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.     

Insecticidal efficacy of diatomaceous earth against Sitophilus oryzae (L.) (Coleoptera: Curculionidae) and Tribolium confusum du Val (Coleoptera: Tenebrionidae) on stored wheat: influence of dose rate, temperature and exposure interval

Laboratory experiments were conducted in order to assess the insecticidal effect of a diatomaceous earth formulation (Silicosec^®, Biofa GmbH, Germany) against Sitophilus oryzae and Tribolium confusum on stored wheat. Adults of the two species were exposed on wheat treated with diatomaceous earth at four dose rates: 0.25, 0.5, 1 and 1.5 g/kg of wheat, respectively. For each dose rate, the treated wheat was placed at 22°C, 25°C, 27°C, 30°C and 32°C. Dead adults were counted after 24 and 48 h, 7 and 14 d of exposure. After the 14-d interval, the live adults were removed and placed for 7 d in untreated wheat (in the case of S. oryzae) or untreated flour (in the case of T. confusum), and the production of F₁ was recorded. For both species, dose rate, temperature and exposure interval significantly affected mortality (P<0.001). Mortality was higher at longer exposure intervals. The efficacy of SilicoSec against S. oryzae increased with temperature, but for T. confusum mortality was lower at 32°C, compared to 30°C, for 24 and 48 h exposure intervals. Tribolium confusum proved less susceptible to SilicoSec than S. oryzae. In general, the rates of 1 and 1.5 g/kg of wheat provided a satisfactory level of protection against the two species examined. For S. oryzae, F₁ emerged only at 22°C, in wheat treated with 0.25 or 0.5 g/kg. However, for T. confusum, F₁ were recorded at 22°C for 0.5 g/kg and at 22°C, 25°C, 27°C and 30°C for 0.25 g/kg.     

Pathogenicity of three species of entomopathogenic nematodes to some major stored-product insect pests

Entomopathogenic nematodes (Nematoda: Heterorhabditidae and Steinernematidae) are commonly used biological control agents of insects in cryptic habitats, but their potential for suppressing stored-product insects in these habitats has not been explored previously. Here, we provide data from the first step in a program to evaluate entomopathogenic nematodes in the genus Steinernema as biological control agents of stored-product pests by determining their pathogenicity to some of the major stored-product pest species. When evaluated against larvae, pupae and adults of six pest species (Plodia interpunctella, Ephestia kuehniella, Oryzaephilus surinamensis, Tenebrio molitor, Tribolium castaneum, and Trogoderma variabile), and the adults of two additional pest species (Sitophilus oryzae and Rhyzopertha dominica), Steinernema riobrave was either the most pathogenic or of similar pathogenicity compared to S. carpocapsae and S. feltiae. A dose of 10 infective juveniles of S. riobrave caused 80% or higher mortality against larvae of P. interpunctella, E. kuehniella, T. castaneum, and O. surinamensis, pupae of T. castaneum and T. molitor, and adults of T. molitor and the two moth species. All stages of Trogoderma variabile exhibited 70% or higher mortality. Adults of S. oryzae and R. dominica exhibited low susceptibility with 15% and 35% mortality, respectively. On the basis of these results, S. riobrave was selected for further evaluation under more field-like conditions.     

Effectiveness of spinosad dust against different European populations of the confused flour beetle, Tribolium confusum Jacquelin du Val

