A. CARPENTER, C. DOWNES, L. HANSEN, M. SHELTON and R. LILL
ABSTRACT
The use of calorimetry as a tool to understand the effects of controlled atmospheres (CA) on insects is briefly reviewed. A variety of data are presented to illustrate the various types of information that calorimetry can make available to researchers. The use of a calorimeter connected to a mass spectrometer to determine the occurrence of anaerobic respiration is described and reported. We conclude that calorimetry is a useful tool to simplify the experimental options when developing new insecticidal CA treatments. It can also be used for development of other treatments such as fumigants.
T.I. OFUYA AND Ch. REICHMUTH
ABSTRACT
(Full paper not available)
Controlled atmospheres (CAs) created in a storage environment, involving high CO2 levels (hypercarbia) or low O2 levels (anoxia) are detrimental to storage bruchid pests. The possibility of enhancing CA action against Acanthoscelides obtectus (Say), an important storage bruchid pest of grain legumes by increasing or decreasing the relative humidity in storage was investigated. Mortality of eggs and adults of the bruchid in 70% CO2 in air and 1.0% O2 in N2 was higher at 10± 3% and 34± 2% r.h. than at 70± 2% and 90± 3% r.h. Relative humidity did not affect the mortality of larvae and pupae of the bruchid in the two controlled atmospheres. At the lower relative humidities (as opposed to the higher r.h.), development period was longer for adults emerging from eggs of the bruchid exposed for 12 h to these atmospheres and freshly emerged adult bruchids exposed for 12 h to these atmospheres were the least fecund.
C.S. ADLER
ABSTRACT
Modified and controlled atmospheres are an alternative to synthetic, residue building agents in stored product protection. They are safer in use than most other fumigants and could gain importance with the phase out of methyl bromide and the institution of stiffer regulations for the emission of toxic agents from treated structures. Modified atmospheres (MAs) require highly gas-tight storage structures in order to be economically feasible. In temperate climates MAs have the additional disadvantage that at temperatures around 20&186;C or less, treatment times are considerably longer than when a fumigant such as phosphine is used. On the other hand, the gas-tightness of a structure may prevent the re-infestation after a treatment, and in the absence of oxygen, product quality remains better than during storage in air. A difficulty of pest control in temperate climates is that with decreasing day length and temperature, arthropods may develop over-wintering stages that could be more tolerant to treatment than other individuals. Diapausing larvae of the Indianmeal moth Plodia interpunctella were tested for their tolerance to various mixtures of N2, O2 and CO2. Whereas normal larvae from a culture at 25&186;C could be controlled at 10&186;C within 3 weeks with 60 vol.-% or 90 vol.-% of CO2 in air, diapausing larvae from a culture, gradually adapted from 25&186;C to 10&186;C, required 6 or 4 weeks exposure to the respective MAs for 100% control. Exposure for 6 weeks was also sufficient to control all stages of the granary weevil Sitophilus granarius, one of the species most tolerant to MAs. A mixture of 98% N2 and 2% O2 controlled normal larvae within 4 weeks and diapausing larvae within 5 weeks of exposure, provided they were not older than 6 months. It became clear that the tolerance to this hypoxic atmosphere increased with the duration of diapause. Diapausing larvae kept for more than one year at 10&186;C were able to survive up to 7 weeks of exposure and developed into adults. After 9 weeks of treatment, 12 out of 30 larvae were found alive, of which one larva was still able to pupate but subsequently died. Thus, diapausing and quiescent stages of stored-product pests may be difficult to control particularly with a CO2-free MA.
M. EMEKCI, S. NAVARRO, J.E. DONAHAYE, MIRIAM RINDNER
AND A. AZRIELI
ABSTRACT
Hermetic storage for the preservation of durables has been proven as an effective storage method. This method aims at taking advantage of interference with respiratory metabolism of the insects and minimizes their damage to the commodity. Tribolium castaneum, at its four developmental stages, was exposed to atmospheres containing 1 to 21% O2 that may be experienced under airtight conditions. All tests were carried out at 30&186;C and 70% r.h. Results showed that an initial acclimatization period of at least 5 h was required before each test to enable the insects to stabilize their response to the different CO2 concentrations. At normal oxygen level, egg respiration was lower than that of other stages and young larvae had the highest respiration rate. For pre-adult stages at reduced oxygen levels respiration rates were proportional to the oxygen levels. However, adult respiration, was higher at 3 and 5% O2 than at normal atmospheric air.
