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.

Reproduction, survival, and life table parameters of the predatory mite Cheyletus malaccensis (Acari: Cheyletidae) at various constant temperatures.

Reproduction, survival, and life table parameters of the predatory mite Cheyletus malaccensis Oudemans were evaluated at six constant temperatures: 17.5, 20, 25, 30, 32.5 and 35°C, feeding on Tyrophagus putrescentiae (Schrank). Preoviposition period of fertilized and virgin females varied with temperature from ca. 9 days at 17.5°C to ca. 1.5 day at 32.5°C and then increased to ca. 3 days at 35°C. Virgin female oviposition period was significantly shorter than for fertilized females at the temperatures examined with the exception of 17.5°C. The mean total number of eggs per fertilized (169.7 ± 6.6) and virgin female (60.7 ± 4.3) was highest at the temperature of 30°C. The data indicated a significant positive and nearly doubling effect of fertilization on female fecundity at the temperatures examined with the exception of 17.5°C. Age-specific fecundity was described by a temperature dependent model from which the maximum daily fecundity rate was estimated for fertilized and virgin females at 10.3 (at 30°C) and 6.8 (at 32.5°C) eggs/female, respectively. Virgin female longevity was significantly shorter than for fertilized females at 20, 30 and 32.5°C, and decreased from ca. 57 days at 17.5°C to ca. 17 days at 35°C. The Weibull function that was used to describe the age specific survival of fertilized and virgin females produced excellent fits to the survival data. Estimates of intrinsic rate of increase, net reproductive rate, mean generation time, doubling time and finite rate of increase, were obtained. The r(m) value increased with temperature from 0.03 (day(-1)) at 17.5°C to 0.21 (day(-1)) at 32.5°C, after which it decreased to 0.15 (day(-1)) at 35°C. These data indicate that C. malaccensis can reproduce at temperatures between 17.5 and 35°C and can be used for biological control of astigmatid mites within the temperature range where the pest occurs.

Acaricidal effect of different diatomaceous earth formulations against Tyrophagus putrescentiae (Astigmata: Acaridae) on stored wheat.

Laboratory bioassays were conducted to evaluate the effect of different diatomaceous earth (DE) formulations against adults and immature stages of the stored-product mite species Tyrophagus putrescentiae (Schrank). Five DE formulations were used in the tests: SilicoSec, PyriSec, Insecto, Protect-It, and DEA-P. The tests were conducted at 25 degrees C and 75% RH, on wheat, Triticum aestivum L., treated with DEs at two dose rates, 0.2 and 0.5 g/kg. The mortality of mite individuals was measured after 5 d of exposure, and after 30 d the treated wheat was checked for T. putrescentiae offspring. Significant differences were noted among the DEs tested. Application of the lowest dose rate (0.2 g/kg) provided mortality of both adults and immatures that exceeded 78%, whereas the respective data for 0.5 g/kg were almost in all cases 100%. The adults of T. putrescentiae were more tolerant to DEs than the immature stages. Generally, PyriSec was the most effective against adults. Progeny production was dramatically reduced with the increase of dose. The results of the present work indicate that T. putrescentiae can be effectively controlled by DEs on wheat, at dose rates as low as 0.2 g/kg.

Temperature-dependent development of the predatory mite Cheyletus malaccensis (Acari: Cheyletidae).

The effect of temperature on the development of immature stages of the predator Cheyletus malaccensis Oudemans, produced by either fertilized or virgin females, was studied at 17.5, 20, 25, 30, 32.5, and 35 degrees C, 80 +/- 5% relative humidity, in complete darkness, and fed Tyrophagus putrescentiae (Schrank). The population maintained at 15 degrees C failed to reproduce. The thermal data obtained were used for the estimation of the thermal requirements (developmental thresholds, thermal constant, optimum temperature) of this predator by a linear and nonlinear model (Logan type I model). Upper and lower developmental thresholds ranged between 37.4-37.8 and 11.6-12.0 degrees C, respectively. Optimum temperature for development was estimated at between 33.1 and 33.5 degrees C. The thermal constant ranged between 238.1 and 312.5 degree-days. Based on the data of the total pre-imaginal period, immatures' survival peaked at 25 degrees C. Arrhenotokous parthenogenesis (haplodiploidy) is confirmed in the species: virgin females always produce males, whereas fertilized females give rise to offspring of both sexes. Survival of the immature stages and offspring sex ratio were not significantly influenced by temperature.

