فصلنامه گیاه پزشکی
سال سی و پنجم شماره 1 (بهار 1391)

Appropriate functional response to prey or host densities is one of the important criteria for evaluating the efficacy of natural enemies in biological control programs. Cryptolaemus montrouzieri Mulsant is one of the main predators of citrus mealybug,Planococcus citri (Risso). In this research, the functional response of fourth larval instars and the female adults of this ladybird to different densities of second and third instars and female adults of citrus mealybug was studied under laboratory conditions. All experiments were carried out inside incubator with 25±1˚C, 80±5 %RH and photoperiod of 14 L:10 D hours. Individual fourth larval instars and female adults of ladybird were kept separately at densities of 4, 6, 8, 16, 20, 30, 40, 50 and 60 preys for 24 hours. Duration of each experiment was 24 hours and all experiments were carried out in 6 replications. A logistic regression was used to determine the type of functional responses and a nonlinear regression was used to fit Rogers and Holling’s equations to data for estimating searching efficiency (a) and handling time (Th) parameters. The results showed that the functional responses of fourth larval instars to different densities of second and third instars and the female adults of citrus mealybug were type III, III and II respectively, while the functional responses of the female adult ladybird to different densities of second and third instars and the female adults of prey were type II, III and II respectively. The rates of searching efficiency (a) for fourth larval instars of ladybird on second and third instars and the female adults of prey were estimated 0.0126, 0.0165 and 0.002, and the rates of handling time (Th) were obtained 0.701, 1.012 and 2.05, respectively. The rates of searching efficiency of female ladybirds on second and third instars and the female adults of prey were estimated 0.048, 0.013 and 0.098 and the rates of handling time were obtained 0.177, 0.843 and 2.79, respectively.

Sugarcane pink stem borers, Sesamia spp., are the key pests of sugarcane in the south of Khuzestan province, Iran. These pests damage heavily the sugarcane crop and sugar product every year. In this research, spatial dispersionof the stem borers populations were studied in three sugarcane fields (25 hectare each, Cp69-1062 cultivar) in 2008. Sampling was carried out monthly in seven stages. External symptoms of pest damage were used as a population indicator and the number of infested stems and internodes of sugarcane were recorded in each sampling station. In order to determine the type of pest spatial dispersionin these three fields, various classical statistics indices were used. In all sampling stages, values of the variance to mean proportion index, index of Patchiness and Morisita’s index were significantly higher than one, and values of 1/k index and Green’s index were higher than zero. The obtained results of all indices indicated that spatial dispersionof Sesamia spp. was aggregated. The regression coefficients of Taylor’s power law b and Iwao’s β were determined 1.45±0.065 and 1.18±0.031, respectively. Thus, they had significant difference from one, and both indicated the aggregated spatial dispersionfor the pest life. Based on R2 and P-values of regression analysis, Iwao’s patchiness showed a better fitness for pest spatial dispersiondata in comparison with Taylor’s power law.

Laboratory trials were conducted to measure the effects of two insecticides, imidacloprid and buprofezin on the functional response of Encarsia inaron (Walker) parasitizing Bemisia tabaci (Gennadius). Young female parasitoids (< 24h old) were exposed individually to LC25 valueof imidacloprid, field recommended concentration of buprofezin and distilled water as the control. Host densities of 2, 4, 8, 16, 32, and 64 third nymphal stages of B. tabaci were offered to treated females wasps for 24 h in clip cages on cucumber leaves. Experiments were conducted in 10 replicates and were carried out in controlled conditions, 25 ± 1oC, 70 ± 5%RH, and a photoperiod of 14: 10 (L: D). The type of functional response was determined using logistic regression and the parameters, searching efficiency (a) and handling time (Th) were estimated by the non-linear regression using SAS software. The functional response was type II in the control and both insecticide treatments. Searching efficiency in the control, buprofezin and imidacloprid were 0.0413, 0.0360 and 0.0373 h-1 and the handling times were 2.9727, 1.2738 and 2.0187 h, respectively. The maximum attack rates (T/ Th) were estimated 8.07, 18.84 and 11.89, respectively. Neither of insecticides had detrimental effect on the searching efficacy of E. inaron.

Species diversity and abundance of curculionids associated with sugar beet fields were surveyed in Khorasan-e-Razavi province in 2009 and 2010. Based on the species richness and their relative abundance, Shannon-Wiener index of biodiversity was calculated for Chenaran region in two years. The value of biodiversity index was the highest in middle of June until late July for both years. In this study, the two species, Adosomus strabus and Lixus incanscens with relative abundance of 17.11 and 14.41 %, respectively, were dominant species in the study area. Among the identified curculionid species, Stephanocleonus (Coniocleonus) vittiger (Fahraeus, 1842) was new to the fauna of Iran and Menecleonus lagopus (Fahraeus, 1842),Conorhynchus kindermanni Faust, 1904 and Tanymecus palliates (Fabricius, 1787) were new records for Khorasan-e-Razavi province. In this study, the number of weevil species associated with sugar beet fields in Iran increased to 53 species.

