جستجوی مقالات مرتبط با کلیدواژه "رشد جمعیت" در نشریات گروه "گیاهپزشکی"

The tomato leaf miner, Tuta absoluta (Meyrick) is one of the most destructive pests of tomato in field and greenhouses. Llife history and population growth of this pest were investigated on three solanaceous plants including four varieties of tomato (Western Red, Matin, Serin, and Rio-Grand), three varieties of eggplant (White-Casper, Ravia, and Pearl-Ground) and three varieties of sweet pepper (Bachata, Lorca, and Nirvin). The developmental time, survival, longevity, and fecundity of the pest on the leaves of tested varieties were investigated. The experiments were conducted at 25 ± 2°C, relative humidity of 65 ± 5% and a photoperiod of 16:8 (L: D) h. The results of the statistical comparison of the varieties within each host plant showed that life table parameters of the insect were not significantly different on tomato varieties and on eggplant varieties. However, among pepper varieties, the net reproductive rate, intrinsic rate of increase, and finite rate of increase rate on variey Lorca were higher than on Nervin and Bachata. The results of comparison among varieties of different hosts showed that the highest immature survival was observed on tomato, varieties Serin and Matin, and the lowest survival was seen on pepper, varieties Lorca and Nirvin. The longest developmental time was obtained on pepper, varieties Bachata and Nirvin. The lowest fecundity and the shortest oviposition period were found on pepper, varieties Bachata and Nirvin. The net reproductive rate, intrinsic rate of increase, and finite rate of increase were lowest on pepper, varieties Bachata and Nirvin, and other varieties showed no significant differences. In general, tomato varieties were susceptible,, and eggplant variety White-Casper and pepper varieties Bachata and Nirvin were partially resistant against T. absoluta. This information provides the possibility of using these varieties in order to manage T. absoluta populations during its outbreak.

Saffron is one the most expensive crops and like other agricultural products, attacked by pest such as bulb Mite Rhizoglyphus robini Claparede (Acari: Astigmata). The bulb mite is one of the most important soil pest attacking plants with bulbs, corms and also tubers. In Iran it has been reported by Rahimi and Kamali (1993) for the first time on saffron corms from Gonabad and Qaen cities. Also it has been recorded that the bulb mite feeding on soil born fungi (Diaz et al., 2000; Nesvorna et al., 2012). On the other hand, there are many saprophytic fungi into the soil of saffron fields. Subsequently it may question whether the mite is primary or secondary pest on saffron corms. Despite many literatures on biology and ecology of Rhizoglyphus mites, there is not sufficient evidence on understanding the biology, behavior and colonization of R. robini regarding its damage to saffron corms when arriving after establishment of the soil born fungi.
To investigate the impact of soil-borne fungi on the biology of the bulb mite, we obtained a cohort of even-aged eggs from the mites in our stock culture. These eggs were then transferred to individual experimental units and monitored until they reached adulthood. Daily observations were made and recorded.
To assess mite fecundity, we selected thirty young ovipositing females and divided them into two groups: one group was exposed to fungal infection while the other group was not. Each saffron corm was placed in a 50mm Petri dish lined with wet filter paper. A starved mated female was added to each dish, and every three days for a period of 21 days, the number of eggs laid per dish was counted and then removed. The number of eggs per day per female was calculated based on these counts.
To study the attraction of bulb mites to the fungus, saffron corm sections with and without fungal infection were placed in a 50mm Petri dish. Four sections, with equal distances from each other and from the center, were arranged. Female R. robini mites were introduced into the dish, and after a four-hour period, the number of mites on each section was recorded.
For evaluating the population dynamics of the mite, we used four types of saffron corms: healthy corms, corms infected by the fungus, mechanically injured corms, and corms both infected and injured. Each experimental unit consisted of three saffron corms of the same size placed in an 80mm Petri dish. Five adult mites were added to each unit. Continuous observations were made daily to track the initial penetration and colonization of the mites in each treatment. The numbers of all motile stages of mites in each experimental unit were recorded using a stereomicroscope. These observations continued until the corms were completely destroyed by the feeding mites.
After culturing of sections of infected corms and mite body, the fungi, Penicillium spp., Aspergillus niger Vantieghem, Embelisia sp. and Fusarium oxysporum Schlecht were isolated and identified mutually in both samples. As the fungus F. oxysporum was the most abundant species, then it was used in the experiments. The fungus significantly affected the generation time (from egg stage to egg produced by adult) of the mite (Table. 1). Also mite fecundity was significantly higher on infested corms with the fungus than on non-infested ones (t = 10.79, d.f.= 27.31, P<0.001)(Figure 1). An obvious attraction of the females was observed toward fungal infected sections and significantly more mites were recorded on them than non-infected ones (W = 400, P<0.001)(Figure. 2).These findings are supported by some other studies (Czajkowska, 1995; Kasuga and Honda 2006; Ofek et al., 2013). Higher fecundity and faster development when mites were fed on the fungus on the infected corms are probably due to availability of a special nutrient source (mycelium). The ability of the bulb mite to digest fungi has been attributed to chitinase-producing symbiotic bacteria (Zindel et al., 2013). Based on the evidence provided by this study and previous ones (Okabe and Amano, 1990; Ofek et al., 2013), the mite R. robini was attracted more to fungal infected corms, it might because of metabolites and alcoholic secretions of the fungi. These findings demonstrate the suitability of saffron corms infected with soil fungi for development and population increase of the Robine mite.
The result on mite penetration and population dynamics on four types of treated corms indicated that the mite on infected corms penetrated within two weeks and thereafter population increased exponentially until the end of 5th week. In comparison on healthy corms and even injured ones the mite showed almost no increase during first three weeks and it was not able to penetrate and develop a stable colony on these corms. Also on infected and injured treatment similar population dynamics was observed as on infected ones (Figure. 3). These observations implying that the mite for penetrating into healthy corms encounters some difficulty and considerable time is needed to establish and colonized on such environment. Okabe and Amano (1991) has been found similar results and suggested that earlier penetrations of mites result in a faster population growth and colonization.
For many years the saffron bulb mite has been considered as a primary pest and historically control strategies has relied on the use of chemical miticides (for disinfection and etc.,) and some non-chemical methods. Subsequently the role of soil born fungi has receiving limited attention in this regards. According to the results of the present study, this acarine pest relies on the soil born fungi to penetrate and establish on the saffron corms. In other words, a close relationship exists between fungal infection and damage by R. robini on saffron bulbs. It suggest that for improving management strategies in regards of this pest, we should consider the role of saprophytic fungi as a main cause which provides condition for the bulb mite colonization and occurring damage. Further researches is proposed using appropriate methods to suppress soil born fungi and subsequent the bulb mite damage on saffron.

