Influence of larval diapause on male response to female sex pheromone in Trogoderma granarium, Everts (Coleoptera: Dermestidae)

A study was made of the influence of temperature-induced larval diapause on the response of adult male Trogoderma granarium Everts to female sex pheromone. With increase in time the larvae remained under diapause, post-diapause males showed progressively reduced attraction to the pheromone source. This reduction in male response was associated with an increase in the threshold concentration of the pheromone required for the arousal behaviour.     

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.     

Toxic and antifeedant activities of potato glycoalkaloids against Trogoderma granarium (Coleoptera: Dermestidae)

The total glycoalkaloid fraction (TGA) and the two glycoalkaloids, α-chaconine and α-solanine of potato, Solanum tuberosum, were isolated. Their toxic and antifeedant activities against the Khapra beetle, Trogoderma granarium Everts were investigated. Results indicated considerable toxicity, especially when adults were topically treated with the glycoalkaloids. The TGA fraction was the most toxic with LC₅₀’s of 16.7 and 11.9 μg/mg insect, 48 and 96 h post treatment, respectively. LC₅₀’s of α-chaconine and α-solanine 96 h post treatment were 18.1 and 22.5 μg/mg insect, respectively. Moderate toxicities were recorded when insects were confined on dry-film residues of botanicals with LC₅₀’s ranging between 26.1 and 56.6, and 19.4 and 45.7, μg/cm² 48 and 96 h post treatment, respectively. Nutritional studies using the flour disc bioassay revealed significant reduction in the growth rate (RGR), food consumption rate (RCR) and food utilization (ECI) by T. granarium at concentrations ranging between 20 and 30 mg g⁻¹ food with feeding deterrent indices reaching 82.4% with the TGA fraction. When tested as binary or crude alkaloidal mixtures, toxic and antifeedant activities of glycoalkaloids were increased, indicating some additive interaction among these botanicals. There is potential for use of such compounds to protect stored grains from insect infestation.     

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

Several developmental stages of a laboratory strain of Trogoderma granarium Everts were subjected to an atmosphere of 60% carbon dioxide (CO₂) in air at 20 or 30°C and 60% r.h. for varying lengths of time. The eggs, pupae and adults all died within 6 days, but some larvae survived for 16 days or more at both temperatures. Larvae were then exposed at 45, 60 and 75% r.h. to 45, 60 or 75% CO₂ in air at 20 or 30°C and additionally to 30% CO₂ in air at 30°C. Mortality increased with CO₂ concentration and temperature. However, only when a CO₂ concentration of 75% at 30°C was applied did all larvae die and, even then, a 15-day exposure was required. Some survival occurred after 18 days in all other conditions. Exposure times of 10 days or less, at temperatures of 20°C or above, have been recommended for use with high CO₂ atmospheres for the control of stored products pests but this investigation shows that these may be inadequate if T. granarium is present.     

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.     

Selective breeding for reduced male response to female sex pheromone in Trogoderma granarium Everts (Coleoptera: Dermestidae)

Through selective screening and breeding, a population of the Trogoderma granarium Everts with reduced male response to the female sex pheromone was isolated. In the eighteenth generation of selection, male response was reduced by 74%, and there was a 5-fold increase in the pheromone concentration required for maximal attraction. Quantitative and qualitative changes in the pheromone secreted by females of the selected population were indicated also.     

Distribution and establishment of Trogoderma granarium everts (Coleoptera: Dermestidae): Climatic and other influences

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

Laboratory determination of the requirements for control of Trogoderma variabile (Coleoptera: Dermestidae) by heat

The use of heat to disinfest storage structures (the bake-out technique) is enjoying a resurgence of interest because it represents a possible replacement for whole structure fumigation with methyl bromide. This technique uses moderately elevated temperatures typically in the range 50-60°C, over a period of hours to days. The objective of this work was to determine the basic requirements to control Trogoderma variabile using heat so that effective bake-out procedures could be developed. The most heat-tolerant stage of T. variabile was shown to be the full-grown larva and it requires 36.4°C-min above the threshold of 49.4°C to achieve 99% mortality. Thus the temperatures used in a practical bake-out should be as high as the other constraints will allow, and maintained somewhat longer than data for other species would suggest. In so doing, a control procedure aimed at T. variabile would be expected to control all other species present.     

