Spatial associations of insects and mites in stored wheat

The spatial association pattern of insect and mite populations in a steel bin containing stored wheat, Triticum durum Desf., in central Greece, was studied using the Spatial Analysis by Distance IndicEs (SADIE). The monitoring was carried out for 7 mo by using grain trier samples and probe traps. The most abundant insect species were Cryptolestes ferrugineus (Stephens) (Coleoptera: Laemophloeidae) and Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae). For mites, the most abundant species were the phytophagous Lepidoglyphus destructor (Schrank) (Acari: Glycyphagidae) and the predator Blattisocius tarsalis (Berlese) (Mesostigmata: Ascidae). Both for P. interpunctella and C. ferrugineus, trap catches were associated with numbers of individuals in the trier samples, but the overall association index calculated among trap and sample counts was significant only in the 33% of trap-sample pairs of values. Generally, P. interpunctella had the main patch areas in the central part of the bin, with few exceptions, during the entire monitoring period. Similar trends also were noted in the case of C. ferrugineus, which was clearly aggregated in the center of the grain mass. Spatial association maps indicated a stable positive association in the central part of the bin, but in most of the other sampling zones the association was negative. However, distribution of L. destructor, based on trier samples, indicated increased presence in peripheral zones of the grain sampling area. Moreover, B. tarsalis presented the most dispersed distribution among all four species. For each species, the association between two consecutive samplings was significant in the majority of cases, indicating a stable spatial pattern. Finally, B. tarsalis was spatially associated to a higher degree with the insects found rather than with L. desctructor. Moreover, there was no association of insect and mite presence with grain temperature and moisture content. The results of the current study suggest that the coexistence of insects and mites in bulked grain follows a complex pattern, with significant interactions, especially in the case of mite predators, which are spatially associated with insect species.     

麦田昆虫群落结构及多样性的季节动态

通过2年对麦田昆虫群落的系统调查,共查得昆虫11目、62科1、13种,其中植食类51种、捕食类23种、寄生类24种、腐食和食血类15种,种类数和个体数分别占群落总数的45.13,20.35,21.24,13.27%和92.89,2.19,3.63,1.35%。麦田昆虫群落可划分为4个营养层、6个功能团和19个类群,麦长管蚜Macrosiphum avenae(Fabricius)是绝对的优势种,其数量变动决定着总群落结构和多样性的季节动态。麦田昆虫群落多样性表现为前期和后期高、中期低的时间格局,类群多样性与物种多样性的变化趋势最为相似,可用类群多样性代替物种多样性进行群落分析。     

Comparison of microglomerular structures in the mushroom body calyx of neopteran insects

Mushroom bodies (MBs) are prominent neuropils in the insect brain involved in higher order processing such as sensory integration, learning and memory, and spatial orientation. The size and general morphology of MBs are diverse across insects. In this study we comparatively investigated the microstructure of synaptic complexes (microglomeruli) in major sensory input regions of the MBs, the calyces, across various neopteran insect species. Pre- and postsynaptic compartments of microglomeruli were analyzed using anti-synapsin immunocytochemistry, f-actin-phalloidin labeling and high-resolution confocal microscopy. Our results suggest that calycal microglomeruli are present across all investigated neopteran insect species, but differences are found in the distribution of synapsin and f-actin within their pre- and postsynaptic compartments. Hymenopteran MBs contain the highest number and packing density of microglomeruli compared to all other species from the different insect orders we investigated. We conclude that the evolution of high numbers of microglomeruli in Hymenoptera may reflect an increase in synaptic microcircuits, which could enhance the computational capacities of the MBs.     

