A wild strain of Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae) from farm-stored maize in South Carolina: Development under different temperature, moisture, and dietary conditions

The purpose of this study was to determine the duration of immature development and survivorship of Plodia interpunctella (Hübner) on maize over a range of temperatures and grain moisture contents encountered in maize stored on farms in 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. The incubation period and percentage hatch of eggs was determined at 18 combinations of temperature and r.h. Hatch was <1% at 15 and 40 °C. In the range 20-35 °C, percentage hatch declined as temperature increased, and the mean incubation period ranged from 3.1 to 8.5 d. Neither percentage hatch nor incubation period were affected by r.h. between 43% and 76%. The relationship between mean developmental period (oviposition to adult eclosion) and temperature was well described by a quadratic polynomial that predicted a decline from 67.6 to 30.1 d as temperature increased from 20 to 31.1 °C, followed by an increase to 38.5 d as temperature increased further to 35 °C. The results suggest a lower temperature threshold for development near 15 °C and an upper limit slightly greater than 35 °C. Moisture content had a significant effect on developmental period at all the temperatures studied, but the pattern of variation with moisture depended upon the temperature.     

Abundance of Plodia interpunctella (Hübner) and Cadra cautella (Walker) infesting maize stored on South Carolina farms: seasonal and non-seasonal variation

Seasonal trends and short-term fluctuations in abundance of Plodia interpunctella (Hübner) and Cadra cautella (Walker) infesting maize stored on two South Carolina farms were studied during three storage seasons (September 1990–June 1993). Coils of corrugated paper placed on the grain surface were used to trap mature larvae seeking pupation sites. Temperatures in the grain (18-cm-deep) and in the bin headspace were recorded hourly, and grain moisture content was measured weekly. Weekly mean numbers of moth larvae, and adults of two natural enemies, trapped in the coils were used for tracking changes in their abundance over time. The most significant findings were: (1) a seasonal pattern of abundance in both moth species that persisted from farm to farm and year to year, and (2) the coincidence of the highest population levels with the lowest temperatures. With few exceptions, the moth populations increased in the fall, reached their highest levels in winter, and then declined to low levels by early spring. The persistence of this pattern suggests a seasonal regulatory mechanism, with onset of low temperature as the primary initiator of population decline and adversely high temperature as a contributor to its protraction through spring into early summer. This view is supported by our observations of temperature and moth abundance, in conjunction with published information on the biological limitations of the two species. However, other factors, such as predators, parasitoids, and viral infection, may have contributed to the final population collapse. Superimposed upon the seasonal trends were short-term, non-seasonal cycles of abundance with variable periods. Population theory suggests that predation, parasitism, disease, and competition may have produced these cycles.     

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.     

The potential of two electrostatic powders as the basis for an autodissemination control method of Plodia interpunctella (Hübner)

A comparison of the retention, horizontal transmission and effect on mating of two electrostatic powders (Entomag™ and Entostat™) was made to evaluate their potential as a component of an autodissemination method for the control of Plodia interpunctella. Both powders were shown to have some effects on mating behaviour and the ability of treated males to locate a pheromone source when applied in high doses. However, no effects were observed at rates consistent with the amount of powder that was actually taken up when the moths visited a prototype autodissemination device. Male and females lost 69.9% and 64.3% by weight, respectively, of Entomag by 48 h after exposure but lost more Entostat, 89.8% and 75.9%, over the same period. Critical to the efficacy of autodissemination is the transfer of powder from males to females and on average a 49% greater weight of Entostat was transferred than Entomag. Due to the different densities of the powders, it was calculated that a 49% increase in transfer of powder equated to over three times more Entostat than Entomag particles being passed from male to female. It was concluded that Entostat would appear to be the carrier of choice for a prototype P. interpunctella autodissemination system.     

