Journal of Entomological Society of Iran
Year:2003 | Volume:22 | Issue:2|Papers Count:5

In order to study biology and seasonal parasitism of alfalfa weevil, Hypera postica by Bathyplectes Spp. wasps, alfalfa fields were visited weekly and sampling was done by a sweep net (30 cm in diameter) in Chahar Mahal Va Bakhtiari province in 1997 to 1999. Bathyplectes curculionis Thomson and B. anurus Thomson were collected from alfalfa fields. B. anurus was the dominant species. In Shahre-Kord climatic conditions adult alfalfa weevil over wintered in soil and litter. Adults of B. anurus emerge from over wintered cocoons in the spring and prefer to parasitize third and fourth instars larvae of alfalfa weevil. One parasite consumes a single H postica larva and ultimately emerges to spin a white-banded, dark brown cocoon, usually inside the weevils own, netlike cocoon, and enters diapause until the fall. After pupation, it changes into adult and remains in diapause in the cocoon until the next spring. Maximum and minimum percentage parasitism in 1998 were 63.5%in Dezak area and 1.25% in Ardal area, respectively and also in 1999 were 57% in Boldagi and 9.8% in Juneghan area respectively. Results showed that both H. postica and B. anurus were univoltine in Shahre-Kord region.

Effects of two host plants, alfalfa (Medicago sativa L.) and locust tree (Robinia pseudacacia L.) and constant temperatures 16, 20 and 30°C were studied on alfalfa black aphid in growth chamber conditions (55±5% R. H., L: D 14: 10 H. and mentioned constant temperatures) during 2000 - 2001 in Kerman, Iran. The objective of this investigation was to identify growth rate of aphid population in various temperatures and host plants. The results indicated that net reproduction rate (Ro) of aphid in 16±2°C on alfalfa and locust tree was 40/2992 and 34/16242 respectively. Gross reproductive rate (GRR) was also 66/3965 and 72/0972 respectively. In 20±2°C, Ro and GRR on alfalfa were 93/2996 and 100/51 and on locust tree 76/514 and 83/34 respectively. In 30±2°C these factors were 34/9053 and 50/9877 on alfalfa and 4/4298 and 5/43 on locust tree respectively. The stable population parameters of alfalfa black aphid include intrinsic rate of natural increases (rm), finite rate of increases (le), intrinsic birth rate (b), intrinsic death rate (d), doubling time (DT), mean generation time (T) and rate of weekly multiplication (rw) which were calculated in mentioned temperatures and host plants. The (rm) and (T) in 16, 20 and 30°C were 0/1859, 19/8834; 0/2865, 15/832 and 0/4462, 7/962 on alfalfa and were 0/1930, 18/2960; 0/2902, 14/946 and 0/1596, 9/3255 on locust tree respectively. The results of this investigation indicated that temperatures and host plants had considerable effects on growth parameters of alfalfa black aphid.

Antixenosis is defined as a resistance mechanism affecting pest establishment on their host plants. In this study, antixenosis mechanism were evaluated in twelve poplar clones belonging to four species namely, Populus alba, P. nigra, P. deltoides and P. x. euramericana against poplar woolly aphid Phloeomyzus passerinii Sign. Poplar cuts of each clone, placed in plastic jars containing water, were rest in growth chamber. The length and diameters of poplar cuts were 20 and 1-1.5 centimeter, respectively. A single cut of every poplar clones along with an aphid - infested cut were wrapped together with an elastic string. The bunch was then placed in controlled conditions of 60-70% RH, 20-22 Celsius and 16: 8 L: D photoperiods. After two days, the infested cut was taken away from the bunch, and aphid numbers were counted on each single cut. The cuts were placed together for second time, and the numbers of aphids were recorded on a two-day interval basis. Subsequently, the experiment was carried out with 18 replications. Statistical analysis revealed a significant difference (P<0.01) in aphid numbers among the clones. Number of aphids settled on Populus alba 58/57 (0.31 aphid/cut) was significantly less than the other clones. Consequently, a conclusion can be reached that this clone might be an immune poplar against the pest. Other than Populus alba 58/57,a number of clones including: Populus nigra 62/149; Populus nigra 62/72; Populus x euramericana 214; Populus deltoides 72/51 and Populus nigra 62/140 exhibited significantly low aphids density (2.54-4.91 aphid/cut). Therefore, it could be concluded that these clones contained a high level of antixenosis resistance. In contrast, aphid number recorded on P. nigra 56/72 (25.98 aphid/cut) was higher than the others, showing the most susceptible clone to P. passerinii establishment.

Poplar leaf weevil Platymycterus marmoratus Fst. is one of the most important pests of poplar plantations in Guilan province. High density of adults were observed on different poplar clones and species in Safrabasteh research station in northern Iran. This study was carried out during 2000-200 I in Safrabasteh poplar nurseries. This assessment is a preliminary study to find out the resistance of poplar clones against this pest. The treatements of the experiment included: 9 clones of P.euramerican and P. delta ides species (Populus deltoides Marsh. And Populus x euramericana Dode) which previously had demonstrated better growth than the others as well as P. caspica Bornm as a native species. 1440 cuttings from ten treatments were planted in 3 replicates in randomized complete block design (RCBD). Based on the results obtained for Astaneh- Ashrafieh, poplar leaf weevil adults appeared since mid May till late September with the peak of population in late June to first of July. The statistical data analysis of variance on abundance of adults weevil in MSTATC software, showed a significant difference (P<0.0001) between poplar species and clones. P. e. costanzo and P. cas pica demonstrated the most and the least density weevil, respectively, using LSD test method.

The results of laboratory studies on the biology of Habrobracon hebetor Say (Hym.: Braconidae) [at: 28±0/5 °C, 65±5% RH, 16L:8D, photoperiod Host: larvae of Galleria mellonella) indicated that this parasitoid completed its development in 12/09 days (egg 1/77±0/03 days; larvae 3/43±0/04 days and pupa 6/89±0/05 days). Newly emerged female parasitoid responded well to the host larvae. The adult lived longest when provided with both honey and water, without food they survived less than 5 days. Results showed that during the oviposition period deposited eggs all day and night long. There were no significant difference, in reproduction and longevity between virgin (74/4±11/27 and 16/67±1/02) and mated (84/4±10/36 and 16±1/4) females.