The toxicity of methyl chloroform to stored product insects

The susceptibility to methyl chloroform of all developmental stages of Cryptolestes ferrugineus, Ephestia kuehniella, Oryzaephilus surinamensis, Rhyzopertha dominica, Sitotroga cerealella, Sitophilus granarius, S. oryzae and Tribolium confusum, diapausing larvae of Ephestia elutella, E. cautella, Plodia interpunctella and Trogoderma granarium and adults of Tribolium castaneum, was studied. Tests were conducted at 15, 20 and 25°C, 55–75% r.h. with concentrations ranging from 25 to 200 mg/l and exposure times from 8 h to 16 days. The toxicity of methyl chloroform was in general similar to that of carbon tetrachloride. Immature stages of R. dominica, S. cerealella and Sitophilus spp, and diapausing larvae of T. granarium, showed the highest levels of tolerance. Methyl chloroform was more effective at the higher temperatures but a concentration of 50 mg/l was below the threshold level for full toxicity against 5 species at 25°C. Depending on the species concerned, the concentration × time (CT) product required for control varied from 3,700 mgh/l at 25°C to 60,000 mgh/l or more at 20°C. At 15°C fewer species were tested but five out of nine survived CT products in the region of 30,000 mgh/l. There was no appreciable difference between the susceptibility of the immature stages of malathion-resistant and susceptible strains of O. surinamensis. Neither were any consistent differences observed between adults of normal susceptibility and those resistant to methyl bromide or phosphine.     

The effect of concentration and exposure in tests with methyl bromide and with phosphine on diapausing larvae of Ephestia elutella (Hübner) (Lepidoptera,Pyralidae)

Fumigations were conducted in a 17001. chamber with methyl bromide or phosphine, subjecting diapausing larvae of Ephestia elutella at 20°C, 70% r.h. to three selected concentration-time (CT) products over a wide range of concentrations and exposure periods. With concentrations of methyl bromide between 2·9 and 15·0 mg/l., the CT product required for 50 per cent mortality was about 80 mg hr/l. The threshold concentration for a lethal response was found to lie between 0·62 and 1·15 mg/l. while with a concentration of 20 mg/l, the LD 50 was increased beyond the selected range of CT products.With the lowest concentration of phosphine tested, 0·02 mg/l., an LD 50 of 4·6 mg hr/l. was obtained. As concentrations were raised from 0·02 to 0·27 mg/l., and exposure periods were correspondingly decreased, there was a gradual increase in the CT product required for a particular level of kill. With higher concentrations, much lower mortalities were obtained at each CT product tested, and with a concentration of 1·4 mg/l., no significant kill was observed with any exposure period tested. At concentrations around 1 mg/l., mortality with phosphine was very low in exposures of less than 6 hr.     

The toxicity of phosphine to all developmental stages of thirteen species of stored product beetles

The toxicity of phosphine to all stages of 13 species of stored product beetles was determined using large numbers of test insects which made possible more accurate assessments of mortality. Species tested were Acanthoscelides obtectus, Caryedon serratus, Cryptolestes ferrugineus, C. pusillus, Lasioderma serricorne, Oryzaephilus surinamensis, Ptinus tectus, Rhyzopertha dominica, Sitophilus granarius, S. oryzae, S. zeamais, Tribolium castaneum and Trogoderma granarium. Tests were conducted as appropriate at 10, 15, 25 and 30°C, all at 70% r.h., with concentrations ranging from 0.013 to 2.96 mg/l and exposure times from 1 to 16 days. Sitophilus spp. proved the most tolerant, and in all species other than T. granarium, in which diapausing larvae were the more tolerant in longer exposures, eggs and pupae were the most tolerant stages. Phosphine was most effective at the higher temperatures, whilst long exposures at low concentrations were far more effective than short exposures at high concentrations. The use of phosphine to control these species of stored-product insects will only be effective at 15°C or below if long exposures can be guaranteed.     

