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.     

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.     

Canonical correlation analysis of abiotic and biotic variates in insect-infested grain bulks

Summary The impact of insect infestation on several biotic and abiotic variates in 3 small bulk-wheat ecosystems was studied by measuring these variates at monthly intervals during 1969–1970. One ecosystem was insect-free, the second was artificially infested with Cryptolestes ferrugineus and Oryzaephilus surinamensis, and the third with Sitophilus granarius and Tribolium castaneum. The relationships between 8 environmental and 8 entomological and microbial variates were examined by canonical correlation analyses. The degree of predictability (R _c ² ) of the first pair of canonical variates in the 3 ecosystems ranged from 80% to 95%. The first 2 pairs of canonical variates were highly significant in all 3 analyses (P<0.01). In the insect-free ecosystems the canonical variates revealed that temperature and the period of storage were the primary environmental antecedents involved and the criterion was composed primarily of the field fungus Alternaria and the storage fungus Aspergillus. In the second ecosystem uric acid level in the grain bulk was an additional environmental factor that affected the population of both species of insects and 3 kinds of fungi Altrnaria, Aspergillus, and Penicillium. In the third ecosystem temperature, time, uric acid and moisture interacted collectively, with density of insect populations, reduction of Alternaria, and increase of Aspergillus.Contribution No. 502 from Research Station, Canada Department of Agriculture, Winnipeg, Canada. Based partly on a paper presented at the Annual Meeting of the Ecological Society of America, Chicago, Illinois, U.S.A., on 28 December, 1970.     

Simulation of generation times of the rusty grain beetle,Cryptolestes ferrugineus, in farm-stored grain in the canadian prairies, 1952-1990

The number of potential annual generations of the rusty grain beetle,Cryptolestes ferrugineus, was simulated in wheat stored in granaries for all crop districts in the prairie provinces of Canada each year from 1952 to 1990 using a population dynamic model driven by ecological variables. Granary size was assumed to be 6 m in diameter. Historical data for temperatures at harvest and times when storage began were used in the simulation model. A second model, which predicted the rate of temperature change at the centre of a 6-m-diameter bulk of wheat, determined environmental parameters for the population dynamic model. (Grain moisture content was assumed constant at 14.5% wet mass basis.) The combined model shows that the initial storage temperature is the most important factor responsible for predicting the number of generations and levels of infestation ofC. ferrugineus. This finding was largely validated by historical grain storage and infestation data. For various years initial grain temperature ranged from 17.7 to 37.4 °C and harvest dates were between 1 August and 20 October. The number of generations annually in simulations based on field conditions ranged from 0.35 to 6.77 with a mean of 3.29. Three or more generations result in a severe infestation and every year at least three simulated generations were completed in some crop districts. In one year, at least three generations were completed in every crop district. Harvest temperature and date permit prediction of crop districts that will potentially have the largest populations of C.ferrugineus so that early monitoring of wheat for infestations can be targeted to areas most at risk. Cereal Research Centre Contribution No. 1660     

Effect of high temperature treatment on disinfestation and quality characteristics of sorghum

Sorghum grain (two varieties) was modified to different water contents (12% to 16% wet weight basis) and heated to 60°C, 70°C and 80°C for periods of 4, 8 and 12 min. Germination, seedling vigour, seedling dry matter, free fatty acid (FFA) content, fungal contamination and infestation with the insect pest Rhyzopertha dominica (F.) were all markedly affected by heat treatment. The effectiveness of the heat treatment was also influenced by the size of the sample used. Heat treatment at 60°C and 70°C resulted in germination being unaffected or stimulated while at 80°C and the higher water contents significantly reduced, when compared to untreated controls. The dry matter of seedlings, and seedling vigour was positively correlated with germination and heat treatment. Heat treatment had no effect on FFA. All stages of the insect pest, R. dominica, were destroyed at 70°C and an 8 min exposure time. However, the water content of the sorghum was critical in determining the efficacy against this pest. The percentage fungal contamination of grain was reduced from 90% to about 25% by heat treatment. However, some grain fungi, particularly Eurotium spp., Aspergillus niger and Penicillium spp. could still be isolated from sorghum grain treated at 80°C for up to 12 minutes.     

