Arthropod Community In Alfalfa Seed Fields And Bionomics Of Bruchophagus Roddi(Gussakovsky)

Alfalfa is one of important crops in Xinjiang, west China. With its expansion of growing areas, alfalfa seeds are in increasing demand. Though arthropods are rich in diveristy, few studies have been undertaken to investigate arthropod community in alfalfa fields. We investigated the arthropod cummunity in alfalfa seed fields from first year after sowing to the next. And an obseevation of bionomics of the alfalfa seed pest, Bruchophagus roddi (Gussakovsky)(Chalcidae).Systematic sampling was conducted in alfalfa seed fields at Hutubi Ecological field station. We found256species, in58families of12orders, including insect natural enemies in21families of8orders, and pests in27families of7orders. Diversity indiceswere measured across the season. The results showed that arthropod species diversity was correlated to alfalfa phenology, field management, and climatic environment. In addition, diversity washigher in2010than in2011, which was attributed to application of chemical pesticides in2011.The study of biological characteristics of the alfalfa seed chalcid found that there were three generations in a year at Hutubi, and the third instar larvae overwintered in alfalfa seeds where about60%was in the3rd instar and about30%the2nd instar. The adults from overwinter had longer life span than those from the1st and2nd generations. Sex ratio was about1.33:1. Temperature influenced development and survival of overwintered larvae. When it was18.0℃in temperature (from October to December,2010) and over27.2%in RH, the overwintering larvae can complete develoment with low mortality by28%and pupated by3.85%. When it was below9.9℃(from Obtober to next Fabruary) and above40.1%in RH, the overwintering larvae delayed their development until next Fabruary with high mortality by34%and puped by5%. In whatever temperature adult emergence ceased in mid-June.By measures of larval head capsule width, four instars were determined. The head capsule width (y) was regressed against number of instar (x) by equation:y=0.0886x+0.0879, r=0.9983. Spatial distribution chalcid larvae was of negative binomial in the field.The alfalfa seed chalcid appeared from overwintering as adults in late May and early June. The1st generation adult appeared in early July, and the2nd generation adult in early August; itdisappeared in mid-September. The adult emergence peaked at12:00, and droped to minimum at00:00. Adults were actively flying at12:00, but inactive from22:00to00:00with only0.84%flying.The alfalfa seed chalcid selected9-day-old seed pods to lay eggs. More concentrated in the11～14days old seed pods. The1st instar larvae began to emerge from the13day-old seed pods; the2nd instar larvae began to emerge from the15-day-old seed pods; the3rd instar larvae more concentrated in the20～23days old seed pods; the4th instar larvae more concentrated in the22-26days old seed pods. Pupation occurred relatively from22to43days old seed pods. The pupae began to appear from22day-old seed pods, and the adult emerged within25-43days old seed pods.Trials of treatments of alfafa seeds with different temeorature and duration showed that larval mortality reached to100%under50℃or-30℃for one day, and the seeds were81.00%、93.33%in germination potential and68.33%、88.33%in germination rate, respectively.