Toxicity of phosphine to the diapausing stages of Ephestia elutella, Plodia interpunctella and other lepidoptera

Diapausing larvae of the stored product moths Ephestia elutella (Hübner) and Plodia interpunctella (Hübner) were tolerant of phosphine only in short exposures, the tolerance of E. elutella being at least twice that of P. interpunctella. The tolerance of a freshly collected wild stock of each species was, at some temperatures, about two or three times that in a laboratory reared stock. The wild stock of E. elutella required concentration-time (CT) products of 36 mg hr/l in 4-day exposures at 10° and 15°C, and 18 mg hr/l in 2-day exposures at 20°C and above for 100% kill. The tolerance of E. elutella larvae in diapause was not dependent on the manner in which diapause was induced, maintained or subsequently terminated. Longer exposures to phosphine were more effective than shorter ones of similar CT product because an initial period of about a day in each exposure was required for insects in diapause to be killed. At 25°C, a concentration of 0.03 mg/l was below the threshold level for mortality of some larvae, long exposures at such very low concentrations proving ineffective.

Diapausing pupae of an outdoor species, Pieris brassicae (L.), and eggs of the univoltine race of Bombyx mori (L.) were highly tolerant of phosphine at 10°C.     

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

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.     

Thermal resistance of different life stages of codling moth (Lepidoptera: Tortricidae)

Phytosanitation regulations in several international markets require postharvest treatments to control codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae), in various commodities. Thermal treatments are gaining acceptance to replace chemical fumigation. Determining the most thermal-tolerant life stage is essential in the development of effective postharvest insect control protocols based on thermal energy. A heating block system was used to evaluate relative heat resistance of five different life stages of codling moth: white-ring eggs, black-head eggs, third-instar, fifth-instar, and diapausing larvae, at a heating rate of 15°C/min. The fifth-instar was the most heat-resistant life stage in the tested temperature range of 50–52°C except for diapausing larvae. Thermal death kinetic data of diapausing fifth-instar larvae were determined and also compared with the published TDT curve of non-diapausing larvae using the same heating block system. Both diapausing and non-diapausing larvae were dead after treatments at 50°C for 5 min and 52°C for 2 min. However, at the lower temperatures or shorter times, diapausing larvae had lower mortality than non-diapausing larvae.     

Tolerance of the diapausing stages of four species of Lepidoptera to methyl bromide

The diapausing stages exposed to methyl bromide were larvae of Ephestia elutella (Hübner) and Plodia interpunctella (Hübner), pupae of Pieris brassicae (L.) and eggs of Bombyx mori (L.). Diapausing larvae of Ephestia elutella were highly tolerant, a few surviving to the adult stage after exposure to concentration-time (CT) products of up to 150 mg hr/l at 25°C and 260 mg hr/l at 15°C. Diapausing larvae of Plodia interpunctella were tolerant at low temperatures but quite susceptible at 25°C. In both species, larvae in diapause were four to six times more tolerant than other larvae at 15°C or below, and strains recently collected from the field were more tolerant than laboratory reared stocks.In E. elutella, differences in the method of induction, maintenance or termination of diapause did not affect tolerance to fumigation. P. interpunctella larvae reared at high population density were more susceptible than those reared at low density. Among strains of these species, a correlation was observed between the duration of larval diapause and tolerance to methyl bromide. Adults emerging after fumigation of diapausing larvae were of lowered fertility but rarely sterile. The CT products required for the complete control of moths in diapause were higher than those currently recommended for the disinfestation of stored products.Diapausing pupae of an outdoor species Pieris brassicae required the very high CT product of 403 mg hr/l for complete control at 25°C and were at least six times more tolerant than non-diapausing pupae. Diapausing eggs of Bombyx mori required 179 mg hr/l for complete control, while non-diapausing eggs were all killed by 125 mg hr/l.     

