Effects of time and concentration on mortality of phosphine-resistant Sitophilus oryzae (L) fumigated with phosphine

The effects of exposure period and phosphine concentration on mortality of susceptible and resistant Sitophilus oryzae (L) were investigated. Although S oryzae is one of the world's most serious pests of stored grain there are few data on the practical significance of phosphine resistance in this species. The strains investigated were an Australian susceptible strain, a homozygous resistant strain exhibiting a level of resistance common in Australia and an unselected field strain from China with a much stronger resistance. Fumigations were carried out at 25 degrees C on adults and mixed-age cultures. For adults of all three strains and mixed-age cultures of the susceptible and resistant Australian strains, the relationship between concentration and time could be described by equations of the form Cnt = k. In all cases n < 1, indicating that time was a more important variable than concentration. In all fumigations of adults the resistant strains were harder to kill than the susceptible strain. However, in fumigations of mixed-age cultures, which contained the tolerant pupal stage, the difference between susceptible and resistant strains was more pronounced at lower concentrations than higher concentrations. For example, at 0.02 mg litre-1 the estimated LT99.9 for mixed-age cultures of the Australian resistant strain (27 days) is 3.4 times that of the susceptible strain (8 days), but at 1 mg litre-1 there is no difference between the two strains (4 days). Limited data on the Chinese resistant strain supported this finding. Twenty-three days exposure at 0.02 mg litre-1 had no effect on mixed-age cultures of this strain, but there were no survivors after 5 days exposure to 1 mg litre-1.     

The response of phosphine-resistant lesser grain borer Rhyzopertha dominica and rice weevil Sitophilus oryzae in mixed-age cultures to varying concentrations of phosphine

The response of Rhyzopertha dominica and Sitophilus oryzae (both phosphine-resistant) in mixed-age cultures to phosphine at fixed concentration-time products (CT) of 10,500 to 168,000 microliters litre 1 h (ppm h) with either constant, rising or falling concentrations for 7 days was studied at 27 (+/- 2) degrees C. At lower CT products, rising concentrations of phosphine led to significantly fewer survivors of R dominica and S oryzae. Conversely, exposure to falling concentrations of phosphine resulted in significantly more survivors. The influence of changing concentrations of phosphine was more pronounced in S oryzae than in R dominica. In the latter, at the lower CT products of 21,000 and 42,000 microliters-1 h, the adult stage proved to be most tolerant, contrary to the accepted belief that the egg or pupal stage are always more tolerant to phosphine. The results indicate that application of phosphine in rising concentrations is more effective than in constant or falling concentrations.     

Effect of exposure period on degree of dominance of phosphine resistance in adults of Rhyzopertha dominica (Coleoptera: Bostrychidae) and Sitophilus oryzae (Coleoptera: Curculionidae)

Degree of dominance of phosphine resistance was investigated in adults of Rhyzopertha dominica F and Sitophilus oryzae L. Efficacy of the grain fumigant phosphine depends on both concentration and exposure period, which raises the possibility that dominance levels vary with exposure period. New and published data were used to test this possibility in adults of R dominica and S oryzae fumigated for periods of up to 144 h. The concentrations required for control of homozygous resistant and susceptible strains and their F1 hybrids decreased with increasing exposure period. For both species the response lines for the homozygous resistant and susceptible strains and their F1 hybrids were parallel. Therefore, neither dominance level nor resistance factor was affected by exposure period. Resistance was incompletely recessive and the level of dominance, calculated at 50% mortality level, was -0.59 for R dominica and -0.65 for S oryzae. The resistant R dominica strain was 30.9 times more resistant than the susceptible strain, compared with 8.9 times for the resistant S oryzae strain. The results suggest that developing discriminating doses for detecting heterozygote adults of either species will be difficult.     

