جستجوی مقالات مرتبط با کلیدواژه "weevil" در نشریات گروه "گیاهپزشکی"

Azolla (Azolla spp.: Salviniaceae) is an aquatic fern that was introduced to the northern region of Iran with the aim of increasing the fertility of paddy fields, but due to suitable climatic conditions and the absence of natural enemies it became a problem in rice production and a destructive factor in aquatic ecosystems. In recent years, the biological control agent of this weed, Azolla weevil Stenopelmus rufinasus Gyllenhal (Curculionidae), was introduced in northern region of Iran. In this study, geographical distribution and seasonal population density of S. rufinasus in northern Iran were investigated through regular monthly sampling. The results showed that the time required to complete one generation in semi-field conditions is about two weeks. Both larvae and adults feed on Azolla. Azolla weevil is well distributed and established in the north regions of Iran and by feeding on Azolla, it has reduced its population in wetlands, permanent ponds and paddy fields. Comparing the population density of the weevil in three regions of Guilan province, indicated that the highest number of total density (667 insect in 1 kg Azolla) and adult (363 adults in 1 kg Azolla) belong to the central region of the province, while the density of larvae (397 larvae in 1 kg Azolla) in the eastern region of the province was higher than other regions. In the survey of the density in different cities, the highest density of total (2690 adults and larvae in 1 kg Azolla) and adult insects (2022 adults in 1 kg Azolla) was observed in Shaft city and the highest density of larvae (1920 larvae in 1 kg Azolla) was observed in the Rudbane of Lahijan. Based on the obtained results, the population density of the weevil is higher in spring and winter, which is not far from the mind considering the climatic conditions of the region and the sensitivity of Azolla to heat and low humidity. Based on the findings of this survey, the weevil has spread and settled well in the northern regions

Different species of weevils (Col.: Curculionidae) are found in oilseed rape fields, which some of those are canola stem-borer weevils. They feed inside petioles, crown and/or stems of the crop in larval stages and cause damage. These weevils are mainly belonging to genus Ceutorhynchus, which little information about their taxonomy, distribution and biology is available in Iran.

During 2016-2018, the biological characteristics of canola stem-borer weevils were investigated in canola fields of Mazandaran, Lorestan and Golestan provinces. In each province, three fields were selected for collecting samples. Yellow water traps were used for weekly collecting adult weevils from the fields during crop growing season. For collecting weevil-infested crops and determining infestation rate, 10 quadrates (0.5 × 0.5 m) were used per field. The adult weevils collected by the traps were identified and the pest biology as well as the infestation rates of the crop by the weevils were studied.

In this study, five Ceutorhynchid species were collected and identified: C. picitarsis and C. chalybaeus from Mazandaran, C. erysimi and C. pallidactylus from Golestan and C. sulcicollis from Lorestan, Mazandaran and Golestan. In late November, the adult weevils migrated to canola fields and after feeding and mating, the females deposited their eggs into main veins, petioles of the lower leaves or inside of the collar area of young canola plants and the emerged larvae penetrated into the host plant. The three larval instars of this pest fed inside host plant tissue during autumn and winter till mid spring season. The feeding activity of the first and second instar larvae were observed in late November and late December, respectively. Third instar larvae were found from beginning until mid-spring season. In late April, third instar larvae left the host plant, dropped in the soil for pupation and new generation adults emerged in May. These weevils are univoltine. The results showed that, the maximum infestation rates of oilseed rape by the stem weevils in Mazandaran, Lorestan and Golestan provinces was 20.1±0.89, 14.8±1.29 and 10.2±0.29 percent, respectively.

Determining the time of adult migration activity, oviposiotion and larval development of the weevils is an integral part of pest management strategy in oilseed rape fields. In this study, flight and oviposition activity of adults and also feeding activity of the first instar larvae were mainly observed in late November, which suggests this time as a suitable time for chemical control, if necessary. These weevils are mostly distributed around the Caspian Sea region (Mazandaran and Golestan provinces) however more investigations are required to conclude the existence of those in other parts of country.