The rose-grain aphid, Metopolophium dirhodum is one of the most important species among wheat and barley aphids and its population trajectory in field is characterized by rapid boom. In the present study, three datasets from M. dirhodum population in a wheat field in Varamin (Tehran) from 1999 to 2001 and two datasets from a barley field in Aleshtar (Lorestan) in 2017 and 2018 were used for modeling the aphid population dynamics. We demonstrate that Normal and Hyperbolic Secant Squared models presented a much better description of M. dirhodum population dynamics in the whole season for all datasets from wheat and barley fields than the Exponential or Logistic Growth models. The Normal and Hyperbolic Secant Squared model analysis of data showed that the models were useful representations of the data, gave biologically reasonable descriptions of rose-grain aphid population dynamics, and were statistically powerful basis for the analysis of experimental data obtained in this research. The parameters of two mentioned models are the predicted peak size, Nmax, the predicted time of peak, tmax, and an approximate per capita birth rate, all of which are of interest in practical applications. Overall, the results of this study showed that the Normal and Hyperbolic Secant Squared regression models were shown to fit diverse abundance curves adequately and the parameters of the mechanical model can be estimated by the parameters of these models.

This study was carried out to determine the effects of the entomopathogenic fungus, Lecanicillium longisporum Zimmermann Strain LRC 190, on survival and population growth parameters of the cabbage aphid, Brevicoryne brassicae (L.) treated by using different conidial concentrations (1×103, 1×104, 1×105, 1×106, and 1×107 conidia/ml). Experiments were conducted at 23±1oC temperature, 60±5 %RH and a photoperiod of 16: 8 h. (L: D) on cabbage seedlings, Brassica oleracea var. capitata under laboratory conditions. Based on the results the longevity of the aphid adults was significantly different based on conidial concentrations of L. longisporum (Petch) Zare and Gams. The shortest longevity of the cabbage aphid adults was 10.70±1.59 days when treated with 1×107 conidia/ml, compared to 22.65±0.94 days in control treatment. The LC50 value was 1.82×106 conidia/ml 7 days after inoculation. Net rate of reproduction (R0), intrinsic rate of increase (rm) and finite rate of increase (λ) were significantly reduced in treated aphids compared to control treatment. There was no significant difference among mean generation times (T) in populations treated with 1×105, 1×106, 1×107 conidia/ml (P>0.05). Fungal infection was detectedin lower rm values and prolonged doubling time (DT) in treated females (3.492 days at the concentration of 1×107 conidia/ml), compared to the control (2.652 days). Considering higher concentrations of L. longisporum can effectively reduce the cabbage aphid longevity, reproduction and population growth under laboratory conditions, it seems that the fungus has ability for biological control of the cabbage aphid.

