During from June to October, 1974, the author set “Fry-ribbon” at the Yukijirushi Yakumo Factory and collected insects there. These insects belonged to 1 family of Collembola, 1 family of Ephemeroptera, 3 families of Plecoptera, 1 family of Psocoptera, 2 families of Hemiptera, 4 families of Coleoptera, 24 families of Diptera and 7 families of Hymenoptera. Identification to species was made only 14 of them, because the collection method was not suitable for this purpose.
In order to survey what insects and mites would be injurious to milk powder the author set traps in Sapporo (5 houses), Yakumo (3), Nakashibetsu (3), Ashyroro (3) and Taiki (3) for a year from May, 1974 to the April, 1975. In each trap milk powder was used as the bait, and the traps was placed for 30 days every month in each house. In addition to this, trappings were carried out for 20 days in all 5 houses in Sapporo and one house of each of the other 4 towns. So the total numbers of traps used in this survey were 312. In 27 traps in 108 traps of the 10-days series (25%) and 51 in 204 traps of the 30-days series (20%) some small insects or mites were detected by Wildman's trapping method. They belonged to 7 species of insects, to 9 species of small mites, to 2 species of Arachnida and to 1 species of Isopoda. From the author's own data of the survey in 1968, 7 species of insects were found in the same traps in addition to the above species, so in Hokkaido a total of 26 species of Arthropoda have been reported by this trapping method. Liposcelis bostrychophilus was found in 24 traps (7.7%) and is thought to be the most important insect. Among small mites Tyrophagus putrescentiae was the most significant and was found in 34 traps (10.9%).
The death watch beetle (Liposcelis bostrychophilus) was found very often in milk powder as an invader. But when this insect was cultured using milk powder, all individuals died in 21 days. The author makes a hypothesis that the grain size of the milk powder would be injurious to this insect physically.
Four species of Arthropoda, i. e., Liposceiis bostrychophilus, Tyrophagus putresceutiae and the larvae of Attagenus japonicus and Musca dometica, were used for this experiment. Living insects and mites were canned respectively with milk powder after filled up with nitrogen gas by the usual method. The results were decided by life or death of the insects and mites when the cans were opened. Liposcelis bostrychophilus and Tyrophagus putrescentiae were not able to survive in the experimental conditions, and all of them died in 24 hours. Other two species of insect larvae were so resistant to the experimental conditions that almost all of them were living. Even after 210 days Attagenus japonicus was still living and Musca domestica was still living after 28 days. But the canned insects seemed to have been harmed because not all of them reached the adult stage.
1. Adults of saw-toothed grain beetles, Oryzaephilus surinamensis were kept in dry milk cans filled with nitrogen gas and air at a constant temperature of 15°C or 28°C. Some of adults survived for two weeks at 15°C in the cans filled with nitrogen gas. But there was no living insect after one week at 28°C. The ovipositing and development were inhibited in the cans filled with nitrogen gas. 2. The adults were possible to survive not less than four weeks in dry milk but no larva developed at a humidity of 0% R.H.
Insects and mites invading into four types of milk powder cans and changes of water content of their cans were investigated after setting them for two weeks in thirty homes which were five kitchens of apartment buildings, five of houses and five of stores (food-stores or restaurants) in both of the downtown and the suburbs. Four types milk powder cans were; 1) A can closed by a metal screw cap. 2) Closed by a polyethylene-cap. 3) Ccovered loosely by a polyethylene-cap without being closed and fixed by vinyl tapes on both sides. 4) Closed by a cap of which one-fourth part was cut off. We tested in summer, autumn and late autumn in 1974. It was found that water content of milk powder was highly correlative with the number of kinds of invading insects and mites. The numbers of insects and mites increased more in cans set in moist places. Also it was found that cans closed by polyethylene-caps were less invaded by insects and mites than cans closed by metal screw caps because the latter cans had more openings than the former. There were no statistical significant differences between downtown and suburbs, among apartments, houses and stores, and among three tests done at three seasons.
