larval development between tropical and temperate populations. Thus, tropical populations did not show a high-temperature tolerance superior to that of the temperate populations. In all populations, the net reproductive rate (number of new females born per female) largely depended on the number of eggs laid per female, and egg production significantly decreased with increasing temperature (P < 0.001). Larval developmental rate also showed a significant positive correlation with temperature (P < 0.001). Per cent hatch of eggs and larval survival did not show a significant correlation with temperature: hatching was constant between 15 and 32.5 degrees C, but considerably lower at 35 degrees C. Larval survival was similar between 15 and 30 degrees C, appreciably lower at 32.5 degrees C and declined to 0% at 35 degrees C. Based on these results, environmental conditions under which P. xylostella can maintain a high population density throughout the year in tropical and subtropical regions are discussed.     

Comparative demography of the sand fly Phlebotomus papatasi (Diptera: Psychodidae) at constant temperatures.

We measured reproductive and population parameters of adult sand flies, Phlebotomus papatasi (Scopoli, 1786) (Diptera: Psychodidae), in environmental chambers maintained at temperatures of 15, 18, 20, 25, 28, and 32 degrees C. Based on cohorts of adults at each temperature regime, horizontal life tables were constructed using established laboratory colonies initiated from specimens collected in Sanliurfa Province, southeastern Anatolia, Turkey. The fecundity and longevity of the insects were both highly variable, depending on the temperature. At 15 degrees C, all of the cohort females died before laying eggs, so the construction of a life table for this temperature regime was not possible. Within a range of 18 to 32 degrees C, the longevity of adult P. papatasi increased as the temperature decreased; at 15 degrees C, the mean survival times of females and males were 19.04 +/- 6.94 days (9-35) and 17.84 +/- 7.11 days (9-33), respectively. While the highest number of eggs was found in the cohort at 28 degrees C (44.08 +/- 7.79), this was only 3.60 +/- 1.55 in the cohort at 32 degrees C and 2.8 +/- 0.9 in the cohort at 18 degrees C. This result showed that extreme temperatures negatively affect the fecundity of this species. The cohort reared at 28 degrees C exhibited the highest intrinsic rates of population increase (r(m)) for P. papatasi. The r(m) ranged from 0.098 at 28 degrees C to 0.007 at 18 degrees C. The cohort placed at 28 degrees C was found to be significantly different (P < 0.01) from the other cohorts producing the fewest progeny in terms of net reproductive rate, R(0), (15.87). The values for mean generation time (T) were estimated to vary from 36 days to 271 days depending on temperature. Principal Component Analysis (PCA) confirmed results from the previous studies that the cohort at 28 degrees C orientated and clustered as a distinct group along the first two PCs.     

Carbon isotope fractionation during photorespiration and carboxylation in Senecio

The magnitude of fractionation during photorespiration and the effect on net photosynthetic (13)C discrimination (Delta) were investigated for three Senecio species, S. squalidus, S. cineraria, and S. greyii. We determined the contributions of different processes during photosynthesis to Delta by comparing observations (Delta(obs)) with discrimination predicted from gas-exchange measurements (Delta(pred)). Photorespiration rates were manipulated by altering the O(2) partial pressure (pO(2)) in the air surrounding the leaves. Contributions from (13)C-depleted photorespiratory CO(2) were largest at high pO(2). The parameters for photorespiratory fractionation (f), net fractionation during carboxylation by Rubisco and phosphoenolpyruvate carboxylase (b), and mesophyll conductance (g(i)) were determined simultaneously for all measurements. Instead of using Delta(obs) data to obtain g(i) and f successively, which requires that b is known, we treated b, f, and g(i) as unknowns. We propose this as an alternative approach to analyze measurements under field conditions when b and g(i) are not known or cannot be determined in separate experiments. Good agreement between modeled and observed Delta was achieved with f = 11.6 per thousand +/- 1.5 per thousand, b = 26.0 per thousand +/- 0.3 per thousand, and g(i) of 0.27 +/- 0.01, 0.25 +/- 0.01, and 0.22 +/- 0.01 mol m(-2) s(-1) for S. squalidus, S. cineraria, and S. greyii, respectively. We estimate that photorespiratory fractionation decreases Delta by about 1.2 per thousand on average under field conditions. In addition, diurnal changes in Delta are likely to reflect variations in photorespiration even at the canopy level. Our results emphasize that the effects of photorespiration must be taken into account when partitioning net CO(2) exchange of ecosystems into gross fluxes of photosynthesis and respiration.     