Variation in cardinal temperatures for germination among wheat (Triticum aestivum) genotypes

In most tropical regions where wheat is grown under irrigation, high temperatures at sowing adversely affect crop establishment and subsequent seedling survival. The objective of this study was to compare wheat (Triticum aestivum) genotypes for their ability to germinate and grow at high temperatures during the seedling stage. Twenty-five seeds each of 14 spring wheat cultivars were placed on moist filter paper at different temperatures (5°C to 40°C) in a one-way thermogradient plate to determine the cardinal temperatures for germination. Rate of germination at each temperature for each genotype was computed as the inverse of time taken for 50% of the seeds to germinate. Rate of germination for each genotype at different temperatures was modelled with temperature to determine the base (t_b), and optimum (t_opt) temperatures. Response of germination to temperature for each genotype was calculated as the slope of a linear regression of the rate of germination on temperature below t_opt. Genotypes differed in their optimum temperatures and Mexipak (= Kalyansona) had the lowest. Range in base temperature among the genotypes was between 0°C and 2°C differences but were not statistically significant though they might be biologically significant. Genotypes differed in their response to temperature with Gomam having the lowest rate, implying that it was slow to respond to increasing temperatures. Debeira and Cham 6 showed a similar response. Three lines which had performed well in spring wheat evaluation trials for moderate rainfall areas under heat stress had the highest response rate. It is concluded that combining higher optimum temperatures with faster response rates would result in better-adapted germplasm for regions where high temperatures persist at sowing.     

Quality changes in granary-stored wheat at 15 and 19% moisture content

Half-bushel parcels of wheat at 15 and 19% moisture content (MC) were implanted in bulks of dry stored oats in a farm granary for 60 weeks to monitor quality changes. Temperature, MC, fat acidity value (FAV), oxygen and carbon dioxide levels, germination, microfloral incidence and abundance, and major storage mycotoxins (aflatoxins, sterigmatocystin, ochratoxin A, citrinin, penicillic acid) were monitored at two-week or four-week intervals during storage. Wheat storage at 19% MC was characterized by higher temperature, MC, FAV, carbon dioxide level, and microfloral abundance, and lower levels of oxygen and germination as compared to 15% MC wheat; no mycotoxins were detected at either moisture. Approximately 19% MC may represent a critical moisture limit for mycotoxin formation in granary stored wheat, given the indigenous mycoflora.     

Evaluation of some plant products for the management of Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae) in stored maize (Zea mays) and their effect on nutritional composition of the kernels

The bioactivity of powder from the leaves of Aristolochia ringens, Dalbergia saxatilis, Dioclea reflexa, Ocimum gratissimum, Chrysophyllum albidum, Moringa oleifera, Citrus limon and Newbouldia laevis was tested against the larger grain borer (LGB) in maize kernels and the effect of the powder on the nutritional composition of the kernels was determined. A total of 72 glass bottles containing 100?g maize kernels was divided into four groups. In the first group of 32 glass bottles, 5?g powder of the experimental plants was admixed uniformly with the kernels (5%?w/w). Ten 1–5-day-old LGB adults were introduced into each of the glass bottles. A second group of 32 glass bottles contains 100?g maize kernels admixed with the plant powder as described above, but LGB were not added. In the third group of four glass bottles, 100?g maize kernels received insects only, while in the fourth group of four glass bottles 100?g maize kernels were neither mixed with plant products nor infested with LGB. The treatments were arranged on worktables using completely randomised design and left for three months. The plant products-treated samples (insect free) were passed through a 30?mesh sieve to sieve out the powder and the clean kernels were analysed for proximate composition. The untreated maize kernel had a significantly (p?<?0.05) higher % of grain weight loss (17.33), grain damage % (70.96), number (122.0) of adult LGB, weight (14.46?g) of grain dust and lower % of grain germination. The adsorption and absorption of some of the plant powder by the kernels had significant effect on the kernel composition of protein, fibre and carbohydrate, but not on moisture, dry matter and fat and ash content. Control of LGB with the powder of the test plants could be used as green insecticide for the management of LGB.     

