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 and residual effect of three pyrethroids against Sitophilus oryzae (L.) (Coleoptera: Curculionidae) on stored wheat

Laboratory tests were conducted to assess the use of the pyrethroids, deltamethrin, beta-cyfluthrin and alpha-cypermethrin at the rates of 0.125 and 0.25 ppm, as grain protectants in stored wheat against the rice weevil, Sitophilus oryzae (L.). For this purpose, clean untreated wheat was sprayed with these insecticides and stored for 6 months. During this period, four bioassays were carried out, in order to evaluate the residual efficacy of each pyrethroid. In each bioassay, treated wheat was infested with S. oryzae adults, and dead insects were counted after 1, 2 and 7 d of exposure. In addition, S. oryzae progeny production was estimated on each bioassay, until the production of the F₄ generation. The results indicated that deltamethrin and beta-cyfluthrin, both at 0.25 ppm, were significantly more efficient than the other treatments. Efficacy was notably higher after 7 d of exposure, than after 1 and 2 d. At the same exposure level, 1, 2 and 3.5 months after treatment, at 0.25 ppm, mortality for deltamethrin was approximately 89%, 92% and 86%, respectively, while the corresponding percentages for beta-cyfluthrin were 97%, 83% and 62%, and for alpha-cypermethrin 50%, 49% and 33%. However, at the rate of 0.125 ppm, mortality was ?58% in all cases. In all treatments appearance of F₁-F₄ generations was observed, with the exception of both deltamethrin and beta-cyfluthrin at 0.25 ppm, where only a few F₁ adults were noted, without the production of subsequent generations.     

Insecticidal activity of Hypnum cupressiforme (Bryophyta) against Sitophilus granarius (Coleoptera: Curculionidae)

The moss Hypnum cupressiforme Hedw. is cosmopolitan throughout the world and is one of the most common moss species in Turkey. In the autumn of 2011, moss samples were collected from Şadıman Hill located in Ilgaz Mountain National Park in Turkey. After drying the collected samples at room temperature, the green gametophytes and brownish rhizoid parts of the plant were separated from other contents and ground up before extraction procedure. The contact toxicities of 14 column fractions and 11 flash fractions of H. cupressiforme were evaluated against granary weevil (Sitophilus granarius) adults. The fractions C-10 (70.62%) obtained from column chromatography and F-11 (64.48%) obtained from flash chromatography showed the highest activity. As a result of dose dependent studies carried out on C-10 and F-11, LC₅₀ values were calculated as 44.8 μg/μl and 45.3 μg/μl, respectively. Two other fractions C-3 (29.9%) and F-2 (32.1%) were determined to have an active substance different from fractions C-10 and F-11. The LC₅₀ values of fractions C-3 and F-2 were determined as 81.3 μg/μl and 124.6 μg/μl, respectively.     

Evaluation of potential use of nootkatone against maize weevil (Sitophilus zeamais Motschulsky) and rice weevil [S. oryzae (L.)](Coleoptera: Curculionidae)

Nootkatone is a natural sesquiterpene ketone that shows insecticidal activity against insects and ticks. Its contact toxicity and repellency against two major stored-product insect pests, maize weevil (Sitophilus zeamais Motschulsky) and rice weevil [Sitophilus oryzae (L.)], were investigated in the current study. Contact toxicity was evaluated using a no-choice test with treated filter paper, while repellency was evaluated using a choice test with treated corn (for maize weevils) or wheat (for rice weevils). Nootkatone showed low contact toxicity (ranging from 0 to 51%) against the two weevil species at the tested concentrations (ranging from 11.58 μg/cm² to 1158.08 μg/cm²) on filter papers. In choice tests, corn treated with 0.10% or higher and wheat treated with 0.5% nootkatone or higher had significantly fewer maize or rice weevils compared with the solvent only treated control, indicating a repellent effect. The repellency percentage ranged between 46.3 and 93.1% against maize weevils and 39.2-67.2% for rice weevils.     

Development-inhibiting activity of some tropical plants against Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae)

Thirteen tropical plants were evaluated for development-inhibiting activity against Sitophilus zeamais. The bioassays were carried out by incorporating seeds or leaves at various dose levels into an artificial diet for the test insect. It was found that seeds of Basella alba and leaves of Operculina turpethum and Calotropis gigantea were potent in delaying development and in reducing adult emergence, and hence the capacity for population increase. At 0.5% concentration, adult emergence in tests with B. alba, O. turpethum and C. gigantea was reduced by 62, 95 and 70%, respectively. In B. alba and C. gigantea, the development periods were 2.2 and 1.8 times those in the control and the capacities for increase/day were only 0.0324 and 0.0328 compared with 0.1004 in the control. B. alba, O. turpethum and C. gigantea were active at concentrations as low as 0.01, 0.05 and 0.1%. The potential of these materials in insect pest management is discussed.     

