Applied Entomology and Phytopathology
Year:2006 | Volume:73 | Issue:2 (80)|Papers Count:9

The relationship between temperature and developmental rate of Brachycaudus amygdalinus Schout (Homoptera: Aphididae) was studied at six constant temperatures (10, 15, 20, 25, 27.5 and 29±0.7°C), 40±10 RH and a photoperiod of 12: 12 (L: D). The linear regression model was used to describe developmental rate as a function of temperature.The duration of nymphal stages decreased from 14.04 to 5.8 days at 10 to 27.5°C, respectively. However, it increases to 8.39 days at 29°C. The mortality rate of the first nymphal stage was high at 30°C so that none of them could develop to fourth stage. The lowest (31%) and highest (89%) survival rate were obtained at 29 and 10ºC, respectively.The Lactin-2 model was the best nonlinear model to describe the relationship between developmental rate and temperature, suggesting the upper threshold temperature of 29-30°C.The linear regression revealed that the lower thermal threshold was -2.84°C, approximately the same temperature that makes this species active in nature. The life span of adult aphids was 6.74 days at 20°C. The following life table parameters have been recorded for B. amygdalinus at 20°C: intrinsic rate of increase (rm= 0.263 1/day) mean generation time (T = 11.49 days), doubling time (DT = 2.63 days), net reproductive rate (R0= 20.62) and gross reproductive rate (GRR = 40.59).

Tobacco plants (Nicotiana tabacum cv. Samsun) were transformed by coat protein gene of potato virus Y necrotic strain (PVYN -CP) using pBINI9 binary vector and Agroinoculation method. The primers designed so that the inserted PVY-CP transgene had not any start codon and so, it was unable to be translated into coat protein product. Resistance of 31 transgenic Nicotiana tabacum cv. Samsun lines containing PVYN coat protein transgene (PVYN _CP), were evaluated against the mechanical challenge inoculation of 3 prevalent Iranian PVY strains. On the basis of biological and serological properties, these PVY isolates included PVYn-H, PYYn-Mz (necrotic strain of PVY) and PVYo-Ar (an Ordinary strain). Symptom evaluation and ELISA tests showed that after challenge inoculation of 31 transgenic lines with PVYn-H, PVYn-Mz and PVYo-Ar isolates, 5,4 and 0 lines showed resistant phenotype, 9, 10 and 2 lines showed moderate symptoms of the disease and 17, 17 and 29 lines showed susceptible phenotype, respectively. Using TAS-ELISA and Western-blot analysis, the protein product of PVYN -CP transgene could not be detected in any of 31 transgenic lines. It seems that an RNA mediated resistance is responsible for resistance in the PVY-CP transgenic tobacco plants. In Nicotiana species, natural resistance sources to PVY infection are poor and development of engineered resistance sources against PVY infections would be useful.

Pheromone baited sticky traps are used as a monitoring tool for the survey of the European corn borer (ECB) populations in Iran. However, they fail to provide any valuable information to agricultural authorities. This is possibly due either to a wrong formulation of the pheromone lure for local moth populations or to the sticky trap design itself. This trap design is generally considered as poorly efficient against the ECB moth. In this paper, we (1) investigate the pheromone type of Iranian ECB females by means of gas-chromatography and gas-chromatography coupled to mass spectrometry and (2) we compare the efficiency of the delta sticky-trap versus a home-made wire mesh cone trap in a field test. Pheromone analyses of 14 individual females clearly showed that their pheromone composition is similar to the pheromone of the ECB Z strain feeding on corn in France, i.e. Z11-14: OAc as major component and E11-14:OAc and 14:OAc as minor components present on the gland surface.This trapping experiment showed that home-made wire mesh cone traps are more efficient than sticky traps (respectively 258 males caught versus 1) and confirmed that a pheromone lure releasing a Z type pheromone is an efficient attractant for ECB males from the Iranian population feeding on corn.

The cotton aphid, Aphis gossypii Glover is a major pest in cotton fields of Gorgan area, north of Iran. Population fluctuation of the aphid and its natural enemies were studied under two sprayed and unsprayed conditions during 2002 and 2003 growing seasons. Correlation analyses were used to determine the most influential variables affecting aphid population on cotton plant. First aphid colonies appeared the plants during late June to early July and reached peak numbers during mid September. Natural enemies' populations fluctuated in a similar pattern. Correlation analyses results showed significant relationships between aphid population, main natural enemies and some climatic factors. However these relationships were depended on species of natural enemies, growing season and chemical treatments.Coccinellids, chrysopids and syrphids as biotic factors and, temperature, daily sunny time and wind speed as abiotic factors were linearly correlated with total aphid population.

