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Spinosad is an effective grain protectant against resistant strains of Rhyzopertha dominica (F.)
Abstract
Grain protectant insecticides are used in many parts of the world to provide long term protection for stored grain. One of the most serious pests of stored grain is the lesser grain borer, Rhyzopertha dominica (F.), which has demonstrated an ability to develop resistance to a range of grain protectants. The biologically derived insecticide, spinosad, has been the focus of recent research, investigating its potential as a grain protectant. In this paper we detail the current status of resistance to grain protectants in R. dominica, and summarise research showing that spinosad is effective against resistant strains of this species.
... They stated that is the first report comparing the field efficacy of spinosad and aeration in managing insects in farm bins, they suggest that spinosad is very effective in suppressing R. dominica and T. castaneum populations in stored wheat. Many research workers determined the efficacy of spinosad (a biopesticide) in laboratory bioassays against a range of stored product insect species (Daglish and Nayak, 2005;Kljajic and Peric, 2007;Daglish (2008), Athanassion et al. (2009. El-Madawy (2013) evaluated spinosad as contact, repellent and fumigant agent against T. castaneum and R. dominica in laboratory. ...
Cowpea beetle, Callosobruchus maculatus (Fabr.) is considered the most important pest of cowpea, Vigna unguiculata (L.) Walp., stored in tropical and sub tropical regions. Laboratory bioassays were carried out in order to evaluate the effectiveness of spinosad (Tracer 24 % SC) by using three application methods, contact, fumigant and repellent toxicity, against the cowpea beetle C. maculates. Regarding to the contact toxicity, when spinosad applicated by thin film residue in petri dishes(9 cm 2 diameter) its LC50s and LC90s recorded 122.55 and 1285.88 ppm, respectively, comperated with 645.06 and 3884.36 ppm, for grain mixing method after 24 h. The percentage of hatching eggs varied from 40.60 to 71.90 %, while the numbers of emerged adults ranged from 10 to 81 insects, comperated with 299 for control. The reduction of progeny ranged from 70.07 to 100.00 with 250 and 1500 ppm. The Main development period (period of generation) ranged from 38.00 to 60 day comperated with 24 days for control. Application of spinosad as fumigant recorded 224.599 and 1464.980 ppm (50 cm 3), for LC50s and LC90s , respectively. The repellent activity of spinosad by two applications methods resulted 100 % percentage repellency for adults at concentrations of 300 and 750 ppm for petri dish and jar techniques, respectively. Spinosad may be a good choice as a potent boinsecticide by thin residue film method against studied stored product insect C. maculatus .
... They stated that is the first report comparing the field efficacy of spinosad and aeration in managing insects in farm bins, they suggest that spinosad is very effective in suppressing R. dominica and T. castaneum populations in stored wheat. Many research workers determined the efficacy of spinosad (a biopesticide) in laboratory bioassays against a range of stored product insect species (Daglish and Nayak, 2005;Kljajic and Peric, 2007;Daglish (2008), Athanassion et al. (2009). El-Madawy (2013) evaluated spinosad as contact, repellent and fumigant agent against T. castaneum and R. dominica in laboratory. ...
... The activity of spinosad during four months was not affected by two moisture and three temperature level tested. Daglish and Nayak (2005) experimented on spinosad that it is an effective grain protectant against resistant strains of Rhyzopertha dominica Fab. They described that one of the most serious pests of stored grain is R. dominica. ...