Study of an infestation by Laemophloeus sp. (Coleoptera Cucujidae) in bulk wheat

Physical and biological data are presented from an infestation by Laemophloeus sp. (unidentified but very near to L. minutus Oliv.) in bulk wheat contained in open-topped silo bins. Much of the life history of this species is spent within the grains of wheat under the conditions of this infestation. It follows that the density of population of this species in whole wheat can be estimatedonly by breeding out or by determining the carbon dioxide output of the grain. Some larvae are free-living for part of their lives. No regular relation has been found between the number of larvae free-living at any time and the number of insects remaining within the grains. The proportion of the total population which is free-living is least when the total population is greatest. There is some evidence that the grain contained a light infestation of Laemophloeus , fairly evenly distributed, before it was loaded into the silo bin. It is supposed that this was the source of the infestation studied. Factors which might be responsible for the uneven development of the population are discussed.     

麦田昆虫群落的结构与时序动态

采用目测法和网捕法 ,通过对小麦整个生长季节内昆虫群落的系统调查 ,共查得昆虫11目 2 3科 36种 ,其中捕食性昆虫有 4目 5科 12种、寄生性昆虫有 2目 3科 4种、植食性昆虫有 5目 12科 15种、粪食性等其他类昆虫有 1目 3科 5种。在捕食性天敌昆虫中 ,瓢虫的种类和数量最多 ,其次为草蛉和食蚜蝇 ;在寄生性天敌昆虫中 ,蚜茧蜂为优势种 ,其次为寄蝇 ;在植食性昆虫中 ,麦长管蚜为绝对的优势种 ,其次为赤须盲蝽、灰飞虱和麦蓟马。天敌昆虫对害虫具有明显的跟随现象 ,不能有效地控制麦长管蚜的发生与危害。依据昆虫群落的组成与结构 ,结合小麦生育期 ,采用最优分割法将麦田昆虫群落动态划分为 5个阶段 ,并指出不同阶段昆虫群落特点及相应的害虫防治策略。     

Spatiotemporal distribution of insects and mites in horizontally stored wheat

Samples were taken from a flat storage facility located in central Greece, filled with approximately 45 tons of hard wheat, to assess the spatiotemporal distribution of stored-product insects and mites. The wheat was stored in a 1.5-m-deep bulk from June 2001 until March 2002. The samples were taken with a partitioned grain trier during the entire storage period, at 10-d intervals. The trier samples were examined separately for the upper, medial, and lower 0.5 m of the bulk. The spatial distribution of the insect and mite species found was examined by contour analysis based on the numbers of individuals in the trier samples. Nine insect and 20 mite taxa were found during the sampling period. The most abundant insect species were Tribolium castaneum (Herbst), Cryptolestes ferrugineus (Stephens), and Rhyzopertha dominica (F.); the most abundant mite species were Lepidoglyphus destructor (Schrank), Acarus siro L., and the predator Cheyletus malaccensis Oudemans. The highest population densities for the majority of the insect and mite species were recorded during autumn. The majority of the individuals of the most abundant insect and mite species were found in the upper 0.5 m of the bulk, with the exception of C. malaccensis, which was equally distributed in the upper and medial 0.5 m of the bulk. The spatiotemporal distribution during the entire experimental period was notably varied according to the insect and mite species.     

Interactions between panicle size, insect density, and environment for genotypic resistance in sorghum to head bug,Calocoris angustatus

Studies were undertaken on interactions between panicle size, insect density, host plant, and the environment for sorghum head bug,Calocoris angustatus Lethiery on five sorghum genotypes in terms of bug population increase, grain damage and loss in grain mass across four panicle sizes (5, 10 or 20 branches/panicle and whole panicle), and three infestation levels (5, 10 and 15 pairs of bugs/panicle). Head bug numbers increased and grain damage decreased with an increase in panicle size in the head bug susceptible cultivars, CSH 1 and CSH 5. However, the increase in bug numbers or decrease in grain damage was not significant in head bug resistant genotypes, IS 17610 and IS 17645. Head bug numbers increased with an increase in infestation level in CSH 1 and CSH 5, however, such an increase was not substantial in IS 17610 and IS 17645. Grain damage was significantly lower in IS 17610 and IS 17645 compared with CSH 1 and CSH 5 across infestation levels. Head bug population increased at a greater rate during the rainy season compared with the dry season. Panicle size and infestation levels accounted for greater variation in grain damage and percentage loss in grain mass during the rainy season than in the dry season. To identify reliable sources of resistance to insects, it is important to study insect host plant-interactions across panicle sizes (levels of food availability), infestation levels and seasons.     

