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.     

Legume type and temperature effects on the toxicity of insecticide to the genus Callosobruchus (Coleoptera: Bruchidae)

Three bruchid pest species, Callosobruchus maculatus, Callosobruchus chinensis and Callosobruchus rhodesianus, were studied for their response to insecticide toxicity taking into account the separate and interactive effects of temperature and pre-adult food. The food types used were cowpea (Vigna unguiculata) and mungbean (Vigna radiata). Callosobruchus maculatus was the most tolerant to malathion and the least affected by temperature change while C. rhodesianus was the least tolerant. Over a 4 °C range (23°, 25°, 27 °C), there was generally a significant impact of temperature on the tolerance of the three species to the insecticide. The food type on which the insects developed influenced considerably the degree of insecticide tolerance. Callosobruchus maculatus and C. chinensis populations reared on mungbean had higher tolerance to malathion than their counterparts reared on cowpea, but the opposite was observed in C. rhodesianus populations. The food influence in this study suggested an ancestral cause or fitness cost depending on the species. The interaction of food-by-temperature had no significant effect on malathion toxicity to this genus. Correlation analysis showed C. chinensis to be relatively less sensitive to insecticide concentration over the range studied compared with the other two species.     

Protection of stored maize from insect pests using a two-component biological control method consisting of a hymenopteran parasitoid, Theocolax elegans, and transgenic avidin maize powder

The hymenopteran parasitoid, Theocolax elegans (Westwood), and transgenic avidin maize powder were tested to determine if their individual or combined use would protect stored grain from infestation by both internal and external insect pests. Small-scale tests were conducted in plastic jars containing 3 kg of non-transgenic maize. We tested treatments of 0.3% powdered avidin maize, the parasitoid wasp, and the combination of the parasitoid plus 0.3% powdered avidin maize. One pair each of Sitophilus zeamais Motschulsky, Tribolium castaneum (Herbst), and Cryptolestes ferrugineus (Stephens) was added to each jar. After 8 weeks, the entire contents of each jar were examined for adult insects. Control and avidin maize powders had no detrimental effects on the beneficial insect parasitoid T. elegans. The parasitoid suppressed populations of the internal feeder S. zeamais. The avidin maize powder treatment had no effect on S. zeamais because these larvae developed inside the maize kernels where no avidin maize powder was present. For S. zeamais, the combination treatment was not significantly different from the parasitoid treatment. In contrast, populations of the external feeder T. castaneum were not suppressed by the parasitoid but were suppressed by the avidin maize powder treatment. The parasitoid-avidin combination treatment produced the greatest percentage reduction for all three insect species and resulted in 78%, 94%, and 70% reductions in populations of S. zeamais, T. castaneum, and C. ferrugineus, respectively, when compared to the control treatment. The percentage reductions for the parasitoid treatment were 70%, 8%, and 20% for S. zeamais, T. castaneum, and C. ferrugineus, respectively. For the avidin maize powder treatment, populations of S. zeamais, T. castaneum, and C. ferrugineus were reduced by 10%, 85%, and 40%, respectively. The combination treatment of avidin maize powder plus the release of parasitoid wasps was superior to either treatment alone when applied to mixed populations of internal and external feeders.     

The efficacy and persistence of diatomaceous earths admixed with commodity against four tropical stored product beetle pests

The efficacy and persistence of two commercially available enhanced diatomaceous earth (DE) products (Dryacide^® and Protect-It^®) against four common tropical storage pests (Prostephanus truncatus, Sitophilus zeamais, Callosobruchus maculatus and Acanthoscelides obtectus) were studied when admixed with typical host commodities at different application rates and relative humidities. Persistence of the enhanced DE treatments was considered after 3 and 6 months storage by assessment of both adult mortality and F1 progeny emergence. Both DEs usually increased parental mortality and reduced progeny emergence of all four insect species in comparison with the untreated control at both 50% and 60% r.h., and at all storage periods. However, efficacy was inversely related to duration of storage and over time the host commodity also became less suitable for insect development. Each insect species differed in its susceptibility to the DE treatments, highlighting the need for field application rates to be based upon the entire spectrum of pest species likely to be present during storage.     