Spinosad is a reduced-risk insecticide derived by fermentation from the soil actinomycete, Saccharopolyspora spinosa Mertz & Yao. Spinosad is currently registered in several countries as a grain protectant at a maximum labeled use rate of 1 ppm (1 mg a.i./kg of grain) and with the Maximum Residue Level (MRL) or tolerance on grains set at 1 or 1.5 ppm. Global launch of spinosad as a grain protectant is expected in the near future, pending final acceptance of international residue tolerances for spinosad by major grain importing and exporting countries. Spinosad effectively controls economically important beetle and moth pests associated with stored grain and is also effective against certain psocid species. Spinosad provides grain protection through control of adult and/or immature life stages of pest insects. The pest spectrum of spinosad under commercial grain storage conditions is still being defined, but it is clear from available laboratory and field evaluations on various grains that the lesser grain borer, Rhyzopertha dominica (F.); larger grain borer, Prostephanus truncatus (Horn); rusty grain beetle, Cryptolestes ferrugineus (Stephens); flat grain beetle, Cryptolestes pusillus (Schönherr); red flour beetle, Tribolium castaneum (Herbst); confused flour beetle, Tribolium confusum Jacquelin du Val; Indian meal moth, Plodia interpunctella (Hübner); rice moth, Corcyra cephalonica (Stainton); Angoumois grain moth, Sitotroga cerealella (Olivier); almond moth, Cadra cautella Walker; and the psocid species Lepinotus reticulatus Enderlein and Liposcelis entomophila (Enderlein) are susceptible to spinosad and complete control is to be expected. Other pest species such as the maize weevil, Sitophilus zeamais Motchulsky; rice weevil, Sitophilus oryzae (L.); and sawtoothed grain beetle, Oryzaephilus surinamensis (L.) are susceptible to spinosad to varying degrees, but their overall level of control remains to be verified under commercial grain storage conditions. Spinosad residues are highly stable on grains stored in bins, with a length of protection ranging from 6 months to 2 years. Numerous factors have been shown to impact the overall performance of spinosad, including insect pest species, pest life stage, grain type, grain variety, and formulation type. Spinosad possesses a unique mode of action in insects and controls insect strains resistant to other grain protectants. When launched globally, spinosad will represent a valuable new addition to the limited arsenal of grain protectants and can positively impact global food security. Its combination of high efficacy, broad insect pest spectrum, low mammalian toxicity, and sound environmental profile is unique among existing products currently used for stored-grain protection.Highlights► Like most grain protectants spinosad effectiveness against a variety of stored product insects at the maximum registered use rate of 1 ppm varies with the species, life stage, commodity treated, and spinosad formulation type. ► Field tests show spinosad to be stable on corn and wheat for a period of six months to two years. ► Spinosad’s unique and non-cross resistant mode of action will make it a valuable new tool in stored grain resistance management programs. ► The practical pest spectrum controlled under commercial grain storage conditions still requires further confirmation after global launch of 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.
Field studies were conducted from July 2002 to January 2003 for evaluating the effects of controlled aeration and a commercial biological insecticide, spinosad, in suppressing insect populations in stored wheat. Six cylindrical steel bins were filled with newly harvested (2002 crop year) hard red winter wheat on 9 and 10 July 2002. Each bin contained 30.7 metric tons (1,100 bu) of wheat. Wheat in two bins was left untreated (control), whereas wheat in two bins was treated with spinosad, and in another two bins was subjected to aeration by using aeration controllers. Spinosad was applied to wheat at the time of bin filling to obtain a rate of 1 mg ([AI])/kg. Aeration controllers were set to run the fans when ambient air temperature fell below 23.9, 18.3, and 7.2 degrees C for the first, second, and third cooling cycles, respectively. We added 400 adults each of the rusty grain beetle, Cryptolestes ferrugineus (Stephens); lesser grain borer, Rhyzopertha dominica (F.); and red flour beetle, Tribolium castaneum (Herbst), to the grain at monthly intervals between July and October 2002. Insect density in the bins was estimated monthly by taking 3-kg grain samples from 21 locations within each bin by using a pneumatic grain sampler. No live T. castaneum or C. ferrugineus and very low densities of R. dominica (<0.008 adults per kilogram) were found in wheat treated with spinosad during the 6-mo sampling period. Density of C. ferrugineus and T. castaneum in aerated bins did not exceed two adults per kilogram (the Federal Grain Inspection Service standard for infested wheat), whereas R. dominica increased to 12 adults per kilogram in November 2002, which subsequently decreased to three adults per kilogram in January 2003. In the untreated (control) bins, R. dominica density increased faster than that of C. ferrugineus or T. castaneum. Density of R. dominica peaked at 58 adults per kilogram in October 2002 and decreased subsequently, whereas T. castaneum density was 10 adults per kilogram in October 2002 but increased to 78 adults per kilogram in January 2003. Density of C. ferrugineus increased steadily during the 6-mo study period and was highest (six adults per kilogram) in January 2003. This is the first report comparing the field efficacy of spinosad and aeration in managing insects in farm bins. Our results suggest that spinosad is very effective in suppressing R. dominica, C. ferrugineus, and T. castaneum populations in stored wheat.