Principal component analyses of bagged wheat infested withSitotroga cerealella (Lepidoptera: Gelechiidae) andSitophilus oryzae (Coleoptera: Curculionidae)

Interrelations among biological and abiological variables over 22 weeks at 28°C and 60% RH were revealed by principal component analysis (PCA) on data collected from simulated bagged wheat (Triticum aestivum L.) which was not infested by insects (control system), was infested bySitophilus oryzae (L.) (SO system), bySitotroga cerealella (Olivier) (SC system) or by both species (SC+SO system). The variables measured were temperature, grain moisture, CO₂, dust weight, fat acidity value, grain weight, germination, insect numbers and frequency of occurrence of microfloral species. The analysis indicated the interrelations among variables involved in degradation of the wheat. In the control system, the dominant interrelations were those among abiological variables, indicating that deterioration of the wheat was minimal. In the SO system, principal components which represented insect effects, seed quality and temperature-fungal relationships, were predominant. Similar factor-loading patterns were extracted both in the SC and SC+SO systems; the principal components suggested thatS. cerealella was mainly responsible for heavy deterioration of the wheat. The principal components, which were rotated orthogonally by 45δ, indicated that the process of wheat degradation in both systems proceeded gradually until week 10 or 15 and thereafter the rate of degradation was accelerated and serious grain quality loss occurred.     

Inhibition of amylases from different origins by albumins from the wheat kernel.

The amylase activity of water extracts from 18 insect species, from 23 marine species and from 17 different species of birds and mammals was determined quantitatively. The inhibition of amylase in these extracts by three albumin fractions from the mature wheat kernel, which had been separated according to their molecular weights (60 000, 24 000 and 12 500 D), was determined as well. The inhibition activity of the three albumin fractions toward amylases extracted from a number of cereal species or from immature and germinating wheat kernel was also tested. The extracts from insects that are destructive of wheat grain and stored wheat products showed much higher amylase activities as compared to the other insect species that do not attack wheat and wheat products. On the basis of the effectiveness with which the three albumin fractions inhibit their activities, the amylase preparations tested were divided into susceptible, partially susceptible and resistent. Susceptible amylases, inhibited by any of the three albumin fractions, were found mainly in insects that attack wheat and in marine species. Partially susceptible amylases, inhibited by only one or two of the three albumin fractions, were present in a few avain and mammalian species including man. Resistent amylases were largely distributed in cereal, avian and mammalian species as well as in insect species that do not usually attack wheat grain or wheat flour products. At no stage of development, wheat alpha-amylase was inhibited by the albumin fractions from the mature kernel. The 12 500 dalton albumin fraction was the most effective in inhibiting insect amylases, but it was inactive toward avian and mammalian amylases. The 24 000 dalton albumin fraction was the most effective in inhibiting amylases from marine avian and mammalian species and inhibited as much as 33 amylases over 66 different amylases tested. It is suggested that protein inhibitors of amylase contributed to natural selection of polyploid wheats by giving some insect resistence to such wheats, even though some insect species were able to overcome this biochemical defense toa large degree by producing higher amylase activities.     