Genetic control of geographic variation for cannibalism in the southwestern corn borer,Diatraea grandiosella

The southwestern corn borer,Diatraea grandiosella Dyar, is a subtropical insect whose range has expanded northward within this century. Geographic variation exists between populations at the extremes of the range for a suite of morphological and behavioral characters, including cannibalism. Laboratory colonies established from a Missouri population (37°N lat.) with a high cannibalism rate and a Mexican population (19° N lat.) with a low cannibalism rate were used to examine the genetic basis of cannibalism by means of a controlled breeding design. When larvae were held in pairs on artificial diet in 30 ml plastic cups at 30° C 16L:8D, the highest incidence of cannibalism in both Missouri and Mexican populations was found in larvae 15 to 18 days-of-age (5th and 6th instars). Under these conditions, cannibalism was expressed in 33% of the pairs formed from Missouri larvae and 11% of the pairs formed from Mexican larvae. First and second generation crosses between Missouri and Mexican populations showed an intermediate level of cannibalism, whereas backcrosses to the parental generations showed a regression to the parental phenotypes. These results indicate that cannibalism is under additive genetic control. Larvae from the Missouri parental population were more likely to consume their victim (i.e., cannibalize) once intraspecific killing had occurred than were larvae from the Mexican parental population or from any of the crosses, and female larvae were cannibals more often than were males. Under the conditions employed, no advantage was detected for cannibalism over instraspecific killing for larval weight gain or growth rate.     

Behavioural responses of Oryzaephilus surinamensis, Tribolium castaneum and Tribolium confusum to naturally and artificially damaged durum wheat kernels

Observations on behavioural activity involved in the host selection by secondary pests of stored grains, Oryzaephilus surinamensis (Linnaeus), Tribolium castaneum (Herbst) and Tribolium confusum J. du Val, with respect to intact and mechanically or naturally damaged kernels are reported. Our results indicate that the attraction of secondary pests is facilitated by broken grain kernels, which resulted from either mechanical damage during harvesting and/or binning procedures, or the feeding activity of primary insect pests. Insect damaged kernels were more attractive to O. surinamensis, T. castaneum and T. confusum than whole kernels; in addition insect damaged kernels elicit more attractiveness than mechanically split kernels. The damage caused by primary pests, such as Rhyzopertha dominica (Fabricius) and Sitophilus oryzae (Linnaeus), on whole kernels may facilitate colonization by secondary pests, which continue damaging the cereals. O. surinamensis, T. castaneum and T. confusum utilize the grain volatile odours to distinguish whether the grain kernels of the stored cereals are damaged mechanically or by insects.     

<Emphasis Type="Italic">Penicillium verrucosum</Emphasis> occurrence and Ochratoxin A contents in organically cultivated grain with special reference to ancient wheat types and drying practice

This study addresses the relationship between the ochratoxigenic strains of Penicillium verrucosum and ochratoxin A (OTA) contents in organically cultivated grain. It included 37 combined, non-dried grain samples from farmers with no drying facilities as well as 19 non-dried and 22 dried samples from six farms with on-farm drying facilities (Case studies 1–6). The study focused on the ancient wheat type spelt but also included samples of wheat, rye, barley, oats, triticale, emmer, and einkorn. All 78 samples were analysed for moisture content (MC) and occurrence of P. verrucosum. The latter was assessed by plating non-disinfected kernels on DYSG agar and counting those contaminated by the fungus. Fifty-five samples were analysed for OTA. Most of the combine harvested samples (82%) were contaminated with P. verrucosum prior to drying. This was ascribed to difficult harvest conditions and many samples of spelt, which was significantly more contaminated by P. verrucosum than oats, wheat and barley. Though not statistically significant, the results also indicated that spelt was more contaminated than rye, which is usually regarded the most sensitive small grain cereal. No correlation was found between number of kernels contaminated by P. verrucosum and OTA content. Despite many non-dried samples being contaminated by P. verrucosum, only two exceeded the EU maximum limit for grain (5 ng OTA g^–1), both being spring spelt with 18 and 92 ng g^–1, respectively. The problems were most likely correlated to a late harvest and high MC of the grain. The case studies showed exceedings of the maximum limit in a batch of dried oats and spring wheat, respectively, probably to be explained by insufficient drying of late harvested grain with high MC. Furthermore, our results clearly indicate that OTA is not produced in significant amounts in samples with MCs below 17%. All dried samples with MCs above 18% exceeded the 5 ng OTA g^–1 limit in grain. However, no correlation between MC and the amount of OTA produced was found.     

