Comparative observations on the activity of purethroids against some susceptible and resistant stored products beetles

The activity of six synthetic pyrethroids, allethrin, bioallethrin, resmethrin, bioresmethrin, cismethrin, tetramethrin and also natural pyrethrins, fenitrothion and malathion was examined against susceptible and resistant adult beetles infesting stored products. Cismethrin applied topically was the most active material, alone or synergized, against susceptible Tribolium castaneum, Lasioderma serricorne or Stegobium paniceum.

Solutions in odourless kerosene applied as direct sprays were an average of 6·9 times more active against susceptible T. castaneum than solutions in mineral oil of pyrethrins, bioresmethrin or cismethrin with or without piperonyl butoxide. The factor of synergism was greater when using mineral oil solutions than when using kerosene solutions. It was thought that the more viscous oil slowed penetration of the insecticide giving longer for detoxification, this being inhibited when the synergist was present.

Applied as a dust on wheat, bioresmethrin plus piperonyl butoxide was more active than malathion and less active than fenitrothion against Oryzaephilus surinamensis or susceptible and malathion resistant T. castaneum. Against Sitophilus granarius and susceptible or malathion resistant S. oryzae, synergized bioresmethrin and cismethrin were more active than either malathion or fenitrothion. Malathion resistant S. oryzae was more easily killed by pyrethroids than the susceptible strain. Synergized bioresmethrin was concluded to be the most suitable pyrethroid for controlling stored products beetles, except Lasioderma serricorne and Stegobium paniceum, and was of value against organophosphorus-resistant strains.     

Bioactivity of the essential oil extracted from Evodia rutaecarpa Hook f. et Thomas against the grain storage insects, Sitophilus zeamais Motsch. and Tribolium castaneum (Herbst)

The toxic, repellent and feeding deterrent activities of the essential oil extracted from Evodia rutaecarpa Hook f. et Thomas, were evaluated against Sitophilus zeamais adults and Tribolium castaneum larvae and adults. Contact toxicity assayed by topical application showed that S. zeamais adults were significantly more susceptible (LD₅₀=0.043 μg/mg body wt) to the essential oil than T. castaneum adults (LD₅₀=0.118 μg/mg body wt) and larvae (LD₅₀=0.093–0.126 μg/mg body wt). However, in the fumigation assays, S. zeamais (LC₅₀=41 μg/L air) was less susceptible to the essential oil than T. castaneum (LC₅₀=11.7 μg/L air). When compared with larvae of various ages, T. castaneum adults were more susceptible to the fumigant toxicity of the essential oil. Also, in the treated filter paper repellency test, the essential oil was more repellent to T. castaneum than to S. zeamais. A flour disk bioassay demonstrated that the essential oil of E. rutaecarpa had a weaker feeding deterrent action against T. castaneum adults than against T. castaneum larvae and S. zeamais adults. The reduction in growth rate of T. castaneum larvae and S. zeamais adults was mainly due to a behavioural (feeding deterrent) action rather than to post-ingestive toxicity of the oil.     

Laboratory evaluation of some additional organophosphorus insecticides against stored-product beetles

The relative susceptibilities of Tribolium confusum Duv. and T. castaneum (Hbst) to seven new organophosphorus insecticides were determined by applying the compounds topically at four dosage rates. SD 8447 (0,0-dimethyl 2-chloro-1-(2,4,5-trichlorophenyl, vinyl phosphate) was more effective than malathion against both species and was evaluated against eight more species of stored-product beetles. It was more toxic than malathion to Rhyzopertha dominica (F.), Lasioderma serricorne (F.), Stegobium paniceum (L.) and Sitophilus zeamais Motsch. but less so against Oryzaephilus surinamensis (L.), O. mercator (Fauv.), Ptinus tectus Boield and Sitophilus granarius (L.). S. zeamais was about eleven times more susceptible to this compound than S. granarius.     