Six populations of the confused flour beetle, Tribolium confusum, obtained from Greece, Italy, Portugal, Denmark, Germany and France were tested for their susceptibility to a spinosad dust formulation, containing 0.125% spinosad. For this purpose, adults and larvae of T. confusum were exposed on wheat treated with two dose rates of the dust formulation, 0.06 and 0.19 ppm of a.i. corresponding to 50 and 150 ppm of the formulation, at 25 °C and 65% r.h. Mortality of the exposed individuals was assessed after 7, 14 and 21 days of exposure on the treated substrate. The increase of dose and exposure interval increased mortality, while adults were more tolerant to spinosad than larvae. Significant differences were noted among populations, for both adults and larvae. The most tolerant to spinosad was the strain from Greece, while the least tolerant were the strains from Germany and Denmark. After 7 days of exposure, on wheat treated with 50 ppm, mortalities of adults of the Greek, German and Danish strains were 2%, 25% and 62% respectively, while the respective figures for 150 ppm were 1%, 31% and 81% respectively. In the case of larvae, of the same strains, mortality at 50 ppm was 6%, 27% and 28% and at 150 ppm 11%, 23% and 40%, respectively. The results of the present study suggest that different strains and stages of T. confusum differ widely in their susceptibility to spinosad-treated wheat.     

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.     

Evaluation of kaolinite-based particle films to control Tribolium species (Coleoptera: Tenebrionidae)

Adults of Tribolium castaneum (Herbst), the red flour beetle, and Tribolium confusum (du Val), the confused flour beetle, were exposed to kaolinite-based particle film dusts. When beetles were continuously exposed to the hydrophobic particle film M-96-018 at the rate of 0.1-0.5 mg/cm², all the T. castaneum at 0.1 mg/cm² were dead after 3 days, but 40±13.8% of the exposed T. confusum were still alive after 7 days. At higher concentrations, all the T. castaneum were dead after 2 days, but 5-6 days of exposure were needed to kill all T. confusum. In a subsequent test, adults of both species were exposed for 8-72 h to 0.5 mg/cm² of the particle film M-96-018, removed, then held without food for 1 week. No T. castaneum survived, while survival of the T. confusum ranged from 0 to 55±17.3%, depending on the exposure interval. In a test conducted at controlled conditions of 40%, 57% and 75% r.h., 27°C, T. confusum were exposed for 8-72 h to the particle film M-96-018 and a hydrophilic particle film M-97-009 at the rate of 0.5 mg/cm², then removed and held either with or without wheat flour for 1 week. All the T. confusum exposed to the particle film M-97-009 usually survived, while survival of the T. confusum exposed to the particle film M-97-018 after the 1-week holding period increased with increasing relative humidity and with the presence of food. The particle film M-96-018 was effective against both the Tribolium species, and appears to have a potential for use in management programs to control beetles within storage facilities.     

Predation by Blattisocius tarsalis (Berlese) (Acari: Ascidae) on eggs of Ephestia kuehniella Zeller (Lepidoptera: Pyralidae)

The mean predation rate of female B. tarsalis on eggs of E. kuehniella was determined at 15°C, 21°C, and 27°C with prey densities of 3, 5, 10 and 15 eggs. Young eggs less than 24 h old were used as prey. Under all experimental conditions most eggs were only partially consumed, confirming the general theory that predatory mites leave most of the food content unutilized. A mean predation rate of 2.2-7.0 eggs destroyed in 24 h was found, reflecting that a large proportion of the available prey was destroyed. The result supports the view that the predatory mite B. tarsalis could be a relevant biological control agent against E. kuehniella in flour mills. It was further demonstrated that frozen moth eggs can be considered as an appropriate food source.     

Insecticidal effect of six entomopathogenic nematode strains against Lasioderma serricorne (F.) (Coleoptera: Anobiidae) and Tribolium confusum Jacquelin du Val (Coleoptera: Tenebrionidae)