A.G. FERIZLI, S. NAVARRO, J.E. DONAHAYE, MIRIAM RINDNER
AND AVI AZRIELI
ABSTRACT
An airtight flexible plastic granary of 600-kg nominal capacity was tested for on-farm storage of grain. The granary was designed to provide food security for rural communities. It has the advantage of sealed storage that obviates the need of employing residual insecticides and fumigants.
To test the efficacy of the granary, an artificial infestation composed of adults of the rice weevil Sitophilus oryzae (L.), of the lesser grain borer Rhyzopertha dominica (F.) and of the flour beetle and Tribolium castaneum (Herbst) (6 insects/kg) were added from laboratory cultures to maize at average moisture content of 12.6%. Insect survival, gas composition, and temperature of the maize were recorded. Maize temperatures were within the range of 34&186;C to 23&186;C. Oxygen concentrations dropped to 0.2% within 13 days and carbon dioxide rose to 12%. For the following 50 days, oxygen and carbon dioxide concentrations remained stable. A moist pocket of maize at the top of the granary was found to be at moisture content of 14.6% that contributed to maintain this atmosphere. In spite of favorable temperatures for development of insects, at the end of two months storage, the initial insect populations of S. oryzae, R. dominica and T. castaneum were successfully controlled without the use of pesticides.
P.C. ANNIS
ABSTRACT
Phosphine has been in commercial use as a grain fumigant since the mid 1950s. It has developed and retained an important role in the control of storage pests since that time. More recently its use has expanded due to the phase-out of methyl bromide and marketing complications caused by grain protectant chemicals. This has challenged conventional phosphine use (aluminium/magnesium phosphide preparations) as the preparations were neither developed for nor suited to either the rapid fumigation of methyl bromide or the long-term unattended pest control of the grain protectants. Attempts to use phosphine under both these conditions are away from the dosage 'window' that was used most successfully for the earlier life of this fumigant. Over 70 individual papers have been published on dosage response of most stored-product insects to phosphine. Data from these papers have been collected into a database containing close to 3,000 records from which it is possible to define a boundary between survival and complete kill or high levels of mortality (>99%). This in turn allows a definition of the combinations of concentration and exposure time, which achieve effective fumigation under a range of conditions. The following combinations are the minimum required to achieve a very high level of kill in almost all stored-product beetles (excluding Trogoderma spp.), psocids and moths, excluding known resistant strains: 10,000 ppm for 1.5 days, 1,200 ppm for 2 days, 1,000 ppm for 8 days, 200 ppm for 10 days, 35 ppm for 20 days, 10 ppm for 30 days.
S. PRATT
ABSTRACT
Cell culture promises to facilitate the study of the toxic effects of gases such as phosphine (PH3), but to date, application of the gas to the cells has been problematic. This report describes a simple and flexible method for treating insect cell cultures with quantitative doses of the fumigant gas PH3. After inoculation with Sf9 cells (Spodoptera frugiperda (J.E. Smith) Lepidoptera; Noctuidae), cell culture flasks with loosened caps were placed inside glass desiccating chambers, which were sealed and injected with concentrated PH3. The time taken for the gas to enter the culture flasks, and the amount of PH3 that dissolved in the medium were determined. Cell growth and mortality after PH3 exposure were monitored for several days by repeatedly carrying out Trypan Blue dye exclusion assays. Phosphine entered cell flasks with an exponential time course. Internal concentrations rose to higher than 90% of the concentration in the exposure chamber in less than 2 h. Phosphine was found to rapidly (equilibrium reached in 10-20 min.) partition into water or cell culture medium under conditions similar to those used during cell exposure, with a partition coefficient (Cw / Ca) of 0.15, which is in approximate agreement with the literature value. After exposure of Sf9 cells to PH3 for 18 h, concentrations of 1,400, 5,200 and 10,400 ppm (1.9, 7.2, 14 mg L-1) produced mortalities of 20%, 50% and 75% respectively, when measured 8 h after exposure ceased. Establishment of total cell mortality of low doses was made difficult by resumption of growth by surviving cells. Control mortality remained below 5%. The high doses, with respect to whole insects, required to cause high mortality are noted. Comparisons are drawn with earlier cell culture work that used aqueous PH3, and implications for the use of the method to expose cells to PH3 and other gases before conducting other assays and reactive oxygen species studies are discussed.