Since the earliest days of their awareness of resistance, entomologists have been concerned with understanding the factors responsible for its development and with divising measures for its control. It is remarkable that in reporting the first case of resistance — in the San José scale toward lime sulfur — Melander (1914) recognized the role of incomplete coverage and genetic recessiveness and speculated that should the scale become resistant also to oil sprays “we might have to introduce a weak strain to cross with the immune and thus return to the normal susceptible population.” Melander and other early pioneers in studies of resistance (Quayle 1922, Woglum 1925) may have been ahead of their time, however, for in the subsequent 30 years or so, resistance evolved slowly, affecting only 12 species of arthropods (review by Babers 1949). Interest in resistance intensified with the introduction of DDT and with the rapid development in cases of resistance to organochlorine, organophos-phate, carbamate and most recently to pyrethroid insecticides. The phenomenon now involves at least 428 species of arthropods and every class of commonly available compound (Georghiou and Mellon, this volume).
Spinosad, a commercial bacterial pesticide, was evaluated against adults of the lesser grain borer, Rhyzopertha dominica (F.), on 12.5 or 14.5% moisture wheat stored at 22, 28, and 34°C. Adults of R. dominica were exposed for 14 days to untreated wheat and wheat treated with spinosad at 0.1 and 1 mg (A1)/kg every month for four months. Mortality of adults exposed to untreated wheat ranged from 0 to 39%. All R. dominica adults exposed to spinosad-treated wheat were killed. The activity of spinosad during the four-month test period was not affected by the three temperatures and two moisture levels tested.
Laboratory experiments were carried out to establish whether there were synergistic or antagonistic interactions in combination treatments of certain grain protectants. Six protectants were applied alone, or in combination, against Rhyzopertha dominica (F.) in stored maize and wheat, and Sitophilus oryzae (L.) and Tribolium castaneum (Herbst) in stored wheat. There were four organophosphorus (OP) insecticides (fenitrothion, chlorpyrifos-methyl, pirimiphos-methyl and methacrifos), one juvenile hormone analogue (methoprene) and one synergised pyrethroid (deltamethrin+piperonyl butoxide); and combination treatments consisted of either methoprene or synergised deltamethrin plus an OP insecticide. Based on the levels of control of adult progeny and periods of protection, there were no interactions between protectants. The results show that there is no need to alter field application rates to compensate for antagonism or to take advantage of synergism. They also support the view that application rates for combination treatments can be estimated from experiments on individual protectants using target species or strains.
Corn was treated with 6 ppm chlorpyrifos-methyl and stored for 10 mo at each of four temperatures (15.0, 22.5, 30.0, and 37.5•C) and three moisture contents (11.4, 12.4, and 14.4%).Every 2 mo, samples were removed from storage and analyzed for chlorpyrifos- methyl residue and infested with maize weevils, Sitophilus zeamais Motschulsky. Initial residues on the corn were 4.95 ± 0.67 ppm. Of the residues that were lost, most were lost during the first 2 mo of storage. The loss rate increased as temperature and moisture content increased. No weevils survived on corn stored at 15.0 or 22.5OC,except for 7.2% of the weevils that survived at month 10 on corn stored at 22.5"C. Weevil survival increased as moisture content increased in corn stored at 30.0 and 37.5•C. The threshold for weevil survival was 1.22 ppm chlorpyrifos-methyl. Population growth, the percentage of insectdamaged kernels, and dockage weight were all correlated with insect survival.
Samples of field populations of Cryptolestes spp., Oryzaephilus surinamensis (L.), Rhyzopertha dominica (F.), Sitophilus oryzae (L.), and Tribolium castaneum (Herbst) were collected from central storages, grain merchants, and farms in Queensland, Australia. First-generation progeny of each sample were exposed to grain treated with commercial formulations of insecticides. These concentrations were chosen to detect new resistances to fenitrothion in T. castaneum, S. oryzae, and Cryptolestes spp., resistance to bioresmethrin + piperonyl butoxide (PB) in R. dominica, and increases in the frequency of resistance to fenitrothion and chlorpyrifos-methyl in O. surinamensis. No new resistance to fenitrothion was detected in T. castaneum, S. oryzae, or Cryptolestes spp. High-level resistance to bioresmethrin + PB (resistance factor ≍130) was detected at three central storages but not on farms or with grain merchants. High-level resistance to fenitrothion was present in almost all O. surinamensis samples from central storages and in more than half the farm samples collected. Resistance to chlorpyrifos-methyl that could result in control failures was detected in 60% of farm samples and in about 40% of samples collected from central storages.