Optimization of insect juvenile hormone bioassays on Tribolium confusum (DuV.) (Coleoptera: Tenebrionidae) by application of central composite rotatable designs

The simultaneous influence of age and temperature on the morphogenetic activity of farnesyl methyl ether (FME) on pupae of Tribolium confusum (DuV.) using the mathematical method of central composite rotatable designs of Box and Hunter is studied. The post-application temperature has little influence on the activity. Conversely, the specimens age represents a decisive factor which can alter drastically the results; maximum activity being attained in the youngest pupae. Surprisingly, with the same dose of FME the whole range of morphogenetic activity can be elicited within the first 36 hr of pupal life. These results show the convenience of a strict systematization of the morphogenetic bioassays, specially as far as the definition of the specimen age is concerned, in order to obtain reproducible results.     

Density-dependent fecundity in Sitophilus oryzae (L.) (Coleoptera: Curculionidae)

An experiment to assess the effect of population density upon the fecundity of Sitophilus oryzae (L.) is described. The range of densities employed is rather wider and somewhat lower than used in the earlier study of MacLagan and Dunn (1935). Whereas the results of this earlier study suggested a hyperbolic relationship between fecundity and population density, the present study suggests that there is an optimum population density above and below which fecundity is reduced. A mathematical model is fitted to the data. The implications of this more complex relationship are discussed.     

Biological and mechanical control of Sitophilus oryzae (Coleoptera: Curculionidae) in rice

The combination of mechanical and biological methods was evaluated in the laboratory to assess their impact on the rice weevil Sitophilus oryzae in rice. Mechanical methods comprising the conventional polishing process applied either before or after infestation, resulting in reduced nutritional quality plus the added effect of mechanical impact in the presence of the pest, biological methods including parasitism by the pteromalids Anisopteromalus calandrae and Lariophagus distinguendus, and combined methods (combinations of mechanical and subsequent biological treatments), were tested in the laboratory. All treatments significantly reduced the number of weevil progeny and individual weevil weight. Of the two parasitoids, L. distinguendus had the greater effect, reducing weevil populations by 98% in unpolished rice. In the combined treatments, parasitism increased the effect of mechanical methods. However, mechanical methods had a detrimental impact on parasitoid survival, especially in A. calandrae. Furthermore, in the presence of mechanical treatments, the sex ratio of A. calandrae was unbalanced in favour of males indicating the high vulnerability of females. The impact of both parasitoid species on weevils was attributed to successful parasitism as well as to aborted parasitism and host-feeding.     

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.     

The effectiveness of six vegetable oils as protectants of cowpeas and bambara groundnuts against infestation by Callosobruchus maculatus (F.) (Coleoptera: Bruchidae)

Traditionally extracted neem kernel oil, karité oil, groundnut oil, palm kernel oil, palm oil and industrially extracted groundnut oil were assessed as protectants of cowpeas and bambara groundnuts against Callosobruchus maculatus (F.). On cowpea, only neem kernel oil reduced oviposition at a treatment of 8 ml oil/kg seed. On bambara groundnut, neem kernel oil, palm oil and groundnut oil (industrially extracted) reduced oviposition at 3 ml oil/kg seed, while karité oil was effective at 5 ml oil/kg seed. With oil treatment, the degree of ovicidal activity was higher on bambara groundnuts than on cowpeas. Only neem oil also showed larvicidal properties. Even after 90 days storage, a major part of the toxic activity was retained by the cowpea testa. Neem oil at 8 ml oil/kg cowpea seed gave good protection up to 3 months, while 5 ml oil/kg bambara groundnut protected up to 6 months.     

