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.     

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.     

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.     

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.     

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.     

Phosphine resistance in immature stages of a laboratory selected strain of Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae)

Responses to phosphine of immature stages of an adult-selected, phosphine-resistant strain of Tribolium castaneum (Herbst) were studied and compared with those of a phosphine-susceptible strain. Larvae (15 and 20-day old) pre-pupae and pupae (early-, mid- and late-) were examined and found resistant to phosphine. The highest resistances were present in early- and mid-pupae at levels much higher than those selected in the adults. Latent toxic effects were observed following treatment of all stages except 15-day larvae and were most pronounced with 20-day larvae.Respiration rates in a normal atmosphere were similar in the two strains on a body-weight basis and differed in terms of oxygen consumption per individual in accordance with the weight differences between the two strains. Normal respiration rates did not account for, or contribute towards, the observed tolerance differences between the two strains. The oxygen consumption of all examined stages of the resistant strain was reduced less by phosphine than that of the corresponding stages of the susceptible strain but the significance of this in terms of phosphine uptake is not known.     

Age-related susceptibility of Tribolium castaneum (Herbst) to synthetic C18 juvenile hormone

Larvae of ten different age groups and pupae of four were kept in flour containing 30 ppm synthetic C₁₈ juvenile hormone (JH-1) for four days. Newly emerged adults were similarly kept in flour containing 100 ppm JH-1 for two weeks. Newly laid eggs (0–24 hr old) were placed for eight days on filter papers impregnated with 6·4 μg/cm² synthetic JH-1. All insects were kept at 25°C and 70% r.h. Larvae exposed when they were 25 days old or older and pupae exposed during the first seven days of the pupal period suffered high mortality and a large number of deformed adults were produced. All other larval and pupal stages were apparently unaffected by the hormone. Treated eggs hatched normally and newly emerged adults survived the treatments and produced normal numbers of offspring. The potential value of juvenile hormones as control agents for Tribolium castaneum is discussed.     

Response and genetic analysis of malathion-specific resistant Tribolium castaneum (Herbst) in relation to population density

Extensive use of malathion for pest control on stored cereals has resulted in worldwide resistance in red flour beetles, Tribolium castaneum. In this paper we investigate population density effects on the malathion-specific resistance in PRm, a strain from the Philippines, in an integrated resistance management framework. Two populations of malathion-specific resistant (PRm) and a malathion-susceptible strain of T. castaneum were bred at different densities: low (4 adults/g) and high (12 adults/g) density on wheat plus brewer's yeast in the laboratory. After eight generations, slopes of probit regression lines and LC₅₀ values were used to monitor the effect of insect rearing density on the progression of malathion-specific resistance. The LC₅₀ of the malathion-susceptible strain (Asm) did not change significantly during selection while LC₅₀s varied for both the high-density and low-density lines of PRm, the LC₅₀ of malathion ranged from 27.51 to 34.06 and from 21.14 to 29.39 μg malathion cm⁻² for high and low density, respectively.More than 33 generations were required to achieve a 10-fold increase of resistance for the low-density line compared to only 17 generations for the high-density line. Calculations from published formulae suggested that the malathion-specific resistance of both high- and low-density lines was under monofactorial control, with complete dominance.The data showed that environmental factors such as population density differences in insect rearing and development may influence the heritability of resistance. Furthermore, the variability in results published worldwide on resistance emphasises the need to standardize test conditions across laboratories.     

Screening of Chinese medicinal herbs for bioactivity against Sitophilus zeamais Motschulsky and Tribolium castaneum (Herbst)

Extracts of 40 species of Chinese medicinal herb from 32 different botanical families were screened for contact, fumigant and feeding-deterrent activities against the two stored-grain insects Sitophilus zeamais and Tribolium castaneum. Thirty Chinese medicinal herbs exhibited insecticidal or feeding-deterrent activities against the two species of insects. Extracts of Artemisia argyi, Dictamnus dasycarpus, Evodia rutaecarpa, Litsea cubeba, Narcissus tazetta var. chinensis, Polygonum aviculare, Rhododendron molle, Sophora flavescens, Stemona sessilifolia, Tripterygium wilfordii, and Torreya grandis were most active.     

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 a new chitin synthesis inhibitor, novaluron, on various developmental stages of Tribolium castaneum (Herbst)

Novaluron, a novel chitin synthesis inhibitor (CSI), was tested against the various developmental stages of Tribolium castaneum (Herbst), at concentrations ranging from 0.1 to 100 ppm. It did not kill T. castaneum adults at these concentrations, but at 1.0 ppm it caused total mortality of third-instar larvae. Novaluron did not affect the number of eggs laid by T. castaneum adults that were exposed to treated wheat flour, but it totally inhibited their hatching after the third day of exposure at a concentration of 1 ppm. On the first day after infestation novaluron did not totally prevent hatching, even at the highest tested concentration of 100 ppm. The time needed to restore egg hatchability after adults were transferred to untreated flour depended on the concentration of novaluron used in the treatment. When the adults of T. castaneum were exposed to novaluron-treated whole wheat grains (at 1 ppm), similar effects to those of the treated flour at the same concentration were observed: egg hatching was drastically reduced. The effect of uptake via contact of adults with novaluron-treated surfaces was examined by exposing them to a mixture of untreated flour and 10% novaluron-treated sand at a concentration of 10 ppm, and only 1% of the eggs hatched after 18 days of exposure. When adults were removed from treated surfaces of Petri dishes to untreated flour, the hatching rate was again reduced by 100%. It was concluded that the contact penetration of novaluron into T. castaneum adults prevents the hatching of eggs subsequently laid.     