Principal component analysis of interrelations in stored-wheat ecosystems infested with multiple species of insects

Principal component analysis (PCA) was used to determine the effects of infestation of bulk stored wheat by multiple species of insects at 30±2°C for 60 wk. Eight 204-liter drums containing wheat at 15.5% moisture content were used as three distinct man-made ecosystems: (a) Control system (2 drums), insect-free; (b) RST system (3 drums), artificially infested with Rhyzopertha dominica (F.),Sitophilus oryzae (L.), and Tribolium castaneum (Herbst ); and (c) COT system (3 drums), infested with Cryptolestes ferrugineus (Stephens ),Oryzaephilus surinamensis (L.), and Tribolium castaneum. The variables measured tri-weekly within each system included carbon dioxide, oxygen, temperature, grain moisture, seed damage, grain weight and volume, dust weight and volume, fat acidity values (FAV) of the wheat, seed germination, microflora including Alternaria alternata(Fr.) Keissler ,Aspergillus glaucus group, Aspergillus candidusLink , and bacteria, insects and the mite Tarsonemus granariusLindquist . PCA provided multivariate synopsis of the data quantifying several important relationships among the variables monitored. Tri-weekly and cumulative 60-wk analyses of each system showed that high bacterial counts were associated with high FAV levels;Tarsonemus numbers were positively related to Aspergillus; Alternaria and seed germination were negatively related to FAV, bacteria and grain damage; and that the number of insects was related to the presence of Aspergillus and negatively related to the presence of bacteria. Seed germination and Alternaria infection often decrease rapidly presumably because of infection by fungi of the Aspergillus glaucus group. The combined action of R. dominica and Aspergillus spp. enhanced seed damage and increased grain moisture content thus promoting bacterial growth which in turn inhibited insect and mold growth. Fat acidity values increased with time unless seed damage and bacterial infection were extensive as in the RST system.     

Effect of temperature, exposure interval, and depth of diatomaceous earth treatment on distribution, mortality, and progeny production of lesser grain borer (Coleoptera: Bostrichidae) in stored wheat

Diatomaceous earth (DE) can be used as a surface treatment in stored wheat Triticum aestivum (L.) to control pest infestations. However, it is not known how the thickness of the DE-treated wheat layer or grain temperature impact effectiveness. Therefore, we conducted an experiment in growth chambers to assess the effect of different surface layers of hard winter wheat combined with DE on spatial distribution, adult survival, and progeny production of lesser grain borer, Rhyzopertha dominica (F.), and to determine whether temperature and exposure interval modified this effect. When adult lesser grain borers were released in experimental towers containing untreated wheat or wheat admixed with DE to a surface layer depth of 15.2, 22.9, or 30.5 cm, they were able to penetrate all DE layers and oviposit in the untreated wheat below. However, survival was significantly reduced in adults exposed to DE. Survival decreased both with increasing depth of the DE-treated wheat and with exposure interval. Temperature had no effect on adult survival, but significantly more progeny were produced at 32 than at 27 degrees C. Progeny production was inversely correlated with the depth of the DE-treated layer. Vertical distribution patterns of parental beetles were not significantly different among treatments or exposure intervals; however, more insects were found at greater depths at 32 than at 27 degrees C. The F1 production was reduced by 22% at the thickest DE-treated layer. However, we conclude that this level of survival could leave a residual population of lesser grain borers that would probably be above an allowable threshold for insect damage.     

Insect herbivores associated with Baccharis dracunculifolia (Asteraceae): responses of gall-forming and free-feeding insects to latitudinal variation

