Seasonal Changes in Mite Populations in Rural Granaries in Japan 1

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1 easonal Changes in ite Populations in Rural Granaries in Japan R. N. INH Research tation, Canada Department of griculture, innipeg, anitoba easonal changes in mite populations were studied in samples of rice, wheat, barley, grain debris, and rice straw from the field, areas adjacent to granaries, granary floors, straw bags, and metal drums in farmhouses and rural granaries in higa prefecture, Japan, during June, eptember, and October 9, and ebruary 97. The mites were identified to species or genus; their frequency on each cereal, seasonal frequency, and abundance in each habitat were recorded. Thirty-four genera with more than 9 species of mites, several of which were undescribed, were identified. Glycyphagus destructor (chrank), Cheyletus cruditus (chrank), Tyrophagus putrcscentiae (chrank), Chclctomorpha lepidopterorum (haw), Tarsoncmus spp., and Tydeus spp. were the commonest mites on granary floors and were the most abundant in summer and generally scarce in winter. Of these species, only G. destructor maintained large populations through autumn and winter in all granaries. Large populations of In Japan, mites commonly infest stored rice, wheat, and other foodstuffs and cause losses in agricultural products (asa 95). oreover, the incidence of various forms of human acariasis presumably caused by the ingestion of mite-infested food is unusually high in Japan (asa 95). Various workers (Hosoya and Kugo 95, atsumoto 9) studied the incidence, infestation patterns, and biology of a few major species of stored-product mites, such as the mushroom mite, Tyrophagus putrescentiae (chrank), in a wide variety of foodstuffs consumed by the Japanese people. lthough these infestations are recurrent, little is known about the ecology of mites on farms and in other rural granaries where home-grown grain is stored immediately after harvest, before being shipped to warehouses and groceries in urban areas for marketing and consumer use. The main aim of this project was to discover the source and the pathway of infestation of mites from the field and rural granaries to urban warehouses and groceries. Thus, it seemed appropriate to study the acarine fauna in the field and in several granaries in a farming area where only Japanese-grown grain is stored. The specific objectives of this research were to investigate the association of single species of granary mites to each major cereal type, and the seasonal changes in the populations of each species of mite in various habitats. In studying the acarine fauna, an ecosystem approach was used (Odum 959). Each granary was considered to be an area in which living organisms and non-living habitat interact to produce an exchange of materials between the living and non-living parts of the ecosystem. small per- BTRCT joint contribution from Entomological Laboratory, Kyoto University, Kyoto, Japan (no. 0); and Canada Department of griculture Research tation, innipeg, Canada (no. ). ccepted for publication July, 97. a This species has been misidentified as Tyrophagus dimidiatus (Hermann) by most Japanese workers in recent years (asa, personal communication). 98 Tyrophagus putrcscentiae and Tarsonemus spp. during autumn and winter were observed in only granary. ore than 9 species occurred in stored grain. The commonest mites, i.e., those present usually in small numbers in 00% 9% of the cereals in bags and drums, were, in descending frequency: on rice G. destructor, Tyrophagusputrescentiae and Cheyletus cruditus; on wheat C. cruditus, G. destructor, and T. putrcscentiae; on barley G. destructor, Tarsonemus spp., and Tyrophagus putrcscentiae. ll these mites appeared in grain samples throughout the year, although their numbers per sample were in most cases progressively lower from summer to winter. The commonest mites on granary floors were represented in rice straw in the field. It is suggested that the infestation of stored grain and grain products originates primarily in the field and secondarily from unclean granary floors in rural areas where it spreads to urban granaries and grocery stores. centage of samples was occasionally infested with a few insects in all habitats studied. These were mainly Psocoptera, Diptera, and Coleoptera and will be reported elsewhere. TERIL ND ETHOD This report is based on a study of samples of stored grain, grain debris, and straw collected from a farming area of approximately 50 km, east of Lake Biwa near Hikone in higa prefecture, Honshu Island, Japan, during June 9-pril 97. ive locations were included in this study. ourteen samples were collected from the field, from grain spills outdoors, 80 from grain debris on granary floors, 7 from bagged grain, and 55 from sheet-metal drums inside granaries. The area near Hikone was chosen for a study of the indigenous mite fauna because home-grown grain is usually stored in local granaries. Of the field samples, consisted of rice straw, each with a volume of about 500 cc, collected from freshly harvested straw and old strawpiles in the field (ig., B, C) during June, eptember, and October 9. One field sample was taken from the straw roof of a farmhouse. Twenty samples of decaying grain debris were collected from the ground in the vicinity of the farmhouses. ll grain samples weighed 0 g. On the farms, rice samples were collected from metal drums (ig., D) each with a holding capacity of 00 kg, and from floors of the premises. In cooperative granaries rice, wheat, and barley samples were collected from 0-kg straw bags (ig., K, ) by inserting a hollow metal rod with a sharp end. amples of floor debris consisting of broken kernels, straw, and dust were gathered beneath a wooden platform on which grain bags were stacked. Collection of many floor samples at each sampling date was avoided, since it was feared that such interference would drastically reduce the mite's food supply and Downloaded from by guest on 9 November 8

2 July %8] INH : ITE POPULTION IN JPNEE GRNRIE thus deter the natural progress of mite populations in the ecosystem. Two of the farmhouses, granaries I and II, were similar in construction. Granary II, x5.x5 m, had a wooden floor, earthen walls, and a tile roof. The storage drums were near the wall inside the house in which farm equipment, bales of straw, and various other commodities also were stored. The cooperative granaries III and IV were similar to each 99 other in construction; each granary was divided into compartments. Granary III, x8x m, had a concrete floor, wooden walls, and a tile roof. Granary V, 0xx m, was the largest and the best constructed of all 5 granaries studied. It was divided into compartments of equal size and its floor, walls, and roof were similar to those of granaries III and IV. amples were collected from all compartments. ince there was a high turnover of grain in these granaries Downloaded from by guest on 9 November 8 IG.. ethod of extraction and habitats of stored-product mites collected from grain and straw samples in higa prefecture, Japan, in 9-7., modified Berlese funnel method for extraction of mites. B, freshly harvested rice and separation of rice paddies and straw by a thrashing machine in the field. C, rice-straw stacks in the field. D, metal drums for storage of hull-less rice inside a farmer's granary. E,, two types of rice-straw bags for storage of rice, wheat, and barley.

