Density-dependent reproductive success in Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae)

Two strains of Tribolium castaneum, one being susceptible to malathion (Asm) and the other malathion-specific resistant (PRm), were used to assess the effect of population density and its interaction with genetic background in reproductive success. A highly significant allometric relationship between female body weight and fecundity (R²=0.413) and another between female body weight and larval survivorship (R²=0.561) were found. Data showed that population density exerted an indirect effect on the reproductive success. The body weight of the Asm female was not affected by variations in population density but the body weight of the PRm female increased with reduced population density.The genetic background (strain) and/or malathion-specific resistance greatly influenced reproductive success. Concerning the percentage survivorship of offspring of the two strains, there was an opposite trend with increased population density: in PRm, survivorship was lower at high density (76.64±13.75; mean±SD) and higher at low density (88.39±7.61), whereas in Asm, survivorship was higher at high density (53.39±15.57) and lower at low density (43.99±20.08). The PRm female laid more eggs than the Asm. Reproductive success was significantly higher in PRm than in Asm. In addition, the genetic background (the strain) and/or the pleiotropic effect of malathion-specific resistance had a significant effect on the fecundity of PRm because the differences in fecundity and reproductive success between Asm and PRm went beyond the body weight of the female and might be explained by their genetic background and/or the pleiotropic effect of malathion-specific resistance.     

Weight-related susceptibility to an insecticide in Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae)

Tribolium castaneum adults, 27–29 days old, were dosed topically with fenitrothion. The time to knockdown of each was determined, together with its dry weight. The times and the weights were significantly and positively correlated. The times for the females were on average about 13% higher than those for the males, but the times adjusted for beetle weight were the same for the two sexes.     

Joint action of methyl bromide and phosphine on Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae)

When Tribolium castaneum adults were fumigated with mixtures of methyl bromide and phosphine for 5 or 10 hr in the proportions 300:1, 100:1 and 100:3 respectively, the mortality was greater than if the fumigants acted independently (P < 0.001). At low and middle-range response levels the mixtures were less potent than would be expected under additivity of doses, but at higher response levels (≥ 80%) the effect was close to, and in some conditions slightly in excess of, additivity in the sense of exchangeability of units of effective dose. In terms of these units, after 5 hr exposure the 100:1 mixture appeared to be slightly more effective than the 100:3 mixture but when the exposure time was increased to 10 hr the higher proportion of phosphine gave an advantage. The 300:1 mixture was in general less effective than the other two.     

The effect of grain damage on development in wheat of Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae)

The effect of severity of grain damage on survival and development of larvae of Tribolium castaneum in wheat was investigated. Exposure of the germ was generally necessary for survival of young larvae. Rate of development increased with degree of exposure of the germ. Survival and development would not be significantly affected by a practicable reduction in the current level of grain damage in mechanically harvested wheat.     

Repellent and fumigant activity of essential oil from Artemisia vulgaris to Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae)

Repellent and fumigant activity of the essential oil of mugwort, Artemisia vulgaris, against the stored-product insect pest, Tribolium castaneum was investigated. Artemisia vulgaris oil had a very strong repellent activity to adults and was significantly repellent at a 0.6 μL/mL (v/v) and higher in a filter-paper arena test. The oil had high fumigant activity against adults and larvae with adults much more susceptible than larvae. At 8.0 μL/mL, mortality of adults reached 100%, but with 12-, 14- and 16-day larvae, mortalities were 49%, 53% and 52%, respectively. The oil also had high-fumigant activity against eggs and toxicity progressively increased with increased exposure time and concentration. At dosages of 10, 15 and 20 μL/L air and a 96 h exposure period, mortality reached 100%. Regression analysis of data on individuals fumigated in the larval stage confirmed that the percentage of larvae reaching the pupal stage and the percentage of pupae that reached the adult stage, decreased significantly with increase in dosage concentration. No larvae, pupae and adults were observed following a 60 μL/L dosage.     

Effect of methoprene on the heat tolerance and cold tolerance of Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae)

Methoprene, a Juvenile Hormone analogue, was evaluated for its ability to alter heat tolerance or cold tolerance of Tribolium castaneum, the red flour beetle. Young adults and late instar larvae were exposed to a series of methoprene concentrations. They were held either at 46 °C or 0 °C for different durations, and survival of adults or the adult emergence from larvae was recorded to determine their tolerance to extreme temperatures. At 46 °C, the lethal time to kill 50% of the population (confidence intervals) for untreated adults was 10.8 (9.6-11.8) h compared to 9.3 (8.3-10.0) h for adults exposed to 3.33 ppm of methoprene for 48 h. Higher concentrations of methoprene also caused adults to be less heat tolerant. In contrast, there was no evidence that methoprene reduced the heat tolerance of larvae. At 0 °C, both unacclimated and cold-acclimated insects were tested. Methoprene did not affect the cold tolerance of adults or larvae, regardless of cold acclimation. As seen in other studies, methoprene was not toxic to adults even at 66.6 ppm, but it was highly toxic to larvae (LD₅₀ 0.015 to 0.020 ppm). Cold tolerance was slightly greater in both adults and larvae, after being held at 15 °C for two weeks. This is the first study to report that a Juvenile Hormone analogue has an impact on insect heat tolerance.     