不同玉米品种对截形叶螨种群参数的影响

在室内28±1℃条件下,应用叶盘法研究了中单2号、农大108、赤单202和巴丹3号个不同玉米品种对截形叶螨种群参数的影响.结果表明,在不同品种玉米上,截形叶螨卵期、若螨期、产卵前期、成螨寿命、单雌产卵量、日均产卵量、净增殖率、周限增长率、内禀增长率、世代平均周期和种群加倍时间均有明显差异(P＜0.05);其孵化率为中单2号95.8%、农大108 94.0%、赤单202 90.0%和巴单3号84.0%;幼、若螨期存活率相应地为90.5%、84.0%、86.0%和72.0%;存活曲线均为Ⅰ型.净增殖率在中单2号上最高为41.4,而在巴单3号上最低为16.8;中单2号是其最喜食的品种,其次为农大108,再次为赤单202,对巴单3号的嗜食性最差.     

Temperature-dependent development and population growth of Tetraneura nigriabdominalis (Homoptera: Pemphigidae) on three host plants

The root aphid Tetraneura nigriabdominalis (Sasaki) (Homoptera: Pemphigidae) is a pest of many Gramineae species; however, little is known about its biology and relationships with host plants. The objectives of this study were to quantify the effects of temperature on development, longevity, fecundity, and population growth of T. nigriabdominalis and to assess the effects of host plant on development of T. nigriabdominalis. The effects of temperature on performance of this root aphid were determined at 10, 15, 20, 25, 30, and 35 +/- 1 degrees C on rice roots, Oryza sativa L. Nymphal stages from birth to adult decreased from 46.3 d at 10 degrees C to 8.5 d at 30 degrees C. Aphid survival and development were lowest at 35 degrees C, and no aphid produced progeny at this temperature. Average adult longevity decreased from 23.3 d at 15 degrees C to 8.2 d at temperatures up to 35 degrees C. Average number of nymphs produced per female was highest at 25 degrees C; averaging near 30 nymphs per female, but it dropped to near zero at both 10 and 35 degrees C. The highest intrinsic rate of increase (r(m)) was 0.241 at 30 degrees C. Net reproductive rate (R(0)) ranged from 29.8 at 25 degrees C to 0.2 at 10 degrees C. The generation time (GT) decreased with increasing temperatures from 60.3 d at 10 degrees C to 13.8 d at 30 degrees C. In addition, root aphids reared at 30 degrees C on three host plants [O. sativa, Zea mays L. and Sorghum bicolor (L.) Moench] revealed that the developmental time of the nymphal stages averaged 6.9 d when reared on O. sativa and 10.7 d when reared on Z. mays. Comparison of the nitrogen content of the three host plants indicated that the root nitrogen content was highest in O. sativa. The effect of nitrogen content on aphid performance, however, is still not clear. Other factors, such as plant secondary chemistry, may play a role in affecting aphid performance.     

Temporal variation in δ<Superscript>13</Superscript>C of ecosystem respiration in the Pacific Northwest: links to moisture stress