A simple curve describing the development pattern of some beetles breeding on stored products

The curve representing the emergence pattern of a generation of Sitophilus zeamais Motsch. developing upon maize was investigated, and it was found that the relationship between the cumulative number of emerged insects (y) and time (t) could be described by the asymptotic model log_ey = a ? bp^t. The model also satisfactorily fitted data for the emergence of S. zeamais breeding on triticale and on barley, Callosobruchus maculatus (F.) breeding on cowpeas and Prostephanus truncatus (Horn) breeding on maize.     

Efficacy of phosphine and insect penetration ability in ZeroFly® bags

The deltamethrin incorporated woven polypropylene ZeroFly® storage bag is a promising novel technology for grain storage. However, if grain stored in ZeroFly bags gets infested and has to be fumigated using phosphine (PH₃), data on the effectiveness of such treatments are needed. Additionally, obtaining field data on ability of stored-product insect pests to breach ZeroFly bags would facilitate insect management. Therefore, efficacy of PH₃ in immature and adult Sitophilus zeamais (Motschulsky), Prostephanus truncatus (Horn), Rhyzopertha dominica (F.) and Tribolium castaneum (Herbst) in experimental cages in maize stored in 100-kg polypropylene (PP), jute and ZeroFly bags was investigated. Post-fumigation mortality of adults was recorded after 7 d, and after 7 wk for immatures. The ability of either S. zeamais or P. truncatus to penetrate fabric of PP, jute and ZeroFly bags was assessed. Phosphine efficacy was good in all the three types of bags and resulted in complete mortality of adults and immatures of the four species tested. Sitophilus zeamais and P. truncatus were more successful in penetrating the PP bag fabric and on average made 84 and 780 holes per bag over a 4 mo-period, respectively; this was followed by jute with 37 and 614 holes. The ZeroFly bag was harder to breach and ≤3 holes per bag were made for both species. This study shows that PH₃ is highly efficacious in insects that infest maize stored in ZeroFly bags, and that these bags are not easily penetrated by stored product insect pests. Hitherto, ZeroFly bags are a good technology for storing grain that is not infested, and fumigation using PH₃ can be effectively conducted if infestation occurs. Therefore, ZeroFly bags can be incorporated in integrated stored product insect management (IPM) programs for bagged grains.     

Progress towards a lure to attract three stored product weevils, Sitophilus zeamais Motschulsky, S. oryzae (L.) and S. granarius (L.) (Coleoptera: Curculionidae)

The behavioural responses of Sitophilus granarius, S. oryzae and S. zeamais to synthetic 4S,5R-sitophinone alone and in combination with volatiles from kibbled carob have been investigated with a view to the development of a single lure to attract all three species. Sitophilus zeamais and S. oryzae were shown to respond to 4S,5R-sitophinone at amounts as low as 0.025 ng. Sitophilus granarius gave a significant response to 50 ng 4S,5R-sitophinone. Volatiles from kibbled carob were also shown to attract all three species. This is the first time that attraction of S. zeamais and S. oryzae to carob volatiles has been demonstrated. Fresh lures containing 4S,5R-sitophinone and carob volatiles attracted significantly more insects in pitfall bioassays for all three species than when either component was used alone. However, after 6 weeks a significant increase in response compared to the control was found only for S. oryzae and S. zeamais. The effect of insect age on response to the pheromone and carob volatiles was also studied for all three species. The response to carob volatiles decreased with increasing insect age for all three species. A significant response to 4S,5R-sitophinone was found only for 1-2-day-old adults of S. oryzae and S. zeamais but for all ages tested of S. granarius. The effect of the combination of pheromone and carob volatiles also decreased with increasing insect age.     

