P.D. Cox

The influence of temperature and humidity on the life-cycle of Ephestia kuehniella Zeller (Lepidoptera: Pyralidae)

Abstract The development of Ephestia kuehniella was followed carefully on white flour at constant temperatures ranging from 7.5° to 31°C at humidities from 0 to 75% r.h. The lower limit of temperature for complete development was about 12°C although a few adults of a stock collected recently emerged at 10°C. Adults emerged at 28 but not at 31°C. Generally, development took longer and survival was poorer at 40 than at 70% r.h. However, at 20 and 25°C survival was good even at 15% r.h., and at 25°C, 18 out of 50 larvae reached the adult stage at a humidity near 0% r.h. Development was fastest at 25°C, 75% r.h., taking a mean of 74 days from oviposition to adult emergence. Oviposition occurred at 7.5 but not at 5°C. Mating was unsuccessful at 12.5°C. Eggs hatched at all temperatures between 12 and 31°C at every r.h. used. A few eggs from two field stocks hatched at 10°C but none did so at 7.5°C. At 12 C no larvae pupated at humidities below 70% r.h., and none pupated at 31°C at any humidity. Larval development was most rapid at 25°C, 75% r.h., taking about 60 days. The shortest mean pupal period, 9 days, occurred at 28°C, 70% r.h. In an experiment with field stocks, many larvae pupated at 10°C but none at 7.5°C. This study confirms E. kuehniella as essentially a temperate species that prefers heated premises such as bakeries and mills for rapid development. Its ability to develop on food at a low e.r.h. fits it further for life in flour mills.

The influence of temperature and humidity on the life-cycles of Ephestia figulilella gregson and Ephestia calidella (Guenée) (Lepidoptera: Phycitidae)

Abstract Limiting temperatures for complete development of Cyprus stocks of Ephestia calidella and E. figulilella on semi-artificial diets at 70% r.h. were about 36°C and 15°C. The lower humidity limit for E. figulilella lay between 30% r.h. and 50% r.h., except above 36°C and below 25·5°C where it rose to between 50 and 70% r.h. The optimum temperature for survival and rate of development for both species was 30°C. For E. figulilella the optimum humidity was 70% r.h., and for E. calidella for which glycerol was added to the diet it was 90% r.h. Under the light regime of 16 hr light/8 hr dark, females of both species began to call, that is to raise their abdomens and expose their pheromone-producing glands, soon after the dark period commenced. Copulation and oviposition occurred throughout the dark period, although most eggs were laid in the first few hours of darkness. Precautions taken to reduce the risk and spread of infection by Bacillus thuringiensis included strict quarantining of freshly-collected stocks, surface sterilisation of eggs, sterilisation of food and equipment, and the use of bacteria spore-proof filter paper to seal cultures.

Factors affecting the refuge-seeking behaviour of Cryptolestes ferrugineus (Stephens) (Coleoptera: Cucujidae).

Abstract The effects of insect sex, density and age on the refuge-seeking behaviour of Cryptolestes ferrugineus (Stephens) were studied by confining adults of several strains in 21 cm dia arenas containing a refuge filled with wheat. Refuge-seeking behaviour was greater in females than males, both in tests where the sexes were kept separate and also when they were mixed in equal numbers. Although more beetles were present in the refuges as density increased, a higher percentage of beetles was recorded in refuges by the end of the 2 week test period at a density of 25 adults/arena than at a density of 150 adults/arena. Similarly, more 0–3 wk old adults were found in refuges than adults aged 10–12 wk and 16–18 wk old. These results are discussed in relation to the known biology of this stored grain pest.

Studies on three moth species in a Scottish port silo, with special reference to overwintering Ephestia kuehniella (Zeller) (Lepidoptera: Pyralidae).

Abstract During the winter of 1973–1974, enormous numbers of fully-fed, last instar larvae of Ephestia kuehniella (Zeller) were discovered in a large Scottish port silo where previously the endemic moth infestation had been almost entirely Endrosis sarcitrella (L.) and Hofmannophila pseudospretella (Stainton). E. kuehniella had previously been uncommon in this silo as in unheated silos elsewhere in Britain. During 1974–1976 E. kuehniella was most abundant on the topmost floors of the silo, particularly inside the tops of grain bins where previously E. sarcitrella had been abundant. E. sarcitrella , however, was still the more abundant on the storage floors and at the bin bottoms. H. pseudospretella was widespread throughout the buildings, though less concentrated locally. In September, most of the E. kuehniella larvae found were early instars less than half grown but by December the smallest larvae seen approached half grown. This gradual increase in mean larval length continued through the winter, although considerable mortality of large larvae occurred after December in some areas. However, some last instar larvae appeared to enter a diapause in the autumn and did not pupate until the following May. Adults of E. sarcitrella commenced to emerge in March, and of the other two species in June.

