Toxic and antifeedant action of nutmeg oil against Tribolium castaneum (Herbst) and Sitophilus zeamais Motsch

The essential oil extracted from nutmeg seeds using steam distillation was tested against the stored product insect pests, Tribolium castaneum (Herbst) and Sitophilus zeamais Motsch., for contact toxicity, fumigant toxicity and antifeedant activity. Filter paper impregnation was employed for contact and fumigant toxicity studies, whereas a flour disc bioassay was used to investigate antifeedant effects. Adults of S. zeamais were about ten times more susceptible than T. castaneum adults to contact action (LC₅₀ values of 1.7 mg/cm² and 18 mg/cm² respectively). However, S. zeamais adults were only 1.7 times more susceptible than T. castaneum adults to fumigant action (LC₅₀ values of 4.5 mg/cm² and 7.7 mg/cm² respectively). Furthermore, the larvae (10–16 days old) of T. castaneum were more susceptible than the adults, but the susceptibility of the larvae decreased with age. Nutmeg oil also significantly (P < 0.05) affected the hatching of T. castaneum eggs and the subsequent survival of the larvae in the concentration range 1.4–3.2 mg/cm². The production of F1 progeny of both T. castaneum and S. zeamais exposed to media treated with nutmeg oil was significantly (P < 0.05) reduced at all concentrations tested. F1 progeny production was totally suppressed at nutmeg oil concentrations of 1.05 g/100 g rice for T. castaneum and 0.35 g/100 g wheat for S. zeamais. Nutritional studies showed that nutmeg oil significantly (P < 0.05) affected the growth rate and food consumption of both insect species, depending on the concentrations used, but the antifeedant activity was more pronounced against S. zeamaisthan against T. castaneum. At 20 g nutmeg oil/100 ml, the feeding deterrence index of T. castaneum was only about 7%, whereas that of S. zeamaiswas 33%. These results suggest that nutmeg oil may be useful as a grain protectant with contact, fumigant and antifeedant activities against these insects.     

A male-produced aggregation pheromone in Tribolium brevicornis (LeConte) (Coleoptera: Tenebrionidae) and interspecific responses of several Tribolium species

Evidence for a male-produced aggregation pheromone in Tribolium brevicornis (LeConte) is reported. Methanol extracts of Tenax^®-trapped volatiles were attractive to both sexes in a Petri dish bioassay. Both sexes, 2–45 days old, responded to male odors. The minimum amount of male pheromone needed to elicit a response was 10⁻⁶ insect day equivalents. Tribolium destructor, T. audax, T. castaneum and T. confusum were attracted to male extracts of their own species. Tribolium brevicornis responded to male extracts from T. castaneum and T. confusum, however the latter two species did not respond to male extracts from T. brevicornis.     

Insecticidal action of Lantana camara against Callosobruchus chinensis (Coleoptera: Bruchidae)

Aerial parts of Lantana camara were investigated for their insecticidal, antiovipositional and antifeedant activity against Callosobruchus chinensis. Petroleum ether and methanol extracts of the plant showed 10–43% mortality at 1–5% concentrations. The extracts also showed complete feeding deterrent action at 5% concentrations. Loss of fecundity was also noticed in both the extracts at higher doses. The antiovipositional values were 30 mg/100 g for petroleum ether extract and 40 mg/100 g of seed for methanol extract.     

Some aspects of survival of starved adult Tribolium castaneum (Herbst)

Three experiments were carried out to investigate different aspects of survival of starved adult Tribolium castaneum Herbst. Survival of females was low when they were placed in medium 5–10 days before starvation, apparently because of oviposition activity. Heavier beetles of each sex survived more than lighter ones. Beetles starved for several days regained their initial weight when medium was made available. Inbred strains of T. castaneum survived less than outbred ones.     

Susceptibility of the saw-toothed grain beetle, Oryzaephilus surinamensis (L.), to gamma radiation

Gamma radiation was applied over the range of 25–125 Gy at five dose levels against 7–10-day-old adults of Oryzaephilus surinamensis, and the sterility and mortality effects were investigated. All experiments were carried out in incubators maintained at 27 ± 0.5 °C and 70 ± 5% relative humidity. The results obtained revealed that the percentage of adults surviving was dependent on the dose level. There were no beetles left alive and no progeny produced when adults were exposed to 125 Gy. LD₅₀ and LD_99.9values were determined to be 55.6 and 216.4 Gy respectively; the sterilizing dose levels (SD₅₀ and SD_99.9) were estimated to be 26.2 and 117.1 Gy respectively.     

