Impact of food source on survival of red flour beetles and confused flour beetles (Coleoptera: Tenebrionidae) exposed to diatomaceous earth

A series of experiments was conducted to determine the effect of a flour food source on survival of red flour beetle, Tribolium castaneum (Herbst), and confused flour beetle, Tribolium confusum (DuVal), exposed to the labeled rate (0.5 mg/cm2) of Protect-It, a marine formulation of diatomaceous earth. Beetles were exposed at 27 degrees C, and 40, 57, and 75% RH in 62-cm2 petri dishes. When beetles were exposed for 1 or 2 d in dishes with the labeled rate (0.5 mg/cm2, or 31 mg per dish) of diatomaceous earth or in dishes containing flour at varying levels from 0 to 200 mg mixed with the labeled rate of diatomaceous earth, survival of both species increased as the amount of flour increased, and quickly plateaued at levels approaching 100%. In a second set of experiments, beetles were transferred to dishes containing flour at varying levels from 0 to 200 mg after they were exposed for 1 or 2 d in dishes with the labeled rate of diatomaceous earth alone. There were no significant differences in beetle survival among the levels of flour, however, survival in dishes with flour was usually greater than survival in dishes with diatomaceous earth alone. In a third test, beetles were exposed for 1, 2, and 3 d in dishes with either the labeled rate of diatomaceous earth alone (clean dishes), dishes with diatomaceous earth and empty straws, or dishes with diatomaceous earth and approximately 300 mg of flour packed in the straws. Survival was not significantly different between clean dishes or dishes with straws, but survival in dishes containing the straws with flour was usually 100%, regardless of exposure interval. In all experiments, confused flour beetles were less susceptible to diatomaceous earth than red flour beetles. In addition, survival was negatively related to exposure interval and positively related to relative humidity.     

Toxicity of diatomaceous earth to red flour beetles and confused flour beetles (Coleoptera: Tenebrionidae): effects of temperature and relative humidity

Red flour beetles, Tribolium castaneum (Herbst), and confused flour beetles, Tribolium confusum (DuVal), were exposed for 8-72 h to diatomaceous earth (Protect-It) at 22, 27, and 32 degrees C and 40, 57, and 75% RH (9 combinations). Insects were exposed to the diatomaceous earth at 0.5 mg/cm2 on filter paper inside plastic petri dishes. After exposure, beetles were held for 1 wk without food at the same conditions at which they were exposed. Mortality of both species after initial exposure was lowest at 22 degrees C but increased as temperature and exposure interval increased, and within each temperature decreased as humidity increased. With 2 exceptions, all confused flour beetles were still alive after they were exposed at 22 degrees C, 57 and 75% RH. Mortality of both species after they were held for 1 wk was greater than initial mortality for nearly all exposure intervals at each temperature-humidity combination, indicating delayed toxic effects from exposure to diatomaceous earth. For both species, the relationship between mortality and exposure interval for initial and 1-wk mortality was described by linear, nonlinear, quadratic, and sigmoidal regression. Mortality of confused flour beetles was lower than mortality of red flour beetles exposed for the same time intervals for 46.7% of the total comparisons at the various temperature-relative humidity combinations.     

Thermal death kinetics of red flour beetle (Coleoptera: Tenebrionidae)

While developing radio frequency heat treatments for dried fruits and nuts, we used a heating block system developed by Washington State University to identify the most heat-tolerant life stage of red flour beetle, Tribolium castaneum (Herbst), and to determine its thermal death kinetics. Using a heating rate of 15 degrees C/min to approximate the rapid heating of radio frequency treatments, the relative heat tolerance of red flour beetle stages was found to be older larvae > pupae and adults > eggs and younger larvae. Lethal exposure times for temperatures of 48, 50, and 52 degrees C for the most heat-tolerant larval stage were estimated using a 0.5th order kinetic model. Exposures needed for 95% mortality at 48 degrees C were too long to be practical (67 min), but increasing treatment temperatures to 50 and 52 degrees C resulted in more useful exposure times of 8 and 1.3 min, respectively. Red flour beetle was more sensitive to changes in treatment temperature than previously studied moth species, resulting in red flour beetle being the most heat-tolerant species at 48 degrees C, but navel orangeworm, Amyelois transitella (Walker), being most heat tolerant at 50 and 52 degrees C. Consequently, efficacious treatments for navel orangeworm at 50-52 degrees C also would control red flour beetle.     

