زيست شناسي و توزيع فضايي زنبور برگخوار رز در گيلان

Biology and Spatial Distribution of Rose Sawfly, Arge rosae (Hym.: Argidae) in Guilan

Biology of rose sawfly, Arge rosae was studied at 25 - 28 °C, 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 t 0.27 day longevity laid 75.66 ± 3.5 eggs. They were able to lay eggs parthenogenetically hut all offsprings 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. Taylorʹs power law model described data well (R2 = 0.6581) and the index of aggregation was greater than 1 (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.