Responses of phosphine-resistant strains of two stored-product insect pests to changing concentrations of phosphine

Abstract: The susceptibility of eggs, pupae and adults of Tribolium castaneum (Herbst) and adults of Rhyzopertha dominica (F.), (both phosphine-resistant strains) to phosphine at fixed concentration-time (ct) products, with either constant or increasing or decreasing concentrations was studied at 25 (± 1)°C. At lower ct products, falling concentrations of phosphine generally caused reduced insect mortality in all the three exposure periods in the range 12 to 72 h. However, in R. dominica, both increasing and decreasing concentrations were less effective than constant concentrations. At higher ct products, no significant change in the mortality response was observed in either species after exposure to constant or changing concentrations. The findings indicate the need to maintain sufficiently high concentrations of phosphine until the end of the fumigation period.     

Inhibition of egg development by phosphine in the cosmopolitan pest of stored products Liposcelis bostrychophila (Psocoptera: Liposcelididae)

Phosphine-induced delay in development of eggs was investigated as a mechanism of resistance to this fumigant in Liposcelis bostrychophila Badonnel. One-day-old eggs of a susceptible and a strongly resistant strain of L bostrychophila were exposed to a range of phosphine concentrations for 6days at 30 (+/- 1) degrees C and 70 (+/- 2)% RH. Delay in mean hatching period occurred in both susceptible and resistant eggs, although it was more pronounced in the latter. A maximum delay of 2.65 days was recorded for eggs of the susceptible strain at 0.01 mg litre(-1) (the highest concentration at which eggs survived) and 13.39 days for the resistant strain at 1 mg litre(-1) (the highest concentration tested). Delay in egg development time was positively correlated with increasing phosphine concentration. Our results reveal that the most successful strategy to control resistant L bostrychophila is to apply relatively low concentrations of phosphine for extended exposure times (eg 0.05 mg litre(-1) for 16 days) that allow all eggs to hatch to the much less tolerant nymph stage.     

Changes in phosphine sorption in wheat after storage at two temperatures

BACKGROUND: Wheat can be stored for many months before being fumigated with phosphine to kill insects, so a study was undertaken to investigate whether the sorptive capacity of wheat changes as it ages. Wheat was stored at 15 or 25 °C and 55% RH for up to 5.5 months, and samples were fumigated at intervals to determine sorption. Sealed glass flasks (95% full) were injected with 1.5 mg L^?1 of phosphine based on flask volume. Concentrations were monitored for 11 days beginning 2 h after injection. Some wheat samples were refumigated after a period of ventilation. Several fumigations of wheat were conducted to determine the pattern of sorption during the first 24 h. RESULTS: Phosphine concentration declined exponentially with time from 2 h after injection. Rate of sorption decreased with time spent in storage at either 15 or 25 °C and 55% RH. Rate of sorption tended to be lower when wheat was refumigated, but this could be explained by time in storage rather than by refumigation per se. The data from the 24 h fumigations did not fit a simple exponential decay equation. Instead, there was a rapid decline in the first hour, with phosphine concentration falling much more slowly thereafter. CONCLUSIONS: The results have implications for phosphine fumigation of insects in stored wheat. Both the time wheat has spent in storage and the temperature at which it has been stored are factors that must be considered when trying to understand the impact of sorption on phosphine concentrations in commercial fumigations. Copyright © The state of Queensland (through the Department of Employment, Economic Development and Innovation) 2009. Published by John Wiley and Sons, Ltd.     

Influence of phosphine on hatching of Cryptolestes ferrugineus (Coleoptera: Cucujidae), Lasioderma serricorne (Coleoptera: Anobiidae) and Oryzaephilus surinamensis (Coleoptera: Silvanidae)

The hatching and mortality response of 0- to 48-h-old eggs of field strains of the stored-product insects Cryptolestes ferrugineus (Stephens), Lasioderma serricorne (F) and Oryzaephilus surinamensis (L) following phosphine fumigation for 24, 48 or 120 h at 27 (+/- 2) degrees C was investigated. Hatching was delayed and reduced in the first few days in a phosphine-resistant strain of C ferrugineus that was treated with 2.0-7.0 mg litre(-1) doses for 48 h (5-80% mortality) and with 1.0-2.0 mg litre(-1) for 120 h (44-84% mortality). In both the exposures there were significant increases in hatching on later days when compared with the corresponding controls. Developmental delay was, however, not evident in susceptible strains of C ferrugineus, L serricorne and O surinamensis that were exposed to phosphine for 24 h.     