Purification and characterization of a second aminopeptidase (pepC-like) from Lactobacillus delbrueckii subsp. bulgaricus B14

A second aminopeptidase was purified from cell-free extracts of Lactobacillus delbrueckii subsp. bulgaricus B14 by ammonium sulphate precipitation and two steps of anion-exchange chromatography. After SDS polyacrylamide-gel electrophoresis in the presence of β-mercaptoethanol, one protein band was detected at 54 kDa. The same molecular mass was estimated by gel filtration. SDS polyacrylamide-gel electrophoresis in the absence of β-mercaptoethanol resulted in a single band at 220 kDa, indicating that the enzyme forms complexes of four molecules under non-reducing conditions. Activity was markedly increased by reducing and metal-chelating agents. Thiol-group inhibitors, such as iodoacetic acid, inhibited the enzyme strongly. In contrast to Mg²⁺ and Ca²⁺, which had slightly activating effects, other divalent cations reduced enzyme activity at a concentration of 1 mM. The aminopeptidase showed highest activity at 50°C and pH 6·5–7 and hydrolyzed a wide range of di- and tripeptides. The most suitable substrates were Leu-Gly, Leu-Gly-Gly, Ala-Ala-Ala, and Met-Gly-Gly. For Leu-Gly and Leu-Gly-Gly, K_m-values of 1·81 mM and 2·17 mM and turnover numbers of 870 s⁻¹ were calculated, with a maximal rate of hydrolysis (V_max) of 4600 and 2780 μmol/min per mg of protein, respectively. The aminopeptidase did not cleave Lys-pNA, a substrate hydrolyzed by all type-‘N’ aminopeptidases from lactic acid bacteria with high velocities. It compared well, however, with pepC found in Lactococcus.     

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).     

Life history of Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae) at optimum conditions of temperature and humidity

At 32°C, 80% r.h. the mean egg, larval and pupal development periods of Prostephanus truncatus (Horn) were 4.86, 25.40 and 5.16 days, respectively. After a pre-oviposition period of 5–10 days, female adults laid most eggs at 15–20 days old and some continued to lay eggs for a further 70–80 days. Mean total egg production was 50 eggs per female and the maximum number of eggs laid in a 5-day period by a single female was 33. On average, 68.4% of all eggs were found inside damaged grains.

Mean adult longevity was 44.7 days for males and 61.1 days for females but these were not significantly different due to high variability in the data. P. truncatus was found to have a finite rate of natural increase (λ) of 1.399 per week and an infinite rate of increase (r) of 0.336 per week.     

Bioactivity of the essential oil extracted from Evodia rutaecarpa Hook f. et Thomas against the grain storage insects, Sitophilus zeamais Motsch. and Tribolium castaneum (Herbst)

The toxic, repellent and feeding deterrent activities of the essential oil extracted from Evodia rutaecarpa Hook f. et Thomas, were evaluated against Sitophilus zeamais adults and Tribolium castaneum larvae and adults. Contact toxicity assayed by topical application showed that S. zeamais adults were significantly more susceptible (LD₅₀=0.043 μg/mg body wt) to the essential oil than T. castaneum adults (LD₅₀=0.118 μg/mg body wt) and larvae (LD₅₀=0.093–0.126 μg/mg body wt). However, in the fumigation assays, S. zeamais (LC₅₀=41 μg/L air) was less susceptible to the essential oil than T. castaneum (LC₅₀=11.7 μg/L air). When compared with larvae of various ages, T. castaneum adults were more susceptible to the fumigant toxicity of the essential oil. Also, in the treated filter paper repellency test, the essential oil was more repellent to T. castaneum than to S. zeamais. A flour disk bioassay demonstrated that the essential oil of E. rutaecarpa had a weaker feeding deterrent action against T. castaneum adults than against T. castaneum larvae and S. zeamais adults. The reduction in growth rate of T. castaneum larvae and S. zeamais adults was mainly due to a behavioural (feeding deterrent) action rather than to post-ingestive toxicity of the oil.     

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.     

Bioactivity of five monoterpenoid vapours to Tribolium confusum (du Val) (Coleoptera: Tenebrionidae)

Five monoterpenoids (terpinen-4-ol, 1,8-cineole, linalool, R-(+)-limonene and geraniol) were tested in vapour form against different stages of Tribolium confusum. Terpinen-4-ol (with LC₅₀ values ranging between 1.1 and 109.4 μl/l air), (R)-(+)-limonene (with LC₅₀ values ranging between 4 and 278 μl/l air) and 1,8-cineole (with LC₅₀ values ranging between 3.5 and 466 μl/l air) were the most toxic to all stages tested, followed by linalool (with LC₅₀ values ranging between 8.6 and 183.5 μl/l air) while the least toxic monoterpenoid tested was geraniol with LC₅₀ values ranging between 607 and 1627 μl/l air. In all cases, except for geraniol, third-instar larvae were the most susceptible stage and 3-day-old eggs most tolerant. Apart from the observed direct toxicity, exposure of females to the vapours led in some cases to lower fecundity and egg hatchability. All monoterpenoids tested revealed insect growth regulator (IGR)-like properties when applied to 3-day-old pupae, producing adultoids and deformed adults.     