C. WATERFORD
ABSTRACT
The total amount of phosphine taken up by susceptible insects for equi-toxic exposure, is generally much higher in susceptible than resistant insects. On a strict uptake basis this would appear to make susceptible insects more tolerant of phosphine. However Ct product data show higher Ct is required to kill resistant insects. One hypothesis for the uptake being so low in resistant strains is active exclusion. This study looked at the distribution of uptake, after fumigation, to gain some insight into the toxicology. Phosphine-resistant and -susceptible Tribolium castaneum (Herbst) were exposed to 0.1 mg L-1 phosphine labeled with isotope 32P at their respective LD50 and LD99 response levels. Uptake and distribution of 32P, after separation of treated samples into sugars, amino acids, organic acids, protein and an insoluble fraction, were assessed using a scintillation counter. Uptake or final distribution in the susceptible strain at the LD50 and LD99 was greater in every fraction than the equivalent resistant fraction except for the LD99 level of the insoluble fraction. This was so despite the increased exposure for the resistant over the susceptible strain at the LD99, 36.5 h vs. 4.25 h. This result is consistent with the mechanism of active exclusion. It also suggests that the lethal part of the uptake may be associated with an insoluble residue of phosphorus.
VICTORIA HARITOS
ABSTRACT
Carbonyl sulfide (COS) is a new fumigant under development as a methyl bromide replacement for fumigation of durable commodities. COS has been shown to be relatively fast acting and toxic to a broad range of stored-product pests but little is known of the mechanism of toxicity of COS to insects. In rats, COS is metabolised to hydrogen sulfide by the enzyme carbonic anhydrase, a widely distributed family of enzymes that usually catalyse the reversible hydration of carbon dioxide. The present study investigated whether hydrogen sulfide was the toxic agent of COS in insects. Firstly, adult stored-product insects Sitophilus oryzae (L.), Tribolium castaneum (Herbst) and Rhyzopertha dominica (F.) were fumigated with hydrogen sulfide for 6 h at a range of concentrations from 1-50 mg L-1. The percentage mortality of insects was ³84% at concentrations of 5 mg L-1 and above suggesting hydrogen sulfide is potently toxic to insects. To determine the role of metabolism in COS toxicity, 17-21 day old larvae of T. castaneum were raised on culture medium containing carbonic anhydrase inhibitors, acetazolamide or methazolamide, at concentrations up to 20 mg g-1 media. Larvae raised on inhibitors and untreated larvae were then fumigated with 60 mg L-1 COS for 5 h, a concentration - time product that had been shown to produce approximately 90% mortality in untreated larvae. The mortality of larvae raised on acetazolamide-containing medium (20 mg g-1) was much lower than untreated larvae (40% versus 95%) after fumigation. Similarly, mortality was reduced in insects administered methazolamide (20 mg g-1) resulting in 53% mortality. Administration of carbonic anhydrase inhibitors to insects protected them from the acute toxicity of COS. This work demonstrates that the acute toxicity of COS to insects is dependent on carbonic anhydrases metabolism to hydrogen sulfide, the toxic agent of COS.
