Effect of moisture on growth rate and development of two strains of Tenebrio molitor L. (Coleoptera, Tenebrionidae)

Larvae of Tenebrio molitor L., reared on dry wheat shorts, grew and developed much more rapidly when free-choice water was available than when it was not. When water was supplied in cotton pads, larvae often burrowed in the moist pads and could obtain water by cuticular absorption or ingestion. Heavier larvae were also produced at pupation with a tendency for reduction of larval and pupal mortality and an increase in adult longevity in the water regimen. Two strains of T. molitor showed highly significant differences in their rates of growth and development. The faster developing strain in the dry condition also developed faster when free-choice water was available and weighed more as prepupal larvae, pupae and adults. Water also reduced the number of molts in the faster-developing strain. Although the mechanisms enabling more rapid growth under both dry and moist conditions are not known, strain differences in mealworms indicate genetic potential for completing life cycles more rapidly in dry environments with extremely rapid development possible under optimum moisture conditions.     

Radiosensitivity of Tribolium destructor Uyttenboogaart (Coleoptera: Tenebrionidae)

The development of adult Tribolium destructor Uyttenboogaart from eggs and larvae was prevented by exposing these immature stages to 5 krad of gamma irradiation. However, some adults did emerge when pupae were exposed to 5–30 krad. Adult longevity was significantly reduced, and sterility of both sexes was effected by doses of 10 krad and above. Control of this species therefore appears feasible with the levels of irradiation currently approved by the U.S. Food and Drug Administration (20–50 krad) for treatment of stored-grain insects in wheat and wheat flour in the U.S.     

Efficacy of the amorphous silica dust, Dryacide, against Tribolium confusum Duv. and Sitophilus granarius (L.) (Coleoptera: Tenebrionidae and Curculionidae)

Amorphous silica dust (Dryacide) was used to treat wheat at concentrations of 0, 250, 500, 750, and 1000 μg silica dust/g wheat. Adult Sitophilus granarius and Tribolium confusum were placed in the grain which was then incubated at 20 or 30°C and 40 or 60% r.h. Mortality counts were taken after 48 and 168 hr. S. granarius was more susceptible to silica dust than T. confusum under the same conditions. At the same temperature, the toxicity of silica dust to both species was more pronounced at 40 than 60% r.h. T. confusum was more tolerant to silica dust at 30 than at 20°C; whereas, S. granarius was more susceptible to it at 30 than 20°C. Silica dust reduced progeny 100% at 40% r.h. in all the concentrations that had been used. Progeny, however, were produced by S. granarius at 30°C and 60% r.h. but with significantly reduced numbers with increasing dosge. Silica dust had no adverse effect on wheat seed germination, wheat flour, and baking quality.     

Genetics of lindane resistance in Tribolium castaneum (Herbst) (Coleoptera, Tenebrionidae)

Dominant or partially dominant factors for resistance to lindane in Tribolium castaneum (Herbst) were demonstrated in linkage groups II, IV, V and VIII and a recessive factor was present in linkage group III. Linkage group VII and the X chromosome were also concerned in expression of the resistance.

A complex multifactorial type of inheritance is involved in lindane resistance in this species in Queensland.     

Effects of fasting and irradiation on the free amino acid content of Tribolium confusum J. Du Val. (Coleoptera: Tenebrionidae)

The aim of this study was to determine whether or not the change of the free amino acid (FAA) contents in irradiated Tribolium confusum male adults could be assigned to a lack of nutrition. The concentration of the amino acid pool (FAA) in Tribolium confusum males irradiated at 63, 315 and 504 Gy changed with time in nearly the same way as in insects deprived of food. This result confirms the inhibitory effect of irradiation on digestive functions. The time-course of FAA changes was dose independent from 63 to 504 Gy. No specific effect on intermediary metabolism was observed. The possibility of using FAA analysis to identify irradiated grains is discussed.     

The suitability of groundnuts for the development of Tribolium castaneum (Herbst) (Coleoptera, Tenebrionidae)

Tribolium castaneum is a major pest of stored shelled groundnuts. It preferentially attacks and develops well on the germ and only subsequently feeds on the less nutritional cotyledons. T. castaneum is capable of coping with high levels of protein in its diet. At levels encountered in whole groundnuts, groundnut protein is adequate for development. T. castaneum larvae use oil as efficiently as starch. Free fatty acids retard development and increase larval mortality at high concentrations; these detrimental effects are overcome by incorporating 3 per cent glucose in the diet. Groundnut saponins in a cholesterol-free diet have no adverse effect on larval development.     