Fumigation with carbonyl sulfide: a model for the interaction of concentration, time and temperature

The new fumigant carbonyl sulfide offers an alternative to both methyl bromide and phosphine as a grain fumigant. Separate mathematical models for levels of kill, based on quantitative toxicological studies were developed for adults and eggs of the rice weevil Sitophilus oryzae (L.). These models suggest that fumigation exposure times for carbonyl sulfide will be a compromise between those of methyl bromide (typically 24 h) and phosphine (7–10 d) to achieve a very high kill of all developmental stages. S. oryzae eggs were more difficult to kill with carbonyl sulfide fumigation than the adults. At 30°C, a 25 g m⁻³ fumigation killed 99.9% of adults in less than 1 d, but took 4 d to kill the same percentage of eggs. Models were generated to describe the mortality of adults at 10, 15, 20, 25 and 30°C. From these models it is predicted that fumigation with carbonyl sulfide for 1–2 d at 30 g m⁻³ will kill 99.9% of adults. Furthermore the models illustrate that fumigations with concentrations below 10 g m⁻³ are unlikely to kill all adult S. oryzae. Significant variation was observed in the response of eggs to the fumigant over the temperature range of 10 to 30°C. Models were generated to describe the mortality of eggs at 10, 15, 20, 25 and 30°C. As the temperature was reduced below 25°C, the time taken to achieve an effective fumigation increased. Extrapolating from the models, a 25 g m⁻³ fumigation to control 99.9% of S. oryzae eggs will take 95 h (4 d) at 30°C, 77 h (3.2 d) at 25°C, 120 h (5 d) at 20°C, 174 h (7.5 d) at 15°C and about 290 h (11 d) at 10°C. The role of temperature in the time taken to kill eggs with carbonyl sulfide cannot be ignored. In order to achieve the desired level of kill of all developmental stages, the fumigation rates need to be set according to the most difficult life stage to kill, in this instance, the egg stage.     

The susceptibility of the immature and adult stages of Sitophilus granarius to phosphine

A concentration of 4 mg/l. of phosphine applied for 8 hr at 25°C permitted a considerable survival of the developmental stages of Sitophilus granarius (L.). Eggs of 3–4 days old were very tolerant and pupae even more so but larvae were very susceptible. A concentration of 1 mg/l. applied for 32 hr completely killed all stages except pupae. The most tolerant eggs were 2–4 days old. At 0·5 mg/l., pupae were again the most tolerant stage and eggs were most tolerant at 1–2 days old. At 0·3 mg/l. or less the majority of eggs were killed during the fifth day of development irrespective of their age at the start of fumigation, but over half were dead by 4 days old at 0·4 mg/l. and about a third survived beyond the sixth day at 0·05 mg/l. It is only at these latter concentrations at these ages that mortality of eggs was clearly related to dosage.

The physiological age range of pupae in samples was more dispersed. Pupae were most tolerant to phosphine at about 32 days old. From 5 to 7 days were needed for complete mortality at concentrations of 0·1–0·05 mg/l.

Adults were very susceptible to phosphine, all being killed by 8 hr at 1 mg/l. which permitted survival of some larvae. Freshly emerged adults were the most tolerant; older adults were very susceptible, at 1 month old being killed by 4 hr at 1 mg/l. and 3 days at 0·01 mg/l. Insects surviving fumigation as larvae or pupae usually laid fewer eggs than controls though their longevity was unaffected. Those surviving fumigation as eggs were not adversely affected. There is a possibility that some individuals surviving, as eggs or pupae, a fumigation causing very high mortality may lay more rapidly than controls.     

Effect of high temperatures on larvae of Ephestia elutella (Lepidoptera: Pyralidae) in diapause

Diapausing larvae of Ephestia elutella (Hb.) were exposed at 40, 43 or 45°C and then transferred to 25°C to observe subsequent development and survival. All larvae died after 96 hr at 40°C, 24 hr at 43°C or 16 hr at 45°C. However, about 80% of larvae exposed to 40°C for 8 hr each day for 18 days and about 50% of larvae exposed at 43°C for 8 hr each day for seven days survived. At 45°C all larvae died after two 8-hr or three 6-hr exposures given on successive days, but eight 4-hr exposures failed to kill more than 25% of larvae exposed. When the gap between 6 and 8-hr exposures was increased from 1 day, some larvae survived, indicating that recovery from heat exposure could occur. Adults emerging after high temperature exposure of diapausing larvae proved fertile. In contrast adults from larvae pupating without diapause at 30°C are known to be infertile.

