On the bionomics of Lyctocoris beneficus (Hiura) and Xylocoris galactinus (Fieber) (Anthocoridae, Heteroptera)
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概要
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The present work was undertaken to make clear the bionomics of two Anthocorid bugs, Lyctocoris beneficus (Hiura) and Xylocoris galactinus (Fieber), with special reference to the possibility of utilizing these species as the controlling agents against the rice stem borer. Both species are commonly found in the giant straw piles, warehouses and also in the field. The rearing of two species was conducted in the laboratory under the constant temperature conditions of 25℃, 30℃ and 33℃. The lengths of egg, nymphal and adult stages at 30℃ are 4, 20 and 31 days in L. beneficus and 3, 13 and 26 days in X. galactinus. Both species have 5 nymphal stadia. The egg production varies a great deal with the individuals, the number of egg per female in L. beneficus being 10-36.5-65 and 24-44.7-63 (mm-avg-max) in X. galactinus. The eggs of both species are oviposited on or in several material, such as cherry twig, corn, filter paper, paddy straw, vermiculite, etc. The eggs laid by the young adults show high rate of hatching. The fecundity suddenly decreases from 4 week old female, and the vitality of off-spring produced from such an old female is also inferior to that from the younger one. In the giant straw pile at Saga Paper Board Co., the spring emergence of L. beneficus and X. galactinus begins at the middle of May and the end of April respectively. The population of the bugs reaches a peak at the middle of June, and then it decreases toward July. The second emergence occurs at the end of August. Generally, X. galactinus is predominent in marshy places, while L. beneficus is found in arid places. They scarcely occur together in the same habitat. The sex ratio of field collected adults of both species is about 1: 1 throughout the year. During the summer season, the nocturnal flight of the male adults begins just before the sunset. They, at first, fly over the ground and later fly up to a higher range. The peak of appearance at the lower range is at 6.30 pm and the peak at the higher place is 7.00 pm. The flying activity of females follows the males about 30 minutes later. They stop to fly at about 9.00 pm. In the field, L. beneficus has 3 generations per year. New adults emerge in May, July, August, September, and X. galactinus has 5 generations, the adults appearing in June, July, August, September and November. But, due to the longer oviposition period, various growing stages are observed throughout the warmer seasons. The emergence of new nymphs stops in October in both species. The feeding habit of two bugs was investigated with more than 60 species of prey. So far as the author's observation goes, L. beneficus is predacious upon 45 species of 23 families and X. galactinus on 43 species of 22 families. The prey have such common characters as sluggish movement and soft-body, etc. The feeding preference was studied among Ceraphis magnolicolens Takahashi, larvae of wax moth (Galleria mellonella Linne), rice stem borer (Chilo suppressalis (Walker)) and red flour beetle (Tribolium castaneum (Herbst)). The aphid is the most prefered and Tribolium larva comes the next. Difference in preference is seldom observed between the two Lepidopterous larvae. The preference experiment was also conducted with various body-sized Galleria larvae, and it appears that the smallsized larvae are more suitable as food. The feeding amount of bug per day is very variable depending upon manv factors. The feeding amount against the Tribolium larvae was 2.00 and 1.20 in the adult of L. beneficus and X. galactinus respectively. The daily consumption of the mature Chile larvae by one predator was 0.60 and 0.20 in the separate and gregarious rearing of L. beneficus and 0.32 and 0.24 in X. galactinus. The reduction of food consumption under a gregarious condition is due to the concentrated attack of many bugs on one prey. In the earlier nymphal stage, the conversion ratio of food is higher than that of the later nymphal stage in both species. The predatory value in the adult stage is lower than that of the nymphal stage. The value is lower in the earlier nymphal stage in both species. The nutritional reliance on plant substances seems to be restricted and the sucking of plant juice keeps the life of nymphs and adults for a very short period. No oviposition is observed under the deficiency of animal diet. The order of suitability of feeding habit in both species is as follows : carnivorous > cannibalistic > necrophagous > fungivorous > phytophagous. The fecundity of bugs is greatly influenced by the kind of foods. The bugs reared with the Tribolium larvae show the highest fecundity and the Chile-fed bugs come the next. The Galleria-fed bugs show the worst result that is characterized by the longest pre-oviposition period and the lowest egg-production. For the purpose of studying this phenomenon in detail, the amino acid composition of Tribolium and Galleria larvae was analyzed and compared. As the result of analysis, the content of free amino acids in the former food was 73.50 μmol/g and that of the latter food was 30.63. The contents of essential amino acids were 23.58 and 8.10 respectively. Among the amino acids, the contents of aspartic acid, serine, alanine, valine, isoleutine, methionine, leucine, tyrosine and phenylalanine in the Tribolium larvae exceed 3 times that of the other foods. The amino acid analysis was also conducted with the adults of L. beneficus reared with the Triboliurn and Galleria larvae. No significant quantitative variation in the composition of amino acid was observed between the bugs reared with different foods. It becomes evident that the Tribolium-fed bug can take more amino acid nitrogen for the reproductive activity than the bug fed with another kind of diets. The contents of ether extract are much more abundant in the Galleria larvae than in the Tribolium larvae, being 0.22 and 0.04 g/g respectively. The paper chromatogram of these extracts was markedly different, although no