Laboratory evaluation of two insect juvenile hormone analogues against Alphitobius diaperinus (Panzer) (Coleoptera: Tenebrionidae)

The insect juvenile hormone analogues methoprene and fenoxycarb have been tested against larval stages of the lesser mealworm, Alphitobius diaperinus. Methoprene completely prevented the formation of adult insects at a concentration of 5.0 ppm in food medium. The same effect was achieved with only 0.05 ppm fenoxycarb. There was no evidence that sub-lethal levels of methoprene decreased the fecundity of insects that successfully completed adult development. The results of these laboratory tests are discussed in relation to the potential use of these compounds for control of A. diaperinus in intensive poultry production units.     

Insecticidal properties of eugenol, isoeugenol and methyleugenol and their effects on nutrition of Sitophilus zeamais Motsch. (Coleoptera: Curculionidae) and Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae)

Eugenol, isoeugenol and methyleugenol showed similar contact toxicity to Sitophilus zeamais (LD₅₀ values approximately 30 μg/mg insect). For Tribolium castaneum, the order of potency of these chemicals compared by the LD₅₀ level was isoeugenol>eugenol>methyleugenol. Furthermore, S. zeamais was generally more susceptible than T. castaneum to these three compounds except for isoeugenol based on the LD₅₀ level. When sublethal doses (doses that produce no appreciable mortality) of eugenol, isoeugenol and methyleugenol were topically applied to adults of either species of beetles pre-treated with deltamethrin, the toxicity of deltamethrin was enhanced. A flour disc bioassay using no-choice tests was employed to assess, in terms of food consumption and growth rate, the susceptibility of S. zeamais and T. castaneum to media treated with eugenol, isoeugenol, and methyleugenol. Only eugenol significantly (P<0.05) reduced food consumption (RCR) in the adults of S. zeamais at a concentration of 13.2 mg/g food. However, it reduced the growth rate (RGR), food consumption and food utilisation (ECI) in adults and larvae of T. castaneum at concentrations of 35 and 99 mg/g food, respectively. Isoeugenol reduced the RGR and RCR in S. zeamais adults and T. castaneum adults and larvae, in a concentration-dependent manner, but only reduced ECI in the adults of T. castaneum at the concentration of 76 mg/g food. In comparison, methyleugenol reduced the RGR and RCR in the three groups of insects, and the ECI of S. zeamais adults and T. castaneum larvae.     

Toxicity of three organophosphorus compounds and pyrethrins to malathion-resistant Tribolium castaneum (Herbst) (Coleoptera, Tenebrionidae)

Malathion-resistant red flour beetles, Tribolium castaneum (Herbst), were tested for susceptibility to Bay 77488 (o,o-diethyl phosphorothioate o-ester with phenylglyoxylonitrile oxime), Bay 78182 (o,o-diethyl phosphorothioate o-ester with (o-chlorophenyl)glyoxylonitrile oxime), diazinon, and pyrethrins by topical applications. The malathion-resistant beetles showed 13·3-fold resistance to pyrethrins, 19·7-fold resistance to Bay 78182, 7·7- and 10·7-fold resistance to diazinon, and only 4·5- and 9·5-fold resistance to Bay 77488. Only about one-quarter as much Bay 77488 as malathion was required for the ₅₀ in the resistant beetles. About one-third as much Bay 78182 as malathion was required. Diazinon and pyrethrins were less toxic than malathion to the resistant insects.     

Comparative studies with Tribolium (Coleoptera, Tenebrionidae) — II: Productivity of T. castaneum (herbst) and T. confusum Duv. on natural, semi-synthetic and synthetic diets

Productivity of T. castaneum and T. confusum has been determined in the following diets: Naylor's synthetic medium; corn supplemented with the amino acids cystine, glutathione, proline and tryptophan in amounts necessary to bring them to the level found in wheat; corn and whole wheat flour without any supplements, and corn and whole wheat flour supplemented with brewer's yeast and vitamins. Relative developmental rates of the two species in these media were also determined by counting the numbers of adults emerging in 14-day periods.

Significant differences in productivity (the number of eggs surviving to the adult stage) have been detected within a species in the different media and between species within a given medium. The Naylor medium is unfavorable for both species, and judging from relative developmental rates less favorable to T. confusum than to T. castaneum.