3 90 NNL O THE ENTOOLOGICL OCIETY O ERIC [Vol., No. - Table. Number of indoor samples collected and temperatures recorded in and around 5 granaries near Hikonc in higa prefecture in 9-7. collection June 9 " 5 Oct. 9 " 7 eb. 97» Granary I II III IV V I II III IV V I II III IV V loor / 0 the total quantity of grain per granary varied from approximately 00 kg to 000 kg at times of sampling. The age of the grain was - months. any locally grown varieties of grain were stored in the 5 granaries. ome of the varieties for each cereal were: rice Yamabuki, an jo, rkai, Ibuki, Kinmase, Chugoku, andyo, Norin 9, Habutai, ukuminori; wheat Norin, Norin ; barley ase. In all cases harvested rice was threshed in the field (ig., B) and rice was dehulled by machine and dried locally before storage in drums or bags. The number of samples and the dates on which the samples were collected from different habitats are given in Table. The samples of straw, grain debris, and grain were brought immediately after collection to the testing laboratory at Kyoto University, Kyoto, in air-tight plastic bags. Each sample was given an accession number and its main characters were recorded. representative portion of each grain sample, consisting of about 00 seeds, was shipped to innipeg, Canada, for fungal analysis. The results of the study of fungi will be published elsewhere. Temperatures of the outdoor and ambient air and of the grain were measured with a mercury thermometer at each time of sampling; the moisture content of the grain was measured in the laboratory to within 0.% by oven-dry method on a dry-weight basis. Berlese-type funnel (ig., ), 7 cm high, and with diameters of.5 cm at the top and.5 cm at the bottom, containing a -mesh/cm screen inserted 5.5 cm from the top, was placed under a 00-w incandescent electric bulb for hr to extract all mobile stages of mites. The efficiency of extraction of the major species of mites by this method was tested earlier (inha 9, inha et al. 9). The mites in each sample were identified and the total numbers of each species were recorded. Table lists the scientific names of all identified genera and species of mites with the authority for each species. or several genera identification to 8 9 No. samples collected BajI Drum Outdoor Temperature C mbient Grain 9 <> 8 (> species level was not possible because undescribed species were present (J. oki; E.. Baker; personal communications). REULT ND DICUION Temperature. Temperatures of the atmospheric and ambient air and the grain at the time of collection of samples in each of the seasons fluctuated within C (Table ), indicating that changes in outdoor temperatures influence the physical environment in which mites occur (inha and Utida 97, inha 98). But temperatures recorded only times in a year do not properly reflect the condition of the niche in which the mite lives. Therefore, the normals of mean monthly temperatures recorded (nonymous 957) at regular intervals every hr during 9-50 at Hikone eteorological tation, which is situated near the farming area investigated, were plotted in ig. for analysis. Temperatures above 0 C, required for breeding of major stored-product mites in Japan (inha 98), are recorded from pril to November. The levels of populations of mites encountered in this study resulted from cumulative temperature exposures preceding the date of sampling for months of spring (June samples), months of summer and of rainy season (October samples), and months of autumn and winter (ebruary samples). The most favorable temperatures for the multiplication of Glycypliagns destructor were recorded from ay to July, and of Tyrophagus putrcsccntiac and Cheyletus eruditus during July and ugust (inha 98). It could therefore be expected on the basis of temperature alone that large populations of G. destructor would be found in June samples and of 7'. putrescentiac and C. eruditus in October samples. The mean monthly temperatures in mouths ranged from. C in January to. C in ugust (nonymous 957). or most major species of granary mites, survival is possible within this range. Thus total elimination of all members of a species during winter is unlikely. 0 Downloaded from by guest on 9 November 8

4 July 98] INH : ITE POPULTION IN JPNEE GRNRIE 9 Relative Humidity of ir and oisture Content of Grain. Low moisture content of the stored cereals was characteristic of home-grown grain in the rural granaries in higa prefecture. The moisture content of the grain samples is shown in Tahle. ince almost all grain is dried immediately after harvest with small home-made driers using a simple fan and heat from coal, high moisture in field samples was of little consequence to mites in granaries. To fully assess the impact of the relative humidity of the air of an area with moderately high precipita- Table. systematic list of identified mites rural granaries and rice fields in higa prefecture. uborder RCOPTIKORE upcrcohort CRIDIE caridae carus farris Oudemans". siro L. carus sp. b Caloglyphus rhicoglyphoides (Zakhvatkin) uidasia ncsbitti Hughes Tyrophagus putrcscmtiac (chrank) lb Tyrophagus sp." Glycyphagidae Glycyphagus destructor (chrank)"" (r. privatus Oudenians b tipercohort ORIHTKI Camisiidae riaiynotltnis sp." Cosmochtlioniidae Cosmochthonius sp. b Haplozetidae Peloribates sp. Nothridac Nothrus sp." Oribatulidae Oribatula sp. b chcloribiues Uu-rcigatus (Koch.)" chcloribatcs sp. b uborder TROHIKOKK upercohort I IKTKROTIGT Pyemotidae Pycmotes sp. b Tarsonemidae Tarsoncmus spp." b upercohort PROTIGT Bdellidac pinibdclla bifurcata tyeo.v. cronini (Baker and Balock) Cheyletidae Chclctomorpha lepidoptcrorutn (haw)" b Chclctomorpha sp. ChcyU'tia jlubcllifcra (ichael) Chcylctia sp. ' Chcylctus cruditus (chrank)" ' C. malacccnsis