The discovery and characterization of the soil actinomycete, Saccharopolyspora spinosa, and the insecticidal metabolite spinosad is presented as a case history of a successful project emerging from a natural products crop protection discovery programme. A who, what and how approach is utilized to communicate the events around the discovery and development of the project. The companies and departments involved are listed with insight into their structure and philosophy. A detailed description of spinosad and its properties is also provided. Finally an overview is given of the various tasks required and hurdles that were overcome to bring the project to a commercial success.© 2000 Society of Chemical Industry
Loss of fenitrothion from post-harvest application to wheat, oats, paddy rice and sorghum followed a second-order rate process, with rate of loss being proportional, at a fixed temperature, to the amount of fenitrothion and the activity of water, which was obtained from the equilibrium partial pressure of water vapour. The effect of temperature on loss was of the form of the Arrhenius equation. A chart relating half-life to temperature and relative humidity is presented in a form suitable for field use, and a mechanism is proposed for loss of fenitrothion.
Effectiveness of the bacterium-derived insecticide, spinosad, was determined against eight storage pests of Australia. Laboratory experiments were carried out on relevant resistant strains of four beetle and four psocid species, with the aim of determining the potential of spinosad as a new grain protectant. To explore the possibility that spinosad could have delayed effects, we exposed all insects for 14 d initially and then a further 14 and 28 d for psocids and beetles, respectively. Adult insects of each strain were exposed to untreated wheat (control) and wheat treated with spinosad at 0.1, 0.5 and 1 mg [a.i.]/kg of grain, and adult mortality and reduction of progeny were determined. Among beetles, spinosad was most effective against Rhyzopertha dominica (F.), with 100% adult mortality and progeny reduction after 14 d exposure at 1 mg [a.i.]/kg. Efficacy of spinosad was less with Sitophilus oryzae (L.), and least with Tribolium castaneum (Herbst) and Oryzaephilus surinamensis (L.). Against the psocids, spinosad was most effective against Liposcelis entomophila (Enderlein), with 100% adult mortality after 28 d exposure at 1 mg [a.i.]/kg and 92% progeny reduction after 14 d exposure and 100% subsequently. Spinosad was only moderately effective against Liposcelis bostrychophila Badonnel, L. decolor (Pearman) and L. paeta Pearman. Our findings suggest spinosad to be a potential protectant against R. dominica and L. entomophila in stored grain in Australia. This potential use would be in combination with another protectant capable of controlling other members of the pest complex.
Silo-scale field trials of chlorpyrifos-methyl (10 mg kg− 1) + methoprene (1 mg kg− 1) and chlorpyrifos-methyl (10 mg kg− 1) + phenothrin (1 mg kg− 1) + piperonyl butoxide (8.5 mg kg− 1) were carried out on maize in north Queensland, Australia. Although these treatments are known to be effective against insects in wheat stored under Australian conditions, they have not been assessed on maize. Samples of maize were taken from 1 m below the grain surface at various times during storage to check for infestations, and to use in bioassays and residue analyses. The bioassays used resistant strains of Sitophilus zeamais Motschulsky, S. oryzae (L.), Rhyzopertha dominica (F.), Tribolium castaneum (Herbst) and Oryzaephilus surinamensis (L.). The study confirmed that chlorpyrifos-methyl + methoprene and chlorpyrifos-methyl + synergized phenothrin were highly effective against the major grain beetles for at least 7 months. Both treatments gave good control of beetles in laboratory bioassays, and no infestations were detected in the silos despite the presence of beetles before treatment. The study also shows that methoprene would be an effective alternative to synthetic pyrethroids for control of R. dominica, and could be used in a rotation program as part of a resistance management strategy. Further study is required on the efficacy of protectants against the moth Ephestia cautella Walker, because infestations developed on the grain surface in each treatment.
The failure to control Rhyzopertha dominica in Brazil has been recorded in many storage units where the insecticide deltamethrin was used to protect grains. Samples from these and other pest populations were taken to investigate their tolerance. Ten strains from Brazil (BR1–10) and one laboratory strain from Imperial College at Silwood Park (UK1), were exposed to deltamethrin on filter paper. Another series of bioassays was carried out on five of the strains where adults were exposed in each of four age ranges. Eggs collected from untreated individuals in each group were reared through to adulthood and these progeny were assayed 10 days after emergence. In all tests the median lethal concentrations were determined and resistance ratios calculated. The results showed two strains, BR4 and UK1, were the most susceptible, and these may represent the normal tolerance level of this species to deltamethrin. Two strains, BR6 and BR7, showed high resistance factors of 132 and 874, respectively. The other seven strains exhibited intermediate resistance factors up to 93 times greater than the most susceptible strain. There were no statistical differences among the age groups in all the strains tested and also no significant differences between the progeny from each age group. These results mean that comparable data may be achieved with populations of differing age structure and that the susceptibility of the progeny was also independent of parental age.
