Journal of Entomological Society of Iran
Year:2008 | Volume:27 | Issue:2 (40 SUPPLEMENT)|Papers Count:14

The Colorado potato beetle, Leptinotarsa decemlineata (Say), is a destructive insect pest of potato and other solanaceous crops. The type, number and distribution of sensory receptors on the labiomaxillary complex of larvae were studied using the scanning and transmission electron microscopy. A total of 32 sensilla were identified on the maxillary and labial palps that were categorized in three basic morphological types: basiconica, trichoid, and digitiform. The maxillary palp had 16 basiconica, four trichoid and one digitiform sensilla, and the labial palp included 11 basiconica sensilla. All basiconica sensilla were on the distal apex of the palp segment. The basiconica sensilla are innervated by 2-6 neurons and function as a gustatory receptor. In addition, three trichoid sensilla were on the distal side of the second segment, one trichoid sensillum on the lateral side of the third segment and one digitiform sensillum on the lateral side of the third segment of maxillary palp. Trichoid sensilla are equipped with 4-6 receptor cells and function as chemo- and mechanoreceptors.

In this study, the genetic parameters and economic weights of some important economic traits in six Iranian commercial varieties (110, 107, 101433, Xinhong1, Koming1 and Y) of the silkworm were estimated and selection indices for these traits constructed. Individual recording of cocoon weight, shell weight and shell ratio were carried out during six generations. Heritabilities and genetic correlation between traits were estimated by restricted maximum likelihood method. The heritability of cocoon weight and shell weight were higher than that of shell ratio. Genetic improvement of cocoon weight and shell weight were high in the line 101433 due to higher heritability and genetic correlation between them.Therefore, the restriction of genetic gain of cocoon weight in this line is expected to cause a severe decrease in improvement of shell weight, and subsequently a decrease of selection efficiency. The genetic improvement of cocoon shell percentage increased in restricted indices due to low genetic correlation with cocoon weight, and selection accuracy in these indices decreased significantly compared to other indices. Considering the difference in genetic parameters and economic values of traits in commercial lines of the silkworm, it would be necessary to define a separate breeding goal and selection strategy in each line.

Current study was initiated to generate the information on the effect of row-to-row distance of brassica crop, Brassica napus L., on aphids population. Three line spacing (20, 30 and 40 cm) with a constant nine cm plant to plant distance were evaluated on aphids infestation and its impact on seed yield.The collected and edited data on fixed parameters indicated that an inverse relation was found between increased line spacing and aphids population. It was evident that the mustard aphid, Lipaphis erysimi (Kaltenbach), population increased significantly as the inter row spacing decreased. Distance of 30 cm was quite respondent towards holding aphids number and grain yield, where optimum number of aphids (103.00 per plant) was recorded with maximum yield (980.00 Kg/Hectare). Maximum mean aphids number (163.5) was observed on the plants spaced at 20 cm apart rows with minimum seed yield (683.20 Kg). Minimum mean number of aphids (63.3) was recorded from the lines grown at the distance of 40 cm from each other with 783.20 Kg yield. The information accruing from this study showed that in areas where aphids problem is endemic, narrow rows spacing would tend to increase aphids population.Therefore, the row-to-row spacing not less than 30 cm with nine cm plant-to-plant distance is recommended in oleiferous brassica especially canola crop, as a component of integrated pest management tool to culturally control of aphids.

In order of carry out of faunistic study on mites and their abundance in stored wheat in Tehran, Karaj and Varamin, mite samples were collected from stored wheat, straw and dust in silos, flour-mills and mills during spring 2005. Twenty-five species belonging to 11 families and three orders including Astigmata, Prostigmata and Mesostigmata were identified, of which five species, viz. Aleuroglyphus ovatus (Troupeau), Tyrolichus casei (Oudemans), Acarophenax tribolii (Newstead & Duvall), Cheyletus eruditus (Schrank) and Erythraeus garmsaricus Saboori et al., are newly recorded from wheat stores of Tehran province. The most abundant predator and pest mites were Acaropsellina sollers (Kuzin) (Cheyletidae) and Acarus siro (L.) (Acaridae), respectively. The highest observed number of mites was, in sequence: Tehran Silo, Ard-Iran flour-mill and Jafar Joshaghani mill.