Oudemans b C\ troucssarti Oudemans Cunaxidae Cunaxa si)." ' C. womcrslcyi Baker and Hoffman Raphignathidae Raphignatlius sp." ' tigtnaeidac liryngiopus sp. Tetranychidae Tctranychtts sp. Tydeidae Coccotydacolus sp. b Lorryia retiatlata (Oudemans) Proncmatulus sp. ' Triophthydcus sp." Tydcus spp. b from Table. Continued. uborder EOTIGT upercohort ONOGYNPIO meroseiidae Klecmannia plumosus (Oudemans)" b scidae Blattisocius dcntriticus (Berlese) B. tarsalis (Berlese) Proctolaclaps hypudaei (Oudemans) Laelaptidae Hacmolaclaps casalis (Berlese)" b Hacmolaclaps sp. Hypoaspis aculeifer Canestrini Hypaaspis sp. Parasitidae Parasitus spp." b Phytoseiidae Typhlodromus sp. b Uropodidae Lciodinychus krameri (Canestrini) b Lcindinychus sp. " Occurred in grain debris on ground outside the granaries. ' Occurred in samples of rice straw and kernels collected in the field. tion rate (00-0 mm/month between pril and October) on storage mites in granaries, the normal of the mean monthly relative humidities (9-50) was plotted in ig.. lmost all species of stored-product mites can breed within the narrow range recorded. armhouses and granaries in Japan are never airtight, and the relative humidity of the ambient air surrounding the floor debris, grain bags, or moderately ventilated drums is close to that of the air outdoors. ince the relative humidity is conducive to mite development throughout the year in Japan, temperature is of the main factors governing the abundance of mite populations (inha 98). ost stored-product mites cannot develop in grain with the low moisture contents shown in Table. The fact that mites are found in bagged grain indicates that the moisture content of grain is probably in equilibrium with the high relative humidity of the air. major species of stored-product mite, carus siro, is highly hygroscopic and absorbs moisture from the air quickly (Kniille 9, olomon 9). Therefore,. siro and possibly other stored-product mites survive and multiply in relatively dry grain when it is in contact with humid air for several months. High J J ONTH 0 N IG.. ean monthly normals of temperature and relative humidity of air at Hikone in higa prefecture, Japan (9-50), based on the records of the Japan eteorological gency, Tokyo. Downloaded from by guest on 9 November 8

5 9 NNL O THE ENTOOLOGICL OCIETY O ERIC [Vol., No. Table. Ranges of moisture content of grain samples. Date of collection June 9 5 ep. 9" 5 Oct. 9 7 eb. 97 Rice oisture content, c, heat Barley a amples were taken from a home-made grain dryer before drying began. relative humidity during the warm months, June- eptember, is likely to enhance the rate of multiplication of mites in so-called dry grain in bags and drums. ites on tored Cereals. Data on varieties of cereals were available for only a part of the total samples. Differences in the varietal reaction of cereals to the mites were negligible. any species of mites were found in granaries and in outdoor field samples (Table ) but only about 9 species occurred on cereals stored in drums in farmhouses and in straw bags in the cooperative granaries. But the frequency with which they occurred varied from one cereal to another (Table ). G. destructor occurred in 5% of the indoor cereal samples and was the commonest species on rice and barley, and the second most common on wheat. inha and allace (9) reported that this graminivorous and fungivorous species (inha 9) infested 9% of all grain samples, and almost equally. ince rice is the main cereal grown in Japan the high frequency of this mite on rice is significant. C. eruditus, a predatory mite, occurred in 7% of the stored cereal samples and was commonest on wheat. lthough the prey of C. eruditus in Japan consists of species somewhat different from those in Canada (inha and allace 9), its role in Japanese granaries may still be quite similar. T. putrescentiae was found in 0% of the stored grain samples and was the second most common species on rice and barley, and the third on wheat. ince it is considered to be the most important mite pest of stored food in Japan (asa 95), its presence in about one-third of all rice and wheat samples I studied is noteworthy. This species is an efficient fungus feeder (inha 9b) and probably feeds on fungi on cereals in addition to the cereals. Tarsonemus spp. occurred in % of the stored grain samples. Tarsonemus mites were recorded in 9% of the grain samples in a similar study with Canadian grain (inha and allace 9). But the Canadian species were commonest on wheat. ince the specific identity of the exclusively female Tarsonemus found in grain was not determined, the reason for this difference cannot be ascertained. Tydeus spp. occurred in 5% of the indoor grain samples. In Canada these mites infested % of grain samples but favored wheat over barley (inha and allace 9). This group is little known, and since the present study involves new species (E.. Baker, personal communication), the significance of their association with stored cereals in Japan is not understood. Each of the remaining species which occurred in stored grain in bags and drums (Table ) was found in less than 5% of the cereal samples. lthough no pattern of infestation of a particular cereal can be established from the few infested samples, the presence of certain species in stored grain may be significant. s far as I know, Pronematulus sp., Chelctomorpha sp., and Cheylctia flabcllifcra have not heretofore been reported to occur in stored grain. However, the tydeid mite Lorryia rcticidata has been found in stored grain only once before (inha 9). Chcletomorpha lepidoptcrorum has been recorded from stored oats (inha 9, Hughes 9). Blattisocius tarsalis is commonly found in stored grain in Canada and other