Susceptibility of stored-product beetles on wheat and maize treated with thiamethoxam: effects of concentration, exposure interval, and temperature

Sitophilus zeamais Motschulsky, the maize weevil, Oryzaephilus surinamensis (L.), the saw-toothed grain beetle, and Tribolium castaneum (Herbst), the red flour beetle, were exposed for 1, 2, 3, and 6 d at 22°C, 27°C, and 32°C on maize treated with 0, 0.5, 1.0, 2.0, or 4.0 ppm thiamethoxam, a new-generation neonicotenoid insecticide. A second series of tests was conducted on hard winter wheat using S. oryzae (L.), the rice weevil, Rhyzopertha dominica (F.), the lesser grain borer, and T. castaneum. Mortality of all species on both commodities generally increased with insecticide concentration, exposure interval, and temperature, and data were described by linear and non-linear regressions with concentration as the independent variable. Mortality of S. zeamais ranged from 58% to 90% on maize treated with 0.5 ppm thiamethoxam, and approached 95–100% as concentration increased to 4 ppm. Oryzaephilus surinamensis appeared to be slightly less susceptible than S. zeamais; mortality ranged from about 18% to 80% at 5 ppm and there was a more gradual increase in mortality as concentration increased. Mortality of T. castaneum generally did not exceed 40% at any concentration unless the beetles were exposed for 6 d. Mortality of R. dominica and S. oryzae was less than 60% when exposed on treated wheat for 1 and 2 d, but increased to nearly 100% when exposed for 6 d at 27°C and 32°C. Mortality of T. castaneum did not exceed 20% at the 1- and 2-d exposures, and approached 100% only when beetles were exposed for 6 d at 32°C. Few F₁ adults of any species were found in treated maize or in treated wheat but the number of F₁ T. castaneum in untreated maize and untreated wheat was very low compared with the other species. Results show that thiamethoxam would be an effective protectant of stored maize seed and stored wheat seed.     

Toxic and antifeedant action of nutmeg oil against Tribolium castaneum (Herbst) and Sitophilus zeamais Motsch

The essential oil extracted from nutmeg seeds using steam distillation was tested against the stored product insect pests, Tribolium castaneum (Herbst) and Sitophilus zeamais Motsch., for contact toxicity, fumigant toxicity and antifeedant activity. Filter paper impregnation was employed for contact and fumigant toxicity studies, whereas a flour disc bioassay was used to investigate antifeedant effects. Adults of S. zeamais were about ten times more susceptible than T. castaneum adults to contact action (LC₅₀ values of 1.7 mg/cm² and 18 mg/cm² respectively). However, S. zeamais adults were only 1.7 times more susceptible than T. castaneum adults to fumigant action (LC₅₀ values of 4.5 mg/cm² and 7.7 mg/cm² respectively). Furthermore, the larvae (10–16 days old) of T. castaneum were more susceptible than the adults, but the susceptibility of the larvae decreased with age. Nutmeg oil also significantly (P < 0.05) affected the hatching of T. castaneum eggs and the subsequent survival of the larvae in the concentration range 1.4–3.2 mg/cm². The production of F1 progeny of both T. castaneum and S. zeamais exposed to media treated with nutmeg oil was significantly (P < 0.05) reduced at all concentrations tested. F1 progeny production was totally suppressed at nutmeg oil concentrations of 1.05 g/100 g rice for T. castaneum and 0.35 g/100 g wheat for S. zeamais. Nutritional studies showed that nutmeg oil significantly (P < 0.05) affected the growth rate and food consumption of both insect species, depending on the concentrations used, but the antifeedant activity was more pronounced against S. zeamaisthan against T. castaneum. At 20 g nutmeg oil/100 ml, the feeding deterrence index of T. castaneum was only about 7%, whereas that of S. zeamaiswas 33%. These results suggest that nutmeg oil may be useful as a grain protectant with contact, fumigant and antifeedant activities against these insects.     

Susceptibility of local strains of Sitophilus oryzae (L.) and Tribolium castaneum (Herbst) to insecticides

The toxicity of several insecticides to two local strains of S. oryzae and T. castaneum was determined by exposure to treated papers or wheat. Malathion, lindane, dichlorvos and diazinon were more toxic than DDT, carbaryl and pyrethrins. The S. oryzae strain was very susceptible to lindane (0·43×) and malathion (0·26×), but the T. castaneum strain was found to be tolerant to lindane (1·95×) and malathion (7·6×). The T. castaneum was more tolerant to all tested insecticides than the S. oryzae strain.     