The spatial heterogeneity hypothesis has been invoked to explain the increase in species diversity from the poles to the tropics: the tropics may be more diverse because they contain more habitats and micro-habitats. In this paper, the spatial heterogeneity hypothesis prediction was tested by evaluating the variation in richness of two guilds of insect herbivores (gall-formers and free-feeders) associated with Baccharis dracunculifolia (Asteraceae) along a latitudinal variation in Brazil. The seventeen populations of B. dracunculifolia selected for insect herbivores sampling were within structurally similar habitats, along the N-S distributional limit of the host plant, near the Brazilian sea coast. Thirty shrubs were surveyed in each host plant population. A total of 8 201 galls and 864 free-feeding insect herbivores belonging to 28 families and 88 species were sampled. The majority of the insects found on B. dracunculifolia were restricted to a specific site rather than having a geographic distribution mirroring that of the host plant. Species richness of free-feeding insects was not affected by latitudinal variation corroborating the spatial heterogeneity hypothesis. Species richness of gall-forming insects was positively correlated with latitude, probably because galling insect associated with Baccharris genus radiated in Southern Brazil. Other diversity indices and evenness estimated for both gall-forming and free feeding insect herbivores, did not change with latitude, suggesting a general structure for different assemblages of herbivores associated with the host plant B. dracunculifolia. Thus it is probable that, insect fauna sample in each site resulted of large scale events, as speciation, migration and coevolution, while at local level, the population of these insects is regulated by ecological forces which operate in the system.     

Insect infestations, incidence of viral plant diseases, and yield of winter wheat in relation to planting date in the northern Great Plains

Planting date effects on arthropod infestation and viral plant disease are undocumented for winter wheat, Triticum aestivum L., in South Dakota and the northern Great Plains. Winter wheat was planted over three dates (early, middle, and late; generally from late August to late September) to determine the effect on abundance of insect pests, incidence of plant damage, incidence of viral plant disease, and grain yield. The study was conducted simultaneously at two sites in South Dakota over three consecutive cropping seasons for a total of six site yr. Cereal aphids (Homoptera: Aphididae) were abundant in three site yr. Rhopalosiphum padi (L.), bird cherry-oat aphid, was the most abundant cereal aphid at the Brookings site, whereas Schizaphis graminum (Rondani), greenbug, predominated at Highmore. Aphid-days were greater in early versus late plantings. Aphid abundance in middle plantings depended on aphid species and site, but it usually did not differ from that in early plantings. Incidence of Barley yellow dwarf virus (family Luteoviridae, genus Luteovirus, BYDV) declined with later planting and was correlated with autumnal abundance of cereal aphids. Incidence of BYDV ranged from 24 to 81% among 1999 plantings and was < 8% in other years. Damage to seedling wheat by chewing insects varied for two site-years, with greater incidence in early and middle plantings. Wheat streak mosaic virus, spring infestations of cereal aphids, wheat stem maggot, and grasshoppers were insignificant. Yield at Brookings was negatively correlated with BYDV incidence but not cereal aphid abundance, whereas yield at Highmore was negatively correlated with aphid abundance but not BYDV incidence. Planting on 20 September or later reduced damage from chewing insects and reduced cereal aphid infestations and resulting BYDV incidence.     

D.D.T. Impregnation of Sacks for the Protection of Stored Cereals Against Insect Infestation

Cotton flour sacks, jute flour sacks, jute bran sacks and jute grain sacks have been impregnated with 1 and 5 % by weight of D.D.T. Treated and untreated sacks, each containing 1 cwt. of a mixture of grain (5 parts) and weatings (1 part), were exposed to severe infestation by adults of Calandra granaria, Tribolium castaneum, Ptinus tectus, Oryzaephilus surina-mensis and Ephestia elutella . After storage for 15 weeks at a mean temperature of 21.3 C. and a mean relative humidity of 65 %, the numbers of adult insects in each sack were determined by sieving the contents.
The results with Ephestia elutella were inconclusive. The results with the four species of beetles showed that the eventual degree of infestation of the contents of the sacks was dependent upon the closeness of weave and the D.D.T. content of the sacking material. Impregnation of sacking with 1 % of D.D.T. should afford adequate protection against insect infestation to clean bagged goods stored in stowages which are not heavily infested. Impregnation with 5 % of D.D.T. should offer a very high degree of protection at all times and can almost entirely prevent infestation, if the treated material is of sufficiently close weave to afford some mechanical hindrance to penetration by insects.     