identification was conducted. For the rearing of bugs with artificial media, four methods were used. Among them, the use of the medium soaked uretank foam is most preferable. The most favourable result was obtained with the medium composed of 2 g dextrose, 2 g soluble starch, 2 g sodium caseinate, 2 g yeast extract, 1 g beef extract, 0.05 g cholesterol, 0.2 g Wassen’s salt per 100 ml water. But the rearing result with this medium is much inferior to that with the animal diets either on the survival or growth rate. The frequent cannibalism was observed when several bugs were reared gregariously with the medium. No egg was produced by the female reared with the medium. The addition of 1.0 or 0.5 mg a-tocopherol to 100 ml medium prolonged the longevity and prevented the cannibalism for a certain extent. The ovarian development relating to the nutritional condition was studied anatomically with the bugs reared with various foods. The ovarian development was the best in the TriboNum reared bugs, and the mature eggs were recognized on the 5th and 3rd day after the emergence of L. beneficus and X. galactinus respectively. The ovarian development of Chile- and Galleria-fed bugs was inferior to that of the Tribolium-fed individuals and no mature egg was observed during the same period. The number of immature eggs was also abundant in the TriboZium-fed bugs. The adult fed with plant juices showed a slight ovarian development till the 3rd day, but the ovary rather degenerated on the 5th day. The survival, egg-production and the rate of egg hatching of bugs under the various population densities were investigated. In the petri-dish of 6 x 9 cm in height and diameter, the best result was obtained to rear 10 and 20 adult pairs of L. beneficus and X. galactinus respectively. The nymphal growth and the rate of survival were superior in 40 and 60 individuals in the same petri-dish. In both species, the adult was more tolerable against the coldness than nymphs. When adult was exposed to-3℃, the activity stopped within 3 minutes and the exposure of 30 minutes was fatal. Under the temperature of 5℃ condition, the paralysis occured within 30 minutes, the lethal time at this temperature being 6 and 5 days in L. beneficus and X. galactinus respectively. Although the young nymphs did not survive under the temperature condition of 4℃, the older nymphs reached very slowly to the adults while no oviposition was seen. In the field condition, both species seemed to overwinter in the adult stage under the shelter of warmer places. The relative toxicities of 10 pesticides against both species were studied with the residual film method. Against the laboratory reared young adults, 0.025 and 0.05 % parathion showed 100 % mortality to L. beneficus and X. galactinus respectively. Sumithion was the next toxic pesticide, the mortality being 86 and 84 % in 0.2 % solution against L. beneficus and X. galactinus respectively. The other pesticides were scarcely harmful in their conventional concentrations. To the field collected individuals, the tolerance was more inferior to the laboratory reared ones, and parathion, sumithion, dipterex and diazinone gave high mortality. The high sensitivity in the field col.lected individuals was partly attributed to the age structure of the field population. And this consideration was verified by the linear increase of the sensitivity to sumithion with the process of age in the laboratory reared population. The pesticidal sensitivity relating to the nutritional condition was also discussed. The pesticidal tolerance in the nymphal stage was higher in the last instar exceeding that of the laboratory reared young adults. When the 1st stage nymphs of both species were reared in the same cage, the nymphs of X. galactinus were always superior in growth and survival. The presence of X. galactinus adults gave serious effect on the survival of younger nymphs of L. beneficus. The mixed rearing of the adult L. bene$cus and the nymphs of X. galactinus gave little effects on the nymphal growth. The mixed rearing of the adults of both species gave bad effect on the oviposition period and egg-production of L. beneficus, but little influence on X. galactinus. A Braconid parasite of rice stem borer, Apanteles chilonis [Munakata], was always influenced by the presence of bugs. The piercing of the borer body by the bugs gave fatal effect on the survival of the wasp which was parasitizing the borer owing to the withering of the host insect. The bug prefered to attack the mature larvae of the wasp just crawled out of the borer body. Therefore the emergence of Apanteles wasps under the presence of bugs was very few. The mass-production procedure of bugs was designed with the use of vermiculite and cracked corn. For the most efficient method, the bugs were reared with cracked corn medium provided with a piece of moist filter paper for an oviposition substratum. The larvae of T. castaneunz were the most suitable food, and the method of mass culture of T. castaneum was also discussed. The separation of bugs from the culture media was designed too. The preying effect of bugs on the rice stem borer is evident when the bugs are in contact with the borer directly. Though the amount of prev consumed by the bugs decreased under the straw condition, the survival rate of the bugs rather increased. The preying activity was higher at 30℃ than at 25℃. The illumination has little influence on the preying activity. Dry straw condition stimulated the activity than the moist condition of material. But, to keep the moderate moisture condition in the straw was indispensable to maintain the rate of high survival of the bugs. Nymphs were almost impossible to attack the freely crawling borers, but accessible to the borer when the latter was confined to the straw. When the adults and nymphs were present in the same container, the adult bugs attacked their nymphs instead of the borers. The preying activity of bugs was not significant against the borers in the paddy stubbles. Under such an environment the bugs preyed on some small creatures which were found in the stubbles or crawling or walking on the soil surface.
- 九州大学の論文
- 1969-03-25