Laboratory evaluation of three novel insecticides inhibiting cuticle formation against some susceptible and resistant stored products beetles

The insecticidal activity of three 1-(2.6-disubstituted-benzoyl)-3-phenylureas was evaluated against a number of susceptible and resistant stored products beetles. The compounds were DU 19111 (1-(2,6-dichlorobenzoyl)-3-(3,4-dichlorophenyl)-urea), PH60-38 (1-(2,6-dichlorobenzoyl)-3-(4-chlorophenyl)-urea), and PH60-40 (1-chlorophenyl)-3-(2,6-difluorobenzoyl)-urea).

PH60-40 was found to be the most effective compound against susceptible strains of Sitophilus granarius, Sitophilus oryzae, Tribolium castaneum and Lasioderma serricorne. All three compounds were ineffective against Stegobium paniceum. A strain of T. castaneum (Kuala Lumpur strain) showing malathion-specific resistance was found to be more susceptible to PH60-40 than its “susceptible” strain. A non-specific resistant strain of T. castaneum (CTC12 strain) showed approximately two times tolerance to PH60-40 compared with the “susceptible” strain.

PH60-40 was shown to have ovicidal properties and also killed young larvae of T. castaneum after short exposure periods. Oviposition was not affected.

Wheat sprayed with an emulsifiable formulation of PH60-40 at 2, 5 or 10 ppm was found to be protected against susceptible T. castaneum, S. granarius and Oryzaephilus surinamensis and against resistant S. oryzae and T. castaneum (Kuala Lumpur strain) following 40 weeks storage at 20°C and 44 weeks storage at 35°C.

Preliminary toxicological data indicates that PH60-40 is of a sufficient order of safety for consideration for grain admixture. The compound is therefore of potential interest as a replacement for the more conventional grain protectants especially in situations where resistance is producing increasing control problems.     

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

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

Laboratory studies on predation by Teretriosoma nigrescens Lewis (Col.: Histeridae) on Prostephanus truncatus (Horn) (Col.: Bostrichidae) infesting maize cobs in the presence of other maize pests

Over 14 weeks at 27°C, 70% r.h., the mean rate of increase of three pairs of Prostephanus truncatus (Horn) was reduced by a factor of ten or four by the addition, after 3 or 6 weeks respectively, of four adult Teretriosoma nigrescens Lewis. The effect of the predator on Tribolium castaneum (Herbst) and Sitophilus zeamais Motschulsky populations was not as great: the mean rate of increase ofT. castaneum was approximately halved; and S. zeamais was not affected by the presence of the predator. T. castaneum had no significant effect on the numbers of P. truncatus or the numbers and predatory ability of T. nigrescens. Selective predation of P. truncatus by T. nigrescens did not encourage significant increases in populations of S. zeamais or T. castaneum.     

Field monitoring Sitophilus zeamais and Sitophilus oryzae (Coleoptera: Curculionidae) using refuge and flight traps baited with synthetic pheromone and cracked wheat

Flight traps with open vertical baffles and refuge traps in the form of rectangular cardboard boxes were used to catch Sitophilus zeamais and S. oryzae in Kenya. Traps baited with the aggregation pheromone (Sitophilure), and for the first time traps baited with pheromone and food bait (cracked wheat), were field tested. Both traps types were effective in capturing Sitophilus spp and gave higher weevil catch when baited with pheromone and cracked wheat combined than with pheromone or cracked wheat alone. The combination of pheromone and cracked wheat had an additive effect on trap catch and not a synergistic effect as reported in earlier laboratory trials. Different pheromone loadings of 0.5, 1 and 2 mg were tested. The catch of S. zeamais in flight traps rose significantly with increasing dosage. For refuge traps, the same effect was observed although the difference between 1 mg and 2 mg was not statistically significant. The trend was for increasing S. oryzae catch with dosage, although total catches were very much lower than those for S. zeamais, and differences did not prove statistically significant. Traps placed on the floor near infested maize cribs captured significantly more Sitophilus spp than those actually placed in the cribs. Adult Sitophilus captured were sexed and in both flight and refuge traps the sex ratio was biased in favour of females even though the sex ratio of weevils from infested maize cobs, which were the source of the captured weevils, was approximately even.     