We measured seasonal and interannual variations in delta(13)C values within the carbon reservoirs (leaves and soil) and CO(2) fluxes (soil and ecosystem respired CO(2)) of an old growth coniferous forest in the Pacific Northwest USA with relation to local meteorological conditions. There were significant intra-annual and interannual differences in the carbon isotope ratios of CO(2) respired at both the ecosystem (delta(13)C(R)) and the soil levels (delta(13)C(R-soil)), but only limited variations in the carbon isotope ratios of carbon stocks. The delta(13)C(R) values varied by as much as 4.4 per thousand over a growing season, while delta(13)C(R-soil )values changed as much as 6.2 per thousand. The delta(13)C of soil organic carbon (delta(13)C(SOC)) and needle organic carbon (delta(13)C(P)) exhibited little or no significant changes over the course of this study. Carbon isotope discrimination within leaves (Delta(p)) showed systematic decreases with increased canopy height, but remained fairly constant throughout the year (Delta(p)=17.9 per thousand -19.2 per thousand at the top of the canopy, Delta(p)=19.6 per thousand -20.9 per thousand at mid-canopy, Delta(p)=23.3 per thousand -25.1 per thousand at the canopy base). The temporal variation in the delta(13)C of soil and ecosystem respired CO(2) was correlated ( r=0.93, P<0.001) with soil moisture levels, with dry summer months having the most (13)C-enriched values. The dynamic seasonal changes in delta(13)C of respired CO(2) are hypothesized to be the result of fast cycling of recently fixed carbon back to the atmosphere. One scaling consequence of the seasonal and interannual variations in delta(13)C(R) is that inversion-based carbon-cycle models dependent on observed atmospheric CO(2) concentration and isotope values may be improved by incorporating dynamic delta(13)C(R) values to interpret regional carbon sink strength.     

Life history of the mealybug, Maconellicoccus hirsutus (Hemiptera: Pseudococcidae), at constant temperatures

Important life history parameters of the mealybug, Maconellicoccus hirsutus (Green), were characterized on hibiscus (Hibiscus rosa-sinensis L.) cuttings at six constant temperatures between 15 and 35 degrees C. The development of M. hirsutus was the fastest at 27 degrees C, where the mealybugs completed development in approximately 29 d. The lower (T(min)) and upper (T(max)) developmental thresholds and the optimal developmental temperature (T(opt)) for the development of female mealybugs were estimated as 14.5, 35, and 29 degrees C, respectively. The thermal constant (K), which is the number of temperature-day or degree-day units required for development, of the females was 347 DD. The original distribution range prediction (based on T(min) = 17.5 degrees C and K = 300 DD) indicated that M. hirsutus could complete at least one generation in all of the continental United States. However, results of this study suggested that the distribution range of M. hirsutus may expand northward because of the lower T(min), and the predicted number of generations in a year may be lower because of the higher K required to complete each generation. The average cumulative survival rate of M. hirsutus at 25 and 27 degrees C was 72%, which was significantly higher than 51 and 62% at 20 and 30 degrees C, respectively. M. hirsutus reproduced sexually, with each mated female producing 260-300 eggs between 20 and 27 degrees C but only approximately 100 eggs at 30 degrees C. Female longevity was reduced from 28 d at 20 degrees C to 19-21 d at 25-30 degrees C. At 27 degrees C, the net reproductive rate (R(o)) was estimated at 165 female symbol/female symbol, the intrinsic rate of population increase (r(m)) was 0.119 (female symbol/female symbol/d), the generation time (T(G)) was 43 d, and the doubling time (DT) was 5.8 d. The life table statistics suggested that the currently released biological control agents, which have higher r(m) than M. hirsutus, will be able to complete more generations than the mealybug within the tested temperature range; thus, they are effective against M. hirsutus.     

Bottom-up effect of different host plants on Plutella xylostella (Lepidoptera: Plutellidae): a life-table study on canola

The effects of 10 commercial canola, Brassica napus L., cultivars widely grown in Iran--'SLM(046),' 'Opera,' 'Okapi,' 'RGS(003),' 'Modena,' 'Sarigol,' 'Zarfam,' 'Licord,' 'Hayula(420),' and 'Talaye'--on the demographic parameters of diamondback moth, Plutella xylostella L. (Lepidoptera-Plutellidae), were determined. The experiments were conducted in a growth chamber at 25 +/- 1 degrees C, 65 +/- 2% RH, and a photoperiod of 16:8 (L:D) h. The comparison of intrinsic rate of natural increase (r(m)), net reproductive rate (R0), and the survival rate of adult stage of P. xylostella on 10 canola cultivars suggested that this pest performed best on SLM(046). The r(m) value of P. xylostella ranged between 0.241 on RGS(003) and 0.304 on SLM(046). The R0, finite rate of increase (lambda), mean generation time (T), and doubling time (DT) values of P. xylostella on SLM(046) were 52, 1.35, 13.4, and 2.35 and on RGS(003) were 31, 1.27, 14.4, and 2.94, respectively. The Weibull model adequately described the shape of the survivorship curve of adult P. xylostella from life-table data. A significant fit was obtained with the Weibull model for P. xylostella in all experimental canola cultivars. As a result, SLM(046), Opera, and Hayula(420) were the most suitable hosts and had least negative impact on life-history statistics of the pest.     