Nutritional behaviour of Trogoderma granarium Everts (Coleoptera: Dermestidae) on leguminous seeds

To make out the nature of dietary deficiencies of pulses for Trogoderma granarium, brewer's yeast was added in different proportions. Additions resulted in no improvement of the dietary values of green gram (Phaseolus aureus Roxb.), black gram (P. mungo L.), Bengal gram (Cicer arietinum L.), kabuli gram (C. arietinum L.) and cowpea (Vigna sinensis Savi.). But in soybean (Glycine max Merr.) or lentil (Lens esculenta Moench.) addition of yeast gave higher adult populations. In French bean (P. vulgaris L.) with or without yeast no adults were formed. Yeast alone proved to be a poor food, but with glucose the growth of insects improved significantly. The addition of cholesterol to lentil, or glucose to French bean greatly increased their food value. This indicated that lentil was qualitatively and/or quantitatively deficient in sterol, but the poor food value of French bean was due to the presence of non-utilizable carbohydrates in the seeds.     

Digestive proteolytic and amylolytic activities in Trogoderma granarium Everts (Dermestidae: Coleoptera)

The Khapra beetle, Trogoderma granarium is a serious post-harvest pest of wheat. Digestive proteinase and amylase activities of larvae and adult insects were investigated using general and specific substrates and inhibitors. Gut pH in larvae was determined to be slightly acidic in the midgut and more acidic in the hindgut. However, midgut extracts from larvae showed an optimum activity for proteolysis against azocasein and haemoglobin at alkaline pH (broad optimum in the range 8–11). Proteinase extracted from larval guts hydrolyzed the synthetic substrates BApNA(N–benzoyl–L–arginine–p–nitroanilide) and SAAPPpNA (N–succinyl–alanine–alanine–proline–phenylalanine–p–nitroanilide) for trypsin- and chymotrypsin-like activities, respectively. The specific substrate for elastase-like activity SAAApNA (N–succinyl–alanine–alanine–alanine–p–nitroanilide) was not hydrolyzed by midgut extract of larvae. The most effective inhibitors of azocaseinolytic hydrolysis were trypsin and chymotrypsin-like serine proteinase inhibitors. Casein zymogram analysis revealed at least six proteinase bands in the larval midgut extract and showed the presence of trypsin-like serine proteinases. No cysteine proteinases were detected in larval midgut extract using specific cysteine proteinase substrates, inhibitors and activators. Carboxypeptidase A activity also was detected in larval midgut extract using FAPP(N-(3-(2-furyl) acryloyl)-l-phenylalanyl-l-phenylalanine) and showed optimal activity at alkaline pH. Activity of -amylase using starch as substrate, was determined to be maximal around neutral pH (pH 6–8), which is correlated with the pH prevailing in the midgut. No proteolytic and amylolytic activities were detected using conventional substrates in the digestive system of the adult suggesting no significant protein and carbohydrate digestion occurs in the adult beetle which does not need to feed.     

Development of the khapra beetle, Trogoderma granarium, in the lower part of its temperature range

The lower temperature limit for breeding of the khapra beetle, Trogoderma granarium, was determined at constant temperatures in the laboratory. The length of female adult life, oviposition, egg incubation period and duration of larval plus pupal development were observed at 25, 22.5, 20 and 17.2 °C, respectively, at 70% r.h. The results show that breeding is slow at 25°, very slow at 22.5° and populations decline at 20 °C and below. Thus cooling of produce to 20 °C and retention at or below this temperature is a sound, safe, environmental friendly method for control of this pest. For newly dried malted barley, the results indicate that cooling to 25 °C would be sufficient to prevent T. granarium populations from reaching levels of economic importance.     

Lindane resistance in Dermestes maculatus Deg. (Coleoptera: Dermestidae)

A discriminating dose test technique has been developed for the detection of lindane resistance in strains of Dermestes maculatus Deg. Using susceptible strains and a laboratory-induced resistant strain as standards, resistance to lindane was found in 12 out of 15 strains of D. maculatus tested. These were laboratory strains from Australia, the U.S.A., the Gambia and the United Kingdom, and strains found on cargoes imported into the United Kingdom from Africa, India, Pakistan, the Lebanon, the U.S.A. and Hong Kong.     

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.     