Apterous viviparous female of Dysaphis inulae sp. n. living on Inula britanica and D. lappae cynarae (Theobald) living on Silybum marianum is described and newly recorded from Iran, respectively.The latter aphid species is redescribed and an identification key for the species of Dysaphis Boerner on Asteraceae is also presented.

L. was collected from Ardebil, Guilan and Mazandaran provinces to assess the fumigant toxicity of its extract and determine LC50 and LC95 values for different developmental stages of Callosobruchus maculatus F. and Tribolium confusum J. du Val. It was extracted by solvents including methanol and dichloromethane. Eggs, larvae and adult of both species were exposed to dichloromethane and methanol extracts of O. vulgare for 72 hours. LC50 and LC95 values of dichloromethane extract were calculated 2084.51 and 4991.24 ml/l air for adults of T. cofusum, and 2282.80 and 6684.71 ml/l air for adults of C. maculatus, respectively. Also, LC50 and LC95 values of methanol extract were 1726.57 and 5395.60 ml/l air for adults of T. cofusum, and 2040.88 and 5607.77 ml/l air for adults of C. maculatus, respectively.

The sunn pest, Eurygaster integriceps Puton, is the most important pest of wheat and barley in most wheat producing regions of Iran, including Lorestan province. The pest overwinters under bushes in mountains and returns to wheat fields in the next spring. Study of spatial distribution of overwintered sunn pest (OSP) in rainfed wheat fields using two quadrate sizes (50×50 cm2=0.25 m2 and 70.71×70.71 cm2=0.5 m2) and their conformity with negative binomial distribution, showed a dispersion pattern of aggregation. In this study, a sequential sampling plan (Wald’s method) was presented by use of 1.5 OSP/m2 as an action threshold and 1.05 OSP/m2 as the safety level, and estimating the common K (Kc) for the both sizes of quadrates in 2004 and 2005. Two sizes of quadrates were used as sample units to estimate densities and dispersion patterns of the pest populations. The decision lines, y=0.32x±7.62 and y=0.63x±7.44 were calculated for 0.25 and 0.5 m2 quadrates, respectively. The operating characteristic (OC) and average sample number (ASN) curves indicated that low numbers of samples are required for control decision making when the population densities are either low (less than 0.22 and 0.44 OSP/q for small and large quadrates, respectively) or high (more than 0.45 and 0.89 OSP/q for small and large quadrates, respectively). However, the number of samples required will be high when the population density is nearly medium and at the point of inflection of OC curve (0.32 and 0.63 OSP/q for small and large quadrates, respectively).

Spatial distribution different natural enemies of the cotton aphid, Aphis gossypii Glover, was determined by fitting data to either Poisson (random) or negative binomial (aggregated) distributions and calculating dispersion indices, during 2002 and 2003 growing seasons in cotton fields of Gorgan, northern Iran. Based on R2 and p-values of regression analysis, for most of the natural enemy groups, Taylor’s power law generally provided a more adequate description of variance/mean relationships than Iwao’s patchiness regression model. Natural enemy populations, especially parasitoids, cecidomyiid species and coccinellid eggs, were aggregated during most of the growing season, and negative binomial models generally fitted the data sets better than the Poisson series in cotton fields. Percentage fit for some species such as larva and adult stages of chrysopids, adult stages of Coccinella septempunctata L. and Scymnus spp., and spider species, showed a distinct tendency to the Poisson distribution and low values of Taylor’s b index. There were no significant relationships between k (a measure of the amount of clumping in negative binomial distribution) and mean values, indicating the existence of a common k for the most of the natural enemy groups. These results can provide a reliable basis to develop proper sampling plans for estimating or classifying natural enemy populations in cotton fields of Gorgan.