Oviposition attractants for Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae) in the volatiles of whole wheat flour

Plodia interpunctella is attracted to whole wheat flour. Volatiles obtained from whole wheat flour by Porapak Q trapping were assayed using pitfall olfactometers, and were attractive to mated females (active at 10⁻¹ gram/day equivalent, gde), but not to males or unmated females, suggesting that the volatiles are oviposition attractants for P. interpunctella. Silicon dioxide column chromatography of the crude volatiles revealed that the fraction recovered with 3% ether in pentane (3% EP) was active and contained at least 27 components, in which alkanals (C₆-C₁₀) and 2E-alkenals (C₇-C₁₁) were active as individual aldehydes or mixtures. Nonanal was most active (the lowest active limit, LAL: 10⁻² μg), followed by 2E-nonenal and 2E-decenal (1 μg each). The synthetic mixture of the 27 components identified from 3% EP was attractive at 1.59×10⁻⁴ μg, which was equal in activity to the crude volatiles at 10⁻¹ gde (LAL) for mated females. The ether fraction (E) showed no activity by itself but synergistically enhanced the activity of the 10% EP fraction (LAL: 10⁻⁴ μg). Alkanols (C₅-C₉), lactones and carboxylic acids (C₅-C₁₈) were identified from the E fraction, in which hexanol and hexanoic acid were the major components. Both hexanol and palmitic acid were synergistic in combination with the aldehyde mixture.     

Development of Ephestia kuehniella (Zeller), Plodia interpunctella (Hübner) and Corcyra cephalonica (Stainton) (Lepidoptera: Pyralidae) on kernels and wholemeal flours of Fagopyrum esculentum (Moench) and Triticum aestivum L.

Three stored product moth pests, Ephestia kuehniella, Plodia interpunctella and Corcyra cephalonica were reared on the following five foods: whole buckwheat with pericarp, decorticated buckwheat, wheat var. “Centauro” (kernels), wholemeal wheat flour and whole buckwheat flour. Results showed that achenes of buckwheat with pericarp are a poor food for the development of these species. A low rate of survival to adulthood for E. kuehniella and P. interpunctella was recorded, with a considerable extension of post-embryonic development. Although the mandibles of larvae are strong, they have trouble in breaking the fibrous buckwheat pericarp. It was observed that when the seed was decorticated there was a higher percentage of adults emerged. The emergence of E. kuehniella began, according to the food given, 34–42 days after the eggs were laid. The susceptibility index (s.i.) of achenes without pericarp (s.i. 9.7) was higher than that observed on wheat (s.i. 8.6). The first P. interpunctella adults were found after 29 days on wheat and after 56 days on buckwheat with pericarp. The shortest mean period of development occurred on wheat (34 days) while the longest was on buckwheat with pericarp at 81 days. The highest susceptibility index was on kernels (s.i. 12.8), the lowest one was on buckwheat with pericarp (s.i. 2.3). C. cephalonica began to emerge, according to the food given, after 40–55 days. In this case, fewer adults were recorded from buckwheat with pericarp, but no significant differences among the means of emerged adults on wheat, wholemeal wheat flour and whole buckwheat flour were observed. The longest mean period of development was recorded on wholemeal wheat flour (72 days) while the shortest was on wheat kernels (58 days). The highest value for the susceptibility index was obtained for wheat kernels (s.i. 7.4) and the lowest one for buckwheat with pericarp (s.i. 4.5).     

Effects of different food commodities on larval development and α-amylase activity of Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae)

The present work was undertaken to study the influence of four commodities (wheat flour, dates, sorghum and barley) on Plodia interpunctella post-embryonic development. Larval weight, larval mortality, pupation and adult emergence were recorded. The study also aimed to find out the effect of these commodities on protein and glycogen production as well as on α-amylase activity. Results indicated that the weight of fourth instar larvae placed on dates increased gradually. Percentage mortality was low. Pupation and adult emergence were delayed. In contrast, the weight of larvae placed on wheat flour, sorghum or barley remained low. Pupation and adult emergence occurred sooner than among those placed on dates and the percentage mortality was highest for larvae placed on barley. Results also showed that protein content and α-amylase activity were lower for larvae placed on dates than for those placed on other commodities. The biochemical composition of different commodities showed that dates are a rich source of glucose, while their protein and starch contents were very low as compared to the other commodities. In contrast, wheat flour, sorghum and barley contained large amounts of starch and protein and low amounts of glucose. Thus, the reduction in α-amylase activity was probably due to the high levels of glucose in dates.     