The insecticidal effect of Heterorhabditis bacteriophora Poinar (Nematoda: Heterorhabditidae), Heterorhabditis megidis Poinar, Jackson and Klein (Nematoda: Heterorhabditidae) and two strains of Steinernema carpocapsae Weiser (Nematoda: Steinernematidae) and Steinernema feltiae Filipjev (Nematoda: Steinernematidae) against the cigarette beetle, Lasioderma serricorne (Fabricius) (Coleoptera: Anobiidae) and the confused flour beetle, Tribolium confusum Jacquelin du Val (Coleoptera: Tenebrionidae) was examined under laboratory conditions. The nematodes were applied at the following doses: 0 (control), 100, 1000, 5000, 10,000 and 20,000 infective juveniles (IJs) per ml, corresponding to 0, 10, 100, 500, 1000, and 2000 IJs per insect, and their infectivity was tested at 27 °C and 70% r.h. after 4 and 8 days of exposure. Adult emergence and progeny production was evaluated 4 and 8 weeks after the initiation of the bioassays. In the case of L. serricorne adults, one strain of S. carpocapsae caused 15.6 and 58.9% mortality after 4 and 8 days exposure, respectively, in semolina treated with 20,000 IJs per ml. On the other hand, larval mortality of L. serricorne did not exceed 19% in all treatments tested. Similarly, larval mortality of T. confusum was low, reaching 15.2 and 22.4% after 4 and 8 days exposure, respectively, at the highest dose tested. This is the first report on the effect of entomopathogenic nematodes against the cigarette beetle L. serricorne. Further experimental work is required to optimize the conditions under which these entomopathogenic nematodes could be used for the effective control of stored-product pests.     

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.     

Effect of three entomopathogenic nematode species to Trogoderma granarium Everts (Coleoptera: Dermestidae) larvae on stored-wheat

Grain commodities are subjected to multiple insect infestations during processing and storage. The kharpa beetle, Trogoderma granarium Everts (Coleoptera: Dermestidae) is categorized as a destructive stored-product pest due to its elevated survival potential, preference for dry conditions and resistance to many insecticides. While public concern about pesticide related risks increases, the development of alternative, environmentally more benign disinfestation methods of stored commodities is pursued. The current study evaluated the effectiveness of three entomopathogenic nematodes, Heterorhabditis bacteriophora Poinar (Rhabditita: Heterorhabditidae), Steinernema carpocapsae (Weiser) (Rhabditita: Steinernematidae) and Steinernema feltiae (Filipjev) (Rhabditita: Steinernematidae) against small and large larvae of T. granarium. Suspensions of nematodes were applied at six doses: 100, 500, 1000, 5000, 10000 and 50000 infective juveniles (IJs)/ml of water on wheat at 30 °C. Mortality of larvae was estimated 4 and 8 days post-exposure to nematodes. All three entomopathogenic nematodes were able to cause mortality on the insect. High mortality rates were accomplished by the two Steinernema species. The most efficient entomopathogenic nematode against small larvae was S. feltiae which attained 98.9% mortality followed by S. carpocapsae which caused 91.1% mortality after 8 days of exposure. Similarly, S. feltiae and S. carpocapsae killed 87.8 and 63.3% of the exposed large larvae on wheat treated with 50000 IJs/ml after 8 days of exposure. In contrast, at the highest dose, H. bacteriophora was less effective than S. carpocapsae and S. feltiae since it caused 76.7 and 60.0% mortalities to exposed small and large larvae after 8 days of exposure. The effectiveness of all three entomopathogenic nematodes was increased at higher doses and longer exposures. The findings of the current study indicate that entomopathogenic nematodes are efficient biological control organisms of T. granarium larvae infesting stored-wheat.     

Control of the lesser grain borer (Rhyzopertha dominica (F.), Coleoptera: Bostrichidae) by treatments with residual formulations of Metarhizium anisopliae (Metschnikoff) Sorokin (Deuteromycotina: Hyphomycetes)

