جستجوی مقالات مرتبط با کلیدواژه « intrinsic rate of increase » در نشریات گروه « کشاورزی »

In this study, the life history characteristics of Trichogramma euproctidis (Girault), an established egg parasitoid species in southwestern Iran, parasitizing Helicoverpa armigera (Hubner) were examined at 18, 21, 24, 27, 30, and 33 °C. The results showed that different constant temperatures significantly affected the number of parasitized eggs, development time, sex ratio, tibial length, number of parasitoids per host egg, progeny longevity, and fecundity. T. euproctidis failed to complete development at 18 °C, the lowest temperature tested. The mean developmental duration from egg to adult female decreased from 15.33 days at 21 °C to 7.25 days at 33 °C. An average of 188-degree days was required to complete development above the lower threshold temperature (7.2 °C). Survivorship was 96.20, 97.20, 98.33, 85.46, and 82.22 % at 21, 24, 27, 30, and 33 °C, respectively. The mean longevity of T. euproctidis ranged from 11.60 days at 21 °C to 4.57 days at 33 °C. Mean total progeny ranged from 19.50 / female at 33 °C to 168.70 / female at 21 °C. Data analysis demonstrated that different constant temperatures had a significant effect on the net reproductive rate (R0), intrinsic rate of increase (r), finite rate of increase (λ), and generation time (T). The intrinsic rate of increase (r) improved with temperature from 0.240/day at 21°C to 0.370/day at 27 °C and then decreased at higher temperatures. Generation time decreased from 16.90 days to 7.53 days with increasing temperature. The optimal temperature for development and reproduction of T. euproctidis was 27 °C. The results of this study showed that this strain of T. euproctidis appears to have the potential to be utilized in integrated management programs targeting H. armigera.

Stress is hypothesized to be one of the primary abiotic factors that influence the structuring of food webs. Drought and salinity stresses are the most serious induced problems of agriculture due to climatic changes. Considering the global warming and drying of Urmia salt lake in northwestern Iran which can result in salinization of agricultural lands nearby, the focus of this study is to examine the effects of the two above-mentioned stresses on a host plant (Medicago sativa L.) and its pest (Tetranychus urticae Koch) performance. Two levels of water deficit (kept dry for 5 and 10 days and received 50% and 25% of field capacity respectively) and three levels of salinity (100, 200 and 300 mM NaCl) were added to alfalfa plants as stress factors and the following characteristics were measured before and after herbivore infestation: relative water, chlorophyll, carotenoid, protein, proline, malondialdehyde (MDA) and H2O2 contents of leaves and catalase (CAT), ascorbate peroxidase (APX) and guaiacol peroxidase (GPX) enzyme activities. The life table parameters of two-spotted spider mite reared on stressed plants were measured and compared with control. We found that drought and salinity stresses led to a decrease of alfalfa plant growth. Morphological and physiological changes included a decrease of relative water, chlorophyll and carotenoid contents and an increase of protein, proline, MDA and H2O2 contents and APX enzyme activity. The net reproductive rate (R0), mean generation time (T), intrinsic rate of increase (r) and finite rate of increase (λ) were significantly higher for mites grown on control host plants compared to mites grown on stressed ones and were 25.66 offspring/ individual/generation time, 16.38 d, 0.1971 day−1 and 1.2180 day−1 respectively. These parameters reduced significantly in mites grown on stressed host plants; the significant lowest values were recorded for mites grown on host plants subjected to high salinity (300 mM) and were 0.5 offspring/individual/generation time, 14.47 d, −0.0514 day−1 and 0.9502 day−1 respectively. In terms of this experiment, the water stress had a stronger influence on the morphological and physiological characteristics of alfalfa plant compared to spider mite infestation.

