Temperature tolerance was investigated in nine populations of Plutella xylostella Linnaeus from tropical and temperate regions of Asia. At all rearing temperatures between 15 and 35 degrees C, no clear differences were observed in female egg production or larval development between tropical and temperate populations. Thus, tropical populations did not show a high-temperature tolerance superior to that of the temperate populations. In all populations, the net reproductive rate (number of new females born per female) largely depended on the number of eggs laid per female, and egg production significantly decreased with increasing temperature (P < 0.001). Larval developmental rate also showed a significant positive correlation with temperature (P < 0.001). Per cent hatch of eggs and larval survival did not show a significant correlation with temperature: hatching was constant between 15 and 32.5 degrees C, but considerably lower at 35 degrees C. Larval survival was similar between 15 and 30 degrees C, appreciably lower at 32.5 degrees C and declined to 0% at 35 degrees C. Based on these results, environmental conditions under which P. xylostella can maintain a high population density throughout the year in tropical and subtropical regions are discussed.
To evaluate the effect of pollen released from transgenic insecticidal corn on non-target lepidopteran insects, corn pollen deposition density on the leaves of sunflower and black nightshade was measured near a cornfield. At 12 d from the start of anthesis, the highest cumulative pollen density on leaves was approximately 160 grains per cm 2 at 1 m from the edge of the cornfield, falling to 20 grains at 5 m and less than 10 grains at 10 m. The pollen density calculated using a mathematical model in a previous study evidently had overestimated values. To evaluate precisely the effect of corn pollen expressing Bacillus thuringiensis (Bt) endotoxin (Cry1Ab) on the survival of lepidopteran larvae, we improved the bioassay methods using the pale grass blue, Pseudozizeeria maha, the leaf disc of the wood sorrel, Oxalis corniculata, and transgenic Bt corn (Event-176). When the surface of the leaf was pretreated with a small amount of 80% acetone solution, the preselected pollen dose was successfully applied onto the leaf disc. Larval survival of P. maha was significantly affected at pollen density of more than 20 grains per cm 2 on the leaf disc. It is unlikely that pollens from Bt corn expressing Cry1Ab have wide-scaled deleterious effects on non-target P. maha near cornfields, because of low pollen deposition dose on the leaves.
Plutella xylostella in the temperate zone shows a clear seasonal change in adult body size. In the laboratory, large and small moths were produced during immature stages at 15°C and 25°C, respectively. These moths were then used to evaluate longevity, age‐specific flight ability, flight ability of mated and unmated females, and the influence of flight experience on the subsequent reproductive success. The large moths lived longer and displayed a greater flight ability over 3 weeks. Irrespective of body size, unmated females flew for a longer time than mated females, and flight experience affected their subsequent reproductive success. Females of both sizes mated and laid eggs soon after emergence, without any obvious pre‐reproductive period. More flight experience did not delay oviposition, but did reduce egg production. It is likely that large moths with a longer adult life span and greater flight ability are better fitted for long‐distance flight and more fecund than small ones. These experimental results may explain why long‐distance migration of P. xylostella is mostly seen during cool seasons, when relatively large moths with long forewing appear in the field.
The effects of temperature, age and mating status on the flight activity of Carposina sasakii were examined using a flight mill system. Flight measurements were carried out for 24 h under dark conditions. No significant difference was observed for the total flight duration of 2-day-old moths at temperatures between 14 and 26°C. The proportion of individuals that did not fly at all was less than 10% at 14 to 29°C, whereas the proportion at 11°C was 67% in females and 83% in males. Total flight duration did not show a significant difference through the ages from 1 to 7 days in either sex. Two-day-old females flew significantly faster than 1-day-old females, whereas flight speed did not differ among ages in males. Flight activity of females was similar to that of males and remained high even after mating. These results are discussed in relation to the control of C. sasakii by mating disruption in the apple orchards.
The adult longevity, reproductive period, age-specific flight activity, suitable temperature range for flight, and effect of adult feeding on the subsequent flight of Spoladea recurvalis Fabricius were studied in the laboratory. Flight activity was evaluated using a tethered flight-mill. Females had a pre-oviposition period of 3 d, and continued to lay eggs up to 20 d post-emergence. Females flew longest between 17 and 23°C, and 10% of females were capable of continuous long-duration flight even at 12°C. Females flew more actively in their pre-oviposition period, but the females' reproduction period was not clearly separated from their active flight period. The mating status of females had no clear effect on their flight activity. Uptake of honey solution (nectar) was essential for adult survival, and the survival rate was reduced markedly when honey solution was withheld. When honey solution was supplied after 5 d of starvation, the overall longevity of the moths was the same as that of the moths continuously supplied with honey solution since emergence. When honey solution was removed even for 1 d, subsequent flight activity was significantly depressed. Thus, the prediction that the strong propensity for long flights by S. recurvalis may be derived from their dispersal flights to seek flower nectar was not supported from the present experiment.
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