Exposures at high temperature significantly hastened the termination of diapause. In general, the higher the level of mortality in the sample, or the greater the number of exposures at high temperature, the sooner pupation occurred in long days at 25°C.     

Effect of low pressures on the survival of three cocoa pests at 30°C

This study forms part of an effort to eliminate the need for methyl bromide fumigation to control insects in stored commodities, through development of a novel “vacuum-hermetic” technology. The effects of low pressures and exposure times on the mortality of insects in stored cocoa beans were studied at a temperature of 30°C in order to simulate cocoa bean storage conditions in tropical climates. Insects were exposed within test chambers containing the cocoa beans at a moisture content in equilibrium with 55% r.h. and at a constant temperature of 30°C. Three species of insects were used, all being major pests of cocoa beans in producer countries: Ephestia cautella (Walker), Plodia interpunctella (Hübner) and Tribolium castaneum (Herbst). At 50±5 mmHg, the egg stage was the most resistant in all three species, times needed to obtain 99% mortality being 45, 49 and 22 h, respectively. Results show that low-pressure treatment can provide an additional and more effective option to the 5 days fumigation with phosphine used today in the replacement of methyl bromide. The use of low pressures allows the control of insect pests at shorter exposure times without the need for toxic chemicals with their environmental impact.     

The tolerance of immature stages of four stored product moths to methyl bromide

Eggs, last instar larvae, and pupae of the Pyralid moths, Ephestia elutella (Hübner). E. kuehniella Zeller, E. cautella (Walker) and Plodia interpunctella (Hübner) reared at 25°C were exposed to methyl bromide over a wide range of concentrations and times at 10–30°C. One laboratory stock, and one field stock of each species were tested, but differences between stocks of the same species were small.P. interpunctella required lower CT products than the other species for complete kill of each stage. At 10°C, larvae of the field stock of E. cautella required a CT product of 110 mg h/l. for complete control. All stages of all species succumbed to a CT product of 64 mg h/l. at 15°C. When exposed at 20°C or above, pupae aged 0–3 days were more tolerant than other stages. Eggs aged 2 days or over were more tolerant than younger ones.The fertility of survivors from fumigated eggs resembled that of controls, but that of some individuals fumigated as pupae was depressed. For fumigated eggs of E. elutella and P. interpunctella at 15°C, the CT relationship held over concentrations from 4·2 to 10·8 mg/l. and exposure periods from 1 to 16 h.     

The tolerance of developmental stages of four stored product moths to phosphine

The tolerance to phosphine of different stages of Ephestia elutella, E. kuehniella, E. cautella and Plodia interpunctella was followed closely at 10–30°C. Eggs of all species were highly tolerant for the first 30–45% of the developmental period, but all other stages were much more susceptible. Maximum exposure periods permitting some survival over a practical range of concentrations were 1 day at 30°C, 2 days at 25°C, 3–4 days at 20°C, and 5–8 days at 15°C. Some eggs of E. elutella survived the very high CT products of 142 mg h/l. in a 2-day exposure at 25°C, and 288 mg h/l. in an 8-day exposure at 15°C. In a 3-day exposure at 25°C, and a 9-day exposure at 15°C, CT products of about 4 and 20 mg h/l. respectively were sufficient for complete control of all species. Eggs of P. interpunctella were susceptible to low temperature and survived exposures to phosphine at 15°C less well than other species. Survivors from fumigated eggs were of normal fertility.Although much less tolerant than eggs, younger pupae, especially those of E. kuehniella, were more tolerant than larvae or older pupae. The fertility of adults of normal weight emerging from surviving pupae was markedly depressed.In most fumigation experiments, differences in tolerance between laboratory and wild stocks were small. However, wild stocks tended to be more tolerant of cold than laboratory stocks, and survived fumigation better in long exposures at lower temperatures.     