countries (inha, unpublished; Hughes 9). However, B. dentriticus is not so common, although Hughes (9) reported it from the surface of wheat and from wet flour in association with acarid mites in England. uidasia vesbitti, which occurred in only sample of rice, is known to infest this cereal elsewhere (Hughes 9). easonal bundance of Common ites on Granary loors. Generally speaking, the most common and probably dominant mites, G. destructor, Chcylctus eruditus, T. putrescentiae, Chcletomorpha lepidoptcrorum, Tarsonemus spp., and Tydeus spp., were the same in floor debris and stored-grain (bags and drums) habitats in the farm and rural granaries investigated. The seasonal incidences in the populations of these species in indoor habitats are discussed separately from the less common mites. ince field samples were not taken at regular intervals, the rarer mites can only provide a clue to the type of Table. requency of occurrence of mites on various cereals stored in bags or drums in 5 granaries in higa prefecture during Names of mites in alphabetical order. sterisks show species that occurred in sample only. pecies carus siro Blattisocius dentriticus B. tarsalis Chcletomorpha lepidoptcrorum Cheletomorpha sp. Cheyletia flabellifera Chcyletus eruditus C. malaccensis C. trouessarti Glycyphagus destructor Haemolaelaps casalis Lorryia reticulata Pronematulus sp. Pyemotes sp. pinibdella cronini uidasia nesbitti Tarsonemus spp. Tydeus spp. Tyrophagus putrescentiae No. of samples Rice % occurrence heat Barley Downloaded from by guest on 9 November 8

6 July 98] IXH: ITE POPULTION IN JPNEE GRNRIE 9 GRNRY CHEYLETU ERUDITU CHELETOORPH LEPIDOPTERORU GLYCYPHGU DETRUCTOR TRONEU PP. TYDEU PP. TYROPHGU PUTRECENTIE II III IV v Li/b0 - IG.. Relative abundance of the commonest kinds of stored-product mites in floor debris in 5 rural granaries in higa prefecture, Japan in 9 7.,, and represent summer, autumn, and winter seasons, respectively. Diameters of the horizontal columns represent the mean number of mites per sample in various seasons. The maximum width of a funnel represents 500 mites; figures are given when this number is exceeded. mite fauna one would expect outdoors in the farming areas of Japan. ll major species of mites were abundant in floor samples in summer (ig. ), but with the exception of G. destructor, Tarsoncmus spp., and Tyropliagus putrcscentiae in granary II, all showed drastic reduction in numbers in autumn and became scarce in winter. Because there is a divergence in the feeding behavior and biology among these kinds of mites, the marked fluctuations in their numbers might result from a combination of several factors. Low temperature of the late autumn and winter would obviously slow down and stop the development and breeding of some of the species. But pressure from an efficient predator, such as Chcylctus cniditus, could also keep the population of the prey T. putrcscentiae down throughout the year. hen there is a smaller population of the predator in summer, the prey species can increase in large numbers and probably maintain a fairly high level of population throughout the year in spite of the usual winter mortality of some of its members. This explanation seems to be true in granary II, in which the summer population of both the predators C. cniditus and Chelctomorpha lepidopterorum was unusually low and the prey, T. putresccntiae and to some extent G. destructor, maintained relatively large populations through autumn and winter. The reason for the maintenance of large populations, throughout the year in 5 granaries, of G. destructor which is coldhardy (inha 9a) may lie in its ability to multiply in autumn and at least a part of winter, when it is relatively less affected by its cheyletid predators and by acarid competitors. C. lepidopterorum, which infests barley stored in bags in the ito district of Kanto area in Japan in large numbers (oki and Hasegawa 9), was abundant on floors in all granaries except no. I in summer in higa prefecture. But in all granaries it became scarce in autumn and absent or extremely rare in samples taken in winter. Hughes (9) observed that Cheyletus eruditus feeds on Chelctomorpha lepidopterormn, although the latter is usually found in association with acarid mites infesting stored grain. Until the predator-prey relationship with respect to C. lepidopterormn and the other mites and psocids associated with it are determined by direct observation, its precise role in the ocosystem cannot be known. In Canada, where C. lepidoptcrorum is occasionally found in stored grain, the number of individuals of this species rarely exceed or /sample. Downloaded from by guest on 9 November 8

7 9 [Vol., No. NNL O THE ENTOOLOGICL OCIETY O ERIC 00 E E l 80 a GRNRY! GRNRY H HBITT LOOR TR BG ETL DRU TYROPHGU PUTRECENTIE HBITT LOOR TR BG ETL DRU GLYCYPHGU DETRUCTOR o 0 ites of this genus are found in moderate numbers, scarcely more than 0/sample, in food, grain, and grain debris in Canada (inha and allace 9) and other countries (Hughes 9). requency of easonal Occurrences of the Common ites in Bags, Drums, and on loors. The seasonal occurrences of each species of the common mites are compared between habitats and granaries, so the pathways of infestation between the debris below the floor and stored grain above the floor become apparent. G. destructor was generally more common in samples from floor debris than from stored grain. There was an appreciable reduction in the percentage of drum samples infested with G. destructor in ebruary, but no such trend was observed in floor samples (ig. ). amples from the habitats in all granaries were infested by G. destructor on each 0 GRNRY I GRNRY TT 00 r r i r i z 0 GRNRY GRNRY JV. JUNE OCT _EB GRNRY