Olfactory and aggregation responses of Oryzaephilus surinamensis (L.) to extracts from oats

Rolled oats and pentane extracts of rolled oats were attractive to the adult Oryzaephilus surinamensis (L.) when tested in a Y-tube olfactometer. Pentane and ether extracts of rolled oats caused aggregation of these beetles when tested in a two-choice petri dish bioassay. Responses to crude extracts obtained by 3 different extraction methods were not significantly different, but responses to various concentrations of these extracts differed significantly. When beetles were starved for periods of 4–7 days, responses were significantly higher than for those starved 1–3 days. Differences in lighting (subdued lighting compared to darkness) did not affect results significantly, nor did variations in the time of day between 0900 and 1700 hr. Fraction-ation of oat extract by column chromatography yielded a number of active fractions whose activity was enhanced by subfractionation. The nature of active constituents from oats are discussed in terms of whether they are attractants or arrestants.     

The influence of wheat kernel damage upon the development and productivity of Oryzaephilus surinamensis (L.) (Coleoptera: Silvanidae)

The development and productivity of a British strain of Oryzaephilus surinamensis (L.) originally collected from wheat, and an Indian strain collected from rice, were studied at 25°C, 70% r.h. on kibbled wheat. Seven grades of the wheat cultivar “Flanders” were used: whole grains (minimal damage), five levels of kibbling with mean particle sizes of 3182.5 μm (grade 10) to 993.8 μm (grade 2), and wholemeal flour.

In both strains, the longest mean developmental period (0–1-day-old larva to adult) and highest mortality occurred on whole kernels. On all diets the Indian strain took, on average 2.6 days longer than the British strain. An increase in kernel damage from grade 8 (mean particle size of 2680.1 μm) did not significantly shorten development (27.3 days) or increase productivity of the Indian strain. For the British strain, development on grade 8 (25.8 days) did not significantly differ from that on all kibbled grades of wheat, including wholemeal flour. The productivity of the British strain did not differ significantly between the kibbled wheat grades and was considerably less than that of the Indian strain on all diets.

The results for both strains suggest that a minimum level of kernel damage is necessary for optimal development and productivity, and that further kibbling has little effect. This minimum level is considered to be that achieved by grade 8 kibbling.     

Thermal inactivation of lectins (PHA) isolated from Phaseolus vulgaris

The influence of the thermal process on the loss of ability to bind a carbohydrate target was studied on lectins (PHA) purified from Phaseolus vulgaris seeds. Thermal inactivation of aqueous solutions of pure PHA occurred according to a biphasic first-order mechanism, the thermodynamic parameters, at pH 7·3, being as follows: ΔH*₁ = ΔH*₂ = 86·2 kcal mole⁻¹, ΔS*₁ = − 54·04 cal deg⁻¹ and ΔS*₂ = − 56·71 cal deg⁻¹. The first-order rate constants appeared to be dependent on pH (minimal around 7) and divalent cations. All different subunits constituting the whole PHA were inactivated at the same rate. The biphasic nature of this process is independent of the presence of 10 m Ca⁺⁺ or Mg⁺⁺ and appeared to indicate a discrete aggregation of PHA molecules.     

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.     

Laboratory evaluation of the entomopathogenic fungus, Metarhizium anisopliae for the control of the groundnut bruchid, Caryedon serratus on groundnut

The pathogenicity of five isolates of Metarhizium anisopliae to adult Caryedon serratus was evaluated in the laboratory. All the isolates tested were virulent to the beetle but pathogenicity varied among the isolates. One isolate, CPD 4 was consistently superior to all other isolates in terms of mortality of the beetle, protection of groundnut pods from damage, reduction in progeny production and repellency to the beetle. At 10 days post-treatment, adult mortality treated with 0.1, 0.5 and 1.0 g of dry conidia equivalent to 3.6×10⁸, 1.8×10⁹ and 3.6×10⁹ conidia of isolate CPD 4 per 50 g of groundnut pods was 100% which did not differ significantly from pirimiphos-methyl-treated pods at 10 ppm. At the lowest dosage of 0.1 g of conidia per 50 g of pods, damage in pods protected with isolate CPD 4 was 5% which did not differ significantly from the 2% damage in pods protected by pirimiphos-methyl at 10 ppm but significantly differed from damage in untreated pods which was 26%. Isolate CPD 4 caused complete reduction in progeny emergence at all dosages tested. It also exhibited some degree of repellency to the beetle with percentage repellency values of between 40–79% at concentrations of 0.1–1.0 g of conidia per 50 g of groundnut pods. These combined virulence and repellency characteristics of this isolate may increase its protectant potential against C. serratus.     