The species, Cybocephalus fodori minor End. (Col.: Cybocephalidae) was first reported in Iran named predatory beetle of pistachio oystershell scale, Lepidosaphes pistaciae Arch.(Hom.: Diaspididae)in Isfahan province in 2001.This study was carried out to investigate some bioecological and behavioral charachteristics of the beetle, C. fodori minor, and its predation rate on L. pistaciae in Isfahan under natural conditions from November 2005 to November 2006. Also, the predation rate of this predatory beetle on pistachio oystershell scale was seperately investigated on the surface of leaves, twigs (including 1-year and 2-year old branches) and fruits with weekly sampling and counting of live scales and feeding signs of this predator on cover of scales. This species overwintered as adult under the bark of pistachio trees. These beetles completed three generations in cages outside the laboratory (in natural conditions) during March until late November 2006. The activity of this predatory beetle resulted in 20.81, 39.18 and 42.01% of predation on L. pistaciae settled on twig, leaf and fruit, respectively.

Podosphaera xanthii and Golovinomyces cichoracearum are the two main species causing powdery mildew on cucumber worldwide. Cucumber powdery mildew and the fungal species involved in this disease have poorly been studied in East Azerbaijan province of Iran. In the present study, 37 cucumber plant samples with powdery mildew symptoms were collected from Tabriz, Ahar, Sarab, Basmenj and Shabestar, from June till September 2007. All collected species were identified based on conidial and cleistothecial morphology (1,3). In total, 48 isolates were studied of which 37 (77%) were identified as G. cichoracearum and 11 (23 %) as P. xanthic. In order to determine the race of isolated species, a set of differential melon cultivars (Iran H, PMR5, PMR45, Vedrantais, Edisto47, Nantais oblog, Mr-1, PI124112, PI414723 and WMR29), were used to determine the race of species. After 15 days of inoculation, the races were determined based on presence or absence of symptoms on differential host. Pitrat chart was used to evaluate and score the results (7). Based on the results, from 37 isolates of G. cichoracearum, 26 isolates were determined at the race level and of these 19 isolates were identified as race 0 and 7 isolates were determined as race 1. Among 11 isolates of P. xanthii, 8 isolates were identified as race 0. However, for the remaining 11 isolates of G. cichoracearum and 3 of P. xanthii, results were not conclusive because of the overlap between the differential set of cultivars. Analysis of variance and mean comparison (P=5%) was performed by using MSTATC software. Resistance assessment of the differential lines to different isolates showed that “Iran H” with 15.17 % mean infection was determined as susceptible and “Edisto 47” with 1.56 % mean infection was determined as resistant to G. cichoracearum. MR-1, PMR 45, PI 414723 and Nantais oblog were completely resistant and no infection was observed when inoculated with G. cichoracearum. For the other species isolates, in comparison to Vedrantais (with 7.5 % mean infection) “Iran H” (with 15.72 % mean infection) was also determined as susceptible to P. xanthii. The other lines were not infected and were considered resistant to P. xanthii.

Since the present pest control strategies aimed at reduced pesticide applications and implementation of various biocontrol measures, it is necessary to know the potentiality of beneficial insects and the role of nutrition on their abilities. In this research, the effect of four dietsincluding Sitotroga cerealella eggs, S. cerealella (adult) dead bodies, Aphis gossypii (nymphs) and Planococcus citri (nymphs) were studied on some biological parameters of the green lacewing, Chrysoperla carnea under laboratory conditions. The eggs of predators were collected from tomato and cucurbit fields of Gorgan. To establish a laboratory colony, the larvae were reared for five successive generations on the eggs of Anagasta kuehniella. The larvae were individually reared on above-mentioned feeding regimes at 26 ± 2oC, 60 ± 5% RH and a photoperiod of 16: 8 (L: D) conditions. Adults were fed pairly on sucrose and yeast in P.V.C. tubes. The results showed that the larval and pupal periods at rearing on the eggs of Sitotroga cerealella and Aphis gossypii decreased and the mortality of the larvae was reduced in comparison with those reared on dead bodies of S.cerealella and nymphs of Planoccus citri. Hence, these diets were recognized suitable food regimes for rearing lacewing. The kind of food had no significant effect on biological parameters of adults. The unsuitability of adult dead bodies due to physical characters and sticky body of citrus mealy bug caused adverse effects on larval development and their survival. Therefore, they were not appropriate food for rearing the green lacewing.

Cotton whitefly, Bemisia tabaci Gennadius, is considered as one of the most important pests of fall cucumber in Khouzestan province. Seasonal dynamics and spatial distribution of Eretmocerus mundus Mercet and Encarsia acauda leyrodis Hayat natural enemies of cotton whitefly were studied weekly during 2006 and 2007 on fall cucumber in Mollasani area. In both years, pupae of both parasitoids first appeared on the plants in middle of September. In 2006, peak population of E.mundus and E.acaudaleyrodis were observed on 5th of October (1.9 pupa) and 12th of October (0.6 pupa) in 2 cm2 leaf, respectively. In 2007, peak population of two aforementioned parasitoids were observed on 27th of September (4.5 pupa) and 4th of October (0.9 pupa) in 2 cm2 leaf area, respectively. In both years, the population of both parasitoids reached zero in late October. Special distribution of both parasitoid were studied using Taylor power law. The slopes of regression lines (b) of two aforementioned parasitoids were 1.274 and 1.447 (2006) and 1.745 and 1.302 (2007), respectively. Spatial patterns of the pupae of both parasitoids on cucumber leaves were aggregated.