Effects of temperature and humidity on development of four pyralid moth pests of stored products

The development of Plodia interpunctella, Ephestia cautella, E. kuehniella and E. elutella was followed carefully at selected temperatures. Infertility prevented successful breeding of the latter two species at 30°C. The first two species bred successfully at 30°C, failed to complete development at 15°C, and, at 20–30°C, completed development more quickly than the other two. All species took longer to develop and survived less well at 25% r.h. than at 70% r.h., and their pupal stages lasted about twice as long as the egg stages at temperatures allowing development of both. At 25°C, the pupal stage lasted about 9 days in P. interpunctella and E. cautella, 11–12 days in E. kuehniella and about 13 days in E. elutella.

In all species other than E. elutella, eggs held at 25°C became more tolerant of cold when aged over 1 day. Younger eggs of P. interpunctella were less tolerant of cold than any eggs of the other species, and were killed outright by holding for 19 days at 15°C.

Stocks of all four species recently collected from the field generally tolerated low r.h. and low temperature a little better than laboratory stocks, but at higher temperatures developed from egg to adult a little more slowly.     

The effect of diapause on the tolerance of larvae of Ephestia kuehniella to methyl bromide and phosphine

Larvae from a stock of Ephestia kuehniella Zeller, recently collected from an unheated flour store in southern England, were exposed at 10 and 15°C to two fumigants commonly used for the control of this species in the U.K. Various exposure periods were tested and the mortality of larvae which had entered diapause was compared with that of non-diapausing larvae.

Diapause increased the tolerance of larvae to methyl bromide and phosphine at low temperatures. The minimum dosage of methyl bromide for complete control of diapausing larvae was about 80 mgh/l during a 20-h exposure period at 10°C and less than 70 mgh/l during a 16-h exposure at 15°C. Complete kill of diapausing larvae at 10°C was obtained after a 4-day exposure to phosphine with a CT product of 8.1 mgh/l, but a slighly higher dosage was required in a test at 15°C.     

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.     

Supercooling point variability in the Indian meal moth, Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae)

Factors affecting the supercooling point (SCP) of the Indian meal moth, Plodia interpunctella (Hübner), were investigated under various conditions. The effects of geographic origin, time under laboratory conditions, laboratory diet, stage of development, age within stage, and season on P. interpunctella SCP were examined. Overall, SCPs ranged from −28.6 to −2.4 °C. At the times of collection, differences in SCP between field-collected individuals and individuals from laboratory sources were negligible. The minimum observed SCP for most of the cultures tested soon after collection was below −20 °C. After 7 months under laboratory conditions, the mean SCP of field-collected and laboratory-reared cultures remained unchanged. No particular trend in SCP was observed when comparing cultures from northern and southern regions. Differences in laboratory diets did not affect mean SCP. Mean SCP for 1- and 4-d-old eggs was similar. Eggs (−24.4 °C), first instars (−23.5 °C), pupae (−22.2 °C), and adults (−22.4 °C) had lower mean SCPs than later instar larvae (−14.4 to −11.6 °C). When confined in the laboratory for 8 months under conditions which were not controlled, monthly mean SCP for the same culture varied by as much as 5.7 °C. Plodia interpunctella appeared to regulate its SCP as the season changed, with a relatively high mean SCP during summer and a marked decline of more than 10 °C in fall. The SCPs obtained in this study suggest that very low temperatures may be needed for disinfestation of P. interpunctella at all stages of development.     

低温冷藏对烟草粉螟亲代和子代适合度的影响

为明确低温冷藏对烟草粉螟亲代和子代适合度的影响,根据年龄-龄期两性生命表理论,对5℃冷藏160d后的烟草粉螟5龄幼虫亲代生殖适合度及其子代发育历期、存活率、繁殖率和种群参数进行研究。结果表明,低温冷藏160d后烟草粉螟F₀代的蛹期显著长于对照,雌雄成虫寿命、平均繁殖力和产卵时间均显著低于对照;但在F₁代中,除了低温处理的平均繁殖力（148.29粒）显著高于对照（113.93粒）外,其他参数均无显著差异。研究表明,低温冷藏显著降低烟草粉螟亲代的适合度,对子代的适合度则无显著影响。     

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.     