Monitoring spatiotemporal variation in abundance and dispersal by a pheromone-kairomone system in the threatened saproxylic beetles <Emphasis Type="Italic">Osmoderma eremita</Emphasis> and <Emphasis Type="Italic">Elater ferrugineus</Emphasis>

Pheromone monitoring could provide unique spatial and temporal information about rare and threatened insect species for conservation purposes. Pheromone traps may be especially valuable in detecting fluctuations and declines in vulnerable species, if trap catch can be related to population density. We exploited the pheromone-kairomone system of the hermit beetle Osmoderma eremita and its predator, the red click beetle Elater ferrugineus, to monitor variation in their flight activity during 7 years (2001–2002, 2005–2009). Spatial and temporal flight activity of O. eremita and E. ferrugineus were highly correlated over individual trap replicates and trap days. Yearly flight activities of both species were correlated within two core sites included during all years of the study, and positively affected by temperature both within and between years. Flight activity could not be directly translated to variation in abundance in either species, however. Dispersal rate was likely the main factor explaining flight activity in O. eremita. Normalizing the flight activity of E. ferrugineus against that of O. eremita did not eliminate most of the variability, however, suggesting that flight activity of E. ferrugineus was governed both by dispersal rate and by population density. Higher fluctuations in population density of E. ferrugineus likely render it more vulnerable to local extinction, which may explain the greater rarity of this species. We suggest that preserving large assemblies of suitable hollow trees would be absolutely essential for buffering against stochastic population fluctuations and securing the long-term persistence of E. ferrugineus.     

Influence of Temperature,pH and Selected Growth Media on Germination,Growth and Sporulation of Aschersonia placenta and Hypocrella raciborskii

Tween 70 at 0.1% provided the best conditions for germination of Aschersonia placenta. Optimum germination and growth of the germ tube occurred over a temperature range of 25–30°C and a pH range of 5.0–6.0. A temperature of 30°C resulted in the longest germ tube at 45 μm. Apparently, temperature and pH did not affect the type of germination, with polar germination being consistently recorded for in excess of 60% of conidia. In general, growth and sporulation seemed to be much better in semi‐solid than in liquid media. Amongst several plant media tested, pumpkin consistently gave the most mycelial growth and sporulation. The ability of A. placenta to sporulate on the surface of liquid culture has increased the possibilty of its mass production for the purpose of formulating a microbial pesticide against the indigenous scale insects of tropical fruits such as durian and guava in Malaysia.     

Influence of Different Storage Conditions on the Mycotoxin Production and Quality of Fusarium-Infected Wheat Grain