Following sugarcane production extension in Khuzestan province, some pests appeared in sugarcane fields and sugarcane stem borers, Sesamia spp. were the most important among them. Development, reproduction and life table parameters of the parasitoid wasp, Telenomus busseolae Gahan on the sugarcane stem borer Sesamia cretica Lederer were studied at five constant temperatures (20, 25, 28, 30 and 35±1°C, 60±5% RH and a photoperiod of 16L:8D h.). The duration of pre-adult stage decreased with increasing temperature from 26.67 days at 20°C to 10.25 days at 35°C. The oviposition period was 4.16, 4.6, 4.99, 4.04 and 3.31 days at 20, 25, 28, 30 and 35°C, respectively, with females laying an average of 56.37, 65.45, 98.59, 57.44 and 33.86 eggs, respectively, at these five temperatures. Life table data were analyzed using an age-stage, two-sex life table method. The intrinsic rate of increase (r=0.262 day-1), finite rate of increase (λ=1.3 day-1) and net reproductive rate (R0=49.28 offspring/individual) were greatest at 28°C. The shortest mean generation time (T=12.17 day) was recorded at 35°C. The results of the current study indicated that temperature is one of the most important factors on life table parameters of T. busseolae. Also the optimum temperature for population growth of this parasitoid was 28°C, therefore this temperature suggests for mass rearing of T. busseolae.

Biology of apterous morph of rose-grain aphid, Metopolophium dirhodum, one of the most abundant wheat aphids, was studied in a laboratory condition with temperature of 25 ± 1˚ C, 50-60% relative humidity, and a photoperiod of 16:8 (L:D) hours. The experiment was carried out by rearing 50 first instar aphid nymphs in leaf cages on wheat (Triticum aestivum cv. Mahdavi). Biological characteristics ofaphid were recorded daily and used for estimating population increase parameters according to Carey (1993). Mean nymphal development time of rose-grain aphid was obtained 10.72 ± 0.37 days. Pre-oviposition period was 1.17±0.09 days and mean generation time of rose-grain aphid (from nymph to next generation nymph) was obtained 11.89 ± 0.37 days. Mean longevity was 42.66 ± 1.87 days. Adult longevity was high (33 ± 2.28 days) and they reproduced during most of their lifespan (17.65 ± 1.37 days). Survival curve of M. dirhodum on wheat was determined as Type І. Regarding to the age specific survival of aphid, nymphs and young adults didn’t suffer any mortality. Like to the development of herbivorous insects on susceptible host plants, there was even no mortality until age 27 (day). Study on stable population parameters revealed that each female produced 33.84 female in next generation (R0). Intrinsic rate of increase (rm) was 0.194 female per female per day. Estimating the finite rate of increase (λ) was also indicated 21.4% increment in aphid population per day. Estimation of doubling time (DT) (3.57 days) and mean generation time (T) (18.18 days) was also showed considerable population increase potential of rose-grain aphid on Mahdavi wheat cultivar.

Population growth parameters of Tetranychus urticae Koch on four bean varieties including Talash (Colorado bean), Sadaf (Navy bean), Goli (Kidney bean) and Parastoo (Black-eye bean) were investigated in laboratory conditions at 25 ± 1°C, 60 ± 5% RH and a photoperiod of 16: 8 (L: D) h. In this experiment, one-day old eggs of T. urticae were selected and reared in growth chamber until the death of the last female mite, and the survival rate and female progeny of the mite were measured. Net reproduction rate (R0) on four bean varieties, was 8.822, 3.622, 4.908 and 2.043, intrinsic rate of increase (rm) was 0.142, 0.079, 0.095 and 0.038, and finite rate of increase (λ) was 1.152, 1.082, 1.099 and 1.039, respectively. Mean generation time (T) was determined 15.381, 16.283, 16.715 and 18.308 and doubling time (DT) was 4.901, 8.787, 7.292 and 18.125 days, respectively. The results indicated that the rate of population growth of T. urticae on Talash variety was more than other varieties. The rates of population parameters on Parastoo variety were the least.