Deltamethrin- and spinosad-mediated survival,activity and avoidance of the grain weevils Sitophilus granarius and S. zeamais

The granary and maize weevils are serious worldwide threats to stored products and their control has heavily relied on synthetic insecticides, which are largely recommended based on studies with acute lethal doses neglecting the importance of potential sublethal effects of insecticides. Deltamethrin has been widely used for managing grain weevils and other stored grain pest species, but reported control failures with this insecticide sparked the search for alternative insecticidal compounds. The bioinsecticide spinosad is one of such alternatives whose use against stored grain insect pests is relatively recent, but encompasses the control of grain weevils. Nonetheless, little is known about the sublethal effects of spinosad on these insect pest species. Here we assessed the insecticidal effects of commercial formulations of spinosad and deltamethrin against the weevil species Sitophilus granarius and S. zeamais. Both spinosad and deltamethrin were able to effectively control the insects, although the latter caused a faster mortality than the former. Behavioral pattern changes were caused by both insecticides, especially deltamethrin, triggering irritability (i.e., avoidance after contact). Different feeding and drinking responses were also detected for both weevil species, which exhibited significant avoidance to deltamethrin and to spinosad, but with a milder response to the latter. Apparently spinosad is not as easily recognizable as deltamethrin by S. zeamais and S. granarius, remaining effective against both species without minimizing as much the potential exposure as deltamethrin.     

Evaluation of three compounds with insect juvenile hormone activity as grain protectants against insecticide-susceptible and resistant strains of Sitophilus species (Coleoptera: Curculionidae)

Three compunds with insect juvenile hormone activity have been tested as protectants for wheat grain against one insecticide-susceptible and two insecticide-resistant strains of Sitophilus granarius. Neither JH I nor methoprene gave complete control of S. granarius at 100 ppm whereas ethyl[2-(p-phenoxy)ethyl]carbamate was effective at only 5 ppm. There was no loss of biological activity of this last compound even after treated grain was stored at 25°C and 70% r.h. for 12 months, and it was also found to be highly active against susceptible strains of Sitophilus oryzae and Sitophilus zeamais. There was no evidence that two insecticide-resistant strains of S. granarius were cross-resistant to any of the compounds tested.     

Residual effects of deltamethrin and malathion on different populations of Sitophilus granarius (L.) on treated wheat grains

The impact of 2-, 7-, 14-, 30-, 90-, 150- and 720-day-old deposits of deltamethrin, applied with or without the synergist piperonyl butoxide (PBO), and of malathion, on adults of different populations of granary weevil Sitophilus granarius on wheat was investigated in the laboratory. The insecticides used were commercial formulations and their application rates were as recommended: deltamethrin (dustable powder) 0.5 mg a.i./kg, deltamethrin + PBO (1:10) (emulsifiable concentrate) 0.25 mg a.i./kg, and malathion (dustable powder) 10 mg a.i./kg. The weevil populations examined were: (a) a laboratory population, (b) field populations with different susceptibility to some insecticides as established previously, and (c) populations selected in the laboratory with deltamethrin or pirimiphos-methyl.The 2-day-old deposit of malathion caused complete mortality of all weevil populations after 7 and 14 days. The corresponding deposit of deltamethrin was 100% effective only against the laboratory weevils after 7-14 days, while deltamethrin at the lower level formulated with PBO caused about 90% mortality of laboratory weevils and much lower levels of kill among field and selected weevils.Deposits of deltamethrin and malathion up to 90 days old killed all field weevils after 14 days of exposure. The 150-day-old deposit of deltamethrin was also 100% effective against field weevils exposed for 14 days, while the effectiveness against selected populations was around 50%. Malathion deposits of the same age gave 40-50% mortality of field weevils, and 4-68% mortality of selected weevils. The 720-day-old deposits of malathion were ineffective against all weevil populations, while the mortality of laboratory weevils after 14 days contact with deltamethrin deposits of the same age was 76%, and that of field and selected weevils about 50%.     

Stored grain pest prevalence and insecticide resistance in Egyptian populations of the red flour beetle Tribolium castaneum (Herbst) and the rice weevil Sitophilus oryzae (L.)