Influence of concentration, temperature and humidity on the toxicity of phosphine to the strongly phosphine-resistant psocid Liposcelis bostrychophila Badonnel (Psocoptera: Liposcelididae)

BACKGROUND: The psocid Liposcelis bostrychophila Badonnel, is a widespread, significant pest of stored commodities, has developed strong resistance to phosphine, the major grain disinfestant. The aim was to develop effective fumigation protocols to control this resistant pest. RESULTS: Time to population extinction of all life stages (TPE) in days was evaluated at a series of phosphine concentrations and temperatures at two relative humidities. Regression analysis showed that temperature, concentration and relative humidity all contributed significantly to describing TPE (P<0.001, R(2)=0.95), with temperature being the dominant variable, accounting for 74.4% of the variation. Irrespective of phosphine concentration, TPE was longer at lower temperatures and high humidity (70% RH) and shorter at higher temperatures and low humidity (55% RH). At any concentration of phosphine, a combination of higher temperature and lower humidity provides the shortest fumigation period to control resistant L. bostrychophila. For example, 19 and 11 days of fumigation are required at 15 degrees C and 70% RH at 0.1 and 1.0 mg L(-1) of phosphine respectively, whereas only 4 and 2 days are required at 35 degrees C and 55% RH for the same respective concentrations. CONCLUSIONS: The developed fumigation protocols will provide industry with flexibility in application of phosphine.     

纯磷化氢熏蒸对桃小食心虫的毒力作用

桃小食心虫在我国温带水果主产区广泛分布,严重威胁水果出口贸易。为明确纯磷化氢熏蒸处理桃小食心虫的可能性,本文系统研究了纯磷化氢在不同温度条件下对桃小食心虫的毒力。耐受性分析结果表明,桃小食心虫各虫态对磷化氢的耐受力有很大差别,1~2龄幼虫耐受性最弱,5龄老熟幼虫耐受性最强。室内毒力试验结果表明,25℃,0.14~0.70mg/L磷化氢熏蒸5龄老熟幼虫81~199h或15℃,0.28~0.84 mg/L磷化氢熏蒸136~166h,桃小食心虫死亡率可达99%;在25℃和15℃下,试虫达到一定死亡率的气体浓度、时间乘积(CT)关系式分别为k=C0.5 T和k=C0.2 T,说明在本试验所取浓度范围内,处理时间是影响磷化氢对桃小食心虫老熟幼虫毒力作用的主要因素,相同条件下高温比低温更有利于磷化氢熏蒸杀虫。本文首次对不同温度条件下纯磷化氢熏蒸桃小食心虫的毒力作用进行了系统研究,明确了纯磷化氢熏蒸技术在水果携带桃小食心虫的检疫处理中极具应用前景。     

Contribution of contact toxicity and wheat condition to mortality of stored-product insects exposed to spinosad