Herbivore induced plant volatiles (HIPVs) can be produced by herbivores attack that affects on ecology and behavioural responses of natural enemies. Damaged plant attracts natural enemies due to change the volatile compounds constitute by an active biochemical processes. This study was conducted to test whether green bean HIPVs, as well as odours emitted directly from spider mites influenced the orientation behaviour of the predatory mirid bug, Macrolophus caliginosus Wagner. A Y-tube olfactometer was used to determine the attraction of the predator to herbivore induced volatiles from Tetranychus urticae Koch infested green bean plants over clean plants and to direct prey odours over clean air. The mirid bugs showed a stronger response to odours from infested plants than to those from clean plants. The mirids, however, did not seem to exploit odours emitted directly from the preys themselves. Compounds of infested and uninfested plant volatile blends were also determined by gas chromatography-mass spectrometry (GC-MS). Of a total of 36 infested green bean compounds, 29 compounds are emitted either by uninfested green bean. The results from GC-MS analysis confirm that volatile blends emanate from bean infested by spider mites is different to clean bean and the attractiveness of predatory mirid bugs to infested plant over clean bean is probably resulting in these differences.

Biology of Scaeva albomaculata (Macquart) was investigated on Brachycaudus amygdalinus (Schouteden) as a prey in laboratory conditions (20±2 oC and 45±5 % RH). Developmental times were 2.57±0.098, 1.57±0.072 and 4.3±0.085 days for the first, second and third instar larvae, respectively.The first and second instar larvae of syrphid fly consumed 21.7±0.87 and 35.1±1.25 the first and second nymphs, respectively, whereas the third instar larvae consumed 613.2±18.43 alate nymphs of B.amygdalinus. Adults of syrphid flies mostly emerged in early morning. Population dynamics of eggs and larvae and larval behavior were studied from emergence time (early March) to late October during 2001-2004 in two regions (Shahrekord and Shorab-Saghir). In natural conditions, the larvae that completed their growth left the almond twigs and pupated at a depth of 3-5 cm below the soil surface. The most important natural enemies of S. albomaculata larvae were identified as Diplazon laetatorius (Fabricius) (Hym.: Ichneomonidae) and Dotriothorax sp. (Hym.: Encyrtidae), which parasitized 34% and 5% of the larvae, respectively. These parasitoids emerged from pupae of S. albomaculata. Another mortality agent was an unknown pathogen, which caused the body content of the pupae to become a milky liquid.

Among the sunn pest populations, melanic phenotype of Eurygaster integriceps Puton is a distinct colour morph. A set of experiments were performed to examine possible differences between typical and melanic phenotypes of E. integriceps using overwintered adults collected from Gharah-Aghaj mountains (southeast of Tehran). Melanics consisted only 0.3% of the total population. The laboratory conditions were: T=24±1 oC, RH=60-70% and L: D=16: 8 h. Incubation period and five nymphal instars were 7.24±0.01, 4.14±0.02, 7.97±0.04, 6.63±0.04, 7.21±0.04 and 11.32±0.07 days in melanics, and 7.19±0.01, 4.14±0.01, 7.83±0.03, 6.19±0.02, 6.88±0.03 and 10.63±0.04 days in typicals, respectively. Melanics with 44.13±0.15 days had a longer developmental time than typicals with 42.33±0.10 days. This difference was mainly related to the feeding instars. Durations of pre-oviposition period, oviposition period and post-oviposition period in both groups were not significantly different: 10.3±0.8 days, 34.1±6.4 days and 5.9±1.9 days for melanics, and 10.2±0.8 days, 34.9±6.4 days and 4.0±1.4 days for typicals, respectively. In general, reproductive table parameters showed an inferior performance of melanics compared to the typicals. There was no clear relationship between female body weight and total number of eggs in both groups. Stable population parameters (mean±SE) of doubling time, Dt (days), mean generation time, T (days), net reproductive rate, Ro (female eggs/female), intrinsic rate of increase, rm (1/time) and finite rate of increase, l (per day), were 13.68±0.68, 60.69±1.71, 20.67±4.09, 0.0502±0.0025 and 1.0515±0.0026 in melanics, respectively. The respective values for typicals were 12.79±0.50, 62.60±2.13, 29.11±5.26, 0.0541±0.0021 and 1.0556±0.0022. None of these parameters were significantly different between two groups. Relatively inferior characteristics of melanics observed in this study need further experiments on their successive generations to elucidate reproductive performances of the group.