H.J. Banks

Distribution and establishment of Trogoderma granarium Everts (Coleoptera: Dermestidae); climatic and other influences

Abstract The recorded world distribution of Trogoderma granarium is reviewed. Using these records an attempt is made to assess its pest status in different countries. Three sets of climatic requirements suggested by previous workers for predicting the distribution of the species are evaluated. These climatic criteria were (1) a mean monthly temperature over 20°C for at least 4 consecutive months, (2) a mean monthly temperature over 20°C and a mean r.h. of over 50% for at least 4 consecutive months, and (3) a mean monthly temperature of over 27°C and a mean r.h. of over 75% for over one month. Areas of the world corresponding to criterion (2) were found to correlate largely with the occurrence of T. granarium as a major pest in unheated environments as predicted by Howe and Lindgren (1957). However, in areas with a prolonged high average temperature a slightly higher mean r.h. limit may prove more appropriate for predicting the pest status of this species. T. granarium is absent from Australia though some parts are apparently climatically suitable. This is discussed in relation to the factors influencing the establishment of exotic stored product pests and the relevance of average meteorological data to stored product pest distributions. It is concluded that climatic factors at the ports may have prevented the establishment and subsequent transport of sufficient numbers to more climatically favourable areas inland. Prevailing temperatures at the ports appear adequate for T. granarium but the high relative humidity there seems to be the main controlling factor. This factor may act indirectly on T. granarium by favouring other species which compete with it.

The effects of high concentrations of carbon dioxide in air on Trogoderma granarium Everts (Coleoptera: Dermestidae)

Abstract Several developmental stages of a laboratory strain of Trogoderma granarium Everts were subjected to an atmosphere of 60% carbon dioxide (CO 2 ) in air at 20 or 30°C and 60% r.h. for varying lengths of time. The eggs, pupae and adults all died within 6 days, but some larvae survived for 16 days or more at both temperatures. Larvae were then exposed at 45, 60 and 75% r.h. to 45, 60 or 75% CO 2 in air at 20 or 30°C and additionally to 30% CO 2 in air at 30°C. Mortality increased with CO 2 concentration and temperature. However, only when a CO 2 concentration of 75% at 30°C was applied did all larvae die and, even then, a 15-day exposure was required. Some survival occurred after 18 days in all other conditions. Exposure times of 10 days or less, at temperatures of 20°C or above, have been recommended for use with high CO 2 atmospheres for the control of stored products pests but this investigation shows that these may be inadequate if T. granarium is present.

Wind forces and their influence on gas loss from grain storage structures

Abstract The wind-generated pressure coefficients likely to be encountered in a free standing cylindrical grain storage with a conical roof are presented as measured from model experiments in a wind tunnel. These take into account the turbulent flow and vertical wind velocity profile likely to be found around such structures. The influence of pulsating wind flows is discussed theoretically and the practical consequences of wind-generated gas losses are detailed for fumigation or controlled atmosphere storage of grain.

Time-mortality relationships for different species and developmental stages of clothes moths (Lepidoptera: Tineidae) exposed to cold

Abstract Time-mortality relationships of different developmental stages of clothes moths, Tinea and Tineola species, were studied for exposure to −20°C. A model presented to describe the survival curves fitted the data well and was useful for estimating exposure times needed to reach a required percentage mortality for disinfestation treatments. Tineola bisselliella was the most tolerant of the four tineid species tested and eggs were the most tolerant developmental stage. Complete kill of T. bisselliella eggs was achieved within 30 h exposure to −20°C.

Simulation of temperature fluctuations near the surface of grain bulks

Abstract A simulation model is presented that predicts the mean and variation of temperatures in the region within 40 cm of the upper surface of grain bulks from a knowledge of the temperatures and their variation at > 40 cm and at the surface. It was found necessary to include consideration of convective as well as conductive heat transfer in order to predict temperatures to within 1.5°C of observed values for all six sets of test data. Moisture transfer effects were not considered. In four of the six sets consideration of conduction alone gave an adequate description. The model is of the form that can be incorporated as a subroutine into calculations of temperatures occurring throughout grain storages.

Studies on the toxicity of phosphine to tolerant stages of Trogoderma granarium Everts (Coleoptera: Dermestidae)

Abstract Tests were conducted at 20 and 30°C at 60% r.h. to find the dosages of phosphine needed for control of diapausing larvae and eggs of Trogoderma granarium. At 20°C, 60% r.h., some larvae from each of four recently acquired field strains of T. granarium survived a 5-day exposure period at a concentration-time (Ct) product of 164 g hr/m3. Under these conditions laboratory stock larvae were killed by a 4-day exposure period of about 120 g hr/m3, and eggs by a 3-day exposure of about 50 g hr/m3. Eggs, aged 0–1 days, proved the most tolerant stage at 30°C, 60% r.h., surviving a Ct-product of 16 g hr/m3 over a 2-day exposure period. At 30°C the diapause of larvae became unstable and their tolerance of phosphine was low. Adults emerging after fumigation of larvae appeared normal and if sufficient numbers emerged together a second generation was produced. Complete control of larvae of several stocks (about 20 weeks in diapause) was achieved within a 4-day exposure at 20°C with a mixture of methyl bromide (2.0 g/m3) and phosphine (1.4 g/m3), whereas 6 days were required for these stocks using phosphine alone. To ensure elimination of all stages of non-resistant T. granarium, exposures to phosphine should last 7 days at 20°C and 4 days at 30°C.