Electroantennographic responses of red flour beetle Tribolium castaneum Herbst (Coleoptera: Tenebrionidae) to volatile organic compounds

The red flour beetle Tribolium castaneum Herbst (Coleoptera: Tenebrionidae) is the most encountered and destructive stored product insect pest of cereal grains and seeds. Although this beetle has been used as a model organism for many decades, there is no systematic knowledge about antennal detection of host and non‐host volatiles. Electroantennogram responses to 94 selected volatile organic compounds including alkanes, alkenes, alcohols, aldehydes, ketones, carboxylic acids, esters, terpenoids and aromatic compounds were recorded from both sexes of T. castaneum. Overall, female and male T. castaneum exhibited similar electroantennography (EAG) responses. Compounds eliciting the strongest EAG responses within compound groups of chemical similarity were undecane, 1‐hexen‐3‐ol, octanal, 2‐heptanone, hexanoic acid and ethyl hexanoate. Comparison of vapour pressure and EAG amplitudes within homologous series of compounds revealed responses to undecane, octadecane, octanal, nonanal, 2‐heptanone, hexanoic acid and octanoic acid as outstanding. Given that systematic EAG screenings have not been conducted before, these are the best candidates for evaluation in future behavioural studies to unravel their potential for application in integrated pest management strategies of T. castaneum.     

Digestive proteolysis organization in two closely related Tenebrionid beetles: red flour beetle (Tribolium castaneum) and confused flour beetle (Tribolium confusum)

The spectra of Tribolium castaneum and T. confusum larval digestive peptidases were characterized with respect to the spatial organization of protein digestion in the midgut. The pH of midgut contents in both species increased from 5.6–6.0 in the anterior to 7.0–7.5 in the posterior midgut. However, the pH optimum of the total proteolytic activity of the gut extract from either insect was pH 4.1. Approximately 80% of the total proteolytic activity was in the anterior and 20% in the posterior midgut of either insect when evaluated in buffers simulating the pH and reducing conditions characteristic for each midgut section. The general peptidase activity of gut extracts from either insect in pH 5.6 buffer was mostly due to cysteine peptidases. In the weakly alkaline conditions of the posterior midgut, the serine peptidase contribution was 31 and 41% in T. castaneum and T. confusum, respectively. A postelectrophoretic peptidase activity assay with gelatin also revealed the important contribution of cysteine peptidases in protein digestion in both Tribolium species. The use of a postelectrophoretic activity assay with p‐nitroanilide substrates and specific inhibitors revealed a set of cysteine and serine endopeptidases, 8 and 10 for T. castaneum, and 7 and 9 for T. confusum, respectively. Serine peptidases included trypsin‐, chymotrypsin‐, and elastase‐like enzymes, the latter being for the first time reported in Tenebrionid insects. These data support a complex system of protein digestion in the Tribolium midgut with the fundamental role of cysteine peptidases. © 2009 Wiley Periodicals, Inc.     

Selection for high and low amylase activity in adult flour beetles (Tribolium confusum) (Coleoptera,Tenebrionidae)

As a result of selection for high amylase activity in two strains of the flour beetle Tribolium confusum, mean activity considerably increased. Selection for low activity was ineffective in one strain, and mean activity increased, contrary to expectation, in the downward-selection line of the other.Heritabilities of amylase activity were 0.52 and 0.18 for the two strains (estimated by offspring-midparent regression in generation 1). Environmental factors have considerable effects on activity.The outcome of selection and possible models for the genetic control of amylase activity in Tribolium are discussed.     