V JUNE OCT GRNRY GRNRY J\ HBITT LOOR I TR BG D ETL DRU CHEYLETU ERUDITU GRNRY HBITT f~l 0 LOOR m TR BG m ETL DRU CHELETOORPH LEPIDOPTERORU GRNRY Ji GRNRY I >8 z 9 0 GRNRY V GRNRY Ji 0 0 u. z JUNE OCT _EB GRNRY HJ. GRNRY]J GRNRY V. GRNRY Hi GRNRY GRNRY V IG. -7. The percent frequency of occurrence of mites in habitats in 5 granaries in higa prefecture, Japan, in 9-7. IG. (upper left). Glycyphagus destructor. IG. 5 (upper right). Tyrophayus putrcsccntiac. IG. 0 (lower left). Cheyletus eruditns. IG. 7 (lower right). Cheletomorpha lepidoptcrorum, Downloaded from by guest on 9 November 8 Tarsonemus spp., which are coldhardy and probably parthenogenetic, maintained steadily small populations throughout the year in granaries III-V (ig. ). In granary I, Tarsonemus was absent after summer, but in granary II the numbers increased markedly between autumn and winter. inha (9b) demonstrated that Tarsonemus feeds on several species of storage fungi which appear during the succession of microflora in aging grain. Its abundance on the floor of granary II may be correlated with the increase in the populations of certain fungi which grow at low winter temperature. Tydeus spp. were most abundant on the floors of granary V. In summer they maintained a small but steady population in all granaries. Their incidence in summer, autumn, and winter suggests that they are cold hardy and well adapted to a granary-floor habitat.

8 July 98] INH: ITE POPULTION IN JPNEE GRNRIE 95 sampling date. This general occurrence shows the remarkable adaptability of this species to the changing climate. G. destructor infests most grain in rural granaries, whether it is stored in drums or in bags in summer, autumn, or winter. Tyrophagus putrcsccntiac was also generally more common in floor samples than in stored grain in bags and drums (ig. 5). In granaries II, IV, and V there was a gradual decrease in the percentage of infested samples in bags and drums from June to ebruary, but this trend was not seen in granaries I and III. The frequency of infestation in floor samples remained fairly high in most seasons in granaries I- IV. loor samples were not infested in granary V, although bagged grain brought to this granary from farms contained -58% infestation. Thus, it is concluded that grain stored in rural cooperative granaries is not always secondarily infested by T. putrcsccntiac from granary floors. The general occurrence of T. putrcsccntiac in summer and winter in a large percentage (-75%) of grain samples in premises where the grain is stored immediately after harvest is significant. It is possible that many infestations which commonly occur in grocery stores in urban areas and cause frequent medical problems in Japan (asa 95) have their origin in rural granaries. Chcylctus cruditus was commonest in floor samples in all granaries in seasons. It occurred in all floor samples from farm granaries I and II, and in 50-00% of all floor samples in cooperative granaries III-V from June to ebruary. But its conspicuous absence in ebruary grain samples from drums and bags in all granaries suggests that it could not overwinter. carcity of prey population (number of mites per sample) could also be a reason for its failure to survive in stored grain. The October populations of C. cruditus in stored grain in drums and bags were markedly reduced in granaries II, III, and IV as compared with the June populations in the same g 0 ^0 z 00 GRNRY I n GRNRY Jl HBITT LOOR TR BG QETL DRU TRONEU PP. habitats. In these habitats in granary I the species did not occur; in granary V, C. eruditus occurred in only about y of the samples in June. ince C. eruditus is a well-known predator of acarid mites, its high or low incidence from season to season is likely to influence the populations of T. putrescentiae and possibly G. destructor. High frequency of occurrence of C. eruditus combined with abundance of this predator in floor samples of rural granaries may result from frequent visits of birds in the nests of which C. cruditus thrives (oodroffe 95). oreover, since C. eruditus feeds on some small insects and on the eggs of insects and mites, it may find an unlimited food supply on granary floors which abound in these organisms. Cheletomorpha lepidoptcrorum was found almost exclusively in samples from granary floors (ig. 7). It infested bagged grain samples in only granary V, where less than % infestation was found in June. C. lepidoptcrorum did not occur in ebruary floor samples except in granary II in which 50% and in granary V in which 5% of the samples were infested by this mite. In cooperative granaries III and IV there was a drastic reduction in the percentage of infested samples from June to October, but no such trend was observed in farm granaries I and II and in granary V. On the contrary, the population of C. lepidopterorum increased from summer to autumn in granaries I and II. Its occurrences in a high percentage of floor samples (ig. 7) and in large numbers in granary V (ig. ) are noteworthy. ince C. lepidoptcrorum has occurred also in large numbers elsewhere in Japan (oki and Hasegawa 9), a study of its precise role in summer months would be desirable. Its scarcity in winter is probably a result of its susceptibility to cold. Tarsoncmus spp. were more common on granary floors than in stored grain (ig. 8). Unlike other common species, percentage infestation of these spe- 00 BO o 0 t- 0 u. z 00 GRNRY GRNRY l i 7 [" TR BG I I ETL DRU Downloaded from by guest on 9 November 8 80 o /J0 z JUNE.OCT EB GRNRY H GRNRY GRNRY y. GRNRY fl[ JUNE OCT _EB GRNRY ]. GRNRY Y IG The percent frequency of occurrence of mites in habitats in 5 granaries in higa prefecture, Japan, in 9-7. IG. 8 (left). Tarsoncmus spp. IG. 9. Tydcus spp.