Treatments with conidia of the entomopathogenic fungus Metarhizium anisopliae formulated in invert emulsion (water-in-oil formulation) or in wheat flour were applied to Rhyzopertha dominica adults infesting Cicer arietinum grains. The application rates were 4.1×10⁵ conidia/cm² of treated area using a concentration of 1.8×10⁷ conidia/ml of the invert emulsion and 8.2×10⁶ conidia/cm² of treated area using a concentration of 6.5×10⁸ conidia/g of the wheat flour formulation. Results have indicated significant mortality (P<0.05) when newly emerged R. dominica adults were introduced and then treated with the invert emulsion and wheat flour formulations (86.7-93.3%, control treatment 10.0-26.7% mortality). When treated grains were left until the emergence of F₁ adults, there was also significant mortality (P<0.05) in both treatments (28.3-60.0%, control treatment 1.7-8.3% mortality). This indicates a residual effectiveness of the treatment with the two formulations against R. dominica adults which extended to >2 months (equivalent to the duration of the insect life-cycle at 23±2°C and 75±5% r.h.). Infestation rate of C. arietinum grains by R. dominica at 23±2°C and 75±5% r.h. was significantly reduced in the treatments with the fungal conidia formulated in invert emulsion (0.7%) or in wheat flour (1.0%) when compared with the control treatment (19.0-23.3%). The preventive treatments significantly retarded R. dominica development (P<0.05) by 8-12 days compared with the control treatment. The infection with the fungus thus delayed adult emergence of R. dominica by 8-12 days. Overall results give promise for control of R. dominica with M. anisopliae mixed with wheat flour or introduced into invert emulsion.     

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.     

Comparison of susceptibility of two stored-product insects, Ephestia kuehniella Zeller and Tribolium confusum du Val to gaseous ozone

In this study, the susceptibility of two stored-product insects, Ephestia kuehniella and Tribolium confusum, to gaseous ozone was investigated. Two ozone fumigation methods were used, an empty space fumigation with only one flush of ozone treatment held for 2 h, and a reflush ozone treatment at 30-min intervals for 5 h in the presence of 2 kg wheat, with an initial ozone concentration of 13.9 mg/L. Toxicity data for empty space ozone treatments indicated a remarkable difference in susceptibility between the life stages of E. kuehniella and T. confusum. For E. kuehniella, empty space ozone treatment resulted in complete mortality of adults, pupae and larvae, while only 62.5% of the eggs were killed. For T. confusum, ozone treatment resulted in very low mortality of adults, pupae and eggs, ranging from 4.2 to 14.1% while only larvae had a high mortality (74%). Generally T. confusum was more tolerant to ozone treatment than E. kuehniella. Ozone flush treatment at 30-min intervals for 5 h resulted in almost complete mortality of all life stages of E. kuehniella placed in the top position of 2 kg wheat, whereas eggs of E. kuehniella placed in the bottom position of 2 kg wheat were hard to kill. For T. confusum, larvae placed in the bottom position of 2 kg wheat were easily killed, whereas eggs, pupae and adults survived.     

Effect of particle size of soft wheat flour on the development of Ephestia kuehniella Zeller (Lepidoptera: Pyralidae)

The effect of soft wheat flours, characterized by different particle size, protein and starch content, on the development of Ephestia kuehniella was studied. The attractiveness of the substrata to first and third instar larvae was also considered.The different protein content of the flours did not significantly affect the development of E. kuehniella, nor did it affect the ability of the flours to attract larvae. In tests with soft wheat flours with the same nutritional value but different particle size, the highest mean number of adults and the shortest developmental period were recorded on samples with greatest particle size (250-419 μm).In order to test the attractiveness of soft wheat flour to larvae, a one-way olfactometer was used. There were no significant differences observed in the number of first and third instar larvae found on flours with different protein composition and particle size. Larvae of this species show limited mobility, in fact few individuals of either instar can reach the flour from a distance of 2 m. No larvae of either instar contacted the different substrata from a distance of 2.5 m.     