Effects of delayed mating on reproductive performance of Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae)

Virgin male and female Indianmeal moths, Plodia interpunctella (Hübner), were mated soon after emergence or delayed from mating for 1-5 d, to determine the effect of age at mating on the number of spermatophores transferred by males to females, number of eggs laid (fecundity), egg viability, and adult longevity. When male and female moths were mated without delay, all females mated successfully. On average, each mated female had 2.2 spermatophores and laid 161 eggs. About 99% of the eggs laid were viable. Fecundity and egg viability were significantly and positively correlated with the number of spermatophores/female. For each day that mating of virgin male or female P. interpunctella was delayed, fecundity decreased by about 25 eggs. Egg viability decreased by 22%/d only when females were delayed from mating. Males delayed from mating for 5 d were unable to inseminate females. However, about 23% of females had one spermatophore when females or both males and females were delayed from mating for 5 d. On average, 22-39 non-viable eggs were laid by a female in treatments where male or female moths were delayed from mating for 5 d. Similarly, unmated (virgin) females laid 33 non-viable eggs. These results suggest that methods that can delay and disrupt mating may be effective behavioral strategies for managing this important pest of stored commodities and processed foods.     

Effects of gamma irradiation on fourth-instar Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae)

Effects of gamma irradiation on fourth-instar Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae) larvae in infested dates (Boufeggous variety) were assessed. Larvae were exposed to different gamma irradiation doses ranging from 300 to 900 Gy. Feeding, pupation, adult emergence and survival were very sensitive to ionizing irradiation. When irradiated at a dose of 300 Gy and higher, food consumption and weight gain were significantly affected, in a dose-dependent manner. Twenty days after irradiation, the weight loss at doses of 300, 450 and 600 Gy was 42%, 47% and 49%, respectively. At doses of 750 and 900 Gy, the weight of larvae diminished by 51% and 54%, respectively. In contrast, the controls gained 20% in weight. Development of larvae to the pupal stage was not prevented completely but none of the pupae emerged as adults. At 300 Gy, 21% of larvae survived 44 d after irradiation and successfully pupated. An absorbed dose of 450, 600, 750 or 900 Gy applied to larvae caused 100% mortality by 44, 38, 38 and 22 d post-treatment, respectively. The minimum dose required to prevent damage from feeding and adult emergence was 300 Gy while doses required to cause death were ?450 Gy.     

A simple wheat germ diet for studying the nutrient requirements of the Indian meal moth, Plodia interpunctella (Hübner)

Indian meal moth infestation of processed cereal products during storage could be managed with little or no use of conventional pesticides if there was a greater recognition and use of the moth's innate vulnerabilities. Slowing the growth rate of the infesting larvae is a simple strategy that can decrease the amount of damage and decrease the frequency of pesticide intervention. The growth rates of Indian meal moths on different cereal products varies widely indicating product-related differences in nutrient availability for the insects. Nutrient availability depends upon both the amounts of nutrients available in the cereal product and upon physical characteristics of the product that restrict the assimilation of nutrients.

The development of control strategies for protecting processed cereal products based upon nutrient availability requires a simple, palatable test diet of known composition. Wheat germ mixed with 30% glycerol (w/w) provides a suitable growth medium for the Indian meal moth whose nutrients have been largely identified and quantified. Our studies indicate that dietary glycerol augments Indian meal moth growth and development on wheat germ by moisturizing the diet and probably provides a source of carbon and energy for larval growth.     

Barrier property and penetration traces in packaging films against Plodia interpunctella (Hübner) larvae and Tribolium castaneum (Herbst) adults

The barrier property of different types of plastic film (with or without pinholes) against two insects, Plodia interpunctella (Hübner) larvae and Tribolium castaneum (Herbst) adults, and the morphology of damage produced in these insects were investigated. Using a penetration apparatus, four types of plastic films varying in thickness were used for insect-penetration tests: casted polypropylene, 20 μm and 25 μm (CPP20 and CPP25); oriented polypropylene, 20 μm and 30 μm (OPP20 and OPP30); linear low-density polyethylene, 40 μm and 50 μm (LLDPE40 and LLDPE50); and polyethylene terephthalate 12 μm and 16 μm (PET12 and PET16). After being fixed and tested in the penetration apparatus, each film was cut into a disc shape and 10 holes (200 μm diameter) were made by a pin. The shape of film damage and the mouthparts of insects were observed using scanning electronic microscopy. Plodia interpunctella larvae could penetrate all films with pinholes, while T. castaneum adults were unable to penetrate any of the films tested, even those with pinholes. The penetration-percentages by P. interpunctella larvae were 38% (LLDPE40), 3% (LLDPE), 53% (CPP20), 37% (CPP25), 63% (OPP20), 43% (OPP30), 83% (PET12) and 63% (PET16). The elongation value, tensile strength and thickness of film were important factors in the penetration test. LLDPE, which has the highest elongation value and the lowest tensile strength value, was the film that best protected against insect penetration. In CPP and LLDPE films, there were many scratches and tears around the holes. In comparison, much less damage was observed around the holes in OPP and PET films. By observing the mouthparts of insects, it was determined that P. interpunctella larvae had sharper mandibles than those of T. castaneum adults.     