Waterferns have caused many problems in aquatic ecosystems and rice fields of northern regions during recent decades. Despite the fact that Azolla spp. are known as one of the most important invasive species worldwide, with management and applying biological control agents in natural habitats they can be used as beneficial species. For Azolla management, it is very important to have enough knowledge about the reproduction, substantial conditions for invasion and biological control agents of the plant in the area. . In northern regions favorable environmental conditions such as high humidity, suitable temperature, absence of specific natural enemies and etc, caused Azolla spp. expansion and invasion. In recent years, it has been demonstrated that some of the native and migratory species such as Cataclysta lemnata, Nomophila noctuella, Diasemiopsis ramburialis and Rhopalosiphum nymphaeae feed on Azolla spp. in the area and have high dispersal. Recently, exotic weevil, Stenopelmus rufinasus, has been recorded in the area as well. Studies indicated that C. lemnata and S. rufinasus as biological control agents and other species as biotic resistance factors can be used for Azolla spp. management in northern regions. According to these findings and existing knowledge we have enough resources to control Azolla, and by providing of the necessary facilities it can be controlled in northern regions of Iran.

The weevil Polydrusus davatchii Hoffmann, is a potential pest for pistachio buds and developing flower clusters in early spring. The effect of winter ploughing on weevil’s population density was investigated using emergence traps in a contaminated pistachio orchard through 2009-2012 in Bayaz, 75 Km North-West of Rafsanjan, Iran. It was found that beetles only emerges from soil where naturally covered by plant litters under the pistachio trees’ canopy during 20 March to 20 April. No adult weevil captured through emergence traps in other parts of orchard. The number of weevils that captured under trees canopy having no any plant litters were significantly less than those captured under trees canopy where naturally covered by plant litters. A significant difference was found for the abundance of weevils in plowed and non-plowed areas. In addition, the present field experiment verified that abundance of weevils on aerial parts of trees in plowed plot were significantly lower than those in non-plowed plot. Based on the results, winter ploughing (30 cm depth) of pistachio orchards causes positive effect on reduction of weevils’ population density

The sugar beet weevil, Lixus incanescens Boh., is an important insect pest of sugar beet, Beta vulgaris L., in Razavi Khorasan Province. In this research, population densities of the sugar beet weevil eggs and larvae were evaluated on plants of six sugar beet cultivars including Ardabili, Aras, Persia, Flores, Laetitia and Rosire in an experimental field in 2011 and 2012. Also, the percentage of larval damage on petioles, the percentage of weight loss of tuber and the percentage of reduction in sugar content of the tuber were studied in these cultivars infected by five larvae under field condition. The lowest and the highest densities of eggs and larvae were observed on Persia and Ardabili cultivars, respectively in both years. Also, the percentage of larval damage on petioles was significantly lower in Persia and Laetitia than the other cultivars. In addition, the percentage of weight loss of tuber and the percentage of reduction in sugar content of tuber were lowest in infected plants of Persia. Therefore, it can be concluded that the sugar beet weevil damage was both quantitatively and qualitatively least in Persia among the examined cultivars and so this cultivar has the potential for being used in an integrated pest management program of L. incanescens in sugar beet fields.

The sugar beet weevil, Lixus incanescens Boh., is an important pest of sugar beet in Razavi Khorasan province. In this research, population density of sugar beet weevil, diversity of its natural enemies, and percentage of larval parasitism were studied on six sugar beet cultivars including Ardabili, Aras, Persia, Flores, Laetitia and Rosirewere studied in an experimental field during 2012 and 2013. In two years, the lowest densities of sugar beet weevil eggs and larvae were observed on Persia. In this study, one larval parasitoid species Bracon intercessor Nees, and three egg predator species: Nabis punctatus A. Costa, Orius niger Wolf. and Chrysoperla carnea Steph. were collected and identified. Amongst the natural enemies of this weevil, B. intercessor had the highest relative abundance. The Shannon diversity index for the complex of natural enemies was greatest on Persia. The value of Morisita–Horn index for the complex of natural enemies between the six sugar beet cultivars were calculated 0.973 to 1. In two years, the highest percentage of larval parasitism was observed on Persia (62.2 and 73.5%, respectively). Furthermore, the percentage of parasitoid females emerged on the weevil-infested plants in Persia and Laetitia was significantly higher than on Ardabili, Aras and Flores. Therefore, it can be concluded that the cultivation of Persia cultivar integrated with using of larval parasitoid B. intercessorcould be useful in the integrated management programs of L. incanescens in sugar beet fields.