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.     

Impact of high temperatures on efficacy of cyfluthrin and hydroprene applied to concrete to control Tribolium castaneum (Herbst)

In laboratory trials, concrete was treated with cyfluthrin wettable powder (WP) at 40 mg active ingredient [AI] cyfluthrin WP/m², then heated for 4, 8, or 16 h at either 45°C or 55°C, or treated but not heated (seven treatment combinations). Bioassays were conducted by exposing adult Tribolium castaneum (Herbst) for 0.5, 1, and 2 h. Survival of T. castaneum was generally greater on unheated concrete compared with the heating treatments, and survival appeared to decrease as heating time increased at both 45°C and 55°C. In a second laboratory trial, concrete was treated with hydroprene (Gentrol) at the label rate of 1.9×10⁻³ mg [AI]/cm², and bioassayed by exposing late-instar T. castaneum larvae on the treated surface. There were significant differences between untreated controls and the heat treatment regimes (P<0.05) with respect to the percentage of live emerged adults, the percentage of those adults with deformities, and the percentage of dead adults, but heating did not reduce efficacy of hydroprene. In a field trial, concrete was treated with cyfluthrin at 2 mg [AI] cyfluthrin WP/m², and placed in a flour mill undergoing an experimental heat treatment and in an unheated office. Treated concrete was bioassayed by continually exposing adult T. castaneum for 0.5-120 h. The effect of heating time on insect mortality was not significant (P?0.05). Except for T. castaneum exposed for 0.5 h, the percentage of beetle survival on unheated concrete was greater (P<0.05) than survival on concrete that had been heated in the mill, indicating a possible beneficial effect on cyfluthrin toxicity due to heating. Results of these studies show that short-term exposures to high temperatures may have no appreciable effect on efficacy of either cyfluthrin WP or hydroprene, and combination treatments of heat plus either of these insecticides may be effective alternatives to methyl bromide for disinfesting milling facilities.     

Distribution of the Medea factor M in populations of Tribolium castaneum (Herbst) in the United States

The distribution of the maternally acting, selfish gene Medea⁴ (M⁴) was determined in populations of the red flour beetle, Tribolium castaneum (Herbst), collected in the southern and midwestern United States. We found clear evidence for the existence of two major regional subpopulations, with a boundary that roughly corresponds to 33°N latitude. All 26 strains collected in 10 states north of this latitude were homozygous for the M⁴ allele, while only two of 29 strains collected in six states south of this latitude were homozygous for the allele. Of the remaining 27 southern strains, 21 lacked the M⁴ allele entirely, while six contained a mixture of M⁴ and non-M⁴ alleles. This is the first evidence of either the existence of biotypes or the presence of major barriers to gene flow in wild populations of this ubiquitous insect species.     

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.     

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.     

Initial and delayed mortality of late-instar larvae, pupae, and adults of Tribolium castaneum and Tribolium confusum (Coleoptera: Tenebrionidae) exposed at variable temperatures and time intervals

Late-instar larvae, pupae, and adults of Tribolium castaneum (Herbst), the red flour beetle, or Tribolium confusum (DuVal), the confused flour beetle, were exposed for variable durations at 36-54 °C. Beetles were placed in laboratory ovens set at a baseline of 27 °C, the temperature was increased by 0.1 °C per minute until the target temperature was achieved, and beetles were then held for specified exposure durations. There was no mortality after initial exposure or after a 1-week holding period of any life stage of T. castaneum or T. confusum exposed for 32 h to 36, 39, or 42 °C. At 45 °C, there was no initial mortality of either species exposed for different time intervals except for those exposed for 28 h. However, there was a significant increase in mortality after the 1-week holding period of those beetles exposed initially for at least 16 h to 45 °C. There was a sharp increase in mortality after the initial exposures of 4 h at 48 °C; mortality of T. confusum larvae was 90.0±5.7% but was only 10.0±10.0% for larvae of T. castaneum, and no pupae of either species were dead. All life stages of both species were killed after the initial exposure of 12 h, and 1-week mortality of beetles exposed for 4 and 8 h was generally greater than initial mortality. At 51 and 54 °C, 2- and 1-h exposures, respectively, killed all life stages of each species. Mortality in conditions of gradual temperature increase was less than previous studies with sudden temperature increases.     

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.