T. castaneum performs poorest in non-supplemented media, better in media supplemented with vitamins, and the best in media supplemented with yeast. While T. confusum also shows an increased productivity in vitamin- and yeast-supplemented media, this increase is not as marked as in T. castaneum. Considering both the productivity and the developmental rates, it appears that the addition of the four amino acids to corn had a beneficial effect to T. castaneum but not to T. confusum. The two species were most productive in corn plus yeast, but this productivity was not significantly higher than in whole wheat flour plus yeast.

Drawing upon the evidence available in the literature, and the present data, it is concluded that T. confusum is better adapted to utilize a wider variety of foods than T. castaneum and in order to satisfy its greater quantitative requirements for certain nutrients, this species engages in cannibalism more often than T. confusum. The result is that, when the two species are introduced into the same container, i.e. compete for food and space, T. confusum is more often eliminated than T. castaneum.     

Comparative studies with Tribolium (Coleoptera, Tenebrionidae)—I: Productivity of T. castaneum (Herbst) and T. confusum Duv. on several commercially-available diets

Productivity (measured as the number of adult progeny produced in a given interval by a number of females) and relative developmental rates (the number of adult progeny found at specific intervals) have been determined for T. castaneum and T. confusum on a variety of different media. The media tested were flours of corn (C), rice (R), soy (S), whole wheat (W), a mixture of corn, rice, soy and whole wheat flour (M), white wheat (WW) and brown rice (BR) with and without a supplement of brewer's yeast.

In T. confusum the ranking of productivity on these seven media was found to be M>W>C>BR>R>WW>S in both unsupplemented and yeast-supplemented media, but the performance on all media was somewhat increased by the addition of yeast. The order of productivity on these media with T. castaneum was similar to that obtained for T. confusum, except that the response to yeast supplements was much more pronounced for all media except soy. In particular, white wheat, brown rice and rice, which must be considered “poor” media for T. castaneum in the absence of yeast, compared very favorably, in terms of productivity, with whole wheat and corn when these media were supplemented with yeast. These data are summarized in Table 6 and Fig. 1.

These productivity results are supported by information obtained about the developmental rates of the two species on these media-in general, developmental rate was much slower on those media showing the lowest productivity.

From considerations of the content of the flours used, the data suggest that soy is more toxic to T. castaneum than to T. confusum, and that T. castaneum requires more vitamins and/or minerals than does T. confusum. This conclusion is largely judged by the performance of the two species on white and brown rice, and their performance on yeastless and yeast-supplemented media. The data are given in Table 5 and shown in graph form in Fig. 2.

It is suggested that T. castaneum may require greater amounts of leucine, alanine, and aspartic acid than T. confusum, and that T. confusum requires larger amounts of threonine, tyrosine and possibly methionine than T. castaneum.     

Radiation sensitivity of successively irradiated generations of Tribolium castaneum (Herbst) (Coleoptera,Tenebrionidae), and Sitophilus oryzae (L.) (Coleoptera,Curculionidae)

Four populations of Tribolium castaneum (Herbst) and of Sitophilus oryzae (L.) were treated with 0 (control), 0·5, 1 or 2 krad of gamma radiation for 7 and 5 successive generations, respectively, and the adults from the subsequent unirradiated generation of each population were checked for fecundity. Groups of 6th generation T. castaneum and S. oryzae adults from each population were tested for resistance to acute radiation by exposure to doses of 16 and 50 krad followed by a check for mortality.No evidence of increased resistance to acute radiation exposures was found. Irradiated T. castaneum populations did not show significant decreases in mean survival time, but some significant decreases in life-span of irradiated S. oryzae populations were found.Fecundity of the 8th generation 0·5 krad T. castaneum was greater than that of the control population, but 1- and 2-krad populations did not show any difference in fecundity. Fecundity of the 6th generation S. oryzae population was not significantly different from that of the control, but 1- and 2-krad populations had significantly reduced fecundities. The test results indicated that possible accidental exposure of some insects to substerilizing doses during commercial radiation disinfestation is unlikely to bring about the development of radiation-resistant insect populations.     