Different host plants can affect the performance of herbivores and their natural enemies. The life history of the mirid predator, Macrolophus pygmaeus Rambur, was studied after feeding on Tetranychus urticae Koch eggs reared on the solanaceous plants, including tomato (Solanum lycopersicum L. cv Nora) and sweet pepper (Capsicum annuum L. cv Kadia) under laboratory conditions. According to the age-stage, two-sex life table theory, developmental time, survival rate, and fecundity were analyzed. The results showed that premature developmental time of the predator was shorter when they were fed on tomato-reared spider mites than on sweet-pepper-reared spider mites. Some population parameters [Intrinsic rate of increase (r), Net reproductive rate (R0) and Mean generation time) of M. pygmaeus were significantly affected by the host plants. Mean number of T. urticae eggs consumed by different stages/sexes of M. pygmaeus was calculated based on the age-stage two-sex consumption rate model. The results indicated that the consumption rate increased from nymph to adult in both sexes. The net predation rate (C0) was 547.98 ± 24.00 and 381.6 ± 18.04 mites on tomato and sweet pepper, respectively. Transformation rate from prey population to predator offspring (Qp) was 7.11 ± 0.18 and 5.60 ± 0.24 on tomato and sweet pepper, respectively. The results showed that the survival and reproductive rate of M. pygmaeus was higher when they fed on T. urticae eggs laid by tomato-reared adults compared to sweet pepper-reared individuals. This study provides an opportunity to better understand the interactions of the three trophic levels through considering host plant importance in the success of biological control.

The bird cherry-oat aphid, Rhopalosiphum padi (L.) (Hemiptera: Aphididae), is a serious pest of Poaceae plants, especially wheat and corn, in the world and in Iran. In this study, the demographic parameters of R. padi were determined at seven constant temperatures (8.5, 15, 20, 25, 27.5, 29 and 31±0.5 °C), 65±5% RH, and 14:10 (L: D) photoperiods on Zea mays L., KSC704 cultivar. The total lifespan, from birth to death, decreased with increasing the temperature from 8.5 to 29 °C, but the nymphal stage duration increased a little at 29 °C. The highest value of life expectancy (ex) was observed at 8.5 °C and at 31 °C, the nymphs died before reaching the adult phase. The percentage of survival for nymphal stages was highest at 15 and 25 °C, and the net reproductive rate (R0=23.671 female/generation) had the highest value at 15 °C. The intrinsic rate of increase (rm) and the finite rates of increase (λ) increased at the temperature interval of 8.5 to 25 °C. At this range, the doubling time (DT) and the mean generation time (T) decreased as the temperature increased. According to the highest value of rm (0.22 day-1) and λ (1.134day-1) and also the lower value of T (9.095 d) and DT (2.16 d), the temperature of 25 °C was determined as the optimal temperature and the data showed that the proper temperature range for growth and reproduction of this aphid was between 15-25 °C. The effect of temperature on reproduction, especially the intrinsic rate of increase (rm), of R. padi would be useful for predicting its long-term population fluctuation over several generations and establishing integrated pest management (IPM) strategies against this pest.

Laboratory experiments were conducted to investigate the influence of two pea cultivars, regular and sweet as substrates on biological aspects and life table analysis of two phytoseiid species, Cydnoseius negevi (Swirski & Amitai) and Neoseiulus californicus (McGregor) fed on nymphs of Tetranychus urticae Koch under laboratory conditions of 27 ± 1 ℃, 70–80 % RH and 16L:8D h photoperiod. The development was faster and reproduction of N. californicus was higher compared with C. negevi. The predatory mite N. californicus showed the highest fecundity when reared on sweet pea cultivar, while C. negevi exhibited the lowest fecundity when reared on regular pea cultivar. Rearing C. negevi on the two pea cultivars led to the greatest female longevity than that of N. californicus. Feeding capacity of females during oviposition period was the highest for N. californicus on sweet pea, but it was the lowest for C. negevi on regular pea cultivar. Life table analysis showed that the shortest mean generation time (T) for N. californicus (13.01 days) compared with C. negevi (14.65 days) on sweet pea cultivar. Also, the intrinsic rate of increase (rm) of N. californicus was 0.29 female/female/day, but the rm value was 0.24 female/female/day for C. negevi on sweet pea substrate. Therefore, it can be concluded that the two predatory mites, C. negevi and N. californicus, are efficient biological control agents against T. urticae on the two pea cultivars.