Ultrasound affects spermatophore transfer, larval numbers, and larval weight of Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae)

Effects of ultrasound from a commercial device on reproduction in the Indianmeal moth, Plodia interpunctella (Hübner), were investigated in paired Plexiglas enclosures, one with ultrasound and one without (control treatment). In each of the five paired trials, 10 newly emerged male and 10 female moths were introduced into each enclosure. The commercial device produced peak frequencies at 21, 25, and 35 kHz, and a 94 dB sound pressure level at a distance of 50 cm. In enclosures with ultrasound, female moths had 27% fewer spermatophores and produced 48% fewer larvae than those not exposed to ultrasound. Furthermore, ultrasound reduced total and individual larval weights by 66% and 35%, respectively, when compared with the control treatment. About 17% more moths were found on the enclosure floor in the presence of ultrasound when compared with those not exposed to ultrasound. This is the first paper documenting the effects of ultrasound on reproductive performance of P. interpunctella. These laboratory data suggest that the use of ultrasound against P. interpunctella may be an appealing and effective behavioral management strategy.     

Mating disruption for control of Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae) in dried beans

We compared the impact of mating disruption and aerosol space treatment using synergized pyrethrins on Indianmeal moth Plodia interpunctella in 2200-2900 m³ structures at a dried bean storage and processing facility in Stanislaus County, CA USA. Mating disruption was applied using a high-volume aerosol timed release dispenser to apply 1.9 mg/d/100 m³ (Z,E)-9,12-tetradecyldienyl acetate (Z9,E12-14:Ac). Biological effects of mating disruption were compared between areas treated with mating disruption, aerosol space treatments, and an untreated part of the facility. The ability of males to orient to a pheromone source, to mate with calling females, and the fertility of resident females was examined using pheromone traps, sentinel females, and oviposition bait cups, respectively. Compared to an untreated area, males in pheromone traps and female mating were greatly reduced in both the aerosol space treatment and mating disruption treatment areas. After the second week of the study, P. interpunctella progeny were recovered from the untreated area and the aerosol space treatment area but not the mating disruption area, despite an active infestation in this area at the start of the study. An experiment examining development on the dried beans stored at this facility found variable development on broken beans, but generally poor development in intact beans. We conclude that the mating disruption treatment was as effective as the space treatment in suppressing population growth under the conditions at this facility, and discuss the potential for mating disruption using high-volume aerosol timed dispensers for phycitine moths in stored products.     

Effects of gamma irradiation on the development and reproduction of Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae)

The inhibitory effects of gamma irradiation were demonstrated on the development and reproduction including egg hatch, pupation, adult eclosion and oviposition of Plodia interpunctella. Failure of all these events increased with increasing doses from 0.1 to 1.0 kGy. However, the rates of developmental inhibition were different among three behavioral events. Egg hatch was almost completely inhibited by 0.5 kGy and higher doses. Pupation was completely inhibited by 0.25 kGy, but adult eclosion was not completely inhibited even by 1.0 kGy. In addition, different age groups within the egg and final larval stages differed in their susceptibility to 0.1 and 0.25 kGy doses; the rates of both hatching and pupation were lower when young individuals were irradiated. Fecundity and hatchability of eggs were greatly reduced when pupae were irradiated at 0.1 kGy and completely inhibited at 0.25 kGy and higher doses. This suggests that although some adults eclosed from pupae irradiated at 0.25 kGy and higher doses, they were not able to lay eggs. Our results suggest that irradiation at 0.5 kGy is appropriate for the inhibition of development and reproduction of P. interpunctella.     

