Research On Life Table Of Laboratory Population And Wing Dimorphism In Alfalfa Weevil, Hypera Postica (Gyllenhal)

Alfalfa weevil, Hypera postica (Gyllenhal) is one of most important pests on alfalfa. Experiments were carried out to construct life tables of lab populations of H. postica at different temperatures, to study the cold hardiness and energy chemicals associated with wing-dimorphisms, and a field survey was madeof wing-dimorphisms as associated with ecological factors. The main results are as follows: Life tables at different temperatures and larval densities were studied in laboratory. Development rate increased with temperature from 18℃to 30℃as fitted by Logistic models, and survival curves were of'Price A'pattern for the temperature regimes examined. The generation survival rate (S) and population trend index (I) could be described as function of temperature (t) as in parabola curves: S =–0.439 1 t~2 + 23.387 t– 265.24 (R~2 = 0.99), I =–2.76 t~2 + 140.97 t– 1 628.6 (R~2 = 0.94). The optimal temperature for development and reproduction was 25℃to 27℃. A decreasing relationship was exhbitted between density (from 1 to 30 per glass tube) and a variey of developmental performances, including development time of the 3rd, 4th instar larvae and pupa, pupe weight, survival rate from larvae to pupae (with the exception of that at 30 insects per tube), and fecundity. The survival rate from 3rd instar larva to adults (S), population growth index (I) could be fitted as function of larval density (x) as the covariate in parabola curves: S =–0.030 1 x~2 + 0.215 2 x + 49.536 (R~2 = 0.96); I = 0.319 8 x~2– 15.92 x + 218.69 (R~2 = 0.98). Field survey showed that the time of fields where alfalfa was growing had an obvious influence on density and dimorphism. The highest density and proportion brachyptera-form were observed in alfalfa fields where alfalfa was continuously planted for five or six years. The generic experimenta showed that the proprotion of brachypteranpupa in F1 was 94.1% or 51.1% when the parents were both of normal wing (N♀×N♂) or of brachyoteren wing (V♀×V♂). Wing dimorphism obviously varied as affected by temperature,density and host quality.The brachypteran morph increased with temperature and density by as high as 47.7% or 48.3% at 30℃or 20 t/tube. The population from feeding on stem produced higher proportion of insects with normal wing than leaf-feeding population 58.2% to 44.9%. The results of chemical analysis of body tissues showed that lipid content of brachypteran pupae was significantly higher than that of normal-winged pupae at temperatures 22℃to 30℃and all density treatments.There was a gerat difference between the protein content of normal and brachypteran pupa, while glycogen content in is higher in the normal wing-morph than in brahcypteran pupa.Studies of cold hardness showed that there weremarked differences between larval instars. Adults had lowest supercooling point at -20℃, and followed by pupae and 3rd-4th larvae. There were no significant differences between pupae and 3rd-4th larvae in suppercooling points and freezing points.