9 9 NNL O THE ENTOOLOGICL OCIETY O ERIC [.Vol., No. Table 5. requency of occurrence in percent () and mean () number per sample, of uncommon mites in samples from floors of 5 granaries in higa prefecture during summer (), autumn (), and winter (), 9-7. Names of mites in alphabetical order. sterisks () indicate occurrences in single samples. Granaries I II III IV V pecies easons.icarus farris 80. siro Culogtypints rhizoglyphoidcs Cliclctomorplia sp. Chcylctia flabcllifcra Chcylctia sp. Clieylctits malacccnsis C. troucssarti Cosmochthonius sp. Cunaxa sp. Hacmolaclaps casalis Hypoaspis aculeifcr Hypoaspis sp. Klecviannia plumosus Lciodinychus kramcri ws :o 9 Downloaded from by guest on 9 November 8 Lciodinyclnts sp. Not lints sp. Paloribatcs sp. Parasihts spp

10 July %8] INH : ITE POPULTION IN JPNEE GRNRIE 97 Table 5. Continued. Granaries I II III IV V pecies Proctolaelaps hypudaci easons I'roncmatulus sp. Pycmotes sp. Raphiynathus sp. pinibdella bifurcata Tctranychus sp. Triophtydeus sp. Tyrapluiyus sp. s s 00 cics did not decline from June to ebruary. The infestation pattern of these mites (ig. 8) suggests that the population fluctuation is not dependent on temperature. It is more likely that the age of the grain spill on floors, the decaying organic debris, and the fungal flora growing on them were deciding factors in the abundance or scarcity of tarsonemid mites in rural granaries. The part played by the minute Tarsoncmus spp. (about 0 /u. long), in granary ecosystems is not clearly understood, although these mites have been associated with stored grain in Japan (asa 95) and elsewhere (inha 9). Only female specimens of Tarsoncmns spp. are usually found in aged grain (inha, unpublished) ; in the laboratory they feed on several species of fungi which grow on stored grain (inha 9b). Tydcits spp., an aggregation of a few undescribed species, were found predominantly in floor debris. Less than 5% of grain samples from bags or drums were infested by these mites. Tydcns spp. were found in 70-00% of all samples from granary floors in all granaries in June, in 5-00% in October, and in 0-00% in ebruary (ig. 9). Obviously low winter temperature is not a deterrent to these mites. The generally high frequency of occurrence of these species and occasional abundance in samples (ig. ) in rural granaries of Japan should justify further ecological and biological study of these mites. easonal Incidence of Less Common ites on Granary loors. Table 5 gives the frequency of seasonal occurrence and abundance of the less common species of granary mites in 5 granaries. ince these species were found in a small fraction of the total samples, their incidence may be of little significance. Both cams farris and. siro, which are important pests of stored grain in Canada, Great Britain, and Europe, occurred on the floor of granary I in summer and autumn (Table 5).. farris is normally equally common in both indoor and outdoor habitats, whereas. siro is usually restricted to indoor habitats in the temperate parts of the world (inha and allace 9). The relative scarcity of these species in granaries in Japan, which is in the Temperate Zone, is unexpected. everal factors could be responsible for the failure of these species to emerge as dominant grain pests. Competition from Tyrophagus putrcsccntiac, G. destructor, and several species of insects, such as itophilus zeamais otschulsky, and.". oryzae (L.), which often dominate the biotic community in granaries, could keep carus spp. from becoming successful. Certain climatic factors, such as heavy precipitation resulting in higher ambient relative humidity in granaries, could also favor their competitors. Of course, there is always the possibility of strong and selective predator pressure on carus spp. from several cheyletid species which are common in Japanese granaries (Table ). everal species of Cheyletidae, occasionally in fair numbers (Table 5), could be effective predators for various species of acarid mites on granary floors. None of these cheyletids occurred in winter samples, indicating that most of these species are not active at low temperatures. Two genera, Cnnaxa and pinibdella, also add to Downloaded from by guest on 9 November 8

11 98 NNL O THE ENTOOLOGICL OCIETY O ERIC [.Vol., No. the assortment of predators on granary floors. lthough cunaxids were active in summer in Japan, and were reported from stored food in Europe (Hughes 9) and from grain bulks in Canada (inha and allace 9), their specific role is not known. The occurrence of Haemolaelaps casalis in all seasons in most granaries confirms the findings of other workers that this predatory species, although still found in bird and rodent nests, is well established in granary ecosystems in most parts of the world (Hughes 9, inha 9, inha and alllace 9). Klccmannia plumosus was found in almost all floor samples in the farm granaries (I and II) in summer, autumn, and winter. It was most abundant in autumn samples. This species is commonly found in stored hay, oats, and wheat, and in grain debris on granary floors in Europe and Canada (Hughes 9, inha and allace 9). It is probably introduced with rodents and birds which visit granaries. I have seen these mites feeding on fungi in the laboratory. Of the tydeids, the