Mites associated with stored products in Greece.

A faunistic survey of mites was conducted in many product stores during a 6-year study period, 2000-2005, in Greece. A total of 1,073 samples were taken from 34 Greek counties. The survey was carried out on grains (wheat, maize, oat, barley), flour, bran, manufactured agricultural foodstuffs, dried fruits (figs, raisins), residues and dust, stored in varying quantities in five types of storage facilities (stores of agricultural cooperative unions, farm stores, commercial stores, flour mills and silos). Dominance-frequency analysis and redundancy analysis (RDA) were used to reveal the preferences of the collected taxa. Approximately 55% of the samples contained mites and 65 mite taxa were identified, belonging to 15 families in four orders. Six species, namely, Acarus gracilis Hughes, A. immobilis Griffiths, Caloglyphus oudemansi (Zachvatkin), Suidasia medanensis Oudemans, Tyrophagus perniciosus Zachvatkin and Kleemania plumigera (Oudemans), were new to the fauna of Greece. Five species, Tyrophagus similis Volgin, Blattisocius mali (Oudemans), Neoseiulus barkeri (Hughes), Cheyletus cacahuamilpensis Baker and Storchia robustus (Berlese), were recorded for the first time in stored products in Greece. Lepidoglyphus destructor (Schrank), Tyrophagus putrescentiae (Schrank) and Acarus siro L. were dominant or intermediate in all storage facilities examined. Cheyletus malaccensis Oudemans was the most common predatory mite. The highest percentage of infestation (65.3) was recorded in the samples from stores of agricultural cooperative unions. Residue-type materials had the highest degrees and percentages of infestation.

Acaricidal effect of a diatomaceous earth formulation against Tyrophagus putrescentiae (Astigmata: Acaridae) and its predator Cheyletus malaccensis (Prostigmata: Cheyletidae) in four grain commodities.

Laboratory bioassays were conducted to evaluate the effect of the diatomaceous earth (DE) formulation SilicoSec (Biofa GmbH, Münsingen, Germany), against two stored-product mite species, Tyrophagus putrescentiae (Shrank) and the predator Cheyletus malaccensis Oudemans. For this purpose, DE was applied in wheat, oat, rye, and maize, at the dose rates 0, 0.5, 1, and 2 g/kg grain. The mortality of the exposed mites was assessed after 24 h, 48 h, 7 d, and 14 d of exposure in the treated substrate. After this interval, the treated grains were checked for oviposition or progeny. The tests were conducted at 80% RH and at two temperatures, 20 and 25 degrees C. Generally, for both species, mortality was higher at 25 degrees C than at 20 degrees C. For T. putrescentiae, at both temperatures, the mortality in grains treated with the highest DE rate was 100% after only 24 h of exposure, with the exception of maize at 20 degrees C, where mortality was 91.7%. The mortality of C. malaccensis after 24 h of exposure to the treated grains, in the absence of prey, did not exceed 29% at any of the temperature- grain-dose combinations, whereas no mites were dead in rye and maize treated with 0.5 and 1 g of DE. Even after 14 d of exposure at the highest DE rate, mite mortality did not reach 100%. The presence of T. putrescentiae individuals as prey in the treated substrate enhanced C. malaccensis survival. Hence, after 14 d of exposure, the mortality of C. malaccensis, in wheat, oat, rye, and maize treated with the highest DE rate was 51.7, 59.7, 70, and 36.9, respectively. No progeny production was recorded in the treated substrate for T. putrescentiae; in contrast, oviposition and F1 progeny were recorded for C. malaccensis. Our results suggest that the use of C. malaccensis with low doses of DE may be an appealing integrated pest management (IPM) approach against T. putrescentiae, and probably against other stored-grain mite species.

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.