Physicochemical changes occurring during post-harvest hardening of trifoliate yam (Dioscorea dumetorum) tubers

Processing of Dioscorea dumetorum tubers into flour could be a means of adding a longer-term value to this tropical plant with a high nutritional potential but which presents a post-harvest hardening problem. This study was carried out in order to investigate the effect of storage under prevailing tropical ambient conditions (19–28 °C, RH 60–85%) for 56 days on the physicochemical characteristics of flours produced from hardened tubers. With the exception of bulk density, the results showed that all the physicochemical properties measured (water absorption capacity, oil absorption capacity, water solubility index, hydrophilic–lipophilic index, swelling capacity and least gelatinising concentration) were significantly influenced by tuber storage time (P<0.05). In general, the physicochemical indices increased with storage in at least two phases, from days 2 to 21 and from days 28 to 56. Since sprouting of most tubers was observed after 28 days of storage, the results suggest that post-harvest hardening and sprouting influence the above-mentioned indices of flours produced from D. dumetorum tubers.     

Spectral analyses of fluorescences in dent maize infected with Aspergillus flavus and Aspergillus parasiticus

Bright greenish yellow (BGYF) and blue white (BWF) fluorescences were associated with Aspergillus flavus and A. parasiticus infected maize. The fluorescences were studied spectrofluorometrically, the BGYF exhibiting a peak wave length between 480–485 nm and the BWF between 440–445 nm. Neither fluorescence varied in maize stored under different moistures and temperatures.

BWF was similar spectrally to the fluorescence of the endosperm of sound kernels but × 5 20 more intense. The spectrum of BWF was similar to Aflatoxin G₁ or a mixture of aflatoxin B₁, B₂, G₁ and G₂ when they were spotted on endosperm tissue. A color reference for BGYF was similar in peak wave length to BGYF. Amsoy soybeans without the seed coat fluoresced with a peak 470–475 nm and the intensity was low compared to BGYF in maize. A fluorescence of maize kernels visually similar to BGYF but not associated with Aspergillus infection or aflatoxin contamination was also investigated. This “false BGY” fluorescence was spectrally similar to the BGYF in infected kernels.     

Olfactory response of Trogoderma granarium adults (Col., Dermest.) to odours of wheat, faeces and some faecal components

The response of Trogoderma granarium adults to the odours of wheat, faeces and some faecal components was studied. The binary-choice tests were performed at constant temperature and air humidity (33±0·5°C, 40–45 per cent r.h.) in darkness. Female beetles exhibited a very strong positive response to the untreated faecal odour, and a moderate response to the wheat odour. The response of males to both odours was low. The results obtained using ether extracts of faeces and/or wheat (1·5 mg of dry extract/ml of ether) were similar to those obtained with untreated odours. Tests with two fractions of faecal lipids show that the unsaponifiable fraction elicits little response from beetles of either sex; the fatty acid fraction elicits maximum response from the adults (66 per cent average female response, 20 per cent average male response).     

Evaluation of culture media for enrichment and isolation of Shigella sonnei and S. flexneri

The performance of Gram-negative (GN) broth with (10 μg/ml) and without novobiocin, Shigella broth (SB) with 0.5 and 3.0 μg/ml novobiocin, all incubated at 37 °C (SB with 3.0 μg/ml novobiocin also at 42 °C) and buffered brilliant green bile glucose (EE) broth with 1.0 μg/ml novobiocin incubated at 37 and 42 °C were evaluated for resuscitation and growth of Shigella sonnei and S. flexneri (eight strains; unstressed, chill-stressed and acid-stressed) and non-shigellae (11 strains). GN broth with or without novobiocin supported significantly less growth of Shigella sp. No significant differences in growth of shigellae were obtained between the other culture media. Performance depended more on the Shigella strain used. None of the tested media were significantly superior for suppressing the competitive flora.

Electivity and selectivity of MacConkey agar (MAC), tergitol-7 agar (T7), desoxycholate citrate agar (DCA), xylose lysine desoxycholate agar (XLD), Salmonella Shigella agar and Hektoen enteric agar (HEA) were determined by ecometric testing. HEA confirmed to be a high selective medium for both non-shigellae and stressed Shigella sp. Klebsiella sp., Enterobacter sp., Citrobacter sp., Salmonella sp. and the Escherichia strains can mask the presence of shigellae.

In vitro competition experiments and experiments with artificially contaminated foods showed higher resistance of S. sonnei than S. flexneri towards the stress imposed by the food matrix and its indigenous flora. Reliable detection, however, of shigellae in foods with the current enrichment and isolation media was not achieved.