Journal of Entomological Society of Iran
Year:2001 | Volume:21 | Issue:2|Papers Count:8

Oviposition preferences based on leaf age, height, surface orientation, and presence of insecticide residues were determined for Bemisia tabaci (Gennadius) on Lantana camara, at 25 ±2°C, 70 - 90% RH, and 14: 10 (L: D) photoperiod. Whiteflies preferred young leaves located in high level to ones in lower and old leaves, and also adaxial leaf surface to adaxial for oviposition, although this preference was overridden by reversing normal leaf position, that is, placing old leaves high and young leaves low. Preference for the adaxial leaf surface did not increased following reversing orientation, leaf age and height did not significantly affect sex ratio and pupal size (body length), but affected longevity, survival and fecundity, which were fewest on lower and old leaves. Effects of 3 insecticides including, deltamethrin, pirimphos - methyl and Nicotiana tabacum extract residues on oviposition were studied in 3 intervals of2, 24, and 72 h after treatment by exposing whiteflies to insecticide-treated leaves. The effect of deltamethrin on ovipositional performance reduction was higher than other insecticides in all intervals, but through the insecticides residue reduction, average number of egg deposited increased in all treatments except for controls. Interactions among leaf age, leaf heights, and insecticide residue were studied on egg deposition. The effects of leaf age and leaf height on oviposition were overriden by repellency to residues of deltamethrin and pirimphos - methyl.

Biology of rose saw fly, Arge rosae was studied at 25 - 28 QC, 70-75% of relative humidity and room light condition. Spatial distribution of sawfly population was also studied by weekly sampling of larvae and adult insects at the college of agriculture, Guilan University Rasht, Iran in 1998. The yellowish coloured females after emerging from overwintering pupae mated and start oviposition. They laid their yellow coloured eggs in slits (20.4±2.72 mm long) cut in the young shoots. Each slit contained 13.5±2.02 eggs. There is a positive correlation between length of slit and number of eggs it contains. Egg slit changes gradually in colour and turns into brown or black. They are easily found and recognized on the shoots and branches of the host plant. Larval development takes 23.7±1.5 days. Early larval instars appear gregariously on the host plant and feed on leaves and flower buds. As the dark green larvae grow older, they feed individually. Due to intensity of pest attack, apical shoots and branches were free of leaves and a considerable damage was caused to flower bearing branches. The mature larvae spin two inner and outer tough silk cocoons and turn into prepupa at first and then to pupa. This took 13.3±1.6 hrs. Pupation lasted 14.2±0.88 days. Female adults with a 5.8±0.27 day longevity laid 75.66±3.5 eggs. They were able to lay eggs parthenogenetically but all off springs were males. The sex ratio (male: female) is 0.35±0.06. Adult insects appear in the late April. They can be found individually on the rose and briar foliages. Taylor’s power law model described data well (R2=0.6581) and the index of aggregation was greater than I (b=1.8003). This indicates that the larvae are aggregated on the host plant and there is a close relationship between oviposition sites and larval feeding place.

The capability of Sunn pest to synchoronize its life span with the phenological stages of wheat and barley was evaluated in experimental field in Varamin Agricultural Research Station for two consecutive years (1996-1998). The experiments were carried out in the form of the two factors complete randomized block design with 3 replications. The first factor was sowing date and the second one was wheat and barley cultivars. Additional experiments carried out in the farmer’s field conditions. The results are as follows: I. In barley field, Sunn pest’s life cycle was completed 7-10 days earlier than that in the wheat fields and Sunn pest synchronized its life cycle with phonological stages of hosts. 2. In barley fields 75% of the pest population were able to complete their life cycle on harvesting time, but at the same time wheat plants were at the waxy stage and only 27% of the individuals were in adult stage. 3. At harvest the weight of males and females was found to be significantly higher in wheat than that in barley and a significant correlation of the weight of newly emerged adults with plant growth span. 4. The earliness of wheat did not significantly affect sunn pest population and adults weight reduction in barley fields could not affect the pest population because they can fly to neigh boo ring wheat fields and complete their feeding cycle. Therefore control of this pest in barley fields should not be overlooked.

Entomopathogenic nematodes in the families, Steinernematidae and Heterorhabditidae are obligate parasite of many insects and two species Steinernema sp. and Heterorhabitis bacteriophora have been used efficiently for biological control of pests. In order to evaluate the efficacy of entomopathogenic nematodes collected from Polyphylla olivieri larvae in 1998-1999, field expriments arranged in a completely randomized block design. Steinernema sp. and heterorhabditis bacteriophora, nematodes were applied with initial inoculum levels of 0, 2.5×105, 5×105 individual per m2. The experiments were conducted in 6×15 cm pots containing a sandy-loam soil mixture. Nematodes at the mentioned rates suspended in 20 cm3 distilled water were sprayed on the surface of the soil in the pots. After releasing a third instar larvae in each pot, they were covered with gauze. After 14 days dead larvae were counted in the pots. The results indicated that steinernema sp. and H. bacteriophora at the rate of 5×105 individuals per m2 were able to parasitize 33.33% and 45.37% of the pest larvae respectively.

The elm leaf beetle is one of the important pests of elm trees. This insect has three instars. Under laboratory condition (25±1°c, 60±5 RH and 14:10 L:D) means of incubation period, developmental time of 1st 2nd and 3rd larval instars, and total larval duration are 5.23±0.05, 4.34±0.19, 4.37±0.0 1 and 13.49±1.56 days, respectively. Means of prepupal and pupal periods are 2.06±0.03 and 4.71±0.03 days, respectively. Means of preoviposition and oviposition period, and fecundity rate in mated and virgin females are 7.62±0.4 and 8.9±0.72, 13.42±2.27 and 10.45±1.25 days, and 174.3±48.3 and 113.1±24.1 eggs, respectively. Mating did not have significant effect the preoviposition duration in mated female, but was effective on the length of oviposition period and fecundity rate. The female longevity in paired and single rearing were 25.68±3.2 and 24.2±1.58 days respectively. Mean of daily feeding in larval instars are 7.56±0.41, 18.78±3.5 and 89.11±7.03mm2 of elm leaf and for male and female adults are 60.84±6.3 and 95.92±15.16 mm2 respectively.

Mulberry thrips Pseudodendrothrips mori Niwa is an introduced pest of mulberry in Iran. This insect widely attacks both native and hybrid varieties and this lowers the economic value of the leaves consumed by silk- worm. In order to investigate the biology of this pest in laboratory, a culture was established by releasing first and second larval instars on leaves whose petioles were inserted to wet cotton swabs placed inside disposable jars 5.24×5.5cm. capacity inside an incubator set at 25±1C°, relative humidity of 75±5% and photoperiod of 14:10h light- dark respectively. To determine seasonal variations in population of the pest in different generations, sampling was done every five days from first half of May- when wintering adult insect appeared - through the second half of October, when its population declined dramatically. Samplings, were performed in varieties of Shin Ichinoise, Kenmuchi, and Ichinoise, simultaneously. The results indicated that the life- cycle of this insect took 29.95 days from egg to adult in lab condition. The sexual ratio was 6.7: 1. The insect over wintered as adults, and had four generations in a year. The highest peak of first larval population in the month of August in Shin Ichinoise were 8.45 and 10.62 in each sample unit, that of Kenmuchi is 9.05 and 12.38 and that of Ichinoise were 5.89 and 16.05 for the years 2000-2001 respectively. The population of second instar and adult were relatively lower in all the generations.