Spinosad, a reduced-risk commercial insecticide derived from a bacterial fermentation product, possesses both contact and oral toxicities against insects. Contact toxicity of spinosad to adults of Rhyzopertha dominica (F), Sitophilus oryzae (L), and Tribolium castaneum (Herbst) was evaluated by exposure for 24 or 48 h to treated glass Petri dishes. Adults were exposed to different deposits (0.001-0.79 mg cm(-2)) of spinosad in 24-h tests and to deposits of 0, 0.0016 and 0.016mg cm(-2) in 48-h tests. Rhyzopertha dominica was most susceptible to spinosad in 24- and 48-h tests, followed by S. oryzae, and T. castaneum. The 24-h LD50 values were 0.0004, 0.077 and 0.189mg cm(-2) for R. dominica, S. oryzae, and T. castaneum, respectively. All R. dominica adults were dead following 48 h exposure to both spinosad deposits, whereas mortality of S. oryzae and T. castaneum ranged from 10 to 85% and 12 to 48%, respectively. Rhyzopertha dominica, T. castaneum, and O. surinamensis adults were exposed for 14 days to whole wheat, cracked wheat and wheat flour treated with 0, 0.1 and 1.0 mg kg(-1) of spinosad. Rhyzopertha dominica adults were highly susceptible to spinosad, followed by O. surinamensis and T. castaneum. Immatures (eggs and larvae) of T. castaneum and O. surinamensis exposed for 14 days were more susceptible on spinosad-treated whole wheat than on treated cracked wheat and wheat flour. This is the first report documenting contact activity of spinosad, and the effect of grain condition on spinosad toxicity, to stored-product insects.     

Efficacy of vaporised ethyl formate/carbon dioxide formulation against stored‐grain insects: effect of fumigant concentration,exposure time and two grain temperatures

BACKGROUND: The ethyl formate/carbon dioxide (CO₂) formulation Vapormate? is a rapid‐acting fumigant being developed for the control of stored‐grain insects. The effects have been investigated of concentration, exposure times of 1, 3, 24 and 72 h and two grain temperatures, 15 and 25 °C, on its efficacy against mixed‐stage cultures of Sitophilus oryzae (L.) Tribolium castaneum (Herbst) and strongly phosphine‐resistant Rhyzopertha dominica (F.) strain QRD569. RESULTS: High mortalities (≥92%) of mixed‐stage cultures of all three species were obtained when grain was fumigated with the formulation (193 g m^?3 ethyl formate) for 1 h. Complete control of R. dominica QRD569 and T. castaneum was achieved with 63 and 76 g m^?3 ethyl formate respectively, with exposure for 24 h, whereas mean mortality of S. oryzae was 86% under the same conditions. Mortalities of S. oryzae juvenile stages were significantly lower than adults under the conditions tested, which was due to pronounced tolerance of mid‐stage pupae to the fumigant. Reducing grain temperature from 25 to 15 °C had no effect on insect mortality. CONCLUSION: Ethyl formate/CO₂ formulation is highly effective against stored‐grain insects over a range of concentrations and exposure times. Efficacious fumigations were conducted in as little as 1 h, and a strongly phosphine‐resistant R. dominica strain was readily controlled with the fumigant. Copyright © 2009 CSIRO, Australia. Published by John Wiley & Sons, Ltd     

The relation between phosphine sorption and terminal gas concentrations in successful fumigation of food commodities

Owing to increased tolerance and the development of resistance in stored product insects to the fumigant phosphine, in recent years there has been a shift in the target terminal concentration from 100 ppm (100 mL m(-3)) to a higher level of 1000 ppm to achieve 100% insect mortality in 7 day commodity treatments. Therefore, there is a need to investigate whether the revised target concentration could be achieved for food commodities fumigated with phosphine at the standard dose of 2 g m(-3) for 7 days under airtight conditions at > or = 25 degrees C. When different types of food commodity (total 74) were fumigated (300 g per replicate) with phosphine at 2 g m(-3) for 7 days, the terminal gas concentrations in the free space of the commodities varied from 0 to > 2000 ppm. In chambers containing no substrate, a 1417 ppm concentration was recorded. Paddy rice, most of the oilseeds, shelled tree nuts, butter beans, cardamom, green gram splits, coriander powder, rice bran and cocoa powder were more sorptive (> or =60%), such that the target concentration of 1000 ppm was not achieved at the end of 7 days. For these commodities, increased doses of 3-6 g m(-3) were required to attain 1000 ppm. In-shell almonds, green cardamom, in-shell peanuts, leaf tea, tamarind pulp and sunflower seeds were exceptionally sorptive (>90%), so that 0, 41, 112, 168, 203 and 217 ppm respectively were noted at the end of 7 days; the dose must exceed 6 g m(-3) for effective fumigation of these commodities.     

