1970 Volume 11 Issue suppl Pages S51-S68
This paper reports results of studies on the stored-product pests in confections conducted from August 1968 to November 1969 at six survey areas in Kochi and of experimental studies on Oryzaephilus mercator, which was first found to be resident in the district of Kochi in our present study, in comparison with O. surinamensis, a common species in Japan of the same genus, and a species of another genus, Plodia interpunctella, as well. Laboratory studies on the development of O. mercator and O. surinamensis depending on different ages of parents and temperatures were made.
To sum up briefly, the important ones among these results are as follows. (1) Out of the total observed number of 1722 of confections, high infestation rates of pests, 2.67% (15 species) and 18.2% (26 species), were found in samples taken from confections for sale and those of return, respectively. And as the results of our survey for a year, we could recognize three common species of pests, O. surinamensis, O. mercator and P. interpunetella. (2) Among different confections, biscuits were most severely infected as compared with chocolate and caramel confections. (3) High infestation rates were observed on the shops at rural areas in Kochi, on the shops of miscellaneous goods and on the wholesale store, hence we may well safely consider that the pest infection of confections is apt to occur severely in goods remaining long unsold and badly controlled at confection retail stores. (4) Seasonal fluctuations of O. mercator in the number collected by traps every week at confectioners factories distinct three peaks of adults and four peaks of larvae in the period from May to February, and it turns out that this pest may have four generations in a year (Fig. 19). But its fluctuation in number at the store of wholesale trade and retail stores never indicates such distinct peaks. (5) Developmental periods (egg to emergency) at 28°C did not show any distinct difference between both species, O. surinameusisand O. mercator, except that O. suriuamensis could not emerge, while another species could do at 32°C, both species emerging at 15°C. (6) In our study, we were aware of the fact that these two species of Oryzaephilus have intensive positive thigmotaxis (stereotaxis). (7) Faculty of boring polyethylene paper (0.02mm thickness), used for chocolate cover, becomes greatest for O. mercator when the population is of intermediate density (32 per cage in size 30cm3), whereas it becomes smaller in cases of lower or higher densities. (8) In O. mercator, the developmental period of offspring of parents of older ages (13 days old or more) was reduced by about two days as compared with that of parents younger than 13 days old, and the length and width of the thorax of offspring became shorter, P. interpunctella has the same tendency. (9) As three pairs of ovariole are found in both species of Oryzaephilus, it is possible that a female of these lays six eggs a day. The breeding period were six months at longest. (10) As to insecticidal activity for two species exposed to DDVP, O. mercator and O. surinamensis were found to be almost equal in LD50 values obtained by the topical application method (24hrs, 28°C). As the result of other experiments, which is shown in Fig. 22 in the LT50 values (y) observed at different distances (x) from DDVP-plates to pests, the relationship between the distances and insecticidal activity for pests seems to be formularized by y=0.433x+14.700. (11) P. interpunctella has 4th instar larval stages, periods of egg to emergence being about 30 days, and the pest comes to maturity in several hours after emergence and periods of egg-laying are almost a week.