Sorption of tritiated phosphine by various stages of Tribolium castaneum (Herbst)

When various stages of Tribolium castaneum were fumigated with 0.14–1.69 mg/l of tritiated phosphine for 5 hr the uptake of the fumigant was found to be considerably greater in larvae and adults than in pupae or eggs. Mature larvae absorbed 2–3 times as much phosphine as pupae at all concentrations tested and mortality was appeciably higher. Uptake by 1-day-old adults was about two fold that of the mature pupal stage from which they had emerged and increased with age so that 14-day adults absorbed about twice as much as newly emerged adults. Uptake by pupae followed a U-shaped curve somewhat similar to the characteristic pattern of oxygen uptake by pupae of different ages. Eggs retained only a small proportion of the radioactive fumigant they absorbed. A considerable amount remained at the surface of the eggs and was converted to soluble compounds that could be washed off with water. The results suggest that the higher tolerance of both eggs and pupae to phosphine may, at least partially, be attributed to the lower uptake of fumigant as compared to larvae and adults.     

Efficacy of a volatile formulation of hydroprene (Pointsource™) to control Tribolium castaneum and Tribolium confusum (Coleoptera: Tenebrionidae)

Three- and 4-week-old Tribolium castaneum (Herbst), the red flour beetle, and Tribolium confusum (du Val), the confused flour beetle, were exposed at five different temperature-relative humidity (r.h.) combinations to a volatile formulation of the insect growth regulator (IGR) hydroprene (called Pointsource™). Typical effects associated with IGR exposure, such as arrested larval growth, morphological deformities in adults, twisted and deformed wings, and incomplete adult emergence were produced in both species. Tribolium castaneum and T. confusum were susceptible to Pointsource™, but T. castaneum appeared to be the more susceptible species. More 3-week-old larvae of both species were arrested in that stage compared to the 4-week-old larvae. Nearly all of the 3- and 4-week-old T. castaneum larvae that were able to complete development to the adult stage quickly died after they emerged and were grossly morphologically deformed. In contrast, some emerged adult T. confusum remained alive after they emerged and were not deformed in any manner or had only twisted and incomplete wings. A greater percentage of larvae of both species were arrested in the larval stage and more adults died after they emerged in exposure studies conducted at 32°C, 75% r.h. as compared with 32°C, 30% r.h., but the reverse was true for exposures conducted at 27°C. Pointsource™ appears to have excellent potential for use in controlling Tribolium species within indoor facilities.     

Life tables of Xylocoris flavipes (Hemiptera: Anthocoridae) feeding on Tribolium castaneum (Coleoptera: Tenebrionidae)

Effects of four constant temperatures (19°C, 21°C, 24°C, and 32°C) on the development and reproduction of Xylocoris flavipes (Reuter) (Heteroptera: Anthocoridae) and on its predatory activity against the red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) were investigated. Survival of eggs and larvae was high at 24°C and 32°C. At 19°C none of the larvae survived longer than the first instar, whereas at 21°C the number of the larvae completing the immature stage was extremely low. Developmental time was significantly shorter at 32°C. Females lived longer at 21°C, but no differences were observed at 24°C and 32°C. Fecundity was greatly reduced at 21°C and was higher at 32°C. At 21°C, the intrinsic rate of increase (r_m) reached the minimum (0.0004), and gradually increased with temperature (0.054 at 24°C and 0.137 at 32°C). At 24°C larvae consumed more prey during their development, but at 32°C the predation rate per day was higher. For adults both total predation rate and predation rate per day were higher at 32°C. The performance of the anthocorid at the various temperatures is discussed in relation to its practical use as a control agent for stored product insects.     

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.     

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.     