Effect of temperature and humidity on the biology of Attagenus fasciatus (Thunberg) (Coleoptera: Dermestidae)

The effect of temperature and relative humidity (r.h.) on the biology of the carpet beetle Attagenus fasciatus was studied under laboratory conditions. The influence of two temperatures (30 °C and 35 °C) and three humidities (40, 60 and 80% r.h.) on the number, duration, mortality and pupation of larval instars, as well as on the biology of fed and starved adult beetles, was investigated. Attagenus fasciatus larvae were reared on dried milk. The mean duration of each successive larval instar generally increased slightly but there was much fluctuation, particularly for the later instars. The highest mortality was recorded during the first two or three instars. At 30 °C pupal duration decreased with increasing r.h. while at 35 °C there was a slight increase. However, the duration at 35 °C was always shorter than at 30 °C. There was 100% emergence of adults from pupae under all test conditions except 40 and 60% r.h. at 35 °C where it fell to about 90%. Humidity and starvation strongly affected egg hatchability under all conditions tested. At 35 °C, eggs took less time to hatch than at 30 °C and there was a positive correlation between egg duration and r.h. The duration of the egg stage was longer for eggs of starved females than those of fed ones. Adult longevity was longer at higher humidity, females lived longer than males and unmated beetles lived longer than mated ones. Starvation reduced adult longevity in all cases. The sex ratio was male biased at 30 °C except at 80% r.h. but the reverse was true at 35 °C.     

Some aspects of the biology of Dermestes maculatus Degeer (Coleoptera,Dermestidae) in dried fish

The development of Dermestes maculatus Deg. in dried fish has been studied under uncontrolled laboratory conditions. Females laid eggs within 12 hr of copulation, and oviposition was improved by the presence of free water. Hatching occurred about 48 hr after oviposition. The characteristic appearance of the egg and the changes that occurred during incubation and hatching are described. Larval development was completed in 33·5 days during which seven moults occurred and a body length of 14 mm was attained. Larval life was prolonged by crowding. When intact pieces of fish were available, the last instar larva bored into one of them and pupated within the hardened larval skin, but when ground fish was provided, a quiescent prepupal stage was observed. The adult emerged about 11 days after the last instar larval stage, irrespective of the mode of pupation.     

Effect of low pressure on the survival of Trogoderma granarium Everts, Lasioderma serricorne (F.) and Oryzaephilus surinamensis (L.) at 30 °C

The effects of low pressure (50 mm Hg) and various exposure times were studied on the mortality of three important storage pest insects at 30 °C as 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. Insects were exposed within test chambers containing cocoa beans with a moisture content in equilibrium with 55% relative humidity and at a constant temperature of 30 °C. Three insect species were used: Trogoderma granarium, Lasioderma serricorne and Oryzaephilus surinamensis. At 50±5 mm Hg and 30 °C, the egg was the most resistant stage in all three species at the LT₉₉ level, times needed to obtain 99% mortality being 46, 91 and 32 h, respectively. Adults of T. granarium and L. serricorne, and pupae of O. surinamensis were most susceptible. These results widen the database established to kill insects at low pressure within the framework of practical exposure times and commercially available equipment, in order to provide an effective alternative to fumigation.     

Factor inhibiting growth of Trogoderma granarium Everts (Coleoptera: Dermestidae) in lentil and French bean: Suppression by addition of natural diets

It is demonstrated that wheat flour suppresses the activity of inhibitors and increases the dietary efficiency of lentil (Lens esculenta Moench.) and French bean (Phaseolus vulgaris L.) for Trogoderma granarium Everts. This antagonism of the inhibitory activity is less marked in green gram (P. aureus Roxb.) and least in semisynthetic glucose-brewer's yeast mixture. Such inhibition of the antagonistic property of natural foods has not been demonstrated before in insects.     

Insecticidal and antifeedant activities of medicinal plant extracts against Attagenus unicolor japonicus (Coleoptera: Dermestidae)

Methanol extracts from 28 medicinal plant species were tested for their insecticidal and antifeedant activities against Attagenus unicolor japonicus larvae by using a fabric-piece bioassay. Responses varied according to plant species, dose, and exposure time. Methanol extract of Allium sativum bulb gave 93% mortality at 5.2 mg/cm² 7 days after treatment (DAT). Eugenia caryophyllata bud extract produced 100% mortality at 2.6 mg/cm² 14 DAT and 90% mortality at 1.3 mg/cm² 21 DAT. Foeniculum vulgare fruit extract gave 67% and 100% mortality at 5.2 mg/cm² 21 and 28 DAT, respectively. Methanol extracts of Angelica dahurica root, Lysimachia davurica whole plant, and Nardostachys chinensis rhizome exhibited complete antifeedant activity at 1.3 mg/cm² over a 30-day period. The plant extracts described merit further study as potential insecticidal or antifeedant agents against A. unicolor japonicus.