نامه انجمن حشره شناسی ایران
سال:1389 | دوره:30 | شماره:2 (پیاپی 47) |تعداد مقالات:19

Effect of five soybean varieties (Sahar, JK, BP, Williams and L17) on life cycle and fecundity of the beet armyworm, Spodoptera exigua Hübner was evaluated at temperature of 25±1°C, 60±5% r.h. and a photoperiod of 16:8 (L:D) h. The preimaginal development period of males and females was longest on L17 (30.17±0.28 and 29.63±0.23 days) and shortest on BP and Sahar. The adult longevity of males and females was longest on Williams (13.86±1.14 and 20.20±1.12 days) and shortest on Sahar (9.36±0.59 and 12.75±0.69 days), respectively. The life span was longest on L17 (44.86±0.85 days) and shortest on Sahar (39.00±0.50 days). The highest percentage of egg and larval mortality was observed on L17 (73.48 and 39.35%, respectively), but the highest percentage of pupal mortality was on Sahar (12.50%). The lowest percentage mortality of egg (57.96%) and larval (10.81%) stages was obtained on Williams. The pupal weight of females was heaviest on Sahar (88.10±3.01 mg) and lightest on BP (73.00±4.18 mg) compared to the other varieties. The highest number of eggs laid per female per day was 58.19±4.53 on L17 and the lowest number of eggs was 37.91±3.01 on BP. The results showed that total number of eggs laid per female was highest on Williams (569.50 ±29.8 eggs) and lowest on Sahar (448.90±19.5 eggs). Knowledge of the biology of S. exigua on soybean varieties can aid us to detect and monitor the pest infestation, variety selection and crop breeding.

Food choice in omnivorous animals is influenced by the balance of nutritional needs, food availability, and quality of a particular food items. Here, we study whether omnivorous onion thrips Thrips tabaci Lindeman (Thysanoptera: Thripidae) feed on the eggs of its competitor Tetranychus urticae Koch (Acari: Tetranychidae) when an alternative supplemental source is, or is not, available. Thrips were either fed a cucumber leaf alone, or this diet was supplemented with pollen, mite eggs, or both. We demonstrated that the supplemental food sources improved several fitness-determining traits of thrips with pollen being nutritionally superior to mite eggs. Pollen reduced the development time and increased the population growth of thrips compared to mite eggs. When both pollen and mite eggs were available, thrips fed on both; pollen to improve nutritional status and eggs to eliminate the opponent, despite the latter’s consisting lower of nutritional benefit. In all, this study showed that omnivorous thrips benefit from a cucumber leaf diet that is supplemented with other food sources and that pollen and mite eggs increase several fitness traits and positively affect the dynamics of future thrips generations.

We investigated the effects of interaction between Cotesia plutellae (Kurdjumov) and Bacillus thuringiensis Berliner on parasitism and an immune effector (phenoloxidase activity) of a Bt-susceptible and a Bt-resistant population of Plutella xylostella (Linnaeus) in laboratory. Parasitism success of C. plutellae varied depending on the use of B. thuringiensis or its toxin, and the timing of application. Percentage parasitism was significantly greater on Cry1Ac-treated hosts than B. thuringiensis var. kurstaki-treated hosts (the susceptible population), and greater when hosts were treated with B. thuringiensis var. kurstaki before parasitism compared to that after parasitism (the resistant population). Specific phenoloxidase activity was significantly reduced in Cry1Ac-treated or parasitized hosts, but combined effect of the toxin and the parasitoid caused a greater reduction in phenoloxidase activity. The lower phenoloxidase activity in unparasitized resistant population of P. xylostella compared with the susceptible one is likely to be due to fitness costs, manifesting a possible trade-off between pathogen resistance and parasitoid resistance. However, C. plutellae overwhelmingly suppressed phenoloxidase activity of both the susceptible and resistant populations of P. xylostella. We found that the interaction between B. thuringiensis and C. plutellae was synergistic, which is promising for integration of the pathogen and the parasitoid in management of P. xylostella populations.

During conduction a survey of entomopathogenic nematodes throughout Arasbaran forests and rangelands, north-west of Iran in 2007-2008, an entomopathogenic nematode was isolated by Galleria baiting method from soil samples collected from rangelands, near Chichakloo, Varzeghan. It was identified as Steinernema kraussei (Steiner, 1923) Travassos, 1927 based on morphology and morphometric characters, cross breeding test, as well as molecular data. This species can be separated from other members of the genus by medium body length of infective juvenile (818 µm), lateral field with eight ridges in which the central pair are less distinct than others, head smooth, long cephalic papillae, secretory-excretory pore located at the level of middle of esophagus and anterior to the nerve ring; broad, slightly yellowish and short spicules, low D% value and tail with fine mucron in males. The analysis of ITS-rDNA sequence placed Iranian population of S. kraussei in the ‘feltiae-kraussei-oregonense’ group in the clade that containing different isolates of the species. It has some morphological and morphometric differences such as long cephalic papillae of IJ, more curvature of spicules and absence of mucron in some males as compared with type species. The mentioned differences are considered as intraspecific variations, and the described population from Iran is another isolate of S. kraussei. This is the first record of S. kraussei from Iran.