The toxic action of phosphine in combination with some alkyl halide fumigants and carbon dioxide against the eggs of Tribolium castaneum Herbst (Coleoptera: Tenebrionidae)

The toxicity of phosphine, three alkyl halide fumigants (ethylene dibromide, methyl bromide and methyl iodide), carbon dioxide, mixtures of phosphine + alkyl halide fumigants, and phosphine + carbon dioxide, to 1-, 2-, and 3-day-old eggs of Tribolium castaneum Herbst was studied. Combinations of phosphine and alkyl halide fumigants showed antagonism as evidenced by their joint action ratios at the LD₉₀ (< 1). The mortality data indicated that mixtures of phosphine and carbon dioxide were more effective than either alone. At LD₅₀, the order of toxicity of the individual fumigants for a 24 hr exposure and on a weight basis (mg fumigant/litre of air) was: phosphine > methyl iodide > ethylene dibromide > methyl bromide. A decline in susceptibility of eggs with age for methyl bromide and ethylene dibromide and a peak tolerance at 2 days for carbon dioxide were noted.     

Dispersal of three species of grain beetles as a function of thermal acclimation, temperature, and larval size

Three species of stored-product insect pests, Tenebrio molitor, Tribolium confusum, and Trogoderma parabile, were acclimated at three temperatures, 15°, 23°, and 30° or 33°C, and then placed in chambers containing an appropriate culture medium held at testing temperatures ranging from 3°C to 14°C.

Cold-acclimated insects demonstrated greater dispersal at low temperatures than did warm-acclimated insects. Dispersal was greater at higher than at lower test temperatures. In a given species large larvae generally showed greater dispersal than did small larvae.     

Simulation studies on the effects of solar heat on egg-laying, development and survival of Callosobruchus maculatus (F.) and Callosobruchus subinnotatus (Pic) in stored bambara groundnut Vigna subterranea (L.) Verdcourt

The effects of simulated solar heat on oviposition, development and survival of Callosobruchus maculatus (F.) and Callosobruchus subinnotatus (Pic) in stored bambara groundnut, Vigna subterranea (L.) Verdcourt, were evaluated at three high temperatures (40°C, 45°C and 50°C) at a constant, low humidity (30% relative humidity). Exposure to these temperatures for 6 h significantly reduced oviposition in C. maculatus and C. subinnotatus females. Females of both species that were exposed to 50°C laid significantly fewer eggs than those exposed to 40°C; and in the case of C. maculatus, females exposed to 45°C also laid significantly fewer eggs than those exposed to 40°C. The percentage of eggs laid by females of both species that reached adulthood after exposure to 50°C for 2–6 h was significantly lower than the percentage that developed from eggs laid by females that were exposed to 40°C. No adult developed from eggs of C. maculatus exposed for 6 h at 50°C or from eggs of C. subinnotatus exposed for 2 h at this temperature. For both species, no adult progeny subsequently emerged from seeds harbouring first instar larvae when exposed at 50°C for 2, 4 or 6 h. Older larvae of C. maculatus were more tolerant of exposure at 50°C: 26.8, 10.2 and 0.9% of late instar larvae exposed for 2, 4 and 6 h, respectively, developed to the adult stage. In contrast, no adults of C. subinnotatus emerged from seeds harbouring late instar larvae when exposed at 45°C for 6 h nor in seeds exposed to the temperature of 50°C for 4 or 6 h. On average, immature stages of C. subinnotatus were more susceptible to heat treatment than those of C. maculatus.     

Contributions of diet quality and diapause duration to the termination of larval diapause in khapra beetle,Trogoderma granarium (Coleoptera: Dermestidae)

Larvae of khapra beetle, Trogoderma granarium (Coleoptera: Dermestidae) have an unusual diapause during which they may sporadically feed for several years, but not complete development. Diapausing larvae have an enhanced tolerance to starvation, insecticides and extreme temperatures. Thus, knowledge of factors that terminate larval diapause may aid in the control of this pest. In the current study, we assessed the effect of diet quality (five mixtures of fresh and spent diet in a replacement series) on diapause termination for diapausing larvae from laboratory cultures aged 3, 10, or 14 months. Larvae (n = 10 replicates for each combination of diet quality and culture, 10 larvae/replicate) were held at 30 °C and observed at different intervals over the course of 188 days to record larval mortality and larval pupation (= diapause termination). Larvae were least able to survive on diets of lower quality; i.e., 88% mortality after 188 days on 0% fresh diet versus 8% mortality on 100% fresh diet (averaged across cultures). Larvae were most likely to terminate diapause on diets of higher quality; i.e., 87% termination after 188 days on 100% fresh diet versus 0% termination on 0% fresh diet (averaged across cultures). Diapausing larvae from older cultures were least likely to terminate diapause and least likely to survive. On 100% fresh diet, diapause termination of larvae from cultures aged 3, 10 and 14 months was 93, 91, and 78%, respectively. On 0% fresh diet, mortality of larvae from cultures aged 3, 10 and 14 months was 67, 97, and 100%, respectively. These results indicate that diapausing larvae can accumulate the nutrients required to terminate diapause and complete development when provided with an opportunity to do so. However, the window of opportunity continues to shrink the longer the larvae remain in diapause.     