Detection and characterisation of strong resistance to phosphine in Brazilian Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae)

As failure to control Rhyzopertha dominica (F.) with phosphine is a common problem in the grain-growing regions of Brazil, a study was undertaken to investigate the frequency, distribution and strength of phosphine resistance in R. dominica in Brazil. Nineteen samples of R. dominica were collected between 1991 and 2003 from central storages where phosphine fumigation had failed to control this species. Insects were cultured without selection until testing in 2005. Each sample was tested for resistance to phosphine on the basis of the response of adults to discriminating concentrations of phosphine (20 and 48 h exposures) and full dose-response assays (48 h exposure). Responses of the Brazilian R. dominica samples were compared with reference susceptible, weak-resistance and strong-resistance strains from Australia in parallel assays. All Brazilian population samples showed resistance to phosphine: five were diagnosed with weak resistance and 14 with strong resistance. Five samples showed levels of resistance similar to the reference strong-resistance strain. A representative highly resistant sample was characterised by exposing mixed-age cultures to a range of constant concentrations of phosphine for various exposure periods. Time to population extinction (TPE) and time to 99.9% suppression of population (LT(99.9)) values of this sample were generally similar to those of the reference strong-resistance strain. For example, at 0.1, 0.5 and 1.0 mg L(-1), LT(99.9) values for BR33 and the reference strong-resistance strain were respectively 21, 6.4 and 3.7 days and 17, 6.2 and 3.8 days. With both strains, doubling phosphine concentrations to 2 mg L(-1) resulted in increased LT(99.9) and TPE. High level and frequency of resistance in all population samples, some of which had been cultured without selection for up to 12 years, suggest little or no fitness deficit associated with phosphine resistance. The present research indicates that widespread phosphine resistance may be developing in Brazil. Fumigation practices should be monitored and resistance management plans implemented to alleviate further resistance development.     

溴虫氟苯双酰胺对小菜蛾的毒力及相关酶活性的影响

溴虫氟苯双酰胺是一种全新的双酰胺类杀虫剂,主要用于防治鳞翅目、鞘翅目、白蚁以及蚊蝇等害虫。为了明确溴虫氟苯双酰胺对小菜蛾的生物活性及解毒酶活性的影响,本研究选择氯虫苯甲酰胺为对照药剂,采用叶片药膜法测定了溴虫氟苯双酰胺对小菜蛾的生物活性,并测定了亚致死剂量(LC20、LC40)的溴虫氟苯双酰胺和氯虫苯甲酰胺对小菜蛾多功能氧化酶、谷胱甘肽S-转移酶和羧酸酯酶活性的影响。结果表明,溴虫氟苯双酰胺与氯虫苯甲酰胺对小菜蛾的生物活性相当,两者对小菜蛾的LC50分别为0.042和0.056μg/mL。与氯虫苯甲酰胺相似,亚致死剂量的溴虫氟苯双酰胺能够诱导小菜蛾体内羧酸酯酶活性升高,但溴虫氟苯双酰胺对多功能氧化酶和谷胱甘肽S-转移酶活性没有显著影响。     

Time,concentration and temperature relationships for phosphine activity in tests on diapausing larvae of Ephestia elutella (Hübner) (Lepidoptera: Pyralidae)