Accumulation and distribution of tricalcium phosphate in the larvae of Corcyra cephalonica Staint (Lepidoptera,Pyralidae) and Tribolium castaneum Herbst (Coleoptera,Tenebrionidae)

The larvae of Corcyra cephalonica Staint and Tribolium castaneum Herbst were allowed to grow in media containing radioactive tricalcium phosphate compounds—⁴⁵Ca or ³²P prepared in the laboratory. Haemolymph and muscle-cuticle complex showed high accumulation of ⁴⁵Ca and ³²P. The radioactivity retained by the tissues increased with time and was highest between 24 and 72 hr.     

Effectiveness of short exposures of propylene oxide alone and in combination with low pressure or carbon dioxide against Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae)

Toxicity of the fumigant propylene oxide (PPO) alone and in combination with low pressure (100 mm Hg) or 92% CO₂ to all life stages of Tribolium castaneum using short exposure times (4 and 8 h) at 30°C was studied. Results indicated that PPO was moderately toxic with Ct products ranging from 120 to 608 mg h/l required to obtain complete mortality of the different life stages. A marked difference in susceptibility between life stages was recorded. Eggs were the most sensitive with a LD₉₉ value of 30.1 mg/l for 4 h, whereas pupae were the most tolerant with a LD₉₉ value of 146.5 mg/l. It was shown that an increase in exposure time from 4 to 8 h resulted in 23%, 42%, 48% and 47% reductions of LD₉₉ values for eggs, larvae, pupae and adults, respectively.There was no or very limited mortality of all stages except the egg (53% to 62%), when exposed to either 100 mm Hg or 92% CO₂ for 4 h. However, when 100 mm Hg or 92% CO₂ were combined with PPO, the LD₅₀ and LD₉₉ values for PPO in all stages except the egg were significantly reduced. Combinations of PPO with 100 mm Hg or 92% CO₂ produced equal reductions in the LD₉₉ value from 146.5 to about 22 mg/l for the most tolerant pupal stage. Both combinations also produced significant reductions in the LD₉₉ values for larvae and adults (6.3- to 6.6-fold) compared with those exposed to PPO alone. These results indicated that 100 mm Hg and 92% CO₂ each had a synergistic effect on the toxicity of PPO to T. castaneum. The combination of PPO with vacuum or CO₂ can thus provide a potential alternative to methyl bromide.     

Studies on resistance to insecticides in Tribolium castaneum (Herbst)—V. Cross-resistance characteristics of a lindane-resistant strain

The cross-resistance characteristics of a lindane-resistant strain of Tribolium castaneum (Herbst) selected under pressure with lindane in the laboratory were studied. The strain was >86 times resistant to lindane as compared to the susceptible, and also showed resistance to eight other insecticides viz. dieldrin (>291 ×), heptachlor (>232 ×), endrin (>165 ×), aldrin (>147 ×), chlordane (>34 ×), endosulfan (>8 ×), toxaphene (>9 ×) and carbaryl (>12 ×). No cross-resistance was indicated to parathion (2·0 ×), diazinon (1·1 ×), malathion (1·0 ×), p,p′DDT (0·7 ×) and pyrethrins (1·5 ×).     

Time matters: delayed toxicity of pirimiphos-methyl on Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) and its effects on efficacy estimation of residual treatments

Three time-related toxicity parameters of pirimiphos-methyl were compared using a common pest of stored cereal and grain products, Tribolium castaneum (Herbst). The effective exposure time sufficient to knock-down half of the beetles was much shorter than the median knock-down time from a continuous exposure test (8.6 min and 80 min, respectively, at the same insecticide concentration). The difference between these two measures can be attributed to delayed toxicity of pirimiphos-methyl. Pirimiphos-methyl was effective against T. castaneum at a low application rate of 0.0047 g a.i. m⁻², when beetles were exposed on the treated surface for short time intervals. The median post-exposure knock-down time for animals placed for 20 min on insecticide-treated surface and then kept on an untreated surface was 180 min. Our results suggest that actual effective exposure time might be a more realistic efficacy measure of pirimiphos-methyl at a given dose than LT50 (median lethal time for continuous exposure), and that the timing of the toxic effects should be included more often in residual toxicity testing.     