KATHERINE A. DAMCEVSKI AND P.C. ANNIS
ABSTRACT
Ethyl formate is a fumigant that is currently used in Australia on dried fruit. Recently, there has been a re-evaluation of the usefulness of this material in disinfesting stored commodities. We have discovered that ethyl formate has a very rapid action and this property could make it useful in rapid disinfestation. We studied the response of Sitophilus oryzae (L.) adults to ethyl formate in a sealed system in preliminary experiments. S. oryzae was chosen because it is generally one of the more difficult stored-product beetles to kill by fumigation. The insects were exposed to three different dosages of ethyl formate for a range of exposure times with a 50% filling ratio of wheat. Ethyl formate required a very short time to kill all adults for the range of concentrations and times studied. Exposures of 12 min and 2 h achieved 100% mortality for concentrations of 340 and 210 g m-3, respectively. For 130 g m-3, an exposure of 3 h. achieved 94% mortality. These results are consistent with the requirements for a potential replacement for methyl bromide as a rapid disinfestant. Ethyl formate has the advantages of rapid loss from the gaseous phase and breakdown by the grain. The high flammability of ethyl formate, which may make its application a potential problem, can be significantly reduced by its application in water. The rapid kill makes ethyl formate suitable for treatments in conditions where long-term gas retention is not possible, for example, the disinfestation of machinery, work-spaces and surfaces.
MADELEINE RAMBEAU, DELPHINE BENITEZ, S. DUPUIS AND P. DUCOM
ABSTRACT
Flour mill fumigations are currently carried out with methyl bromide (MB). By 2005, this gas will be phased out in developed countries because it has been listed under the Montreal Protocol as a substance that depletes the ozone layer. Hydrogen cyanide (HCN) was used as the fumigant of choice for mills in the first part of the last century, and was then replaced by MB. Consequently, it should now be re-evaluated as a potential alternative to MB. However, knowledge about HCN's efficacy as a fumigant is outdated and does not conform to the notion of concentration time (Ct) product. Therefore, the objective of this study was to determine the biological efficacy of HCN in terms of Ct product for the different stages of three of the most prevalent species infesting mills and food manufacturing premises, the confused flour beetle Tribolium confusum, the red flour beetle Tribolium castaneum, and the Indianmeal moth, Plodia interpunctella. In addition, the granary weevil Sitophilus granarius was studied in the adult stage only, since this is the only stage present in mills. Two series of trials were carried out: one consisted of, dose-trials to define the relationship between Ct product and insect mortality without presence of a rearing medium; the other consisted of trials in which inserts were placed at different depths in flour to measure HCN efficacy in penetrating residual heaps of flour. Our findings on the different stages of each species (eggs, young larvae, old larvae, pupae and adults) show that the Ct product required to obtain a LD90 ranged from 1 to 4 g.h m-3, according to developmental stage, this being very low when compared to MB. Nevertheless, in contrast to MB, large differences were found between the species as shown in the high tolerance of granary weevils to HCN. The poor penetration of HCN into flour is due to significant sorption. Consequently, to be effective against T. confusum adults buried in flour, a Ct product as high as 60 and 100 g.h m-3 is required to kill this species at depths of 10 and 15 cm, though it does not kill S. granarius. In practice, the Ct product needed to kill all stages of these major mill and food factory pests should be around 10 g h m-3, though to obtain HCN penetration and kill insects at a depth of about 10 cm in flour heaps, the prevailing Ct products should be around 60 g.h m-3. This implies that the corresponding initial dose should be 5 g m-3, taking into account the presence of minor leaks.
GLORY SABIO, S. NAVARRO, J.E. DONAHAYE, MIRIAM RINDNER, A. AZRIELI AND R. DIAS
ABSTRACT
The potential application of low levels of methyl bromide (MB) in combination with CO2 gas mixtures as a rapid disinfestation technique was evaluated under laboratory conditions at 30&186;C and 70% relative humidity (r.h.), using the tropical warehouse moth, Ephestia cautella as test insect. CO2 concentrations of 0, 10 and 20% in air were examined when mixed with different MB concentrations. Eggs, larvae, pupae and adults were exposed to the various gas mixtures for periods ranging from 4 to 32 hours. The influence of CO2 on reducing the MB concentration required for control was assessed by calculating products of concentration x time (CtP) as expressed in mg.h L-1. CtP99 values of MB in normal air for E. cautella eggs, larvae, pupae and adults were 25.4, 30.1, 50.2 and 16.6 mg.h L-1, respectively. These values were markedly reduced as the CO2 concentration was increased to 10 and to 20%. In the presence of 20% CO2 the effective MB dose was reduced to 18.7, 20.3, 29.7 and 4.3 mg.h L-1 in eggs, larvae, pupae and adults, respectively. The resistance of the developmental stages of E. cautella to MB was (in decreasing order): pupae, larvae, eggs and adults. In the presence of 20% CO2 the CtP99 of MB was decreased by 1.4 times in eggs, the least sensitive stage and by 3.8 times in adults, the most sensitive stage responding to the gas mixture. This work was carried out as part of a Ph.D. study of the first author, at the Hebrew University of Jerusalem, Israel.