occurrence of an undescribed species of Proncmatulus is noteworthy. Pyemotes sp. occurs sporadically in summer, autumn, and winter samples in most granaries. ites in Grain Debris Outside the Granaries. Table lists the mites occurring in grain debris on the ground around granaries. It is significant that all the mites commonest on granary floors and in stored grain in bags and drums were represented in this outdoor habitat. uch a mite fauna existing so close to the primary grain storage areas is a reservoir from which recurrent infestations of freshly stored grain occur inside the granaries. ites can be easily transported indoors with rodents, birds, and even men who move in and out of the rural granaries throughout the year. ites on traw and Thrashed Grain in ields. Table lists the mites occurring in samples of rice straw and in threshed rice kernels with hulls collected in the field (ig., B). The commonest granary mites (ig., Table ) are represented in this list. Obviously, some of the infestations of stored rice and probably other cereals by all important mites originate from the fields in the rural farming areas. ield samples yielded also such well-known stored product mites as Kleemania plumosus, Haemolaelaps casalis, and G. privatus. G. privatus is a mite pest of stored food in Europe (Hughes 9) and has no previous record of infestation of stored foodstuffs in North merica and Japan. The occurrence of these species in freshly harvested rice suggests that a field in a rural area harbors species of mite pests which have not yet moved into grain and food stored indoors. Pathivays of Infestation of tored Grain in Various easons. It is not possible, from this limited study of the acarine fauna in rural granaries and fields of Japan, to be certain of the pathways of infestation of stored grain and foods by mites in Japan. However, a few tentative observations are made to stimulate further study. Infestations of the major species of stored-grain mites, including T. putrcsccntiacj G. destructor, and Chcylctus crudiius, originate in field straw stacks. ites enter grain-storage containers in farm and larger rural cooperative granaries with freshly harvested grain. Humid ambient air elevates the moisture content of the grain. ith the onset of warm weather in late spring, mites begin to breed, and sizable populations in summer result. The beginning of cooler weather in late autumn slows or stops increase in populations. any individuals, especially these of a cold-susceptible species die during winter. Consequently, only a few coldhardy adults represent the overwintering species. The cycle repeats with the beginning of spring. ince grain is rarely stored for more than a year in a rural granary, it is moved with undetected small populations of mites to the granaries and grocery stores in urban areas, where the mites probably infest various other foodstuffs. hen the infested grain is stored in rural granaries, grain kernels fall on the floor, dust gathers, and the mites breed in the floor debris. If the granary floors are not immaculately cleaned and disinfected at frequent intervals, colonies of many species flourish and communities of animals and microorganisms eventually become well established. If left undisturbed these colonies serve as a secondary and probably the most important reservoir for mite infestation of newly stored grain. In Japan, the traditional practice of storing grain in bags made of rice straw provides the mites an ideal sanctuary from which they can absorb the humidity of the air and move a few millimeters to feed on the moisture-conditioned grain. The mites that are transported to the granaries by casual visitors, such as insects, birds, and rodents, may provide another source of infestation of stored grain in rural granaries. Because winter temperatures in most parts of Japan rarely kill all stages of most mites, the vicious cycle of infestation and reinfestation continues. CKNOLEDGENT I am most grateful to Prof.. Utida, Entomological Laboratory, Kyoto University, Kyoto, Japan, for his constant encouragement in this study and for review of the manuscript. I am indebted also to Dr.. Takahaski of the same laboratory for facilitating my work with the Japanese farmers through his interpretation and assistance in the field work; to Dr.. L. atters, Canada griculture Research tation, innipeg for reading the manuscript and suggesting editorial changes; to Dr. E.. Baker, gricultural Research ervice, U.. Dep. of griculture, ashington, and to Dr. J. oki, National useum, Tokyo, Japan, for identifying Tydeidae and Oribatei, respectively. REERENCE CITED nonymous onthly Normals of Pressure, Temperature, Relative Humidity, Precipitation and Duration of unshine (9-950). The Japan eteorological gency, Tokyo. p. oki, J., and K. Hasegawa. 9. On epidemic of grain itch in barley storehouses in the central part of Japan and mites concerned. Jap. J. anit. Zool. 7: 9- [In Japanese.] Hosoya, H., and J. Kugo. 95. ites occurring in Downloaded from by guest on 9 November 8