Effect of wood ash and conidia of Beauveria bassiana (Balsamo) Vuillemin on mortality of Prostephanus truncatus (Horn)

A series of experiments was carried out to investigate the effect of treating maize with wood ash and entomopathogenic fungus on the mortality of the larger grain borer Prostephanus truncatus. Jars of maize were treated with ash and/or conidia of Beauveria bassiana at doses of 0.0005, 0.005, 0.05 and 0.2 g conidia/g ash/100 g maize. Adult P. truncatus were placed on the maize and numbers of live and dead insects were assessed weekly.Ninety-five per cent mortality of P. truncatus was observed after 1 week and 100% mortality after 2 weeks in maize treated with the highest dose of conidia with ash (0.2 g/g). Mortality of P. truncatus in all ash with conidia treatments was significantly higher than untreated controls over a 4-week period, except the lowest dose of conidia at week 4. The three highest concentrations of conidia per gram of ash resulted in significantly (1% level) higher mortality of P. truncatus than ash alone.In an experiment to investigate the possible synergy of ash and conidia, there were no significant differences in mortality of P. truncatus between treatments with the same concentration of conidia regardless of whether the conidia were mixed with ash or applied alone. Larval populations of P. truncatus were observed in all treatments without ash, but only one larva was observed in one replicate of a treatment containing ash suggesting that ash has an important effect in preventing the establishment of a second generation of insects.     

Effect of Pisum sativum fractions on the mortality and progeny production of nine stored-grain beetles

Yellow field pea (Pisum sativum L.) fractions that were mainly protein (50%), fibre (90%) or starch (85%) were obtained from a commercial pea mill and mixed with wheat kernels or wheat flour. Based on the mortality and the number of offspring produced, protein-rich pea flour was more toxic than fibre, which was more toxic than starch. For the protein-rich pea flour mixed with wheat kernels, the most sensitive insects were Sitophilus oryzae (L.), Sitophilus zeamais Motschulsky and Sitophilus granarius (L.), followed by Cryptolestes ferrugineus (Stephens) which was more sensitive than Tribolium castaneum (Herbst) and Rhyzopertha dominica (F.). For the protein-rich pea flour mixed with wheat flour, Cryptolestes pusillus (Schönherr) was most sensitive, followed by C. turcicus (Grouvelle) and T. confusum (Jacquelin du Val), with T. castaneum being the most resistant. Although protein-rich pea flour did not kill adults to a great extent when mixed with flour, it reduced offspring production significantly. Again C. pusillus was the most sensitive, followed by T. confusum, with T. castaneum offspring being the most resistant. The insecticidal activity of pea fractions decreased after treated wheat kernels were held at 30 °C, 70% r.h. for 8 months. The potential of using pea fractions to control stored-product insects is discussed.     

Inherited sterility in Mediterranean flour moth Ephestia kuehniella Zeller (Lepidoptera: Pyralidae): Effect of gamma radiation on insect fecundity, fertility and developmental period

The effects of gamma radiation on the fecundity, fertility, longevity, development and level of inherited sterility in the Mediterranean flour moth Ephestia kuehniella were determined. Newly emerged virgin Mediterranean flour moth adults were irradiated with 100, 200, 400 and 600 Gy in a ⁶⁰Co irradiator with a source strength of ca. 3811 Ci and a dose rate of ca. 1 Gy/min. Laboratory studies revealed that radiation did not effect the longevity of irradiated male and female adults. Inherited deleterious effects of gamma radiation were observed in the F₁ and F₂ generations. Fecundity and the daily egg laying pattern of irradiated and unirradiated females mated to irradiated males was not significantly different from untreated controls. Adverse effects of gamma radiation were observed in the percentage egg hatch and rate of development. Levels of sterility in the P₁, F₁ and F₂ generations were higher than that of untreated controls. The doses of radiation also had a significant effect on the time from oviposition to larval eclosion or adult emergence. Mortality increased with radiation dose. The incidence of larval and pupal mortality was higher in the F₂ than in the F₁ generation.     