Methyl bromide sorption and residues on sultanas and raisins

Abstract Methyl bromide is widely used as a fumigant for dried fruit, such as sultanas and raisins. Results from samples of unprocessed and processed (washed and oiled) Thompson seedless sultanas treated with methyl bromide showed that it was sorbed in a manner consistent with an initial physical sorption followed by a more gradual reaction phase. At 25 °C, 60% r.h. the reversible physical sorption approached equilibrium after about 8 h of exposure. Methyl bromide partitioned between the gas phase and the fruit, according to a simple partition coefficient, with an average ratio of 0.95 and 0.99 in unprocessed and processed fruit, respectively, at 25 °C and 60% r.h. The partition coefficient was constant for different filling ratios, but decreased with increase in temperature. Estimates for different varieties of unprocessed sultanas and raisins ranged from 0.36 to 1.11 at 25 °C and 60% r.h. Reaction of methyl bromide with sultanas followed simple pseudo first order kinetics, with a mean rate constant for reaction of 0.0096 and 0.0065 per hour for unprocessed and processed fruit, respectively, at 25 °C and 60% r.h. Similar values were found for a range of sultana and raisin varieties. The rate constant increased with an increase in both temperature and humidity, with the rate of increase not significantly different for unprocessed and processed fruit. Accumulation of bromide residues was found to be directly related to the number of fumigations and to the concentration of methyl bromide applied. Approximately 0.17 and 0.13 mg of bromide was added per kilogram of unprocessed and processed fruit, respectively (dry weight), for a 24 h exposure and for each unit of initial methyl bromide concentration expressed in g/m3 in free air space. For a typical commercial dosage of 24 g/m3, this corresponds to about 6 mg/kg bromide residue added per treatment for processed sultanas. About 82% of applied methyl bromide was released on airing after a 24 h exposure at 25 °C, 60% r.h. and 0.90 filling ratio. A model was developed to predict residue formation, concentration profile with time and proportion of methyl bromide released on airing after a typical fumigation of sultanas.

Uptake of carbon dioxide by concrete and implications of this process for grain storage

Abstract The sorption of carbon dioxide (CO 2 ) on concrete was investigated by exposing concrete test cylinders (105 mm dia × 205 mm length) to a range of carbon dioxide concentrations (14–133 kPa partial pressures) at 30°C and 60% relative humidity. Sorption was almost all by the irreversible chemical reactions known as carbonation, with less than 1% of uptake desorbing on airing. The initial rate of uptake was dependent on CO 2 concentration. At 96 kPa CO 2 , 70% of total sorption occurred within 24 hr. CO 2 was still being absorbed appreciably (0.12 g CO 2 kg −1 d −1 ) even after 42 d exposure though the commonly used phenolphthalein test indicated carbonation was complete after 32 d. Depth of carbonation assessed by this test was independent of exposure period between 1 and 16 d. Cylinders coated with sealants (three types tested) exposed for 8 d at 96 kPa CO 2 took up only 7% of the CO 2 absorbed by uncoated ones. At 30°C and 60% r.h. it is estimated that the carbonation front will penetrate 75 mm into unprotected concrete of the type tested, sufficient to reach the reinforcing steel in large, cylindrical, concrete grain storages, and thus place it at risk from corrosion in the presence of free water, after between 1 and 2 months exposure to pure CO 2 . Cumulative exposures equivalent to this could occur in less than 10 years of use of CO 2 for insect control. Extensive carbonation resulting either from added CO 2 or that produced by respiration was observed commonly in the internal faces of old concrete grain stores. No corrosion was observed even in 50-yr old stores, suggesting that there is no risk associated with carbonation at least as long as the storage atmophere maintains a dry environment around the steel. The substantial and possible hazardous reduced pressures developing in well sealed, new concrete bins treated with CO 2 are attributable to the carbonation reaction. The implications of carbonation to pest control and corrosion of reinforcing steel in storages are discussed.

Toxicity of dichlorvos vapour to insects in aerated and non-aerated wheat and comparison of the vapour action of dichlorvos and malathion

Abstract Bioassay tests demonstrated the potent vapour toxicity of dichlorvos to Sitophilus oryzae and Rhyzopertha dominica . On freshly treated wheat at 20°C the lethal effect of dichlorvos was predominantly due to a mobile form of dichlorvos. This contrasts with the action of malathion. Dichlorvos vapour at toxic concentrations was moved through grain for up to 4 m using air flows comparable to those used in aeration of bulk stored wheat. There was a marked increase in efficiency of dichlorvos under forced air-flow conditions. Effect of air flow on movement of dichlorvos through wheat is discussed quantitatively.

The production and accumulation of carbon monoxide in stored dry grain

Abstract Carbon monoxide was identified as a common constituent of head space atmospheres in storage containing dry grain (