| Investigation of the occurrence of yellow peach borer, Conogethes punctiferalis (Guenée), on maize, Zea mays L. , grain sorghum, Sorghum bicolor (L.) Moench. and sunflower, Helianthus annuus L. at three different seeding dates. The threshold development temperature and effective accumulated temperature, diapause, cold hardiness and death rate of overwintering larvae were also studied. The main results are as follows:1. Preliminary studies on occurrence of C. punctiferalis in maize, grain sorghum and sunflowerIt was investigated the parts which of host plant of maize, grain sorghum and sunflower that the C. punctiferalis like to oviposit on and numbers of eggs laid during different developmental stages, and also the numbers of larvae and injured rate before harvest. Female moth laid eggs in maize, grain sorghum and sunflower field from July to October in Beijing and Langfang, Hebei Province,and the generations were overlapped. Female laid eggs mainly on tassel, ear and sheath of maize during tasseling, blister and milking stages. Female moth mainly laid eggs on bract, nectar gland, sepal and tubiform floret of sunflower, which could last for a long period. As to the three crops which were seeding in the same date, the larvae do the most serious damage to sunflower, and then grain sorghum, the maize was the minimum. Also, the population of yellow peach borer in different hosts were related to the seeding dates. In addition, the borer mainly injured the kernels and cob of ear of maize, and occasionally boring in the stalk, and the larvae feed on grains in sorghum panicles or suuflower head, sometimes the sorghum panicles or the sunflower seeds were webbed with silk and frass, and when the grain sorghum and sunflower begin to mature, but the larvae seldom bore into the stalks of sorghum or sunflower.2. Determination of threshold temperatures and effective accumulated temperatures for C. punctiferalisThe threshold temperatures and effective accumulated temperatures for C. punctiferalis were tested at the following five constant temperatures (16 oC, 20 oC, 24 oC, 28 oC and 32 oC). The results showed that threshold temperature was 8.39±1.45oC, 7.34±1.96oC, 11.31±2.56 oC, respectively. The effective accumulated temperature was 71.24±6.24, 383.73±90.71 and 126.57±26.53 day-degrees, individually, for egg, larvae and pupae of C. punctiferalis.3. Overwintering ecology of C. punctiferalisThe larvae of C. punctiferalis for overwintering are diapaused, and diapause termination does not need the low temperature treatment.4. Study on the supercooling point of overwintering larvae and pupae of C. punctiferalisThe effects of host plants, larval weight, sex and also the different sampling time, on cold hardness of overwintering larvae of C. punctiferalis were compared by measuring the supercooling points (SCP) and freezing points (FP). The results showed that the mean SCP and FP of overwintering larvae feeding on different hosts were not significantly different. No significant correlation was observed between the SCP and larval weight, and were also among the larvae feeding on different hosts of maize, sorghum and sunflower. The mean SCP and the FP was significant between the overwintering larvae collected in September and October, respectively. No significant difference was found between the male and female larvae. The SCPs of 5 geographic populations (Beijing,Langfang, Jiaozhou, Anqing and Huaihua)from maize plants were also tested without significant differences.5. Studies on the winter mortality and biology of overwintering larvae of C. punctiferalisThe winter mortality of the overwintering larvae of C.punctiferalis is very high, and the most important key factor is the low temperature.
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