The effect of carbon dioxide gas alone or in combinations on the mortality of Tribolium castaneum (Herbst) and T. confusum du Val (Coleoptera, Tenebrionidae)

Adults of Tribolium castaneum (Herbst) and T. confusum du Val exposed to various mixtures of N₂ or He and O₂ were killed when the O₂ concentration reached to 1·7% or below, whereas the adults exposed to CO₂ : O₂ mixtures were killed mostly due to the deleterious effects of CO₂ itself. At 26·7°C and 38 ± 6%r.h., 95 per cent mortality of T. confusum adults was obtained by an exposure of 271 hr to 45% CO₂ : 55% air mixture; 58 hr to 62% CO₂ : 38% air mixture; and 47·5 hr to 80% CO₂ : 20% air mixture, while for T. castaneum adults 95 per cent mortality required 192, 60, and 44 hr respectively. Data obtained by exposing mature and immature stages of both species to 100% CO₂ suggest that adults were the most susceptible, followed by larvae, eggs and pupae. Generally speaking, inactive stages (egg and pupal) were more tolerant to CO₂ than active stages (larval and adult). Increasing the temperature from 15·6° to 26·7°C resulted in increased insect mortalities; the degree of response varying in different stages. Increasing r.h. decreased the susceptibility of adult insects to 100% CO₂.

Under airtight conditions 200 adult T. castaneum with 8 g of food medium sealed in 1·2 1. glass flasks depleted the O₂ supply from 20·9% to a critical 1·7% level in 7 days, and adults of T. confusum depleted to the 1·6% level in 5 days of airtightness, and both species produced about 20% of carbon dioxide gas.     

Toxicity of amorphous silicas and silica-pyrethroid mixtures to Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae)

The toxicity of some pyrogenic and precipitated amorphous silicas to Tribolium castaneum (Herbst) was assessed in admixture with wheat grain. A good correlation (r² = 0.82, n = 7) was found between the 48 h LC50 of the toxic dusts and their adsorption capacity for a saturated hydrocarbon oil. The pyrogenic silicas Cab-O-Sil M5 and Aerosil R972 were used as carriers to prepare dust formulations of permethrin, cypermethrin and deltamethrin at various concentrations, and 48 h (Cab-O-Sil M5 and Aerosil R972) and 168 h (Cab-O-Sil M5) LC50s were determined using the same bioassay system. Low and intermediate concentrations of the pyrethroids substantially reduced the 48 h LC50s of these silicas while high concentrations antagonised their toxic action due to knockdown effects. The 168 h LC50s of Cab-O-Sil/permethrin formulations were approx 15 and 150 × lower than those of talc/permethrin formulations at 2% w/w and 0.1% w/w respectively. The 168 h LC50 of the Cab-O-Sil/cypermethrin formulation was comparable with that of the talc/cypermethrin formulation, and that of the Cab-O-Sil/deltamethrin formulation was about 5 × less than a talc/deltamethrin formulation, at 2 and 0.2% w/w pyrethroid respectively on the dust carrier.     

Bioactivity of five monoterpenoid vapours to Tribolium confusum (du Val) (Coleoptera: Tenebrionidae)

Five monoterpenoids (terpinen-4-ol, 1,8-cineole, linalool, R-(+)-limonene and geraniol) were tested in vapour form against different stages of Tribolium confusum. Terpinen-4-ol (with LC₅₀ values ranging between 1.1 and 109.4 μl/l air), (R)-(+)-limonene (with LC₅₀ values ranging between 4 and 278 μl/l air) and 1,8-cineole (with LC₅₀ values ranging between 3.5 and 466 μl/l air) were the most toxic to all stages tested, followed by linalool (with LC₅₀ values ranging between 8.6 and 183.5 μl/l air) while the least toxic monoterpenoid tested was geraniol with LC₅₀ values ranging between 607 and 1627 μl/l air. In all cases, except for geraniol, third-instar larvae were the most susceptible stage and 3-day-old eggs most tolerant. Apart from the observed direct toxicity, exposure of females to the vapours led in some cases to lower fecundity and egg hatchability. All monoterpenoids tested revealed insect growth regulator (IGR)-like properties when applied to 3-day-old pupae, producing adultoids and deformed adults.     

Efficacy of alpha-cypermethrin and thiamethoxam against Trogoderma granarium Everts (Coleoptera: Dermestidae) and Tenebrio molitor L. (Coleoptera: Tenebrionidae) on concrete