Factors affecting capture of Cryptolestes ferrugineus (Coleoptera: Laemophloeidae) in traps placed in stored wheat

Cryptolestes ferrugineus (Stephens), the rusty grain beetle, infests grain externally and is a common pest of stored wheat throughout the world. Detection and population estimation of this insect are important in avoiding discounts at the point of sale. Laboratory experiments compared number of insect captures in the WNB II probe and PC trap in stored grain with a known insect density. Capture rates were strongly related to insect densities in wheat. In a simultaneous test of insect density, ranging from one to three insects per kilogram, and temperatures between 20 and 40 degrees C, insect captures in WB II probe traps increased linearly with insect density in the grain but had a quadratic response to temperature. Hole density, ranging from 40 to 120 holes along a 15-cm stretch of the trap body, was unrelated to number of insect captures. Probe trap diameters ranging from 26 to 60 mm were also unrelated to insect captures. Finally, dead rusty grain beetles were recovered in probe traps. The recovery of dead insects increased with insect density when insects were found in an aggregated dispersal pattern, such as would be found following phosphine fumigation of grain. Experiments discussed here will help grain managers understand how probe traps may be used in C. ferrugineus population estimation.     

Phenology and spatial pattern of Typhaea stercorea (Coleoptera: Mycetophagidae) infesting stored grain: estimation by pitfall trapping

The hairy fungus beetle, Typhaea stercorea (L.), occurs frequently in stored grain, often in large numbers. Populations infesting stored barley in Minnesota, corn in South Carolina, and wheat in Florida were sampled by means of grain probe traps. Spatial distribution of the species was examined by contour analysis of trap catch. In South Carolina, corn was sampled at 2 locations over 2 storage seasons, and temperature, moisture content, and malathion residues were measured. These data were used to examine phenology as well as spatial distribution, and showed peak trap catch shortly after harvest in the fall, and in the spring. This pattern followed seasonal changes in grain temperature, but there was no apparent relationship of trap catch to either grain moisture content or malathion residue. The populations of T. stercorea were not distributed randomly, but were largely concentrated in 1 or very few aggregations associated with the "spoutline," a region high in foreign material and broken grain that forms near the center of a bin as it is loaded. However, the spatial patterns were dynamic, even on a very small time scale (week to week). Numbers of insects in aggregations rose and fell, the areas involved expanded and contracted, the centers shifted, and secondary centers appeared and disappeared. These changes were apparently in response to changing patterns of grain temperature and moisture content. Secondary centers of aggregation often formed in warmer grain along bin walls.     

Voracity of the main stored-product insect pests on wheat grain

The results of an experimental study of voracity of adults and larvae of seven main stored-product insect pests are described. One adult of Sitophilus oryzae, S. granarius, Rhizopertha dominica, Tribolium castaneum, T. confusum, and Oryzaephilus surinamensis consumed 0.38, 0.48, 0.89, 0.15, 0.16, and 0.11 mg of wheat grain per day, respectively. During their development, larvae of these insects consumed 7.60, 13.77, 7.92, 3.32, 3.60, and 2.32 mg of wheat grain, respectively. One larva of Sitotroga cerealella consumed 17.46 mg of wheat grain. The coefficients of harmfulness of these species are calculated, and a method for estimating the “total infestation density” of grain is proposed.     

Wheat in bins and discharge spouts,and grain residues on floors of empty bins in concrete grain elevators as habitats for stored-grain beetles and their natural enemies