Evaluation of two new diatomaceous earth formulations, enhanced with abamectin and bitterbarkomycin, against four stored-grain beetle species

Two new natural diatomaceous earth (DE) formulations, enhanced with abamectin (DEA-P/WP), or bitterbarkomycin (DEBBM-P/WP), were tested under laboratory conditions against adults of the rice weevil, Sitophilus oryzae, the lesser grain borer, Rhyzopertha dominica, the red flour beetle, Tribolium castaneum and the rusty grain beetle, Cryptolestes ferrugineus. The bioassays were carried out on wheat, at 30±1 °C and 70±5% r.h. The two enhanced DEs were applied either as dusts (P) or as wettable powders (WP) at the dose rates of 75, 100 125 and 150 ppm. Adult mortality was assessed after 14 and 21 d of exposure on the treated substrate. After this interval, the treated wheat was retained for an additional period of 49 d in the case of S. oryzae and 63 d in the case of the other three species, in order to evaluate progeny production. Generally, for all species tested, mortality was higher on wheat treated with powders in comparison with wettable solutions. After 14 d of exposure, all adult rice weevils were dead even at the lowest dose rate of DEA-P, while 100% mortality was noted at doses 125 ppm of DEBBM-P. For the other species, mortality was 100% on wheat treated with 75 ppm of DEBBM-P, with the exception of T. castaneum for which all adults were dead at doses 100 ppm. Progeny production was low, and no progeny were produced in the cases of R. dominica and C. ferrugineus, for both DEs. However, for S. oryzae, progeny production was high on wheat treated with WP formulations, at dose rates 100 ppm. Similar trends were noted for T. castaneum, at 100 ppm of DEBBM-WP. The results of the present study indicate that both DEA-P/WP and DEBBM-P/WP are more effective against the four beetle species examined in comparison with the currently commercially available DE formulations.     

Repellent effect of pea (Pisum sativum) fractions against stored-product insects

Peas (Pisum sativum) are toxic to some stored-product insects. The repellent effect of fractions of pea seed to stored-product insects was evaluated in multiple-choice tests in which wheat kernels were dusted with fractions rich in either protein, fibre or starch at 0.001 to 10% (wt:wt). There was a negative correlation between pea protein concentration and the number of adults found in grain for Cryptolestes ferrugineus and Sitophilus oryzae, but not for Tribolium castaneum. Pea fibre repelled C. ferrugineus adults but not S. oryzae and T. castaneum. Pea starch did not repel any of the insects. One-week old and 6-week old C. ferrugineus were equally repelled by pea protein. Repellency was detectable 1 h after exposure. Cryptolestes ferrugineus and S. oryzae did not become habituated to the repellent action of pea protein even after 4 weeks of exposure. Habituation was observed, however, when C. ferrugineus was exposed to pea fibre for 4 weeks. In a two-choice bioassay (0 vs. 0.1% and 0 vs. 1% pea protein), the pea-protein-treated grain had significantly fewer insects (C. ferrugineus, S. oryzae, Sitophilus zeamais, T. castaneum, and Tribolium confusum) than untreated grain. The properties of the pea protein fractions seem well suited for developing a natural stored grain protectant.     

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

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

Some effects of the carbon dioxide absorbency of humidity controlling solutions on the results of life history experiments with stored products insects

The longevity of Sitophilus granarius (L), S. zeamais Mots., and Tribolium castaneum (Herbst) and the fecundity and rate of development of T. castaneum were all adversely affected when the insects were kept in desiccators with relative humidity controlling solutions which did not adsorb carbon dioxide. Gas samples taken and analysed every 3–4 days, revealed that the rate of oxygen consumption was higher when carbon dioxide was allowed to accumulate than when it was not. The relevance of the experimental results both to normal storage conditions and to airtight storage is discussed.     