Wheat seed samples with different initial infection levels of Fusarium culmorum were kept under different storage conditions for 36 weeks. Samples for analysis were drawn before storage and at intervals of 6‐8 weeks to determine the mycotoxin contents, seed health and seed quality. Zearalcnone (ZEA) accumulated to higher kernel contents towards the end of storage, when the seed was stored under warm and humid conditions [25°C/90% relative humidity (RH)], whereas the deoxynivalenol (DON) content of severely infected kernel samples (> 50%) remained unchanged under any of the conditions. On the other hand, DON contents increased in samples with a slight (4%) or moderate (15%) Fusarium infection level. when the seed was stored under Warm and humid conditions. Nivalenol (NIV) was not found in any samples immediately after harvest but later on in storage, and only under cool or warm but very humid conditions (15°C/84% RH and 25°C/90% RH). During storage, the mycotoxin contents of the samples did not reflect the percentage of Fusarium infected kernels. Under warm but dry conditions (25°C/62% RH) the seed germination rate showed a slight increase or remained nearly constant; at the same time the Fusarium infection level of the kernels decreased fairly fast. Cool and dry conditions (15°C/56% RH) maintained good seed quality but the Fusarium infection level of the kernels remained largely the same. Warm and humid conditions are not appropriate to maintaining quality of both seed and grain product.     

Cannibalism of parasitoid‐attacked conspecifics in a non‐carnivorous caterpillar

Cannibalism, the killing and consumption of conspecifics, can even occur in insect species typically considered to be non‐carnivorous. Of particular interest is the cannibalism of parasitoid‐attacked conspecifics, which could reduce parasitism levels in subsequent generations for that conspecific population. This study reports on the occurrence and some of the consequences of cannibalism in parasitoid‐attacked obliquebanded leafroller, Choristoneura rosaceana (Harris) (Lepidoptera: Tortricidae). We show that larvae of C. rosaceana, which is considered to be an herbivorous caterpillar species, did not prey upon live conspecifics, but readily consumed conspecifics attacked by Habrobracon gelechiae Ashmead (Hymenoptera: Braconidae). Further examination found that C. rosaceana larvae feeding on parasitoid‐attacked conspecifics, since their fourth instar, suffered a higher mortality and reduction in body size than those fed on plant material only. The cannibalism of attacked conspecifics did not appear to offer any nutrient benefits for the cannibal. To our best knowledge, this is the first empirical example of the occurrence and some of the consequences of cannibalism by a non‐carnivorous insect on its parasitoid‐attacked conspecifics. We discuss the adaptive significance of such cannibalism on parasitoid‐attacked conspecifics with respect to a trans‐generational fitness gain for the population through the killing of the parasitoids, thereby reducing parasitism in subsequent generations.     

Cascading effects of cannibalism in a top predator

1. Predator interactions are often driven by size differences, with larger predators consuming smaller ones. Cannibalism is widespread among predators, and can be more intense than antagonistic interactions between different predator species. 2. In a series of greenhouse experiments and a field experiment, we investigated the role of size structure in shaping the impacts of a top predator (the wandering spider Cheiracanthium mildei L. Koch) on an insect herbivore in vineyards of Napa County, California. 3. In greenhouse cages, survival of small C. mildei was lower when large C. mildei were present, and the combined effects of small and large C. mildei on leafhopper numbers and grape leaf damage were non‐additive. The frequency of cannibalism in C. mildei did not change when the abundance of leafhoppers was manipulated. However, in the field experiment small and large C. mildei combined additively to reduce leafhopper numbers. 4. Results show that cannibalism has the potential to dampen the cascading effects of C. mildei in a vineyard food web, but that it may be less important than other mortality factors in the field. Nonetheless, C. mildei substantially impacted leafhoppers in both the greenhouse and the field, suggesting that mortality caused by cannibalism or other factors may not compromise its overall predatory impacts.     

Effect of laboratory culture conditions on population growth of Proisotoma minuta (Tullberg) (Collembola: Isotomidae)

The collembolan Proisotoma minuta (Tullberg) was successfully maintained in a laboratory culture that could be used to produce large numbers of P. minuta of standard size and physiological condition. The general life history of P. minuta was studied using a substrate comprising a mixture of plaster of Paris and charcoal with baker's yeast as food. The mean time taken for eggs to hatch following oviposition was 10.6 ± 1.3 days at 17.5°C and 6 ± 0.5 days at 23°C. Conditions in the culture were very important for the production of large insect populations. Growth of the cultures was limited by the increasing population size and was probably affected by contamination of the habitat by the deposition of excretory materials. Proisotoma minuta from a population that had ceased egg production started oviposition after individuals were transferred to a fresh plaster of Paris and charcoal habitat.     