The influence of photoperiod on the life-cycles of Ephestia calidella (Guenée) and Ephestia figulilella Gregson (Lepidoptera: Phycitidae)

When reared at 30°C 70% r.h. and fed on a diet of wheat-feed, glucose and yeast, some larvae of Ephestia calidella and E. figulilella entered diapause at photoperiods of 13 hr light and less per day. In continuous darkness for 60 days, no E. calidella larvae exhibited diapause, but two E. figulilella larvae showed some delay in development in food infested by psocids. Under a light regime of 13 hr light followed by 11 hr darkness (13L11D), 45 per cent of E. figulilella but only 3 per cent of E. calidella larvae entered diapause. The critical photoperiod for both species was between 12L12D and 13L11D. For both species, survival was good in continuous darkness and poor in continuous light. Wherever diapause was detected, it delayed adult emergence by an average of 48 days for E. calidella and 74 days for E. figulilella. When reared at 20°C 70% r.h. in continuous darkness for 140 days, 96 per cent and 91 per cent of E. calidella and E. figulilella larvae, respectively, entered diapause. In neither species was diapause observed at 20°C 16L8D. In E. figulilella diapause did not appear at photoperiods longer than 13L11D at this temperature. Transfer of larvae which were in diapause after 60 days at 30°C in a 12L11D photoperiod to one of 16L8D reduced the range of emergence period for E. calidella by 15 days and for E. figulilella by 75 days, compared to controls left at 12L12D. Mean development periods were shortened by 13 days and 54 days respectively. Insertion of a 30 day cold period at 5°C did not significantly hasten the termination of diapause. Similar effects were obtained when E. calidella larvae entered diapause at 12L12D and 20°C. In this case, transferring diapause larvae to the longer photoperiod reduced the development period range by more than half that of controls at 12L12D. Mean development period was reduced by 63 days. E. calidella larvae entering diapause at 20°C appeared to possess a more intense diapause than those entering at 30°C. The significance of diapause in these species in relation to their potential as pests is discussed.

Effects of refuge content and food availability on refuge-seeking behaviour in Cryptolestes ferrugineus (Stephens) (Coleoptera: Cucujidae)

Abstract The effects of the contents of the refuge and the presence of food in the arena on refuge-seeking behaviour in two strains of Cryptolestes ferrugineus (Stephens) was investigated in the laboratory by confining adults in 21 cm dia arenas containing a central refuge. Some beetles were recorded in the refuges even when they contained only glass balls, although considerably fewer than when they contained whole wheat grains of flour. This suggests that a refuge retains some attraction for beetles even when food is absent, perhaps by providing physical contact around the insects body. The addition of wheat or flour to the arena also reduced the numbers of beetles recorded in the refuges. Results were less clear-cut for a strain of C. ferrugineus that had been reared in the laboratory for over 25 yr than for a strain more recently obtained from the natural storage environment. These results are discussed in relation to the importance of insect behaviour in laboratory bioassays and control in grain stores.

Variations in the refuge-seeking behaviour of four strains of Cryptolestes ferrugineus (stephens) (Coleoptera: Cucujidae) at different temperatures

Abstract The refuge-seeking behaviour of insecticide resistant and susceptible strains of Cryptolestes ferrugineus (Stephens) was investigated in the laboratory by confining adults in arenas containing a refuge filled with wheat. Three strains had been collected from grain stores and mills, and the fourth (Insectary) had been reared in constant conditions for over 25 years. The effect of temperature on behaviour, in the range 15–30°C, was also examined. The Insectary strain was particularly affected by low temperatures with far fewer adults being recorded in the refuge at the end of the 2-week test period compared to other strains. Differences in refuge-seeking behaviour between strains increased with decreasing temperature, and were greatest below 20°C; this corresponds with the temperatures at which grain is usually stored in Britain and in other countries of temperate climate. These differences in behaviour appear to be unconnected with the biochemical/physiological resistance of the strains to malathion.

The influence of temperature and humidity on the life-cycle of Ectomyelois ceratoniae (Zeller) (Lepidoptera: Phycitidae)

Abstract Adults of Ectomyelois ceratoniae would not mate in small containers kept in constant conditions. Mating occurred and fertile eggs were laid when the adults were placed in a large conical cage, kept in regularly fluctuating conditions of light, temperature and humidity resembling their native habitat. The dusk/dawn light intensity changes were particularly important. Most mating and oviposition occurred from dusk until the following dawn, with adults motionless during daylight. At 70% r.h. eggs hatched on average in 4·2 days at 25°C, 3·0 days at 30°C and 3·6 days at 35°C. At 30°C, this period varied from 3·4 days at 30% r.h. to 3·0 days at 90% r.h. On a diet of soybean meal, sucrose and water at 30°C, the larval period averaged 30 days at 30% r.h., 13 days longer than at 70% r.h., and the low relative humidity also increased larval mortality. At 90% r.h., no larvae emerged from food that became very mouldy. The total developmental period from egg hatch to adult emergence at 70% r.h. averaged 48 days at 20°C, 30 days at 25°C and 23 days at 30°C.

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

Abstract 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.

The incidence of diapause in seventeen populations of the flour moth, Ephestia kuehniella Zeller (Lepidoptera: Pyralidae)

Abstract Samples of Ephestia kuehniella were examined for diapause at 20 and 25°C in continuous darkness, continuous light and three other photoperiods. The samples came from five flour mills and five unheated stores in England, and from Scotland, Egypt, Finland and Japan, together with three laboratory reared stocks. Some larvae entered diapause in all but three of the English stocks, in all stocks from other countries, and in a 10-yr old laboratory stock from Japan but not in two other stocks reared in the laboratory for over 30 yr. In continuous darkness at 25°C, the incidence of diapause exceeded 10% in eleven stocks, 25% in eight, and 50% in three stocks, while in darkness at 20°C the proportions were usually much smaller. In other light regimes there was a much lower incidence of diapause, 10% being reached in only six experiments out of more than eighty. Markedly more larvae entered diapause when reared on the maize or wheat flour available in mills than on a nutritious laboratory diet of wheatfeed, glycerol and yeast.