As a consequence of the widespread use of insecticides against insect pests in grain warehouses and in the food industry, insecticide resistance has greatly increased among these species all over the world. Nonetheless, insecticide resistance in stored grain insects in Egypt was little studied. Therefore, our study aimed to forecast infestation risks and determine the insecticide resistance level in Egyptian populations of the main insect pests of stored grains. To achieve this goal, we surveyed the populations of stored-product insects in wheat in two different sites in the Alexandria governorate (Egypt) between June and August 2017. Moreover, insecticide resistance levels in Egyptian populations of Tribolium castaneum (Herbst) and Sitophilus oryzae (L.) collected from wheat storage facilities (granaries and flour mills) in Alexandria governorate were also determined. Three contact insecticides, namely malathion, pirimiphos-methyl and cypermethrin, were tested. Tarsal contact bioassays on filter paper were carried out on adults following FAO methods and concentration-mortality lines were estimated to determine the resistance ratios for each insecticide and population. The data from the monitoring of insects revealed that T. castaneum and S. oryzae were the most common species infesting wheat in both Alexandria granaries and mills. Populations of S. oryzae were generally more resistant to malathion than the populations of T. castaneum. However, T. castaneum populations were more resistant to pirimiphos-methyl than the S. oryzae populations. Both populations of T. castaneum and S. oryzae were susceptible to cypermethrin. The detected levels of insecticide resistance indicate that this phenomenon takes place and should be a concern in Egyptian populations of T. castaneum and S. oryzae requiring monitoring and design of resistance management practices.     

Bioactivity of Jatropha curcas L. to insect pests of stored products

The objective of this research was to assess insecticidal activity of seeds and derivatives of Jatropha curcas to insect pests of stored grains. Lethal exposure times were estimated for 50 and 95% (LT₅₀ and LT₉₅) of the adults of Sitophilus zeamais and Rhyzorpertha dominica to seeds of four genotypes of J. curcas: Gonçalo, Paraguaçu, Filomena and Bento. Toxicity of powders and aqueous extracts from seeds and pericarps of J. curcas were tested on S. zeamais, R. dominica, Tribolium castaneum and Oryzaephilus surimanensis. A uniform toxic response was observed among the four genotypes for S. zeamais and R. dominica. The powders and aqueous extracts from seeds and pericarps were lethal to S. zeamais, R. dominica, T. castaneum and O. surimanensis. However, insect mortality was higher in the treatments from seeds, compared to the treatments from pericarps.     

Varietal effects of cowpea, Vigna unguiculata, on tolerance to malathion in Callosobruchus maculatus (Coleoptera: Bruchidae)

The impact of cowpea variety on the response of cowpea bruchid, Callosobruchus maculatus, to malathion was investigated. The interaction of six cowpea varieties (Adamawa Brown, Ife BPC, Ife Brown, Lilongwe, Ntcheu and NCRI-L25) with the geographical strains of C. maculatus (Brazil and Cameroon), temperature (23, 25, 27 °C) and insecticide concentration were considered. Cowpea variety (V) had an unpredictable effect on C. maculatus response to malathion. Bruchid populations produced by Ife BPC were the most susceptible to malathion while those yielded by NCRI-L25 were the most tolerant. Regardless of the cowpea variety, the Brazil strain showed higher tolerance than the Cameroon strain. There was significant effect of temperature (T) and insecticide concentration (C) on malathion tolerance in both strains (S). Likewise, there was significant impact of all two-way interactions on cowpea bruchid tolerance except V x C. Significant three-way interactions on C. maculatus tolerance to malathion was only observed in S × T × V and S × T × C. The predictability of changing one of the factors on the susceptibility of C. maculatus to insecticide was very low. This study suggests a need to take the insecticide tolerance of insect populations produced by novel varieties into account during plant breeding in addition to factors such as yield and resistance to insect and disease attack.     

The cross-resistance spectrum of Sitophilus granarius (L.) (Coleoptera: Curculionidae) heterozygous for pyrethrin resistance

Dose-response data were obtained from the F₁ progeny of crosses between virgin Sitophilus granarius (L.) from pyrethrin-resistant and susceptible strains. These data were compared with data from the parental strains. The insects were tested with pyrethrins, bioresmethrin, malathion, pirimiphos-methyl, lindane, DDT and propoxur. The exposure method was confinement of the insects on filter papers impregnated with insecticide in oil. The pyrethrin-resistant strain showed resistance to all seven insecticides. The probit lines of the heterozygotes fell approximately half-way between those of the resistant and susceptible strains for all the compounds tested. R-strain males responded to lindane more slowly than did the females, whereas there was no significant difference in the rate of response of the sexes of the S-strain.     