Wheat stored in upright concrete bins at seven grain elevators in central Kansas was sampled intermittently for insects over a 2.5-yr period by collecting samples from the upper half of the grain mass, from the discharge spout at the base of the bins, and from residue remaining in empty bins before the 2000 wheat harvest. Samples were taken from the grain mass with a power vacuum sampler (PV) and from the discharge spouts (DS) by dropping grain onto the reclaim belt beneath the bins. The density and species distribution in the residue samples were compared with those found in the DS samples and samples from the grain mass (PV). Cryptolestes spp. dominated the insect populations in all types of samples, constituting >40% of all insects in the PV samples in three of five time periods and >60% of all insects in DS samples in four of the five time periods. Cryptolestes spp. was an early colonizer, being found in the grain mass shortly after new grain was added. Rhyzopertha dominica appeared to be slower to colonize grain and grain residue, but sometimes developed large populations (i.e., 2.4 +/- 0.7 adults/kg between July and December 2000). Sitophilus spp. weevils often were present in grain masses, were often abundant in grain in the discharge spouts (i.e., 11.1 +/- 2.9 adults/kg between July and December 2000), and were abundant in grain residue in empty bins in May/June 2000 (5.3 +/- 0.7 adults/kg). Differences in density and species distribution of insects in grain in the upper part of the grain mass and those in the discharge spouts indicated that the populations were not closely related. Grain in discharge spouts usually was densely infested, and parasitic wasps, natural enemies of several of the beetles, were found when the density of the pest insects was greater than approximately 10/kg. The population of natural enemies appeared to increase when the density of pest insects increased after a lag of about one month, and decreased when the population of pest insects decreased. Grain in discharge spouts appeared to provide an incubation chamber for pest insects, and removing this grain periodically should reduce the resident populations. Residue in empty bins often was densely infested compared with samples from the grain masses. Cleaning the empty bins before refilling with newly-harvested wheat resulted in a significantly-reduced density of pest insects in discharge spouts later, and the effect lasted at least 12 wk after filling.     

Stored-product insects associated with a retail pet store chain in Kansas

The types and numbers of insect species associated with eight Kansas retail stores belonging to a pet store chain were surveyed during February to August 2001. Insects were monitored at 1-3-wk intervals using food- and pheromone-baited pitfall traps for beetles and pheromone-baited sticky traps for moths. Thirty traps of each type were placed within a store. Thirty insect species belonging to 20 families in four orders were recorded from the eight stores. The weevils, Sitophilus spp.; Indianmeal moth, Plodia interpunctella (Hübner); and merchant grain beetle, Oryzaephilus mercator (Fauvel), were the most common and abundant species in all stores, whereas the red-legged ham beetle, Necrobia rufipes (Degeer), and red flour beetle, Tribolium castaneum (Herbst), were abundant only in one store. The numbers of each insect species captured varied from store to store. In each of the stores, a total of 12-19 stored-product species were captured in traps, and seven of the eight stores had relatively high species diversity. With the exception of one store, the different types of insect species found among the remaining seven stores were essentially similar. The mean density of insects in infested bulk-stored and bagged pet food products removed from a store ranged from 65 to 656 adults/kg. The types and numbers of insect species captured in traps indicated that infestations were well established in the surveyed stores. Early detection and management of these infestations is critical for maintaining quality and integrity of food products sold in the pet stores.     

谷蠹感染的小麦储存环境中二氧化碳浓度变化研究

在25℃和密闭条件下测定了谷蠹Rhyzopertha dominica(F.)密度分别为0、2、5、10和20头/kg的小麦储存环境中二氧化碳浓度的变化情况。主要结果为:含水量为12%的小麦,未感染谷蠹成虫时,在180d内二氧化碳浓度从0.048%增加到1.157%;以2头/kg密度感染后,同样时间内二氧化碳浓度从0.048%上升到9.910%。害虫密度增加,产生的二氧化碳浓度都相应地增高,但二氧化碳的浓度与害虫密度不是相应地成比例升高。感染不同害虫密度的粮食,二氧化碳浓度随时间的延长呈"S"型曲线增长。这些结果表明,小麦感染谷蠹后在很短时间后即可检测到储存环境中二氧化碳浓度显著增加,二氧化碳浓度的变化与虫口密度相关。同样害虫密度时,储存时间延长,二氧化碳浓度呈"S"型曲线增加。一定条件下可通过检测二氧化碳浓度反映粮情和虫情变化。