The activity of phosphine against diapausing larvae of Ephestia elutella was shown to depend on several different interactions of duration of exposure, temperature and gas concentration. Using the model proposed by Knight, (C? C₀) × (t? t₀) = k, a constant for mortality, the minimum effective concentration C₀ was raised and the minimum effective exposure t₀ extended as temperatures were increased. The effect of temperature on these thresholds was reduced at higher mortality levels. A range of concentration levels, influenced by temperature, elicited an increase in tolerance at the LD₉₉ level over that evident at higher or lower concentrations. These concentration ranges were 0.9–2-1 mg litre-¹at 25°C,0.7–2.3 mg litre-¹ at 20°C and 0.1–1.5 mg litre-¹ at 15°C. A mathematical model was fitted to relate concentration and time thresholds, mortality and temperature. At the LD₅₀ level, values for t₀ ranged from 2.5 h at 15°C to 5.0 h at 25°C. C₀ values increased from about 0.6 to 7.0 μg litre-¹ over this temperature range. At the LD₉₉ level, t₀ values ranged from 21 to 28 h and C₀ values from 11 to 19 μg litre-¹. Phosphine appeared most effective at each temperature at concentrations from about 40 to 60–100 μg litre-¹.     

Effect of phosphine dose on sorption in wheat

BACKGROUND: In spite of the extensive use of phosphine fumigation around the world to control insects in stored grain, and the knowledge that grain sorbs phosphine, the effect of concentration on sorption has not been quantified. A laboratory study was undertaken, therefore, to investigate the effect of phosphine dose on sorption in wheat. Wheat was added to glass flasks to achieve filling ratios of 0.25-0.95, and the flasks were sealed and injected with phosphine at 0.1-1.5 mg L(-1) based on flask volume. Phosphine concentration was monitored for 8 days at 25 degrees C and 55% RH. RESULTS: When sorption occurred, phosphine concentration declined with time and was approximately first order, i.e. the data fitted an exponential decay equation. Percentage sorption per day was directly proportional to filling ratio, and was negatively correlated with dose for any given filling ratio. Based on the results, a tenfold increase in dose would result in a halving of the sorption constant and the percentage daily loss. Wheat was less sorptive if it was fumigated for a second time. CONCLUSIONS: The results have implications for the use of phosphine for control of insects in stored wheat. This study shows that dose is a factor that must be considered when trying to understand the impact of sorption on phosphine concentration, and that there appears to be a limit to the capacity of wheat to sorb phosphine.     

Effectiveness of allyl acetate as a fumigant against five stored grain beetle pests

Five esters, butyl acetate, allyl acetate, ethyl acetoacetate, isopropyl acetate and propyl acetate, were screened as fumigants in the laboratory for 24 h at 27 (+/-2) degrees C against the adults of Rhyzopertha dominica (F), Sitophilus oryzae (L) and Tribolium castaneum (Herbst). Of the compounds tested, allyl acetate was the most toxic, with LD(99) values of 7.56, 12.81 and 11.42 mg litre(-1) against R dominica, S oryzae and T castaneum, respectively. Tests with allyl acetate against mixed-age cultures of Cryptolestes ferrugineus (Stephens), Oryzaephilus surinamensis (L), R dominica, S oryzae and T castaneum revealed that doses of 50-150 mg litre(-1) with 24-120-h exposures were necessary to achieve 100% mortality of all life stages. Cryptolestes ferrugineus was the most tolerant insect tested, whilst R dominica was highly susceptible. The insect toxicity data indicates that allyl acetate has potential as a fumigant of stored food grains.     