Species diversity and relative abundance of Callosobruchus (Coleoptera: Chrysomelidae) in stored cowpea in four major agricultural produce markets in the central region,Ghana

A study was conducted to investigate species diversity and relative abundance of Callosobruchus (Coleoptera: Chrysomelidae), a major insect pest infesting stored cowpea in the central region of Ghana. Cowpea stocks from Burkina Faso, Ejura, Ghana and Niger were obtained from the markets, and held to collect adults emerging from the cowpeas. Adult Callosobruchus spp. were identified based on the pattern of their hind femora and elytra. Five species, Callosobruchus maculatus, Callosobruchus rhodesianus, Callosobruchus chinensis Callosobruchus analis and Callosobruchus subinnotatus, were identified, with C. maculatus being the most abundant.     

Susceptibility to contact insecticides of granary weevil Sitophilus granarius (L.) (Coleoptera: Curculionidae) originating from different locations in the former Yugoslavia

The insecticides dichlorvos, malathion, chlorpyrifos-methyl, pirimiphos-methyl, deltamethrin and cypermethrin were applied to filter paper to assess their toxicity to granary weevil Sitophilus granarius adults. Based on discriminating doses obtained from tests on a susceptible laboratory population, the susceptibility of 12 populations originating from different storage facilities (11 in Serbia and 1 in Bosnia-Herzegovina) was tested. The facilities included silos, floor stockpiles and attic stockpiles. Weevils originating from Apatin, Belgrade Port, Bijeljina and Kikinda were submitted to toxicity testing, and determination of ld-p lines, LD values and levels of susceptibility/resistance. Chlorpyrifos-methyl proved the most toxic and cypermethrin the least toxic insecticides against all populations. Dichlorvos, malathion and pirimiphos-methyl had the least toxic effect on weevils originating from Belgrade Port and Kikinda, While deltamethrin was most toxic to weevils from Belgrade Port, and least toxic to weevils from Kikinda. The resistance ratios (RR) for deltamethrin at the LD₅₀ and LD₉₅ levels 48 h after exposure to treated filter paper were 11.2 and 14.5 for Bijeljina weevils, and 20.9 and 25.5 for Kikinda weevils.     

Efficacy of diatomaceous earths and their low-dose combinations with spinosad or deltamethrin against three beetle pests of stored-maize

A key element in postharvest IPM is the reduction of chemical residues in food through the use of reduced dosages of less toxic grain protectants. Two laboratory experiments were conducted: Experiment I determined the efficacies of straight diatomaceous earths (DEs) – “Chemutsi” (African raw DE), MN51 (new formulation) and Protect-It^® (enhanced DE), and two new food grade DE-based formulations (A2 and A3) against adult Prostephanus truncatus (Horn), Sitophilus zeamais (Motschulsky) and Tribolium castaneum (Herbst) admixed with shelled maize. In Experiment II, Chemutsi and Protect-It^® were further tested in varying combinations with low-dose deltamethrin and spinosad. At 21 days post-exposure, MN51 800 ppm and 1000 ppm, Chemutsi 1000 ppm, Protect-It^® 600 ppm and food grade A3 150 ppm caused S. zeamais mortalities that were not significantly different from the positive control (Protect-It^® 1000 ppm). However, after the same exposure period, all the straight DEs (applied at ≤ 1000 ppm) and the DE-based food grade formulations were not effective on P. truncatus and T. castaneum. In low dose combinations, 7 day mortalities showed high S. zeamais susceptibility to both DE-spinosad and DE-deltamethrin while P. truncatus was more susceptible only to DE-spinosad and T. castaneum to Protect-It^®-deltamethrin only. At 21 days, all DE-spinosad and DE-deltamethrin treatments were effective and not significantly different from the commercial grain protectant (fenitrothion 1.0% w/w (10000 ppm) + deltamethrin 0.13% w/w (130 ppm)) on all test species. DE-spinosad and DE-deltamethrin combinations significantly suppressed (P < 0.001) F₁ progeny for the three test species whereas straight DEs and DE-based food grade formulations did not. Our results showed that at half the label rates or lower, DE-spinosad and DE-deltamethrin combinations were effective alternative grain protectants that are safer and possibly cheaper. We also give the first report on the effectiveness of Chemutsi in combination with spinosad or deltamethrin on maize grain.     