Developmental times and life tables for shore flies, Scatella tenuicosta (Diptera: Ephydridae), at three temperatures

Development times and survivorship of immature shore flies and longevity and reproduction of adult shore flies, Scatella tenuicosta Collin, reared on algae-infested filter paper, were studied at three temperatures (constant 20, 26, and 28.5 degrees C) through life table analysis. The development time for each individual life stage and the total time from egg to adult decreased with increasing temperature. Duration of the third (ultimate) larval instar ranged from 3.3 +/- 0.09 d at 20 degrees C to 1.4 +/- 0.04 d at 28.5 degrees C and was 1.7-1.9 times longer than the approximately equal first and second instars. Development of male and female shore flies from egg to adult needed an average of 14.5 +/- 0.13, 8.2 +/- 0.05, and 7.0 +/- 0.04 d at 20, 26, and 28.5 degrees C, respectively, and needed an estimated 154.4 +/- 1.2 thermal units (degree days). At these respective temperatures, adult females lived 21.8 +/- 2.2, 19.9 +/- 2.4, and 15.0 +/- 1.4 d and produced 379 +/- 62, 710 +/- 119, and 477 +/- 83 eggs during oviposition periods of 14.3 +/- 2.1, 15.0 +/- 2.2, and 10.8 +/- 1.4 d; daily lifetime egg production averaged 16.3 +/- 2.3, 33.5 +/- 3.8, and 29.7 +/- 3.5. Developmental stage-specific mortality was relatively low for all life stages at all temperatures, with maximum percent mortalities of 5.7% occurring in both the egg stage and in the third instar. The highest net reproductive rate (R(o)) was obtained for insects reared at 26 degrees C and was 329.6. The intrinsic rate of natural increase (r(m)) was highest at 28.5 degrees C and was 0.430. Generation time and doubling time of the population were shortest at 28.5 degrees C and were 12.4 and 1.6 d, respectively. Results suggested that 26 degrees C was near optimum for reproduction.     

Effect of reproductive mode on host plant utilization of melon aphid (Hemiptera: Aphididae)

Variation in the reproductive mode of melon aphid Aphis gossypii Glover occurred on the large geographic scale, but the performance of different reproductive modes to use host plant is poorly understood. Life tables of melon aphid population that undergo the anholocyclic, androcyclic, and intermediate reproductive mode were conducted on different host plants. The results showed that the anholocyclic and androcyclic strains could become adults and produce offspring on cotton Gossypium hirsutum L., whereas the intermediate strain could not. The survival rate, net reproductive rate (R(0)), and intrinsic rate of natural increase (r(m)) of the androcyclic strain on cotton were significantly greater than that of the anholocyclic strain. The three strains could aptly use cucurbits host plants including cucumber Cucumis sativa L., pumpkin Cucurbita moschata (Duchesne ex Lam.), and zucchini Cucurbita pepo L.; survival rate and R(0) were not significantly different on these two host plants. Moreover, the r(m) of the anholocyclic strain on cucumber and the androcyclic strain on pumpkin and zucchini were significantly greater than that of the other two strains. The abilities of the three strains to use a host plant were flexible, because their r(m) on pumpkin or zucchini became equal after rearing for four successive generations; furthermore, the intermediate strain attained the ability to use cotton, and the performance of anholocyclic and intermediate strains to use cotton also significantly increased after feeding on pumpkin or zucchini for one or three generations. It was concluded that the reproductive mode and feeding experience affected the performance of melon aphid to use a host plant.