SHUIT H. HO
ABSTRACT
Essential oils derived from four spices - star anise, nutmeg, cinnamon and garlic - were found to have fumigant activity to Tribolium castaneum and Sitophilus zeamais. The fumigant activity of anethole, derived from star anise, was similar for both adults of T. castaneum and S. zeamais, when compared at the LC50 level. However, at the LC95 level, S. zeamais was ~200x more tolerant than T. castaneum. S. zeamais adults were 1.7x more susceptible than T castaneum adults to the fumigant action of nutmeg oil, (LC50 of 4.5 and 7.7 mg/cm2 respectively). T. castaneum adults were twice as susceptible as S. zeamais adults to the fumigant activity of cinnamaldehyde, from cinnamon oil (LC50 of 0.28 and 0.54 mg/cm2 respectively). T. castaneum larvae became progressively more tolerant with age. Three constituents of garlic oil were tested for fumigant activity to these two species of insects. Allyl disulfide, methyl allyl disulfide and diallyl trisulfide all had more potent fumigant action against T. castaneum adults than against their larvae or against S. zeamais adults. The larvae of T. castaneum became also more tolerant with age to the three compounds from garlic oil. Among these compounds, diallyl trisulfide was the most potent for both species of beetles (LC50 for T. castaneum adults = 0.83 mg/L air; LC50 for S. zeamais adults = 6.32 mg/L air). It was also the most potent of all the essential oils studied. These essential oils and their constituents, particularly diallyl trisulfide, have the potential to be developed as fumigants for stored-product protection.
A.C. SHUKLA, S.K. SHAHI, A. DIKSHIT AND V.C. SAKSENA
ABSTRACT
Of some essential oils screened against dominant storage fungal pests viz., Aspergillus flavus, Penicillium italicum, Altemaria alternata as well as stored-product insects viz., Rhyzopertha dominica, Trogoderma granarium, Sitophilus oryzae, Corcyra cephalonica and Ephestia cautella, the oil of Cymbopogon flexuosus (Steud.) Wats. [Poaceae], was the strongest toxicant. The oil killed the tested fungi within 4-6 days but required only 6-8 h to kill insect pests at 10 µL mL-1. In addition to its broad pesticidal spectrum, the oil was found to inhibit heavy doses of inocula, was thermo-stable and persisted up to 36 months. Encouraged by these results, further tests were conducted along with in vivo investigations. By observing the maximum phyto-tolerant concentration, formulations were developed. Further investigations have been carried out on various toxicological, organoleptic and pharmacological parameters, to determine the minimum effective dose of the formulation. A preliminary comparison of some common characteristic features of the 'formulated herbal fumigant' with some synthetic fumigants showed that the herbal formulation is superior. As such, after a successful multi-site trial, it was recommended that the fumigant formulation of Cymbopogon flexuosus oil could be commercialized for the management of stored-product pests.
F.A. EL-LAKWAH, R.A. MOHAMED, AND A.E. ABD EL-AZIZ
ABSTRACT
A petroleum ether extract of cumin seeds (Cuminum cyminum L.) was investigated in the laboratory, alone and under controlled atmospheres (CA) of 25% C02, 50% CO2, and 99.8% N2 for its toxic effect on the rice weevil, Sitophilus oryzae (L.), lesser grain borer, Rhyzopertha dominica (F.) and red flour beetle, Tribolium castaneum (Herbst). Results indicated relatively high adult mortality levels for S. oryzae and R. dominica at the highest concentration (10%) of cumin seed extract 2 weeks after treatment. In contrast, very low mortality levels were attained with T castaneum. Inhibition of F1 progeny was much higher than mortality especially at higher concentrations. Cumin seeds extract under CA was more effective than the extract alone. The combined action of 2.5% and 5% concentrations + CO2 showed an additive or synergistic effect on the three insect species at various exposure periods. Co-toxicity resulting from CA of 99.8% N2 + 2.5% or 5% extract concentrations produced synergistic or additive effects on S. oryzae and T castaneum for all exposure periods. However, in the case of R. dominica, an antagonistic effect was observed for all exposure periods with 99.8% N2 + 2.5% extract. With 99.8% N2 + 5% extract, the antagonistic effect for a short exposure period of 2 days changed to an additive effect at longer periods (3 and 5 days).