Detection of phosphine resistance in major stored-product insects in Greece and evaluation of a field resistance test kit

The use of phosphine has been effective against a wide range of stored-product pests in different types of commodities and facilities. However, its continuous and improper use has led to resistance development in -several major insect species. Although phosphine resistance has been reported from many countries across the globe, reports from Europe have been very limited. In the present study, we determined phosphine resistance in insect populations that had been collected from a range of storages across Greece, using two different diagnostic protocols. Apart from the traditional Food and Agriculture Organization (FAO) protocol, a field test kit (known as the Detia Degesch Tolerance Test Kit, DDTTPK) was utilized, for “same day” determination of the resistance status of field collected insects. In total, 53 populations belonging to Rhyzopertha dominica, Sitophilus oryzae, Sitophilus granarius, Cryptolestes ferrugineus, Tribolium confusum, Tribolium castaneum and Oryzaephilus surinamensis were tested. For the majority of the species and populations tested, both FAO and DDPTTK provided similar results, for the susceptibility to phosphine and thus, the quick test could be used with success for an initial same day screening of phosphine resistance. Among the tested species, the populations recorded with the most frequent survival at the FAO testing dose of phosphine was that of R. dominica. The dissimilar evaluation and characterization of resistance to phosphine between diagnostic protocols is particularly important, as it poses risks in the over or underestimation of the resistance status of a given population. Our data indicate that the DDPTTK could be used to determine resistance to phosphine in the field, before the initiation of fumigations to disinfest stored commodities.     

The influence of temperature on the susceptibility to eight organophosphorus insecticides of susceptible and resistant strains of Tribolium castaneum,Oryzaephilus surinamensis and Sitophilus granarius

Susceptible strains of adult Tribolium castaneum, Oryzaephilus surinamensis and Sitophilus granarius were exposed for 24 hr to a range of deposits (from 10 to 5000 mg/m²) of eight organophosphorus insecticides (bromophos, chlorphyrifos-methyl, fenitrothion, jodfenphos, malathion, phoxim, pirimiphos-methyl and tetrachlorvinphos) at 10, 17.5 and 25°C. Based upon knockdown and kill, the effectiveness of all insecticides was greater at 25°C than at 17.5°C and was markedly lower at 10°C. At 10°C tetrachlorvinphos, bromophos and jodfenphos were virtually ineffective to S. granarius even at 5000 mg/m². By contrast at 25°C, 100 mg/m² was adequate to give complete knockdown of all species with most insecticides, the exceptions being malathion and tetrachlorvinphos. The three most effective insecticides, chlorphyrifos-methyl, pirimiphos-methyl and fenitrothion were also tested, in comparison with malathion, against a known malathion-resistant strain of each of the test species. Chlorpyrifos-methyl and pirimiphos-methyl were the most effective materials against both susceptible and resistant strains of all species. Knockdown was inevitably followed by mortality although at the lower temperatures this took several days.     

Bioactivities of cymol and essential oils of Cupressus sempervirens and Eucalyptus saligna against Sitophilus zeamais Motschulsky and Tribolium confusum du Val

The essential oils extracted from Eucalyptus saligna and Cupressus sempervirens leaves were analysed by GC-MS and evaluated along with cymol, one of their main constituents for their repellent and toxic effects on Sitophilus zeamais and Tribolium confusum. Contact toxicity assayed by impregnation on filter paper discs or coating onto maize grains showed that these chemicals caused significant mortality of the test insects. Eucalyptus oil was more toxic than Cupressus oil to both insect species (LD₅₀=0.36 μl/cm² for S. zeamais and 0.48 μl/cm² for T. confusum) on filter paper discs, and was more toxic to S. zeamais on maize (LD₅₀=38.05 μl/40 g grain). Both oils considerably reduced the F₁ progeny production and grain weight loss. Moreover, both crude oil extracts produced a stronger repellent activity against the test insects than did cymol. These results suggest that the essential oils from E. saligna and C. sempervirens may be used in grain storage against insect pests.