The efficacy of diflubenzuron (1 mg kg−1)+methoprene (1 mg kg−1) against Sitophilus oryzae (L.) and Rhyzopertha dominica (F.) in sorghum was evaluated in a silo-scale trial in southeast Queensland, Australia. Sorghum is normally protected from a wide range of insects by mixtures of grain protectants. The chitin synthesis inhibitor diflubenzuron was evaluated as a potential new protectant for S. oryzae in combination with the juvenile hormone analogue methoprene, which is already registered for control of R. dominica. Sorghum (ca 200 t) was treated after harvest in 2000 and assessed for treatment efficacy and residue decline during 6.5 months storage. The reproductive capacity of S. oryzae and R. dominica was greatly reduced in bioassays of treated sorghum throughout the trial, and efficacy remained relatively stable during the trial. An initial exposure of S. oryzae adults to treated sorghum for 2 weeks reduced F1 progeny production of all strains by 80.8–98.8%, but a second exposure of 4 weeks reduced F1 progeny production by 98.5–100%. In addition, the reproductive capacity of any S. oryzae progeny produced was greatly reduced. Exposure of R. dominica adults to treated sorghum for 2 weeks reduced F1 progeny production of all strains by 99.6–100%, including a methoprene-resistant strain. The results indicate that S. oryzae or R. dominica adults invading sorghum treated with diflubenzuron (1 mg kg−1)+methoprene (1 mg kg−1) would be incapable of producing sustainable populations.
Insecticide residue degradation and pest survival were observed in wheat treated with a low dose of chlorpyrifos-methyl. Treated wheat was stored in small batches at three controlled temperatures and two levels of moisture content of grain, in equilibrium with r.h. in order to stabilise the water activity in the grain during a storage period of 126 d after insecticide application. Every 3 weeks, samples were taken from treated and untreated control grain in each storage condition. Chlorpyrifos-methyl residues declined regularly with time of storage and an exponential negative regression was fitted with high correlation coefficients in most situations of storage temperature and grain water activity (Aw). A multivariate model to show the respective influence of controlled variables involved in the model of residues breakdown (time, Aw, and temperature) was built up through a multiple regression. This model showed the respective importance of the water activity of grain kernels, temperature and formulation of chlorpyrifos-methyl and their combinations on the decline of residues. Simultaneously, the effectiveness of the residues was checked through bioassays with two target species: Sitophilus oryzae and Tribolium castaneum. Taking into account the intentionally low initial applied dose of chlorpyrifos-methyl, the period after application achieving complete kill of the two test insects was rather short and did not exceed 105 d for S. oryzae in the best conditions for control, i.e. low moisture content and temperature. For high Aw (0.8) and storage temperature 30°C, T. castaneum was effectively controlled (more than 95% kill) only on the day after the treatment, survival occurring at the next test date 21 d after the application. High moisture content and temperature and their interactions were the main variables influencing the decrease in the biological effectiveness with time. The concentration threshold for insect survival was slightly below 1 ppm chlorpyrifos-methyl and was influenced by storage and grain conditions. Implications of these findings on storage pest management practices and on the ability to predict the period of biological effectiveness of residues of chlorpyrifos-methyl are discussed.
The pesticides chlorpyriphos-methyl, pirimiphos-methyl and permethrin were applied to wheat and stored for 52 weeks at 25, 30, 35 and 40°C, and at 10 and 13% m.c. Rates of loss were calculated from the residue analyses of pesticides in treated wheat at monthly intervals during the storage period. Calculated half-lives and pseudo first-order rate constants of these pesticides are discussed with reference to temperature and moisture.