Minimum concentration levels of methyl bromide required for full efficacy against seven species of stored-product beetle at two temperatures

The dosages of methyl bromide required to control insect pests can be expressed as concentration, time (Ct) products for concentrations down to a certain minimal level, here defined as the efficacy threshold, below which Habers Ct rule (C×t=k,a constant for mortality) no longer applies. Twelve strains of seven species of stored-product beetle were tested to identify efficacy threshold concentrations at 15°C and 25°C. For each strain the efficacy threshold was higher at 25°C than at 15°C. Different species differed widely in the threshold levels identified. Strains with a higher than usual tolerance to methyl bromide than their standard stock counterparts had slightly higher efficacy thresholds at 25°C but not at 15°C. The order of tolerance of the standard stocks to methyl bromide at 15°C was Tribolium confusum> T. castaneum> Oryzaephilus surinamensis> Rhyzopertha dominica> Sitophilus granarius> S. zeamais> S. oryzae, and at 25°C Tribolium castaneum > T. confusum> R. dominica> O. surinamensis> S. granarius> S. zeamais> S. oryzae. The order of efficacy thresholds largely reflected the order of susceptibility, S. oryzae and S. zeamais having the lowest efficacy thresholds of about 0.6 mg litre^?1 at 15°C and 1.3-2.0 mg litre^?1 at 25°C, while Tribolium spp. had the highest, 1.3-2.0 mg litre^?1 at 15°C and 2.5-4.0 mg litre^?1 at 25°C.     

Persistence and efficacy of two diatomaceous earth formulations and a mixture of diatomaceous earth with natural pyrethrum against Tribolium confusum Jacquelin du Val (Coleoptera: Tenebrionidae) on wheat and maize

Laboratory tests were conducted to assess the insecticidal and residual effects of three diatomaceous earth (DE) formulations, Insecto, PyriSec and SilicoSec, against Tribolium confusum Jacquelin du Val on wheat and maize. Quantities of wheat and maize were treated with the above formulations at 500, 1000 and 1500 mg kg(-1) and stored at 25 degrees C and 55% relative humidity (RH). Samples were taken on the day of storage and every 30 days until completion of a 360 day period of storage. Adults of T. confusum were exposed to these samples at 25 degrees C and 55% RH and the mortality was measured after 24 and 48 h and 7 and 14 days of exposure. Adult mortality was higher on wheat than on maize. At the beginning of the storage period, mortalities after 14 day exposure on maize treated with the highest rate were 60, 63 and 81% for Insecto, PyriSec and SilicoSec respectively, while on wheat the mortality was 100% for all DEs. On the same commodities 360 days after treatment the respective mortality figures for wheat were 99, 98 and 100%, while in the case of maize they did not exceed 7%. Generally, mortality at exposures < or =48 h decreased with increasing storage time. Furthermore, although mortality on wheat increased with dose, the increase in DE dose from 1000 to 1500 mg kg(-1) resulted in only a small increase in mortality. Thus a DE treatment of 1000 mg kg(-1) was shown to provide long-term protection of wheat against T. confusum, although higher DE application rates and exposure intervals are needed for a satisfactory level of protection of maize against this pest.     

Influence of killing agents and water on the capture of six coleoptera species in probe traps

The introduction of propylene glycol, DDVP and water inside perforated probe traps was evaluated on the basis of their effectiveness in trapping adults of six species of Coleoptera infesting stored cereals. Adults ofSitophilus oryzae, Tribolium castaneum, Cryptolestes ferrugineus, Tenebroides mauritanicus, Rhyzopertha dominica andOryzaephilus surinamen-sis were placed in plastic cylindrical bins each containing 14 kg of wheat. One probe trap was then introduced into each container and the adults trapped were counted 72 h later. Experiments were conducted at two population densities, of 30 adults (approx. one insect per 0.5 kg of wheat) and 90 adults (approx. three adults per 0.5 kg of wheat) of each species per container. The highest percentage of adults trapped was observed forC. ferrugineus andT. castaneum, and the lowest forR. dominica andS. oryzae. No significant differences in number of adults captured (% of the total number of adults) was noted between the two population density levels. At the lower density, the presence of killing agents in the traps did not increase the captures significantly; on the other hand, at the higher density, the killing agents helped to increase significantly the catches of 5.oryzae, T. castaneum, T. mauritanicus andO. surinamensis, as compared with the catches in the control traps. No significant differences were noted forC. ferrugineus andR. dominica.