Susceptibility of Sitotroga cerealella (Oliv.) (Lepidoptera: Gelechiidae) to two insect juvenile hormone analogues

The effect of topical application of the insect juvenile hormone analogues methoprene (isopropyl-11-methoxy-3,7-11-trimethyl dodeca-2,4-dienoate) and hydroprene (ethyl-3,7,11-trimethyl dodeca-2,4-dienoate) on last instar larvae and newly-formed pupae of Sitotroga cerealella was examined. Topical application of methoprene at 10 μg/pupa to maize grains containing pupae resulted in 94% adult emergence whereas the same treatment applied to pupae removed from the grains reduced adult emergence to 45%. At 100 μg methoprene/pupa, adult emergence was 91% when grains containing pupae were treated and 32% when pupae were treated after removal from grains. Hydroprene (10 μg/pupa) was more effective than methoprene against insects both inside grains and after removal from grains, giving adult emergence of 48% and 8% respectively. At 100 μg/pupa, hydroprene completely prevented adult emergence when applied to insects removed from the grain. After treatment of the pupal stage with 10 or 100 μg methoprene per insect, adult males produced the same numbers of spermatophores as untreated males and the treatment did not affect either the number or fertility of eggs deposited by adult females.     

Phosphine resistance in Brazilian populations of Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae)

Phosphine resistance was assessed in adults of 22 Brazilian populations of Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae). The concentration-mortality bioassays for the detection of phosphine resistance followed the FAO standard method. Twenty populations of S. zeamais were resistant to phosphine and the resistance ratios at the LC₅₀ ranged from 1.1- to 86.6-fold. This is the first report of phosphine resistance in populations of S. zeamais in Brazil, where previous surveys did not detect resistance in this species. There was significant variation in respiration rate (CO₂ production) among the populations (P < 0.05). Respiration rate was significantly inversely correlated with phosphine resistance for this species (P < 0.05). The populations with lower respiration rates showed higher levels of phosphine resistance, suggesting that the lower respiration rate is associated with the physiological basis of phosphine resistance due to reduced fumigant uptake.     

Insecticide resistance and synergism in Brazilian populations of Sitophilus zeamais (Coleoptera: Curculionidae)

Insecticide resistance to three organophosphate (chlorpyrifos-methyl, malathion and pirimiphos-methyl) and three pyrethroid (cypermethrin, deltamethrin and permethrin) insecticides was surveyed in nine field-collected populations of the maize weevil from six Brazilian States and contrasted with a standard susceptible population and a DDT and pyrethroid resistant population. Bioassay tests were carried out in glass vials (20 ml) impregnated with dried insecticide residue and the resistant populations were recognized by using discriminating concentrations established from LC₉₅s estimated for a standard susceptible population. Four field-collected populations had reduced susceptibility to cypermethrin (64-77% mortality) and to chlorpyrifos-methyl (76-77% mortality). All populations were susceptible to malathion and pirimiphos-methyl and only the DDT and pyrethroid resistant check showed resistance to all pyrethroids. Concentration-mortality curves showed non-significant levels of insecticide resistance in the field-collected populations and moderate (10-100-fold) to very high levels (>1000-fold) of resistance to pyrethroids in the DDT and pyrethroid resistant population. Results from insecticide bioassays with synergists (diethyl maleate, piperonyl butoxide, and triphenyl phosphate) suggested a major involvement of esterase as the cypermethrin resistance mechanism, while no clear result was obtained for chlorpyrifos-methyl. Synergism results provide support for target site resistance to pyrethroids in the DDT and pyrethroid resistant population used in this study.     

Efficacy of powder and essential oil from Chenopodium ambrosioides leaves as post-harvest grain protectants against six-stored product beetles

Powder and essential oil obtained from dry ground leaves of Chenopodium ambrosioides were tested under laboratory conditions (25±1°C, 70-75% r.h.) for their ability to protect grains from damage by six insect pests, Callosobruchus chinensis, C. maculatus, Acanthoscelides obtectus, Sitophilus granarius, S. zeamais and Prostephanus truncatus. The insects were reared and tested on whole maize grain for S. zeamais and P. truncatus, whole wheat for S. granarius, green peas for C. chinensis, mung bean for C. maculatus and white bean for A. obtectus. The powder prepared from dry leaves of C. ambrosioides was mixed with grains at different dosages ranging from 0.05-0.80% (wt/wt) for C. chinensis, C. maculatus and A. obtectus and from 0.8-6.4% (wt/wt) for S. granarius, S. zeamais and P. truncatus. The dosage of 0.4% killed more than 60% of all the bruchids 2 days after treatment, while a dosage of 6.4% induced total mortality of S. granarius and S. zeamais within the same exposure time. All levels of the dry ground leaf concentrations inhibited F1 progeny production and adult emergence of the tested insects. The dosage of 0.2 μl/cm² of the essential oil killed 80-100% of the beetles within 24 h except C. maculatus and S. zeamais, where this dosage induced only 20% and 5% mortality, respectively. These results indicate a scientific rationale for the use of this plant in grain protection by local communities in the western highlands of Cameroon.     