Higher level molecular phylogeny of darkling beetles (Coleoptera: Tenebrionidae)

Insect diversity represents about 60% of the estimated million‐and‐a‐half described eukaryotic species worldwide, yet comprehensive and well‐resolved intra‐ordinal phylogenies are still lacking for the majority of insect groups. This is the case especially for the most species‐rich insect group, the beetles (Coleoptera), a group for which less than 4% of the known species have had their DNA sequenced. In this study, we reconstruct the first higher level phylogeny based on DNA sequence data for the species‐rich darkling beetles, a family comprising at least 20 000 species. Although amongst all families of beetles Tenebrionidae ranks seventh in terms of species diversity, the lack of knowledge on the phylogeny and systematics of the group is such that its monophyly has been questioned (not to mention those of the subfamilies and tribes contained within it). We investigate the evolutionary history of Tenebrionidae using multiple phylogenetic inference methods (Bayesian inference, maximum likelihood and parsimony) to analyse a dataset consisting of eight gene fragments across 404 taxa (including 250 tenebrionid species). Although the resulting phylogenetic framework only encompasses a fraction of the known tenebrionid diversity, it provides important information on their systematics and evolution. Whatever the methods used, our results provide strong support for the monophyly of the family, and highlight the likely paraphyletic or polyphyletic nature of several important tenebrionid subfamilies and tribes, notably the polyphyletic subfamilies Diaperinae and Tenebrioninae that clearly require substantial revision in the future. Some interesting associations in several groups are also revealed by the phylogenetic analyses, such as the pairing of Aphtora Bates with Phrenapatinae. Furthermore this study advances our knowledge of the evolution of the group, providing novel insights into much‐debated theories, such as the apparent relict distribution of the tribe Elenophorini.     

Susceptibility of lady beetles (Coleoptera: Coccinellidae) to entomopathogenic nematodes

We investigated differential susceptibility of lady beetles to entomopathogenic nematodes, for two reasons: (1) to estimate potential nontarget effects on natural lady beetle populations, (2) to compare the susceptibility of exotic versus native lady beetle species. We hypothesize that successful establishment of some exotically introduced arthropods may be due, in part, to a lower susceptibility relative to competing native species. In laboratory studies, we compared the pathogenicity, virulence, and reproductive capacity of Heterorhabditis bacteriophora and Steinernema carpocapsae among two native (Coleomegilla maculata and Olla v-nigrum) and two successfully established exotic (Harmonia axyridis and Coccinella septempunctata) lady beetles, and a known susceptible lepidopteran host, Agrotis ipsilon. After 1 and 2 days of exposure to either nematode species, mortality of A. ipsilon was higher than in all lady beetles. Thus, we predict that nematode field applications would have significantly less impact on lady beetle populations than on a susceptible target pest. Additionally, the impact of soil-applied nematodes may be lower on lady beetles than on soil-dwelling hosts because the former spends relatively less time on the soil. Exotic lady beetles were less susceptible to nematode infection than native species. Reproductive capacity data also indicated lower host suitability in H. axyridis, but not in C. septempunctata. Overall, the hypothesis that low susceptibility to pathogens in certain exotic lady beetles may have contributed to competitive establishment was supported (especially for H. axyridis). Additional studies incorporating different hosts and pathogens from various geographic locations will be required to further address the hypothesis.     