Mass rearing of Habrobracon hebetor Say (Hymenoptera: Braconidae) on larvae of the Indian meal moth, Plodia interpunctella (Lepidoptera: Pyralidae): effects of host density, parasitoid density, and rearing containers

Habrobracon hebetor Say (Hymenoptera: Braconidae) is a larval ecto-parasitoid of several species of Lepidoptera in the family Pyralidae including the Indian meal moth, Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae), and other pyralid pests of post-harvest commodities and finished food products worldwide. Rearing methods for H. hebetor were investigated in a series of laboratory experiments designed to develop a mass rearing procedure for H. hebetor as a biological control agent against P. interpunctella and other stored products pyralid moths. The effects of parasitoid density, host density and the size of the rearing containers on adult progeny production and secondary sex ratio of H. hebetor were tested. In parasitoid density experiments, a density of eight male–female pairs of H. hebetor produced a higher number of progeny (188 adults) on 50 last-instar P. interpunctella larvae than the densities of one and two pairs of H. hebetor. Similarly, in a host density experiment, a density of 50 last-instar P. interpunctella larvae produced a significantly higher number of parasitoid progeny (160 adults) among the tested host densities when two pairs of H. hebetor were used. In experiments that assessed the size of the rearing containers, a glass jar with a volume of 236.6 ml (8 U.S. ounce “jelly jar”), produced a relatively higher number of parasitoid progeny (166 adults) than other sizes of containers when two pairs of H. hebetor were used. The parasitoid’s secondary sex ratio was female-biased in all experiments and there were no significant effects on sex ratio from variation in parasitoid density, host density, or size of the rearing containers.     

Methoprene and synergized pyrethrins as aerosol treatments to control Plodia interpunctella (Hübner), the Indian meal moth (Lepidoptera: Pyralidae)

Aerosol insecticides (also known as ULV or fogging treatments) delivered through an ultra-low-volume application system, are available commercially to control insect pests such as Plodia interpunctella Hübner, the Indian meal moth. However, little is known about the susceptibility of eggs of P. interpunctella to aerosol insecticides applied in active field sites. We conducted several trials by exposing eggs of P. interpunctella to synergized pyrethrins, alone and in combination with the insect growth regulator methoprene. Eggs in diets and packaging materials containing the food products were directly exposed to the aerosols. There was significant variation among the food products, as assessed by adult emergence from exposed eggs, but in general there was no difference in adult emergence from eggs exposed to a 1% versus a 3% pyrethrin formulation when methoprene was included. There was no difference in efficacy between diets and diet packages placed in open areas versus areas that were in some way obstructed to the aerosol. Adult emergence was generally reduced in the treatment combinations compared to untreated controls. A partial budget analysis indicated that the combination treatment of 1% pyrethrins + methoprene represented the lowest risk, lowest cost, and would seem to be the optimum combination. Results show that field applications of aerosols could be used to control P. interpunctella in storage facilities.     

Development, reproduction, and control of the Indian meal moth, Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae), in stored seed garlic in Mexico

Developmental time, fecundity, and egg hatch rate were determined for the Indian meal moth, Plodia interpunctella (Hübner), reared on fresh garlic seed at room temperature in Mexico. Duration of the egg stage averaged 4.7±0.8 days with an egg hatch rate ranging from 82% to 95%. Five larval instars were determined based on head-capsule width. Total larval developmental time from egg hatch to adult emergence ranged from 42 to 47 days. Adult females began to oviposit within 12-48 h after mating with the maximum oviposition rate occurring during the first 24 h after mating. The mean (±SE) number of eggs laid by females was 212±34 with a range of 117-303. Application of pirimiphos-methyl, malathion, and permethrin to 30 kg lots of garlic seed failed to prevent infestation and bulb damage by the larvae. However, compared with controls, the percentage of damaged bulbs and the number of larvae detected during 12 weeks of storage was smaller on garlic treated with four doses of pirimiphos-methyl.     

Cooking oils and “Triplex” in the control of Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae) in farm-stored maize

The uses of some cooking oils viz., noug oil, soybean oil, sunflower oil, corn oil and olive oil, and the reputedly non-toxic botanical “Triplex”, were evaluated against maize weevil, Sitophilus zeamais, in stored maize grain under local Ethiopian storage conditions in 2003. For comparison, an untreated sample and the synthetic insecticides, malathion 5% dust and Actellic 2% dust, at the recommended rates of 0.05% (w/w) were included. All the cooking oils tested had a significant toxic effect on the weevils in stored grains. The oil treatments showed significantly higher mortality of adult weevils at each sampling period compared with the untreated grains. The cooking oil treatments also significantly reduced weight loss and grain damage as compared with the untreated control. The Triplex treatment was of comparable effectiveness to the synthetic insecticides, causing high mortality of adult weevils, low-percentage grain damage and low-percentage weight losses. These promising oils and Triplex could be recommended for use as part of an integrated pest management program in stored maize, particularly at low levels of pest infestation and, in the case of cooking oils, for grain intended for home consumption.