Trissolcus grandis Thomson (Hymenoptera: Scelionidae) is a solitary egg parasitoid of Sunn Pest, Eurygaster integriceps Puton (Hymenoptera: Scutelleridae). Although widely distributed, it has often been overlooked in field surveys. Our objectives were to develop an efficient rearing technique for T. grandis, and to determine the basic bionomics and demographic parameters, necessary for future augmentative biological control programs. Exposure of 0-4h-old Sunn Pest egg masses to parasitoids at 1-1, 2-1 and 3-1 host-parasitoid ratios resulted in a parasitism rate of >80%. The results demonstrated that the age of the host and the exposure time affected parasitism rate. However, parasitism rate did not differ significantly among 24, 48 and 72h-old Sunn pest eggs. The percent of emerged parasitoids during the 24-h host exposure period was relatively high when host eggs were 24-h old. Moreover, the mean sex ratio showed a definite trend, suggesting that host age had an effect on the sex ratio of the T. grandis offspring. The mean developmental time obtained as 11.091 ±0.1 and 9.68±0.15 d. for female and male progenies, respectively. The longevity of females was~30% lower compared to that of males. The average net fecundity reached 181.83 eggs per female. On the other hand, a female laid averagely~7 eggs per day. Similarly, the daily population increase and mean generation time were 34.2%, and 14.61 d, respectively. The developing population consisted of 99% immature (egg, larvae, pupa), and only 1% adults. The importance of these findings to the population biology of this parasitoid is discussed.

During the spring 2007, a survey was carried out at Chavarzagh area, in Zanjan province (Iran) in order to collect and identify aphidiine parasitoids attacking to the black bean aphid, Aphis fabae Scopoli. Samples of Vicia fabae plants bearing the colonies of healthy and mummified aphids were taken from fields into the laboratory. Parts of plants with aphid colonies were cut and put in plastic containers covered with nylon mesh. The containers were kept at a constant temperature of 20ºC, 65% relative humidity and under a 16: 8 (L: D) photoperiod until the emergence of parasitoids. Some of the emerged parasitoids were identified as Lysiphlebus fabarum (Marshall).

The cosmopolitan mite family of Cheyletidae includes more than 360 predacious and parasitic species in 73 genera (Bochkov & Fain, 2001). Predacious species occur on plants, soil and stored products, as well as in vertebrate nests where they feed on mites or small insects (Volgin, 1987; Gerson et al., 1999; Gerson et al., 2003). Bochkov et al. (2005) reviewed the Iranian Cheyletidae and included a key to 18 genera and 28 species. Herein we report six species of cheyletid mites associated with stored rice in Guilan province, Iran, including the first report of Chelacheles strabismus Baker from Iran. A key for their identification is provided.

During the faunistic studies on Auchenorrhyncha (Hemiptera) of sugarbeet fields in Isfahan province (Iran) between 1995 and 1997, specimens of genus Empoasca Walsh (Cicadellidae: Typhlocybinae: Empoascini) belonging to the group species Empoasca decipiens were collected. Based on reliable literature (Ribaut, 1936; Emeljanov, 1967; LeQuesne & Payne, 1981), the collected specimens were then determined as Empoasca decipiens (Paoli) (Karimzadeh, 1997; Karimzadeh et al., 1998). However, this determination was somewhat controversial because of the earlier report of Empoasca meridiana Zachvatkin from the same region (Kheyri & Alimoradi, 1968). Due to lack of data on discrimination of the two mentioned species and inaccessibility of the original description of latter species the problem remained unsolved.

The family Issidae is one of the largest families of the Fulgoroidea which has worldwide distribution, with many species in arid regions of Western Palaearctic. The members of this family are usually subbrachypterous, with rounded or ovoid body shape.Around 43 issid species have been recorded from Iran (Dlabola, 1971, 1974, 1980, 1981, 1982; Behdad, 1988; Mirzayans, 1995; Abaii, 2000). Dlabola actually discovered Iranian issid fauna, he described 37 species which is 86 % of the fauna. At least 3 of them have been recorded as pests on almond and oaks. (Abaii, 2000). About 11 species had been identified by Dr. J. Dlabola in 1970s and deposited in the Hayk Mirzayans Insect Museum (Mirzayans, 1995).