麦蛾茧蜂对烟草粉螟的控制潜能研究

为明确麦蛾茧蜂对烟草粉螟的控制潜能,研究了麦蛾茧蜂对烟草粉螟幼虫的偏好性、功能反应、种内干扰和雄蜂存在对雌蜂的干扰效应。结果表明,麦蛾茧蜂偏好麻痹5龄幼虫,平均麻痹率74.00%±2.67%,对5龄幼虫的功能反应符合Ⅱ型,瞬时攻击率、处理时间、最大麻痹量分别为0.085/h、0.187 h和128.06头;麦蛾茧蜂种内干扰系数为0.316,该蜂对烟草粉螟幼虫的平均麻痹率（0.226~0.566）和搜寻效率（0.476~0.836）均随着雌蜂密度的增加而显著降低,但雄蜂的密度不影响雌蜂对烟草粉螟的麻痹量。研究证明,麦蛾茧蜂对烟草粉螟的控制潜力大,在烟仓烟草粉螟的绿色防控中具有良好的开发利用前景。     

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.     

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.     

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.     

A wild strain of Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae) from farm-stored maize in South Carolina: Effect of temperature on mating, survival, and fecundity

The purpose of this study was to develop age-specific survivorship and fecundity schedules for adult Plodia interpunctella (Hübner) relevant to maize storages, with special reference to the southeastern states (USA). Laboratory cultures were established with moths collected from farm-stored maize in South Carolina and maintained on cracked maize at 30 °C and 60% r.h. Age-specific schedules of survivorship and fecundity, the length of the oviposition period, mating success, and mating frequency were determined at 20, 25, 30, and 35 °C and about 75% r.h. The maximum oviposition period was longest (18 d) at 20 and 25 °C, and shortest (8 d) at 35 °C. The optimum temperatures for reproduction (mating frequency and fecundity) were 25–30 °C, but mean life-span was longest (13.2 d) at 20 °C and declined linearly with increasing temperature. Mean total (lifetime) fecundity ranged from 16.9 eggs at 35 °C to 227.7 eggs at 25 °C.     

Some laboratory observations on the development of two African strains of Plodia interpunctella (Hübn.) (Lepidoptera: Phycitidae), with particular reference to the incidence of diapause

Laboratory investigations were made on the development of two African strains of Plodia interpunctella on a mixture of wheatfeed, glycerol and dried yeast at four teperatures from 17·5°C to 25°C at 50% r.h. and at 17·5°C and 30°C at 70% r.h. Particular attention was given to the possible incidence of a pre-pupal diapause in the two stains, one from Kano, Nigeria and the other from Pretoria, South Africa.

At 30°C there was little difference between strains, but at 22·5 and 25°C the development period of the larva and possibly also of the pupa was longer in the Pretoria strain. At 20 and 17·5°C this difference was extremely large for larvae and at 17·5°C reached 4 days for pupae. The difference in the time for larval development, e.g. average 164·8 and 206 days in the Pretoria strain, and 38·1 and 57·5 days in the Kano strain, at 20 and 17·5°C (50% r.h.) respectively, was due to a prolonged pre-pupal diapause in the former strain.

It was shown that diapause was induced in the Pretoria strain when eggs were incubated at 25 or 30°C and newly-hatched larvae transferred to 20°C; also when larval development commenced at 30°C and larvae were transferred to 20°C before the end of the second instar.

The incidence of diapause in the Pretoria strain and its absence in the Kano strain is discussed in relation to climatic data and reference is made to the possible implications of diapause in relation to control, with particular reference to fumigation.     

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.     

Residual susceptibility of Plodia interpunctella to deltamethrin dust: Effects of concentration and time of exposure

Wandering phase fifth instarPlodia interpunctella (Hübner) were exposed at ten weekly intervals for 6, 12 and 24 h or 1 week to 0.05% deltamethrin dust at application rates of 38, 47 and 56 mg per 0.016 m². The percentages of pupating larvae and adult emergence at all three rates were greatest at the 6-h exposure and least at the 1-week exposure, but there was no consistent decrease in pupation or emergence as the exposure was increased from 6 to 24 h. Pupation and emergence decreased with increasing application rate of deltamethrin dust at each weekly bioassay, and the percentage of emerged adults was usually less than the percentage of larvae that pupated. At the conclusion of the test (9 weeks), curve-fit adult emergence data for larvae exposed for 1 week to deltamethrin dust at application rates of 38, 47 and 56 mg per 0.016 m² were calculated by linear regression to be 26.6%, 20.5% and 17.3% respectively. For all other exposure times at each rate, adult emergence usually exceeded 20% after 2–4 weeks.     