C. VINGHES AND P. DUCOM
ABSTRACT
At harvest, chestnuts are often infested at a high rate (10-20%) with young larvae of the chestnut fruit tortrix, Cydia splendana (HŸbner) and/or the chestnut weevil, Curculio elephas (Gyllenhal). These larvae are barely or not at all visible and do not cause any loss in quality if they are killed early on. The systematic fumigation of chestnuts with methyl bromide (MB) (50 g m-3 for 12 h, at 15&186;C) before their commercialization has become common practice. Because the use of MB must be discontinued by the end of 2004, alternatives have to be found. A good candidate could be sulfuryl fluoride, a gas that has been used for 40 years in the USA against the dried wood termite. It has not been able to compete with MB in post-harvest use essentially because the egg stage is much more tolerant than the other stages. However, in the case of chestnuts, this stage is not present and therefore the problem does not arise. Fumigations were carried out in 43 L Altuglas chambers with a single dose of 40 g m-3, variable gas exposure periods of 2, 4, 6, 8 and 10 hours at 15&186;C which corresponds to the normal temperature of chestnuts at the time of harvest. The loading rate was 64% (8 kg of fruit) or 80% (10 kg). Results showed that this dose at 15&186;C or higher for an exposure period of 8 h is completely effective. Furthermore, sulfuryl fluoride is much more efficient against the chestnut weevil than against the chestnut fruit tortrix which is contrary to the effect of MB. Finally, sorption was much lower with sulfuryl fluoride than with MB, which would explain its higher efficacy. No significant odor or particular taste was noted in the taste test, and a panel of 4 people rated the nuts treated with sulfuryl fluoride to be superior even to the control.
J.L. ZETTLER, R. GILL, J.W. ARMSTRONG AND P.V. VAIL
ABSTRACT
Exotic pests such as fruit flies pose the greatest threat to California's agricultural production. It is estimated that the economic impact of the Mediterranean fruit fly (medfly), Ceratitis capitata, would be as high as US$ 1.4 billion annually if it were to become established in the state. Additionally, direct costs of embargoed exports to Japan and other trading partners could total nearly US$ 500 million. The impending loss of methyl bromide (MB) poses a significant threat to quarantine security presently insured by MB treatments. Thus, alternative chemical fumigants are needed as commodity quarantine treatments for successful management of this pest and other exotics. One alternative fumigant is sulfuryl fluoride (SF). It is presently labeled for use as a structural fumigant against termites and wood boring beetles but does not yet have a food tolerance. Laboratory tests were conducted against life stages of the medfly, melon fly (MFF), Bactrocera curcubitae, and Oriental fruit fly (OFF), Bactrocera dorsalis, to determine if SF is sufficiently toxic to be used as a fumigant for control of these exotic pests. Results of 4-h atmospheric fumigations at 23.6&186;C showed that 1st and 3rd instars of each species were relatively susceptible to SF with LC95 values ranging from 4.7 mg/L to 70.6 mg/L. One-hour old eggs of each species were relatively tolerant compared with 1st and 3rd instars with LC95 values ranging from 116.3 mg/L (medfly) to 224.2 mg/L(OFF). Susceptibility of eggs was directly related to egg age, the 1-day-old eggs being the most susceptible and the 24- and 48-h-old eggs more tolerant. Fumigations at fixed doses with variable exposure times were conducted against OFF eggs, which were the most tolerant among the stages tested. Exposures ranging from 2 to 12 h indicated that the relationship between concentration and time is nonlinear throughout the tested range, being weighted toward the time variable - favoring long exposure periods for efficient control. Thus, the large doses required for control of fruit fly eggs would preclude exposure times shorter than 48 h, at which time the eggs begin to hatch. These results indicate that SF has potential for controlling active life stages of fruit fly pests in short exposure periods but has little or no potential in quarantine treatments due to the relative tolerance of the egg stage.