Effect of whole-pea flour and a protein-rich fraction as repellents against stored-product insects

Studies conducted to test the repellency of pea (Pisum sativum L.) products against the red flour beetle, Tribolium castaneum (Herbst), the rice weevil, Sitophilus oryzae (L.) and the lesser grain borer, Rhyzopertha dominica (F.) showed that paddy grains treated with a protein-rich fraction derived from peas var. Bonneville at 1% concentration were repellent to adults. Tribolium castaneum was repelled most quickly followed by S. oryzae and R. dominica.     

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

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

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

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

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

The toxicity of phosphine to all developmental stages of thirteen species of stored product beetles

The toxicity of phosphine to all stages of 13 species of stored product beetles was determined using large numbers of test insects which made possible more accurate assessments of mortality. Species tested were Acanthoscelides obtectus, Caryedon serratus, Cryptolestes ferrugineus, C. pusillus, Lasioderma serricorne, Oryzaephilus surinamensis, Ptinus tectus, Rhyzopertha dominica, Sitophilus granarius, S. oryzae, S. zeamais, Tribolium castaneum and Trogoderma granarium. Tests were conducted as appropriate at 10, 15, 25 and 30°C, all at 70% r.h., with concentrations ranging from 0.013 to 2.96 mg/l and exposure times from 1 to 16 days. Sitophilus spp. proved the most tolerant, and in all species other than T. granarium, in which diapausing larvae were the more tolerant in longer exposures, eggs and pupae were the most tolerant stages. Phosphine was most effective at the higher temperatures, whilst long exposures at low concentrations were far more effective than short exposures at high concentrations. The use of phosphine to control these species of stored-product insects will only be effective at 15°C or below if long exposures can be guaranteed.     

Fumigant toxicity of essential oils from the Myrtaceae family and 1,8-cineole against 3 major stored-grain insects

Six out of 42 essential oils extracted from species of the family Myrtaceae found in Australia were shown to have potent fumigant toxicity against three major stored-grain insects: Sitophilus oryzae, Tribolium castaneum and Rhyzopertha dominica. These were the essential oils from Eucalyptus nicholii, E. codonocarpa, E. blakelyi, Callistemon sieberi, Melaleuca fulgens and M. armillaris. The LD₅₀ and LD₉₅ of the selected essential oils against S. oryzae adults were between 19.0–30.6 and 43.6–56.0 μl/l air, respectively. Also, these oils were approximately twice as toxic to T. castaneum and R. dominica at the LD₉₅. Fumigant effects of the essential oils rich in 1,8-cineole were considered to warrant further research into their potential for commercial use.     

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

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

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

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

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

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

A novel use of modified atmospheres: Storage insect population control

The research described here aimed to establish the feasibility of using modified atmospheres (MA) to protect commodities throughout their storage life by using oxygen (O₂) levels that disrupt the life cycles of the target beetle species. Rather than achieving complete mortality of all stages, the aim was to identify more easily obtainable MAs that would kill the most susceptible stage and prevent population growth. Simulated burner gas and nitrogen (N₂) atmospheres with O₂ contents between 3% and 6%, were tested, along with a N₂-based MA with elevated carbon dioxide (CO₂) (10–20%).

Laboratory tests were carried out on five species of stored-product beetles, Cryptolestes ferrugineus, Oryzaephilus surinamensis, Sitophilus granarius, S. oryzae and Tribolium castaneum. After exposure to the MAs for 28 d an assessment was made of the mortality of adults, the number of adults from progeny produced under the MAs and, for the simulated burner gas, the number of adults from progeny produced in a 28-d period after exposure to the MA. The tests were carried out at 20 and 25 °C with 75% and 85% r.h. at each temperature.

The O₂ content preventing population growth varied with species and temperature. For simulated burner gas or N₂ it was about 4% for O. surinamensis, S. granarius and S. oryzae, and about 3% for C. ferrugineus and T. castaneum at 25 °C. At 20 °C it was about 3% for all species tested. When CO₂ was increased to 10% or 20%, reducing O₂ to 5% was sufficient to eliminate emergence of S. granarius at 20°C, but a few individuals emerged at 25 °C. For C. ferrugineus there was a 95% reduction with 5% O₂ plus 20% CO₂ at 20 °C, but not at 25 °C.