Insecticidal potential of natural zeolite and diatomaceous earth formulations against rice weevil (Coleoptera: Curculionidae) and red flour beetle (Coleoptera: Tenebrionidae)

Insecticidal potential of natural zeolites and diatomaceous earths originating from Serbia against Sitophilus oryzae (L.) and Tribolium castaneum (Herbst) was evaluated. Two natural zeolite formulations (NZ and NZ Modified) were applied to wheat at rates of 0.50, 0.75, and 1.0 g/kg, while two diatomaceous earth (DE) formulations (DE S-1 and DE S-2) were applied at rates of 0.25, 0.50, 0.75, and 1.0 g/kg. A bioassay was conducted under laboratory conditions: temperature of 24 +/- 1 degrees C, relative humidity in the range 50-55%, in tests with natural zeolites, and 60-65%, in tests with DEs, and in all combinations for progeny production. Mortality was assessed after 7, 14, and 21 d of insect contact with treated wheat, and the total mortality after an additional 7-d recovery on untreated broken wheat. Progeny production was also assessed after 8 wk for S. oryzae and 12 wk for T. castaneum. The highest mortality for S. oryzae and T. castaneum was found after the longest exposure period and 7 d of recovery, on wheat treated with NZ at the highest rate and DEs at rates of 0.50 -1.0 g/kg. Progeny reduction higher than 90% was achieved after 14 and 21 d of contact of both beetle pests with wheat treated with DE S-1 at 0.50-1.0 g/kg and DE S-2 at 0.75-1.0 g/kg, while the same level of reduction was achieved only for T. castaneum after its contact with the highest rate of NZ formulation. NZ Modified, applied even at the highest rate, revealed much lower insecticidal potential.     

Compensatory proteolytic responses to dietary proteinase inhibitors in the red flour beetle, Tribolium castaneum (Coleoptera: Tenebrionidae)

Increasing levels of inhibitors that target cysteine and/or serine proteinases were fed to Tribolium castaneum larvae, and the properties of digestive proteinases were compared in vitro. Cysteine proteinases were the major digestive proteinase class in control larvae, and serine proteinase activity was minor. Dietary serine proteinase inhibitors had minimal effects on either the developmental time or proteolytic activity of T. castaneum larvae. However, when larvae ingested cysteine proteinase inhibitors, there was a dramatic shift from primarily cysteine proteinases to serine proteinases in the proteinase profile of the midgut. Moreover, a combination of cysteine and serine proteinase inhibitors in the diet prevented this shift from cysteine proteinase-based digestion to serine proteinase-based digestion, and there was a corresponding substantial retardation in growth. These data suggest that the synergistic inhibitory effect of a combination of cysteine and serine proteinase inhibitors in the diet of T. castaneum larvae on midgut proteolytic activity and beetle developmental time is achieved through the prevention of the adaptive proteolytic response to overcome the activity of either type of inhibitor.     

Critical examination of postulated cladistic relationships among species of flour beetles (genus Tribolium,Tenebrionidae, Coleoptera)

Cytological considerations have led to the hypothesis that Tribolium confusum (CF) evolved from an ancestor similar to T. castaneum (CS) by translocation of an autosome to the X chromsome, and that T. destructor (DEST) was derived from CF. T. brevicornis (BREV) is regarded as the most primitive on morphological grounds. Electrophoretic analyses of 19 strains of CS, 7 of CF, and 1 each of DEST and BREV do not support this postulated evolutionary pathway. CF and CS are much more similar to BREV than they are to each other. (Comparisons of morphological mutations in CS and CF also indicate that the two species are not similar genetically.) DEST and CF are very dissimilar electrophoretically. It is likely that the species evolved independently from an ancestral stock which may be represented by BREV. Recognition of gene homology in different species is the keystone for all attempts at constructing genetically meaningful evolutionary pathways. The difficulties involved in doing so are pointed out.     

Climatic correlates of body size in European tenebrionid beetles (Coleoptera: Tenebrionidae)

Tenebrionidae are one of the largest families of beetles and are known for their adaptations to hot and dry climates. An increase in body size also increases the volume/surface area ratio, which reduces transpiration, and hence water loss. If an increase in body size is an important adaptation in tenebrionids to cope with increasing aridity, we expect a correlation between body size and climatic gradients in the major tenebrionid clades. Alternatively, we can postulate that arid climates do not drive body size evolution, but rather select, from a wider fauna containing species of any size, those that have larger bodies. In this case we expect that drier regions will host faunas that contain, on average, larger species. To test the first hypothesis, we correlated inter-specific body size variation in the main tenebrionid clades with climatic gradients in Europe. We found only weak trends. To test the second hypothesis, we regressed mean body size of European country faunas against climatic characteristics. We found a strong increase in body size in southern faunas experiencing hot and dry climates. Therefore, increase in body size is not a major adaptation in tenebrionid evolution, but climate is an important filtering factor that determines a prevalence of larger species in southern Europe.     