J. L. ZETTLER AND S. NAVARRO
ABSTRACT
We investigated the possibility that California prunes stored in modified atmospheres (MAs) will tolerate higher water activity (aw) levels than those required at normal atmospheres and that the naturally occurring microfloral infection level on the prunes may generate the MAs that inhibit mold activity in airtight conditions. Dry prunes were moisturized to a range from 16 to 38% moisture content (m.c.) to acquire samples with 0.575 to 0.858 aw. In unsealed conditions at 35&186;C, there was a level of naturally occurring microorganisms (aerobic plate count, yeast and mold count) that generally increased above 0.70 aw. However, incubating these samples in a sealed container for 35 days at 35&186;C indicated that levels of naturally occurring microorganisms remained unchanged throughout the range of water activities. Microfloral respiration as a function of temperature was determined by incubating similarly moisturized prune samples at 25, 30 and 35&186;C and then measuring the declining O2 concentrations through time. Results showed that the higher both the water activity and temperature, the more intense the O2 consumption by the product. A nearly linear relationship was observed between O2 depletion and time. Anaerobic conditions were reached in less than 2 days at 25&186;C and 0.858 aw, the highest water activity tested. At higher temperatures, anaerobic conditions were achieved at water activities of 0.824 and above. These results indicate that under aerobic conditions microorganisms can flourish on and cause deterioration of prunes if the water activity of the fruit is above 0.7 (m.c. of 24.6%). However, under sealed conditions, prunes can tolerate a higher water activity without microorganism growth or deterioration of the fruit.
MARIA F.P.M. DE CASTRO, M.F.F. LEITAO, J.O. DO VALE, NEURA BRAGNOLO, ELIANE SALVADEGO ANICHIAREO AND K.A. MILLS
ABSTRACT
The objective of this research was to investigate the effect of phosphine on the growth of A. flavus and aflatoxin production in maize stored at different moisture contents. In this experiment samples were previously inoculated with an A. flavus toxigenic strain. The experimental design used surface of response methodology to assess the various effects of different moisture contents. (water activities from 0.85 to 0.98), phosphine concentrations (from 0 to 4 g m-3) and exposure periods (from 1 to 15 days) to the fumigant. Analyses of m.c., water activity, mycological composition, ergosterol content and aflatoxins were carried out on the samples subjected to the different treatments. Previous results showed that as the exposure time increased, more complete control of A. flavus was achieved. Mainly at lower water activities an increase in the phosphine exposure period is more important than increasing the concentration to achieve good control of A. flavus. As moisture content increases the increase in phosphine concentrations becomes more important. Fusarium verticillioides seems to be particularly tolerant of phosphine mainly under the high m.c. conditions which also favours its development. Since this species is a potential fumonisins producer, more information is needed to aid in the formulation of practical control recommendations. The Penicillium species tolerant to phosphine were those mainly found in freshly harvested maize. It is encouraging that aflatoxin production was severely affected by phosphine even at low concentrations.
NEETA SHARMA
ABSTRACT
Thirty fungal species were found to be associated with the stored kernels of cashewnut (Anacardium occidentale L.), chironji/cuddapah almond (Buchanania lanzan Spreng.), walnut (Juglans regia L.), dried fruits of cardamom (Elettarra cardomomum Matan), and raisin (Vitis vinifera L.). Because of their wide distribution, high incidence as well as enormous potential to produce mycotoxins, Aspergillus flavus Link: Fr. and A. ochraceous Wilhelm. were selected as test fungi for antifungal screening of leaf extracts of 126 species of higher plants belonging to 45 families of angiosperms. Ocimum gratissimum exhibited the strongest bioactivity. Minimum inhibitory concentrations (MIC) of the volatile antifungal oil fraction against A. flavus and A. ochraceous were found to be 400 ppm and 700 ppm, respectively; higher concentrations (>900 ppm) were fungicidal and not fungistatic. The toxicity of the oil did not change even with high inoculum density during storage periods of 270 days, at its exposure to 100&186;C, and on autoclaving.