During the period from May 1974 to Febrary 1975, a monthly survey was carried out on the visiting pests in milk powder at kitchens of 20 homes by means of the trap method in Kanagawa Prefecture. The collection of 10 species from the traps indicated that the main noxious pest was the common grain mite, Tyrophagus putrescentiae, and majority of the population was appeared in the late summer season.
The ecology of injurious insect in the milk powder was surveyed using opened and closed traps. Injurious insects caught at 31 homes were classified two groups, Insecta and Acaridae. Most of them appeared between June and October through the year. On these available data, it was the most interesting result that Palidae and Psocoptera were found in the milk powder stored in closed can. Two causes of invasion of injurious insects were supported, one of the causes was the structural defect of the can stored milk powder and another was careless control of it by the consumer.
It was investigated in this paper on the food insects found in milk powder in Osaka area for about one year since May, 1974. The results obtained were as follows: The main insects found in the milk powder were Blattella germanica and Periplaneta fuliginosa. Other insect was Liposcelis bostrychophilus. The food insects were found from the late in July to the late in September, and the acme was in August. Two species of cockroaches were used for enclosed tests under the filling up nitrogen gas in flask. The results of the studies showed that cockroaches could not exist within 24 hours.
Food preferences of five species of stored-product insects between wheat flour and milk powder were observed in an apparatus that allowed insects to choose their food. All the species preferred wheat flour to milk-powder. The preferences shown by Oryzaephilus spp. and Cryptolestes pusillus were marked relatively. Tribolium castaneum exhibited less marked preference. Any appreciable effects of adding water to milk powder were not found on the preference of T. castaneum. The attractiveness of milk powder to T. castaneum and C. pusillus was determined. The adults of C. pusillus were markedly attracted to milk powder, although these of T. castaneum were not attracted practically.
The rearing of twelve coleopterous secondary pests of stored grains and one species of grain psocids was tested under the condition of 30°C and 70-80% RH on the five kinds of milk powder on the market. The five coleopterous species, Tribolium castaneum, Cryptolestes pusiiius, Tribolium confusum, Oryzaephilus mercator and Oryzaephilus surinamensis, grew quite well and produced many progenies on milk powder. For the other five coleopterous species, Lasioderma serricorne, Gnathocerus cornutus, Palorus subdepressus, Patorus ratzeburgii and Alphitobius diaperinus and one grain paocid, Liposcelis bostrychophilus, milk powder was a poor diet and only some growth had taken place and small numbers of specimens had completed development. Milk powder proved a very unsatisfactory food for the rest. Stegobium paniceum and Latheticus oryzae did not produce any living larva. Adding water to milk powder was not necessary for insects to grow, although an addition of water showed favour to reproduction in a few species.
With a view to reveal the process of existence of the pest insects of food and food product into milk powder, two series of experiments were carried out: one of them was done by the tmp-method, according to which the insects and other arthropods seemed most likely to exist in the milk powder stored for the ordinary housholds nursing were investigated at three different seasons, and the other was performed in such a manner that the survival days of the larvae of cockroach allowed to exist in the dry milk in process of production were investigated in the closed can. The results of the above mentioned experiments can be summarized as follows. 1. Species of Arthropods found in the trap with milk powder are as listed in Table 1, in which the pest insects and mite of food and food products, the pest insect of rice and the spider were 4 species, 1 species and 1 species respectively. 2. Comparison with the result from the earlier investigations conducted by the similar method for the confectionary pest insects showed the lower property of the milk powder for attracting the pest insects of food and food products. 3. 1 to 4 nymphal instars of cockroach (Periplaneta fuliginosa) put in the sealed can were found dead with no exception at 10th day, and no individual could be found survived by inspection done with the cans opened at 20th day, 30th day, 40th day and 50th day after sealing on the can. 4. Consideration of various factors of days from the completion of milk powder manufacture to the delivery to the consumer, the experimentally confirmed the survival days of various tested pest insects of food and food products in the sealed can, the fact that the troubles of the pest insects found in the milk powder by consumer more often concern the state the insects' survival and others favors the estimation of a large probability of the entrance of the insects and other arthropods in the milk powder after opening of the milk powder can by the consumer.