Life forms and strategies of lichen-feeding darkling beetles (Coleoptera,Tenebrionidae: Helopini)

Trophic relations of lichen-feeding darkling beetles of the tribe Helopini in Turkey, the Caucasus, and Anti-Atlas are considered. This group is the most diverse in relict Anatolian forests of Cedrus libani, Abies cilicica, Pinus nigra, Juniperus spp., and Quercus cerris, where multitaxon lichenophagous assemblages exist. Three life strategies for attenuation of interspecific competition are distinguished: (1) differentiation of the consumed lichens, (2) separation of the life forms based on the types of the lichens consumed, and (3) segregation of circadian activity in adults. We assume that adaptation of the Helopini larvae to the soil life promoted their wide distribution in different landscapes by elimination of the limiting factor for completing their life cycles, namely the need for ligneous substrate of old rotting trees. The possibility of using lichen-feeding beetles of the tribe Helopini in ecosystem and lichen indication is considered.     

A multidimensional characterization of rarity applied to the Aegean tenebrionid beetles (Coleoptera Tenebrionidae)

This paper attempts to use museum collection data to estimate measures of species rarity and then to relate these measures to extinction risk. For this purpose, 170 taxa (138 species and 32 subspecies) of tenebrionid beetles from 32 Aegean Islands (Greece) were considered. For each taxon, rarity was evaluated as geographic distribution (mean incidence on islands in the archipelago), potential habitat exploitation (total area of the islands occupied on the total area of the study system) and contactability (number of decades of taxon’s records on the total number of decades of assumed persistence from 1870 to 2000). All of these indices were correlated to each other. Whether expressed in terms of range size or habitat exploitation rarity was a major determinant of a species’ risk of extinction (evaluated as extinction decade). Thus, the designation of rarity provides a good basis for identifying species that are most in need of conservation at a particular scale.     

Susceptibility of Tribolium castaneum (Coleoptera: Tenebrionidae) life stages to flameless catalytic infrared radiation

The susceptibility of various life stages of the red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae), a pest of stored wheat, Triticum aestivum L., to flameless catalytic infrared radiation in the 3-7-microm range was evaluated in the laboratory. Immature stages were collected from flour infested with T. castaneum adults only for 1 d. Stages collected after 1 d represented eggs (collected on day 0); those collected after 7, 14, and 21 d from day 0 represented larvae in different developmental stages, whereas those collected after 24 d represented pupae. Adults (2 wk old) were collected after 42 d. Each of these stages was exposed for 45 or 60 s in 113.5 or 227.0 g of wheat at a distance of 8.0 or 12.7 cm from a bench top infrared emitter. The mean temperatures attained during exposures were measured continuously using a noncontact infrared thermometer connected to a computer. The mean grain temperatures attained increased with an increase in exposure time and were inversely related to distance from the emitter. Grain quantity least influenced mean temperatures attained. Pupae were the least susceptible stage and larvae collected after 7 d were the most susceptible stage. Variation in probability of death of various life stages decreased with an increase in mean grain temperatures attained. All life stages were killed after a 60-s exposure at a distance of 8.0 cm from the emitter in 113.5 g of wheat, where the mean +/- SE temperatures attained ranged from 107.6 +/- 1.2 to 111.4 +/- 0.5 degrees C. Our laboratory results using small grain quantities and short exposure times showed that flameless catalytic infrared radiation can be a valuable tool for managing insects in stored organic and nonorganic wheat.