Studies on host preference and its biological effects on the Red Palm weevil,Rhynchophorus ferrugineus Olivier in Egypt B. vegetable crops

The investigation on some Egyptian vegetables preference by the Red Palm weevil (RPW), Rhynchophorus ferrugineus has been carried out under laboratory conditions to explore a suitability of alternative host plants. The choice test of insect larvae showed that Taro, Squash, Eggplant, common potato, yellow carrot, tomato and sweet pepper were accepted food, while the Table beet (Vegetable) was rejected. Non-choice feeding of R. ferrugineus larvae on vegetables affected larval body weight and increased larval mortality. Highest rate of pupation was recorded from larvae fed on C. pepo (92%) and B. vulgaris (97%). Adult emergence reached 80% and 92% on C. pepo and Sugar beet (field crop) (field crop). The external skin of sugar cane was not acceptable food for insect larvae, while injured sites and internal soft fibres were preferred as food. Therefore, vegetable fruits, stem of sugarcane are believed to be the most vulnerable hosts for red weevil attack. The alternative host plant examined can be used to monitor the dynamics of the population of RPW in order to take effective preventive measures and most powerful tool available for use in pest management.     

Three-dimensional temporal and spatial distribution of adult Rhyzopertha dominica in stored wheat and corn under different temperatures, moisture contents, and adult densities

Three-dimensional temporal and spatial distributions of adult Rhyzopertha dominica (F.) at adult densities of 1.0, 5.0, and 10.0 adults per kg grain and at 20 +/- 1, 25 +/- 1, and 30 +/- 1 degrees C were determined in 1.5 t bins filled with wheat (Triticum aestivum L.) with 11.0 +/- 0.8, 13.0 +/- 0.6, and 15.0 +/- 0.5% moisture content (wet basis) or corn (Zea mays L.) with 13.0 +/- 0.2% moisture content (wet basis). At each of five sampled locations, grain was separated into three 15-kg vertical layers, and adult numbers in each layer were counted. Inside both corn and wheat, adults did not prefer any location in the same layer except at high introduced insect density in wheat. The adults were recovered from any layer of the corn and >12, 65, and 45% of adults were recovered in the bottom layer of the corn at 20, 25, and 30 degrees C; respectively. However, <1% of adults were recovered in the bottom layer of wheat. Numbers of adults correlated with those in adjacent locations in both vertical and horizontal directions, and the temporal continuous property existed in both wheat and corn. Adults had highly clumped distribution at any grain temperature and moisture content. This aggregation behavior decreased with the increase of adult density and redistribution speed. Grain type influenced their redistribution speed, and this resulted in the different redistribution patterns inside wheat and corn bulks. These characterized distribution patterns could be used to develop sampling plans and integrated pest management programs in stored grain bins.     

Über den Kannibalismus bei Larven der Baumwollblatteule

On cannibalism of the larvae of the cotton leafworm Spodoptera littoralis (Boisd.) . Some ecological studies on the larvae of the cotton leafworm Spodoptera littoralis (Boisd.) were carried out in the laboratory to prove the appearance of cannibalism under different conditions of temperature, relative humidity, population density as well as abstraction of food, and furthermore the effect of food and food quantity. Results obtained showed, that when food was sufficiently provided the different instars did not show any cannibalistic habit. Cannibalism only appeared in case of insufficient quantity of food and reached its maximum at total withdrawal of food. The cannibalism rate was different for the various instars, the fourth stage showed the highest rate. During moulting time the rate was very low. The cannibalism rate was higher at 35° C than at lower temperatures and at lower relative humidity (30–40%) higher than at higher relative humidity (70–80%). In a limited space under withdrawal of food the rate was higher with greater initial numbers of larvae than with lower initial numbers. This rate was also higher for the cultures of mixed larvae instars than for the cultures of unmixed larvae instars. Records after 72 hours showed that only the eldest instars of larvae survived. The cannibalism rate increased with the length of the fasting period.