Laboratory bioassays were conducted to evaluate alpha-cypermethrin and thiamethoxam for the control of adults, small larvae and large larvae of the khapra beetle Trogoderma granarium, and the yellow mealworm beetle Tenebrio molitor, on concrete. Factors such as dose (0.025 and 0.1 mg alpha-cypermethrin or thiamethoxam/cm²), exposure interval (1, 3 and 7 d), and formulation (alpha-cypermethrin SC and thiamethoxam WG) were evaluated. Apart from immediate assessment at end of exposure, an assessment of delayed mortality was performed with the survivors of the 7-d exposure by removing them from the treated substrate and keeping them on untreated surfaces for 7 more days. After the 7-d exposure, more T. granarium adults were dead on dishes treated with alpha-cypermethrin than with thiamethoxam. Small larvae were generally less susceptible than adults. After 7 d, small larval mortality reached 64.4% for alpha-cypermethrin, while for thiamethoxam it was <6%. Large T. granarium larvae were more tolerant than the small ones. Delayed mortality of T. granarium adults was generally high for both insecticides and doses, and ranged between 43.3 and 63.3% of those that were still alive immediately after the 7-d treatment. For both larval categories, delayed mortality was higher for larvae that had been previously exposed to alpha-cypermethrin, than with thiamethoxam. For T. molitor, after the 7-d exposure, significantly more adults were dead on dishes treated with alpha-cypermethrin than with thiamethoxam. For small larvae mortality was 38.9% at the lowest thiamethoxam dose, but in the other cases ranged between 88.9 and 95.6%. In the case of large larvae, the overall mortality was low in all tested combinations. Regarding delayed mortality of this species, it remained at low levels, for both adults and small larvae. Our results indicate that T. molitor was more susceptible than T. granarium in both insecticides tested, but alpha-cypermethrin was more effective than thiamethoxam.     

Efficacy of chlorfenapyr against Tribolium castaneum and Tribolium confusum (Coleoptera: Tenebrionidae) adults exposed on concrete, vinyl tile, and plywood surfaces

The insecticidal pyrrole chlorfenapyr was applied to concrete, vinyl tile, and plywood surfaces, at an application rate of 1.1 g AI m⁻². Adult Tribolium castaneum (Herbst), the red flour beetle, and adult Tribolium confusum (Du Val), the confused flour beetle, were exposed for 2 and 4 h, removed, and held without food for 7 d post-exposure. All beetles survived the initial exposures, but survival of both species decreased during the 7-d holding period, with T. confusum being the more susceptible species. Survival was generally lower on concrete than on tile or plywood, and was greatly reduced on all three surfaces after 4 h of exposure compared to 2 h. Survival of T. castaneum after 2 h of exposure on concrete, tile, and plywood was 2.5±2.5%, 25.5±15.4%, and 40.0±7.1%, respectively, after 7 d. In contrast, all T. confusum exposed on concrete and tile were dead after 4 and 5 d, respectively, while survival on plywood after 7 d was 20.0±16.8%. After 4 h of exposure, all T. castaneum and T. confusum exposed on concrete and tile were dead after 2–4 d post-exposure, while survival on plywood after 7 d was 41.5±6.4% and 0 for each species, respectively. Non-linear and linear regressions were fit to the data for both species. Results show exposure to chlorfenapyr is effective against T. castaneum and T. confusum, but efficacy will vary depending on the surface substrate.     

A new measure of uptake: desorption of unreacted phosphine from susceptible and resistant strains of Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae)

Previous studies of phosphine (PH₃) uptake by insects have concentrated on the process as a whole (“gross uptake”), without distinguishing between absorption of the gas and oxidation to non-volatile products. The lower gross uptake by phosphine-resistant (R) strains of stored product pests has given some insights into resistance mechanism(s). In this study, a recently described method of fumigant residue analysis in grains (microwave irradiation followed by headspace gas chromatography) was adapted to measure absorbed unreacted PH₃ (“reversible uptake”) in a susceptible (S) and an R strain of the rust red flour beetle Tribolium castaneum. At a concentration of 0.9 mg l⁻¹, S insects contained 20 ng g⁻¹ after 15 min exposure, rising slowly to 50 ng g⁻¹ after 5 h. The R strain yielded 190 ng g⁻¹ after 15 min, falling to 50 ng g⁻¹ over 5 h. Falling PH₃ content corresponded with increasing mortality in the R strain, while all except the shortest exposure killed 97% or more of the S strain. Insects of either strain, killed prior to PH₃ exposure by freezing in liquid nitrogen, contained 130–140 ng g⁻¹ after 30 min, rising to 190–200 ng g⁻¹ after 5 h. Gross uptake under the same conditions was 50 μg g⁻¹ (S) and 8 μg g⁻¹ (R) after 5 h, which accords with the literature. Reversible uptake by living insects of either strain under anoxia was 40–50 ng g⁻¹ over 30 min to 2 h. By examining the time-course of reversible PH₃ uptake, a new hypothesis of phosphine action and uptake, in which PH₃ oxidation in vivo is a consequence of reactive oxygen species generation, rather than a direct cause of toxicity, is discussed.