Effects of gamma irradiation on fourth-instar Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae)

Effects of gamma irradiation on fourth-instar Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae) larvae in infested dates (Boufeggous variety) were assessed. Larvae were exposed to different gamma irradiation doses ranging from 300 to 900 Gy. Feeding, pupation, adult emergence and survival were very sensitive to ionizing irradiation. When irradiated at a dose of 300 Gy and higher, food consumption and weight gain were significantly affected, in a dose-dependent manner. Twenty days after irradiation, the weight loss at doses of 300, 450 and 600 Gy was 42%, 47% and 49%, respectively. At doses of 750 and 900 Gy, the weight of larvae diminished by 51% and 54%, respectively. In contrast, the controls gained 20% in weight. Development of larvae to the pupal stage was not prevented completely but none of the pupae emerged as adults. At 300 Gy, 21% of larvae survived 44 d after irradiation and successfully pupated. An absorbed dose of 450, 600, 750 or 900 Gy applied to larvae caused 100% mortality by 44, 38, 38 and 22 d post-treatment, respectively. The minimum dose required to prevent damage from feeding and adult emergence was 300 Gy while doses required to cause death were ?450 Gy.     

Inhibition of Callosobruchus maculatus (F.) (Coleoptera: Bruchidae) development with essential oil extracted from Cymbopogon schoenanthus L. Spreng. (Poaceae), and the wasp Dinarmus basalis (Rondani) (Hymenoptera: Pteromalidae)

The control of the development of Callosobruchus maculatus was studied using a method that combined exposure to essential oil extracted from Cymbopogon schoenanthus and the introduction of a pteromalid natural enemy of the bruchid, Dinarmus basalis. The effect of the essential oil used was evaluated on all developmental stages of C. maculatus and on adults of D. basalis. At the highest concentration tested (33.3 μl/l) all adults of C. maculatus were killed within 24 h of exposure to the oil and the development of newly laid eggs and neonate larvae was also inhibited. However, the oil had variable efficacy against the bruchid instars developing inside the seeds: 5-day-old larvae (63% LI and 37% LII) of C. maculatus developing inside the seeds proving to be highly susceptible while 15-day-old insects (84% of pupae and 16% of larvae) were tolerant. Under the same conditions (33.3 μl/l), adults of D. basalis were very susceptible to oil vapours and to the residual activity of the oil after 3 or 6 days. However, the introduction of 10 pairs of adult D. basalis into a jar containing 100 hosts aged 10 days, 3 or 6 days before the oil application, gave respectively an emergence of 26 or 18 adults of the parasitoid compared to 28 in the control and there was no adult emergence of the host. The possibility of an integrated pest management strategy by using allelochemicals such as essential oils and indigenous natural enemies to control C. maculatus development in cowpea stocks is discussed.     

Insecticidal activities of constituents identified in the essential oil from leaves of Chamaecyparis obtusa against Callosobruchus chinensis (L.) and Sitophilus oryzae (L.)

Analysis by gas chromatography-mass spectrometry led to the identification of 20 volatiles from the steam distilled oil of the leaves from Chamaecyparis obtusa Siebold et Zuccarni. Seven constituents of the oil were tested for contact and fumigant activity against adults of Callosobruchus chinensis (L.) and Sitophilus oryzae (L.). Responses varied with compound and dose rather than increasing exposure time beyond 1 or 2 days. In the impregnated-paper test with the constituents [bornyl acetate, (+)-limonene, myrcene, α-phellandrene, α-pinene, sabinene and terpinolene], at 0.1 mg/cm², bornyl acetate, α-phellandrene and terpinolene caused 97%, 97% and 87% mortality, respectively, against C. chinensis adults 1 day after treatment. At 0.05 mg/cm², moderate activity was achieved with bornyl acetate (56% mortality), α-phellandrene (75%) and terpinolene (55%). Against S. oryzae adults, at 0.26 mg/cm², terpinolene caused 93% mortality 2 days after treatment, whereas 80% mortality 4 days after treatment was observed with bornyl acetate and α-phellandrene. The toxicity of these compounds was significantly decreased at 0.18 mg/cm². In a fumigation test with S. oryzae adults, bornyl acetate and terpinolene were much more effective in sealed containers than in open ones, indicating that the insecticidal activity of these compounds was largely attributable to fumigant action. These naturally occurring materials derived from leaves of Chamaecyparis could be useful for managing populations of C. chinensis and S. oryzae.