Impact of physical and biological factors on susceptibility of Tribolium castaneum and Tribolium confusum (Coleoptera: Tenebrionidae) to new formulations of hydroprene

Three separate experiments were conducted to: (1) evaluate two new commercial formulations (202-080 and 202-084) of the insect growth regulator hydroprene, (2) determine residual efficacy of hydroprene-treated concrete stored at different environmental conditions, and (3) assess the impact of accumulated flour on residual efficacy. In the first test, late instars of Tribolium castaneum (Herbst), the red flour beetle, and Tribolium confusum (du Val), the confused flour beetle, were exposed on concrete treated with hydroprene. At 40% relative humidity (r.h.), there was no difference between species regarding the percentage of individuals that stopped development in the larval stage (arrested larvae), but at 75% r.h. there were more arrested T. castaneum than T. confusum in all treatments except the low rate of formulation 202-084. No adult T. castaneum lived after emergence (live adults) at either relative humidity, but the percentage of live adult T. confusum ranged from 1.0% to 41.0%, depending on treatment. In the second test, late instars of T. confusum were exposed at 6 and 12 weeks post-treatment on concrete treated with the two experimental formulations and stored under different environmental conditions. At 6 weeks there was no difference between formulations. At 12 weeks, fewer live adults and more dead emerged adults with gross morphological deformities were found on concrete treated with formulation 202-084 and stored at 32°C, 75% r.h. compared to other treatment combinations. In the final experiment, wheat flour was added to treated concrete for 5 weeks before the bioassays were conducted with late-instar T. confusum. There were few live adults produced in the initial bioassays, and dead adults with gross morphological deformities ranged from 83.1% to 97.6%. However, in bioassays conducted with late-instar larvae at 6 weeks, most adults eventually emerged with few deformities. The presence of the flour apparently compromised residual control and the hydroprene was no longer effective. In summary, the new hydroprene formulations were equivalent to the registered product Gentrol^®. Tribolium confusum was less susceptible than T. castaneum, and residual control of T. confusum on a clean surface without flour lasted about 6-12 weeks.     

Fecundity of wild Tribolium castaneum (Herbst) from southeast Queensland, Australia

Fecundity was investigated in wild Tribolium castaneum (Herbst) from southeast Queensland, Australia. Although the fecundity of T. castaneum has been investigated in laboratory studies, the reproductive potential of wild females may be less than that of females reared and tested under favourable laboratory conditions. Adult T. castaneum were trapped using corrugated cardboard traps baited with whole wheat flour on four occasions during May-July 1997 in a grain-growing area of southeast Queensland. After each trapping period, fecundity of individual wild females was assessed on whole wheat flour at 30°C and 55% erh. In addition, F₁ adults were pooled, a sample was taken and fecundity of individual females was assessed similarly. Almost 90% of the adults were trapped on four of the 10 grain storage sites, and these sites yielded females on all four trapping occasions. There was no systematic effect of trapping period on fecundity of wild females, and in three of these four sites there was no effect at all. There were no significant differences between numbers of progeny produced by F₁ females derived from different trapping periods, so the data were pooled for comparison with the results from wild females. Generally, fecundity of wild females was high relative to that of F₁ females which had been reared under uniformly favourable conditions in the laboratory. Despite the trapping occurring during some of the coldest months of the year, females were clearly active and capable of reproducing, demonstrating the importance of maintaining high levels of grain hygiene throughout the year.     

The toxicity of phosphine to adults of Tribolium castaneum (Herbst): Phosphine-induced narcosis

The narcotic effect of phosphine on adults of Tribolium castaneum was examined over concentrations ranging from approx 0.2 to 50 mg/l. Times to narcosis decreased with higher concentrations as did the rate of decrease of these times consistent with a decreasing rate of uptake with increasing concentration. Correlations between narcosis times and mortality were examined but were only of limited value for rapidly estimating mortality response. Moreover, from these correlations it was not possible to resolve the question as to whether narcotised insects have a better chance of survival. Narcosis may have practical implications in terms of phosphine resistance.     

A potential method for simultaneous,semiochemical-based monitoring of Cryptolestes ferrugineus and Tribolium castaneum (Coleoptera: Cucujidae and Tenebrionidae)

Capture and analysis by gas-liquid chromatography of volatiles from adult Cryptolestes ferrugineus (Stephens) infesting rolled oats disclosed that the naturally-produced ratio of the aggregation pheromones 4,8-dimethyl-(E,E)-4,8-decadienolide (I) and (3Z, 11S)-dodecen-11-olide (II) is 1.6:1.0. Approximately 990 and 640 pg/male beetle/h of the 2 pheromones, respectively, were produced in a culture with 76 beetles of mixed age and sex/g of oats. A newly designed trap, which confines beetles responding to attractive odors within an enclosed chamber, was very effective in recapturing released C. ferrugineus when baited with a 13:16 mixture of I and (±)-II released at 1.25 μg/24h, and also in recapturing released adult Tribolium castaneum (Herbst), in response to the aggregation pheromone, 4,8-dimethyldecanal, released at 0.08 μg/24h. Moreover, the capture of each species to traps baited with both species' pheromones was no different than to traps baited with its pheromone alone. Thus the pheromones of both species can be used together in the same trap in semiochemical-based, pest monitoring systems.