Trap catches of stored-product insects before and after heat treatment in a pilot feed mill

The pilot feed mill at Kansas State University was heated to temperatures of 50°C for 28–35 h during August 4–6, 1999 using natural gas heaters to kill stored-product insects. A three-parameter nonlinear regression model satisfactorily described temperature profiles on each of the four mill floors and was useful in showing differences among floors in the number of hours taken to reach 50°C and hours above 50°C. Pitfall traps with food and pheromone lures and sticky traps with pheromone lures were used to sample adults of beetles and moths, respectively, between July 8 and December 1, 1999 to evaluate heat treatment effectiveness. A total of 32 insect species representing 26 families in seven orders were captured in traps. Immediately after heat treatment, there was 95% reduction in total beetle captures in pitfall traps and 99% reduction in moth captures in sticky traps. Trap captures of the almond moth, Cadra cautella (Walker) and cigarette beetle, Lasioderma serricorne (L.) were significantly reduced and remained low after heat treatment. However, trap captures of the flat grain beetle, Cryptolestes pusillus (Schöenherr), Indianmeal moth, Plodia interpunctella (Hübner), and red flour beetle, Tribolium castaneum (Herbst) increased gradually after heat treatment, especially on the 1st and 4th floors. Our results indicated that traps are valuable tools for gauging the degree and duration of insect suppression obtained by heat treatment. In addition to trapping, visual inspection of the mill areas and absolute sampling of ingredients, products and spillage should be undertaken, so that areas of incipient insect reinfestation can be identified and potential problems rectified or averted.     

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.     

温度和烟草粉螟密度对麦蛾茧蜂觅食行为的影响

为明确温度和烟草粉螟密度对麦蛾茧蜂觅食行为的影响,设置15、20、25、30和35℃梯度温度,测定了麦蛾茧蜂在不同密度烟草粉螟5龄幼虫条件下的功能反应、寄生量和产卵量。结果表明,麦蛾茧蜂的麻痹量随温度的升高和烟草粉螟密度的增大而增大,其功能反应为Holling Ⅱ模型;麦蛾茧蜂的瞬时攻击率（a）随温度的升高先增大后降低（25℃最大）,处理时间（Th）随温度的升高而缩短;在30～35℃条件下麦蛾茧蜂对烟草粉螟的控害潜力（a/Th和T/Th）最大。麦蛾茧蜂的寄生量、产卵量和转化率均随温度的升高而增大,随烟草粉螟密度的增大而减小。当温度在30～35℃和烟草粉螟为5～10头/盒时,麦蛾茧蜂的寄生量、产卵量和转化率较高。本研究为大量饲养和利用麦蛾茧蜂防治烟草粉螟等仓储害虫提供了理论依据。     

The termination of diapause in Trogoderma granarium Everts (Coleoptera, Dermestidae)

When subjected to an increase in temperature from 30 to 37°C, both the density-dependent diapause (DDD) and the density-independent diapause (DID) of Trogoderma granarium were terminated in about 10 days. However, under severe crowding, a few DDD larvae took as much as 100 days to pupate at 37°C.

At 30°C, most larvae that had entered diapause in isolated cultures pupated spontaneously during a brief period sometime after they were 3 months old; for most populations of larvae studied such pupation occurred at about 5 months of age. Renewal of food had little influence on the termination of DID. A corresponding burst of pupation, although of only one quarter of individuals, was also recorded for DDD larvae kept crowded in old flour. The most effective termination of DDD, at 30°C, was achieved by isolating the larvae and providing new food together. This treatment brought about a small immediate burst of pupation and also enhanced the subsequent spontaneous pupation so that altogether about 86 per cent of the larvae pupated.

The adaptive value of these reactions in the warehouse environment is discussed. It is suggested that the significance of some of the features of the diapause of T. granarium may be explicable only in relation to its primitive habitat, possibly the nests of insects, in which the diapause must have originated.     

The influence of photoperiod on the life-cycle of Ectomyelois ceratoniae (Zeller) (Lepidoptera: Pyralidae)

Diapause in fully grown larvae of Ectomyelois ceratoniae was induced by low temperature and short photoperiods. When larvae were reared at 30°C, 70% r.h. there was no diapause in a light regime of 12 hr light followed by 12 hr darkness (12L/12D), and only 20% entered a weak diapause in continuous darkness. However, at 20°C, 70% r.h. there was no diapause in 16L/8D but almost all larvae entered diapause in 12L/12D. At 20°C diapause delayed adult emergence by an average of 111 days, compared with about 50 days at 30°C. Survival to adult at 30°C was 75% or more at most photoperiods, but at 12L/12D and 13L/11D it was less than 50%. At 20°C survival was about 70% at the two photoperiods tested.

A slight effect of photoperiod on non-diapause growth rates was observed. Above 16 hr light longer photoperiods reduced the mean developmental period from egg hatch to adult emergence, by 4 days at 20L/4D and 6 days at 24L/0D.

The significance of diapause in this species in relation to its potential as a pest is discussed.     

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.