| Summary: | 碩士 === 國立屏東科技大學 === 熱帶農業暨國際合作系所 === 98 === Life history of Leptocoris abdominalis (F.) was investigated by feeding bugs with seeds of Taiwan golden rain tree (Koelreuteria formosana Hayayta) under different temperatures, namely 15, 17, 20, 25, 28 and 30 oC, and room temperature (24 ± 4oC). The results showed that it takes 51.7 ± 5.7 days for eggs developing to adults and sex ratio of female:male was 1:1.45. Developmental duration for each stage was about 6~8 days with eggs duration being longer (11 days) at room temperature. The body color of new hatched nymph was bright red, and black wing-buds appeared on the back of third instar nymph. The genitalia of adults can only be observed after their emergence. The longest egg duration was 18.7 ± 1.6 days at 15oC while the shortest was 5.2 ± 0.8 days at 30oC. However, there was no individual can survival to adult at both 15 and 30oC. For other 4 tested temperatures, the longest time needed to develop from eggs to adults was at 17oC (109.4 ± 44.3 days) and the shortest one was at 28oC (34.9 ± 13.9 days). Thus, the most suitable temperature for rearing L. abdominalis is 20 to 28oC and the higher the temperature is, the shorter generation time they have. The longevity of female is longer than that of male. The sex ratio of female and male ranged from 1 : 1.2 to 1 : 1.5 at temperatures of 17, 20, 25, and 28oC. The critical developmental temperature (development zero) was estimated as 13.6 ± 2.2oC and the Degree-Day accumulations for this bug was 420.3 ± 92.3 DD. Mating tests showed the highest mating frequency occurring when put 1 female and 2 males together. Female seems play the leading role and decide whom it wants to mate. Oviposition tests showed that females prefer laying eggs on gauze, following on capsule leaves in laboratory test. It coincided with the observation of bugs prefer ovipositing on coarse walls, tree bulk, and capsule leaves in the field. The comparison of eggs produced between single pair and cluster treatments showed cluster treatments have more eggs produced (23.9 ± 5.6 eggs/♀) than that of single pair. Although number of eggs produced by single pair can be as high as 60 eggs/♀ while some of them did not lay any eggs. Hatching rate of eggs was highest (93.0 ± 0.8%) at 28oC and which almost the same as that at room temperature (88.5 ± 5.4%). The lowest egg hatching rate was 45.0 ± 1.3% at 15oC. The higher the temperature is, the higher the hatching rate is. However, the hatching rate decreased when temperature higher than 30oC. L. abdominalis uses the seeds of Koelreuteria formosana as its major food and its population is changing through the seasonal phenology of this tree. The population peak of L. abdominalis is reaching at the time of fruits dropping in each year. When new buds germination during March and April, the bugs always leave the trees and alternatively feed on the fruits of balloon vines (Cardospermum halicacabum L.). The population of L. abdominalis dramatically decreased during this period. Clustering behavior observation showed that the first to forth instar bugs are significantly clustering together in the field. The fifth instar and adult bugs always act independently. Young nymphs prefer to cluster at the basis of trees while aged nymphs and adults prefer stay on trunk and leaves of tree. Population of bugs was found positively correlation to seed number. Moreover, piercing and sucking of L. abdominalis on K. formosana did not cause the death of tree, on which new buds still can germinate at March and April for each year.
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