12 July 98] IXH: ITE POPULTION IN JPNEE GRNRIE 99 food. Jap. J. Public Health (5) :. [In Japanese.] Hughes,.. 9. The ites of tored ood. H.. tationery Office, London. 87 p. Knulle,. %. Die bhangig Keit der Luftfeuchte- Reak hirven der ehlmillee (carus siro L.) vom assergeluilt des Korpers. Z. Vergl. Physiol. 5: -. atsumoto, K. 9. tudies on the environmental factors for the breeding of grain mites. Part IV. Comparison of the effects of humidity and temperature on the breeding of the grain mites, Tyrophagus dimidialus, leuroqlyphus ovatus, and Glycyphagus destructuor. Jap. j/anit. Zool. (): 8-^88. [In Japanese.) Odum, E. P undamentals of Ecology.. B. aunders Co., Philadelphia. 5 p. asa,. ^)5. ites, n Introduction to Classificiation, Bionomics and Control of carina. Univ. Tokyo Press, Tokyo 8 p. [In Japanese.].inha, R. N. 9. Insects and mites associated with hot spots in farm stored grain. Can. Entomol. 9: note on associations of some mites with seedborne fungi from the Prairie Provinces. Proc. Entomol. oc. anitoba 8: tored product acarology in Canad. In J.. Naegele [ed.] dvances in carology, Vol., Cornell Univ. Press, Ithaca, X. Y., 80 p. 9a. Effect of low temperatures on the survival of some stored product mites. carologia : -. 9b. Ecological relationships of stored products mites and seed-borne fungi. Proc. irst Int. Congr. carology, carologia : eeding and reproduction of some stored-product mites on seed-borne fungi. J. Econ. Entomol. 59: Climate and potential range of distribution of stored-product mites in Japan. Ibid. : inha, R. N., and. Utida. 97. Climatic areas potentially vulnerable to stored product insects in Japan. ppl. Entomol. Zool. : -. inha, R. N., and H.. H. allace. 9. ssociation of granary mites and seed-borne fungi in stored grain and in outdoor and indoor habitats. nn. Entomol. oc. mer. 59: inha, R. N., E.. R. Liscombe, and H.. H. allace. 9. Infestation of mites, insects, and microorganisms in a large wheat bulk after prolonged storage. Can. Entomol. 9: olomon,. E. 9. oisture gains, losses and equilibria of flour mites, carus siro L., in comparison with larger arthropods. Entomol. Exp. ppl. 9: 5-. oodroffe, G. E. 95. n ecological study of the insects and mites in the nests of certain birds in Britain. Bull. Entomol. Res. : Unisexual train of the alt-arsh Caterpillar, Estigmene acrea N.. ERLE' ND JOHN CRLNE 5 BTRCT predominantly female strain of the salt-marsh caterpillar, a cytoplasmic factor that kills male embryos. hen Estiymenc acrca (I)rury), has been maintained in hemolymph from a pupa of the unisexual strain was in- the laboratory for 7 generations. emales must mate before jected into a female pupa of a bisexual strain, the result- they can produce viable eggs, but there has been no ing adult produced only females. The induced unisexual evidence of mating-induced parthenogenesis. The unisexual condition was not permanent, since the progeny of the injected female produced moths of both trait is maternally inherited and appears to be caused by sexes. n abnormal sex ratio was accidentally discovered in the first salt-marsh caterpillars, Estigmene acrca (Dmry), ever colonized at our laboratory. single ejj mass found in a nearby field of cotton was brought into the laboratory in the spring of 9. bout 00 insects were reared to maturity on cotton leaves for identification and for sex-attractant studies. ll were females. ertile eggs were obtained from moths after they were allowed to mate with males caught about Yz mile from the laboratory. Two groups of larvae, 7 in all, were reared and again were found to consist of all females. This virtually unisexual strain has since been maintained for several generations in the laboratory with only an occasional appearance of males. orkers in Texas and rizona, where colonies of this species have been maintained, have never reported any pronounced deviation from the usual : sex ratio (E. Vanderzant and R. ye. Lepidoptera: rctiidae. -' In cooperation with the Louisiana gricultural Experiment tation, Baton Rouge, Louisiana. ccepted for publication ugust, m7. a ention of company name does not necessarily imply endorsement hy the UD. Kntomology Research Division, gr. Res. erv., UD, Baton Rouge, Louisiana. Graduate assistant. Department of Entomology, Louisiana tate University, Baton Rouge.,, Entomology Research Division, UD; personal communication). The sex ratio also was found to be close to : at a laboratory in California (Vail et al. 97). The present report is concerned with preliminary studies of the factors responsible for the abnormal sex ratio found in the colony from Louisiana. PLN O INVETIGTION It was soon discovered that tew, if any, of the moths from the unisexual strain reproduced parthenogenetically. However, the possibility remained that they were gynogenic. Gynogenesis has been reported in beetles (oodroffe 958, Lanier and Oliver 9), in mosquitoes (Laven 95), and it probably occurs in other orders of insects. e therefore tested for gynogenesis by exposing males from a bisexual culture of E. acrca to gamma irradiation; we then allowed them to mate with moths from the unisexual strain. e assumed that parthenogenetic development had been induced if the entry of irradiated sperm into the egg resulted in normal egg hatch. e also considered the selective mortality of male embryos as a possible cause of the biased sex ratio. e were guided in our investigation by the extensive studies of maternal transmission of microorganisms Downloaded from by guest on 9 November 8