A field study of potential ecological costs of resistance by ‘stem ducking’ in tall goldenrod,Solidago altissima

Culex quinquefasciatus Say (Diptera: Culicidae) is an abundant urban mosquito that is the vector of filariasis. Breeding in septic tanks, where there are very high levels of bacterial food, it is likely to have a different reaction to crowding compared with other mosquitoes. To test for the presence and type of crowding effects, four larval densities of C. quinquefasciatus varying from 0.4 to 3.2 larvae ml^?1 of water were reared in tubes. Mortality was found to greatly increase at densities above 0.8 larvae, whereas larval duration increased even above 0.4 larvae ml^?1. Changing the water in the tubes daily gave a small (but significant) response in reducing mortality and larval duration. However, when larvae kept at a low density shared the same water with larvae at high density, there was no chemical influence on their growth rate and mortality. The effect of crowding was primarily due to physical disturbances between larvae. When larvae were kept at a high density in the same volume of water, but in shallow trays with a large surface area and therefore much less contact between them, mortality was the same as for the lowest density. There was still, however, a significant increase in larval duration from 8.6 days at 0.4 larvae ml^?1 to 12.1 days at 3.2 larvae ml^?1. It is therefore concluded that the larvae respond to physical rather than chemical factors by prolonging larval development and having some increase in mortality.     

Interannual distribution of Pacific hake Merluccius productus larvae in the southern part of the California Current

The interannual distribution of early life stages of Pacific hake Merluccius productus , within the southern part of the California Current (32–23° N) from 1951 to 2001, was examined to describe the relationship between spawning habitat and environmental conditions. Mean annual abundance was affected by different factors along the west coast of the Baja California Peninsula. In the northern areas (Ensenada and Punta Baja), reduced abundance of larvae coincided with the El Niño and a North Pacific Ocean climatic regime shift, but in the southern areas (San Ignacio to Bahía Magdalena), the drastic reductions suggested a fishery effect for large adults of the coastal migratory population, starting in 1966. Two spawning stocks, coastal and dwarf, were evident in comparisons of latitudinal differences in occurrence of early stages and differences in temperature preferences that seemed to break at Punta Eugenia.     

中华真地鳖低龄若虫消化道结构及取食习性

解剖喂食不同饲料中华真地鳖EupolyphagasinensisWalker的低龄若虫 ,结果表明 ,低龄若虫消化道与成虫消化道结构相同 ,具有胃盲囊和马氏管 ;嗉囊、中肠和后肠分别占消化道总长的比率与中龄若虫相同 ,具有消化食物的能力。观察消化道各部分的滞留物变化情况 ,发现 1龄若虫取食了饲养土中的腐殖质和配合饲料 ,表明孵化后的若虫需要喂食以满足营养需要。     

Photoperiodic and Thermal Regulation of Development and Cold Hardiness in Larvae of the Clover Leaf Weevil, Hypera punctata

Effects of photoperiod and temperature on the development and cold hardiness were investigated in larvae of Hypera punctata. At a relatively low temperature (15°C), the larvae fed less and developed more slowly under a 12L:12D (SD) photoperiod than under a 16L:8D photoperiod (LD). SD larvae had lower gut weight against the whole body weight and lower supercooling point (SCP) than the LD counterparts for the same instar and same body weight. This was because the larval SCP is markedly affected by the quantity of the gut content. Laboratory experiments indicated that the low temperature mortality of this larvae occurred mainly due to freezing irrespective of the photoperiod and temperature, suggesting that the lower lethal temperature (LLT) depends on the supercooling ability of larvae. The SD larvae tended to have a lower SCP and hence a lower LLT than the LD counterparts at 15 or 10°C, unlike at 20°C. Thus, the slower larval development under SD conditions at relatively low temperatures may prevent larvae from reaching the later instar, which have a higher SCP and thus less cold tolerance, during the coldest season. The suppressed feeding activity under SD conditions would lower the SCP, thereby reducing the possibility of lethal tissue freezing. Such a photoperiodic and thermal regulation of the larval development and the supercooling ability appear to represent adaptive mechanisms for winter survival in this beetle.     

Some factors affecting spore replication of Nosema algerae (Microspora,Nosematidae) in Pieris brassicae (Lepidoptera)

The production of Nosema algerae spores was examined in Pieris brassicae. Spore replication in the insect host followed a logistic pattern of development. The factors studied which affected spore production and replication were dose level (5 × 10², 5 × 10³, and 5 × 10⁴ spores per insect), larval instar (fourth and fifth), and cool pretreatment of the insects at 20°C prior to inoculation compared with a constant temperature of 26°C. A three-way analysis showed the interactions between these factors. The logistic pattern of spore replication was used to explain the results.     

Methods of DNA extraction and PCR amplification for individual freshwater mussel (Bivalvia: Unionidae) glochidia,with the first report of multiple paternity in these organisms

Freshwater mussels (Unionidae) are among North America's most imperilled organisms. Mussels produce small larvae (glochidia) that parasitize aquatic vertebrates. We modified the Epicentre QuickExtract protocol to extract DNA from a single glochidium, collected directly from the marsupium of a female mussel, to use as template in polymerase chain reactions (PCRs). Yield per glochidium in a 40 µL extraction volume provided enough DNA for ≥ 15 PCRs per individual. We were successful in using this DNA for microsatellite analysis of up to three loci per individual. Offspring from one female showed evidence for multiple paternity within her brood. Our results are the first documentation of this phenomenon in freshwater mussels.