Persistence and activity towards Sitophilus zeamais (Coleoptera: Curculionidae) of pirimiphos-methyl sprayed at different temperatures on maize

The air temperature in storage units in tropical areas frequently exceeds 50°C during the warmest periods of the day. Since protectant insecticides are sprayed on grains under these conditions, such high temperatures may interfere with the insecticidal activity. To assess this possibility we sprayed maize grains with pirimiphos-methyl 500 EC (0.8 ml c.p./l and 1.5 l/t) at different temperatures (25°C, 30°C, 35°C, 40°C, 45°C, and 50°C) and 55% r.h. The grains were then maintained at 27±1°C and 55±5% r.h. throughout the experiment which lasted 90 days. Residues of pirimiphos-methyl on the sprayed grains were analyzed every 30 days. Grain samples were assessed every 15 days after the insecticide spraying for their effect on the maize weevil, Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae). Insect mortality was evaluated after 24 and 48 h of exposure to the treated grain. The level of pirimiphos-methyl residue on maize grains decreased with an increase in storage period and air temperature during the insecticide spraying (varying from 11.0±0.1 to 1.1±0.1 ppm, corresponding to the residue levels at 25°C on the day of the spraying and after spraying at 50°C and 90 days of storage). The same trend was observed for mortality of the maize weevil, which dropped from 95.4±13.3% to 2.5±2.5% after 90 days storage after insecticide spraying at 50°C. These results indicate that temperature at spraying can affect insecticide persistence and activity during storage.     

Fecundity and ability of the parasitoid Lariophagus distinguendus (Hymenoptera: Pteromalidae) to find larvae of the granary weevil Sitophilus granarius (Coleoptera: Curculionidae) in bulk grain

Fecundity and host finding behavior in the storage environment were examined for the parasitoid Lariophagus distinguendus (Förster), a potential agent for biological control of stored-product pest beetles. Larvae of the granary weevil, Sitophilus granarius (L.), in wheat were used as hosts. The fecundity varied considerably among strains of different geographical origin, from 1.3±2.4 to 92.5±23.6 offspring per female parasitoid. Host finding ability was examined in a small acrylic cylinder (about 42 kg wheat), a silo-bin (20.5 t wheat grain), and the flat storage grain bin in a commercial facility (3000 t rye). Experiments in the cylinder and the silo-bin revealed that the number of hosts found by the parasitoids decreases with increasing depth. Moreover, parasitoids were more likely to find hosts in the cylinder than under field storage conditions in a silo-bin. This indicates that the density of parasitoids per unit volume of the grain might be an important factor in determining how deep they penetrate a grain layer. In the silo-bin and the commercial grain store, parasitoids were able to find and parasitize hosts located up to 4 m vertically and horizontally from the release point. The significance of these results with respect to the suitability of L. distinguendus for biological control of the granary weevil is discussed.     

Efficacy of Silicosec, filter cake and wood ash against the maize weevil, Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae) on three maize genotypes

The effectiveness of the diatomaceous earth Silicosec, a mineral industrial filter cake and domestic wood ash, applied at three different rates for the control of the maize weevil, Sitophilus zeamais, on three maize genotypes was determined. Treatment with Silicosec was the most effective followed by filter cake and wood ash. The treatments reduced progeny emergence, percentage grain damage and grain weight losses, but did not affect percentage seed germination. Grain treated with wood ash at all rates resulted in a relatively low mortality 3 days after infestation as compared to other treatments. However, all treatments caused high mortality (97-100%) after 15 days of exposure. Therefore, Silicosec, filter cake and wood ash can be considered as potential components of an integrated pest management strategy against the maize weevil.     

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.     

Insecticidal and antifeedant effects of Junellia aspera (Verbenaceae) triterpenes and derivatives on Sitophilus oryzae (Coleoptera: Curculionidae)

Triterpenes from Junellia aspera (Gillies ex Hook) (Verbenaceae) and chemical derivatives were evaluated for their antifeedant and toxic effects against adults of Sitophilus oryzae (L.). Five triterpenoids were acutely toxic by ingestion. The compounds maslinic acid (II), daucosterol (III), and 3β-hydroxy-12α-bromine-(28→13)-oxide-oleanane (IX) showed the highest toxic effects, while oleanolic acid (I) and oleanonic acid (VII) showed less toxicity. Daucosterol also exhibited important feeding deterrence activity. No toxicity was observed when the assayed compounds were topically applied.