Spinosad is a commercial reduced-risk pesticide that is naturally derived. Spinosad's performance was evaluated on four classes of wheat (hard red winter, hard red spring, soft red winter, and durum wheats) against adults of the lesser grain borer, Rhyzopertha dominica (F.); rice weevil, Sitophilus oryzae (L.); sawtoothed grain beetle, Oryzaephilus surinamensis (L.); red flour beetle, Tribolium castaneum (Herbst); and larvae of the Indianmeal moth, Plodia interpunctella (Hübner). Beetle adults (25) or P. interpunctella eggs (50) were exposed to untreated wheat and wheat treated with spinosad at 0.1 and 1 mg (AI)/kg of grain. On all untreated wheat classes, adult beetle mortality ranged from 0 to 6%, and P. interpunctella larval mortality ranged from 10 to 19%. The effects of spinosad on R. dominica and P. interpunctella were consistent across all wheat classes. Spinosad killed all exposed R. dominica adults and significantly suppressed progeny production (84-100%) and kernel damage (66-100%) at both rates compared with untreated wheat. Spinosad was extremely effective against P. interpunctella on all wheat classes at 1 mg/kg, based on larval mortality (97.6-99.6%), suppression of egg-to-adult emergence (93-100%), and kernel damage (95-100%), relative to similar effects on untreated wheats. The effects of spinosad on S. oryzae varied among wheat classes and between spinosad rates. Spinosad was effective against S. oryzae, O. surinamensis and T. castaneun only on durum wheat at 1 mg/kg. Our results suggest spinosad to be a potential grain protectant for R. dominica and P. interpunctella management in stored wheat.
Degradation and insecticidal effectiveness of spinosad residues were evaluated in Kansas during November 2000 to November 2001 in farm bins holding wheat (34-metric ton capacity). About 50 kg of hard red winter wheat from each of three bins were brought to the laboratory and treated separately with 1-ml aqueous suspensions of spinosad to provide rates of 0.1, 0.5,1, 3, 6 mg (AI)/kg of wheat. Wheat treated with distilled water served as the control treatment. Untreated and spinosad-treated wheat samples (250 g each) were placed in three plastic pouches of two different mesh sizes, and buried 2.5 cm below the grain surface. Pouches with large mesh openings were used to monitor insect infestations and kernel damage in untreated and spinosad-treated samples. Pouches with small mesh were used for extracting spinosad residues and for conducting laboratory bioassays with adults of the lesser grain borer, Rhyzopertha dominica (F.) and red flour beetle, Tribolium castaneum (Herbst) at 28 degrees C and 65% RH. Wheat temperature and relative humidity near the pouches during the 1 yr of storage ranged from -10 to 32 degrees C and 50 to 70%, respectively. Moisture of wheat samples varied from 12.4 to 13%. Observed spinosad residues on wheat samples were 25% less than the calculated rates of 0.1 to 6 mg/kg. However, these residues were stable during the 1 yr of storage, and killed all R. dominica adults exposed for 14 d in the laboratory. Mortality of T. castaneum adults increased with an increase in spinosad rate. The linear regression slope of LD50s (0.3-2.7 mg/kg) against storage time was not significantly different from zero, indicating no loss in spinosad toxicity to T. castaneum adults. Insect species, insect numbers, and kernel damage over time in wheat samples inside pouches with large mesh openings were highly inconsistent, and failed to accurately characterize spinosad performance. Laboratory bioassays with R. dominica and T castaneum adults using grain from pouches with small mesh openings accurately gauged spinosad persistence and insecticidal activity under the field conditions.
The efficacy of bifenthrin (0.5 mg/kg) + piperonyl butoxide (7 mg/kg) + chlorpyrifosmethyl (10 mg/kg) against beetle and psocid pests of sorghum was evaluated in silo-scale trials in southeast Queensland, Australia. The pyrethroid bifenthrin was evaluated as a potential new protectant in combination with the organophosphate chlorpyrifos-methyl, which is already registered for control of several insect pests of stored cereals. Sorghum (approximately 200 metric tons) was treated after both the 1999 and 2000 harvests and sampled at intervals to assess treatment efficacy and residue decline during up to 7 mo of storage. Generally, test strains of the beetles Rhyzopertha dominica (F.), Tribolium castaneum (Herbst), Oryzaephilus surinamensis (L), and Cryptolestes ferrugineus (Stephens) were prevented from producing live progeny for up to 7 mo. The treatment failed against one strain of R. dominica known to be resistant to bioresmethrin and organophosphates. Two malathion-resistant strains of O. surinamensis were marginally controlled with 94-100% fewer adult progeny produced. For psocids, no strains of Liposcelis bostrychophila Badonnel, Liposcelis decolor (Pearman), or Liposcelis paeta Pearman produced live progeny, although the control of a field strain of Liposcelis entomophila (Enderlein) was generally poor. Results show that this treatment should protect sorghum for at least 7 mo against most prevalent strains of grain insect in eastern Australia, although control may be limited in areas in which L. entomophila or pyrethroid-resistant R. dominica are present.
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Reprinted from International Pest Control, Volume 47, Issue 3 (May/June 2005)
This article appeared in the May/June 2005 issue of
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