The effect of temperature and humidity on the developmental period and mortality of Typhaea stercorea (L.) (Coleoptera: Mycetophagidae)

The development of Typhaea stercorea (L.) on kibbled wheat was investigated at temperatures from 15 to 30°C in combination with humidities from 70 to 90% r.h. Eggs hatched at 17.5–30°C but not at 15°C. Incubation periods ranged from 2.5 days at 30°C to 9.5 days at 17.5°C. Larval periods ranged from 9.7 days at 30°C, 90% r.h. to 83.6 days at 17.5°C, 80% r.h. and were more than doubled for each 10% decrease in humidity. At 70% r.h. all larvae died outside the temperature range 22.5–27.5°C. Mortality increased with decreasing humidity in the range tested. Pupal periods ranged from 2.9 days at 30°C, 80% r.h. to 13.8 days at 17.5°C, 90% r.h. At 70% r.h. the lowest temperature for pupal development was 25°C whereas at 90% r.h. it was 17.5°C. The results suggest that this species is essentially a mould feeder and confirm that it requires relatively high humidity to develop.     

The toxicity of twelve fumigants to three species of mites infesting grain

Eggs of Tyrophagus longior, Acarus siro and Glycyphagus destructor were highly tolerant of each fumigant tested at 10°C while mobile stages were susceptible. Some eggs of T. longior survived the highest test dosages of methyl bromide, phosphine, ethylene oxide, ethyl formate, methallyl chloride and ethyl bromide. The ascending order of toxicity for the other fumigants, as judged by the ct product needed to kill all eggs, was methyl chloroform (MC), carbon tetrachloride (CTC), ethylene dichloride (EDC), methyl formate, ethylene dibromide and acrylonitrile. The toxicity of EDC was generally enhanced by the addition of MC or CTC, though dosages for control were still high, and a single fumigation can only be expected to provide a short-term absence of mobile stages. If complete control is required, this can be achieved by two treatments at a low dose if these are separated by an interval during which the surviving eggs hatch but do not reach the adult stage. The length of this interval depends on temperature and at 10°C is about 7 weeks, at 15°C 3 weeks and at 20°C 2 weeks.     

Thermal death kinetics and heating rate effects for fifth-instar Cydia pomonella (L.) (Lepidoptera: Tortricidae)

Thermal death kinetic parameters of fifth-instar codling moths (Cydia pomonella (L.)) and the effect of three heating rates (1°C min⁻¹, 10°C min⁻¹, and 18°C min⁻¹) on larval mortality were determined by a heating block system. The insects were heated to four temperatures (46°C, 48°C, 50°C, and 52°C) held for predetermined periods followed by 24 h storage at 4°C before mortality evaluation. Thermal death kinetics for fifth-instar codling moths followed a 0.5th order of kinetic reaction. Minimum time required to achieve 100% mortality of a given population decreased with temperature in a semi-logarithmic manner. No larval survival was observed in samples of 600 insects after exposure to 46°C, 48°C, 50°C, and 52°C for 50, 15, 5, and 2 min, respectively. Activation energy for thermal kill of fifth-instar codling moths at the heating rate of 18°C min⁻¹ was estimated to be about 472 kJ mol⁻¹. The lethal time accumulated during the ramp period was about 1.8, 0.2, and 0.1 min for the heating rates of 1°C min⁻¹, 10°C min⁻¹, and 18°C min⁻¹, respectively.