s. aghajanzadeh

Seasonal population dynamics of the aphids on two important commercial citrus species, Thomson navel orange (TNO) and Satsuma mandarin (SM) were investigated in the west of Mazandaran province, Ramsar, during 2015-2016. Samplings were performed biweekly from April 2015 to July 2016. In each sampling date, four young shoots were randomly selected from each main geographical direction of each tree and the number of aphids was counted under a stereomicroscope. The Pearson correlation coefficient was used to determine the relationship between aphid density and temperature and relative humidity as variables. For both species of citrus, the results showed that the first and second population peaks of the aphids occurred in May and October, respectively. Furthermore, there was a significant difference between the infestations of both citrus host plants by the aphids, with Satsuma mandarin showing more infestation. There was a significant difference among the population densities of different aphid species on both citrus species. Aphis spiraecola, Aphis gossypii, and Toxoptera aurantii had the highest population abundances, respectively. A positive and significant correlation was observed between these citrus aphid population densities and temperature (r= 0.689, n=49, P=0.04), however, the correlation was not significant for relative humidity (r= 0.661, n=49, P=0.53). In total, seasonal population dynamics of the citrus aphids were affected by the host plant species and different species showed different population fluctuation trends.

Citrus yellow vein clearing virus (CYVCV), a new member of the genus Mandarivirus (family Alfafelxiviridae), has been recently reported from Iran after being recognized in Pakistan, India, Turkey and China. Typical symptoms of infection on the leaves of sour orange, lemon and Persian lime, as local sensitive hosts, consist of yellowing lateral veins with corresponding water-soaked appearance on the lower surface of the leaves. Biological and molecular detection, some modes of transmission and phylogenetic analysis of CYVCV isolates of Mazandaran province have been investigated in the present study.

Typical induced symptoms by CYVCV infection; namely yellowing and water soaking of the lateral veins, was considered as the initial criterion for diagnosis of the disease within seedlings and trees of sour orange, lemon and Persian lime cultivars in nurseries and orchards in Mazandaran province.  Three isolates, out of 53 samples, were selected for more analysis from the region collected during the spring of 2016, 2017, and 2018. Inoculation of these isolates into bean plants, sour oranges and lemons were performed using mechanical and grafting methods under greenhouse conditions with controlled temperatures. In order to confirm the infection, total RNA of the collected samples and the inoculated plants were extracted by the SDS-Potassium acetate method. A two-step Reverse Transcription Polymerase chain reaction (RT-PCR) was carried out using a specific primer pair of the virus coat protein (CP) gene.

Characteristic symptoms of the disease were expressed after top-work grafting of the susceptible virus-free orchard cultivars on the trunks of diseased trees. Using specific primer pair in RT-PCR, an expected 614 bp fragment was amplified in symptomatic samples. The consensus sequences, obtained from direct sequencing the PCR products of the studied isolates based on forward and reverse specific primes, were similar to the sequences of other CYVCV isolates of China, India, Pakistan and Turkey at the level of 95.75 to 98.37%. A phylogenetic tree of this part of the genome, grouped Iranian isolates with two isolates from India and Turkey and two Pakistani isolates.

The present study confirmed the presence of Citrus yellow vein clearing virus in the north of the country. Lemon and Persian lime are the two most important susceptible hosts of the virus. These citrus varieties are also valuable cultivars in the south of the country and are considered tolerant genotypes to Witches' broom disease, which is prevalent in these areas. Preventing the spread of the yellow vein clearingdisease to the new infection foci by continuous monitoring of the citrus nurseries should be seriously considered.

Citrus, as a critical horticultural product, has a special place in our country's economy. Meanwhile, scale insects such as Planococcus citri and Pulvinaria aurantii are the most important pests of citrus in northern Iran and cause economic damage. To prevent the damage of these pests, various insecticides are recommended. Due to a waxy layer on their bodies, it is difficult to control them chemically. Excessive use of pesticides and repeated spraying can have adverse effects on non-target organisms. In the present study, the effect of three compounds was conducted on some biological and reproductive characteristics of a coccinellid predator, Cryptolaemus montrouzieri. Also, these compounds were grouped according to the criteria of the International Organization for Biological Control (IOBC).

The effect of three compounds at field recommended concentration and half dosage of them in 9 treatments, including: 1, 2: mineral oils, EC, at two concentrations of 5 ml/L and 10 ml/L, 3, 4: mineral oils mayonnaise, at two concentrations of 5 ml/L and 10 ml/L, 5, 6: insecticidal soap palizin 1.25 and 2.5 ml/L, 7, 8: buprofezin 0.25 and 0.5 ml/L and 9: water (control) were investigated on C. montrouzieri. Treatments were done on eggs via dipping method and on the fourth instar larvae and adults via direct spray on mealybug-infested citrus seedling after releasing the ladybeetle.

Mayonnaise oil (10 ml/L) caused a 43.4% reduction on egg hatching compared with that of control. Buprofezin treatment (0.5 ml/L) with 36.6, 35.5 and 40% mortalities on fourth instar larvae, male and female adult respectively, was significantly different compared to the control. In the treated females with buprofezin 0.5 ml/L, mean of longevity and fecundity were 30.9 days and 26.1 eggs compared to the control 87.8 days and 114 eggs, respectively. According to IOBC standard method, mayonnaise (5 ml/L) as harmless (E=24.6, class 1), buprofezin as moderately harmful (E=84.1, class 3), and other compounds as slightly harmful (class 2) were classified. Used compounds at half doses had a low adverse effect on tested parameters compared with field recommended concentration.

Many researchers emphasize the harmlessness of oils to pests' natural enemies. Also, the safety of palizin on them has been reported by some researchers. The use of buprofezin in the larval stage reduced the percentage of adult exit from the pupa, and in the maturing stage, reduced the number of ladybeetle eggs compared to other compounds, so its toxicity is observed to this predator. On the other hand, the effectiveness of mineral oils and palizin in reducing the population of citrus scales has been positively evaluated by researchers. Therefore, these compounds can be used as alternatives to chemical pesticides in the integrated management of citrus pest programs. Also, the mentioned compounds had a less adverse effect on the ladybeetle at the half dosage of the recommended concentrations, which can be used in combination with the ladybeetle to pest control.