Adults and larvae of the poplar leaf beetle are among the most severe pests of poplar plantations. In order to study development and reproduction of Chrysomela populi under laboratory conditions (T = 25±1°C; R. H. = 70±10%; Photoperiod (L:D) 16:8 h) pairs of overwintering adults were separately confined in a plastic container provided by fresh leaves of Populus nigra. Longevity of females and males were 27.4 and 43.4 days, respectively.Total number of eggs/female, number of eggs/batch and oviposition rate (eggs/female/day) averaged 415.6, 40.7 and 23.9, respectively. Developmental times of egg, three larval stages and prepupa and pupa were 4.9, 3.4, 3.5, 5.2, 1.6 and 3.5 days, respectively. Stage specific mortality was as egg> 1st instar > 2nd instar > 3rd instar > pupa> prepupa. In a poplar plantation near Neyshabour (Northeast of Iran), over wintering adults appeared in early April, fed on fresh leaves, copulated and started to lay their eggs two weeks later. First instar larvae appeared in late April. After spending three larval stages, prepupa and pupa, newly moulted adults emerged in late May. They fed on poplar leaves for a few days then left the trees to start their long diapause period within litter and grasses until the next spring. Thus, C. populi has one generation a year in the studied region. Data from the field were subjected to the Popsys 1f software, using Kiritani-Nakasuji-Manly (KNM) model. Estimations of duration of different immature stages were: 4.32, 5.85, 4.15, 6.21 and 2.95 days for egg, three larval instars and pupa (induding prepupa), respectively. The survival rates for the respective stages were 0.44, 0.33, 0.45, 0.31 and 0.57. Estimations of the model were compared with the findings of laboratory and nursery.

The dynamics of seed bank is the qualitative and quantitative variation in density and combination of seed bank among time. The dynamics of seed bank and weed population and relations between them, was separately studied in 3 corn fields. Between 4 stages of sampling in every 3 fields, density of seed bank decreased. In the stage of corn stem elongation, number of weed seed in some points was zero. Chemical control prevented the seed production of weeds and decreased the density of weed seed bank. Plowing changed the density and combination of seed bank. Similarity index was 92% and correlation coefficient was significant. The results showed that the density and combination of weed flora related to density and combination of seed bank. Results of this research show that studying the variation of seed bank and weed flora and relations between them is benefitial to predict the pollution level of weed and selection the better and more effective management system for reducing of density of seed bank.

Eriophyes fie us Cotte (Acari: Eriophyidae) is a serious mite pest and vector of Fig Mosaic Virus on fig trees in Iran and elsewhere. Effects of different pruning methods (one, two, three, four shoots trees, fan and indigenous types) were investigated on population E. fieus for two years (2000-2001) in Saveh region. The one square centimeter of underside of fig leaf selected for counting mites. Four section of each leaf used in four replications to determine mite abundance. A fortnight sampling intervals applied from month of May till October of both years. The SAS program was used to analyse mean of collected mite data.Mean analysis of mite data statistically were found significant at one percent level in all pruning methods. Results also indicated that, maximum mean of mite population recorded 42.24 and 40.06 mites for two and three shoots type of pruning in first years respectively while in second year this means were 56.47 and 53.9 mites in four shoots and indigenous type of pruning and placed them in low affecting group of DMRT.Least mean of eriophyid mite among pruning methods recorded for one shoot type of pruning while maximum mean of mite observed for two, four and indigenous types pruning. Adult female mite diapause initiated with decreasing mean of temperature and day period from Sep. till November in Saveh region.

Samples of pistachio nuts including two types of damage, early splits and mature fruits with cracked hulls, were checked separately as possible sources for aflatoxin contamination under the pistachio orchard conditions in Rafsanjan. Hull cracking was found to be a common feature in pistachio fruits shortly after the maturation phase; it was a main route for subsequent insect infestation as well as aflatoxin contamination. Although the early split nuts were almost always contaminated with aflatoxin, this mycotoxin was also detected in the mature pistachio nuts with cracked and tattered hulls, with or without insect infestation, from all samples throughout three months of sampling (19 August to 19 November) at very high levels. It was found that the carob moth (Apomyelois ceratoniae), thrips (Liothrips austriacus) and ants (two unidentified species) only infest fruits with ruptured hulls, either at prematuration (early splits) or afterwards (mature fruits with cracked hulls). However, the pistachio fruit worm (Recurvaria pistaciicolla) and the pistachio fruit hull borer moth (Arimania komarofJi) are able to bore the hulls. These insects commonly prepare an appropriate passage for mould development inside the nuts and may transfer the fungal spores into the nuts. Furthermore, hull rupture due to damage by birds was found to be another mean for aflatoxin expansion in the pistachio nuts. It is concluded that the hull cracking phenomenon, which occurs closely after nut maturation, plays an important role in aflatoxin development in pistachios. Therefore, harvesting must be completed promptly after physiological maturity of the pistachio nuts.