Augmented release of Teretrius nigrescens Lewis (Coleoptera: Histeridae) for the control of Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae) in stored cassava chips

A trial was set up in northern Benin to evaluate the potential of Teretrius nigrescens to reduce the infestation and damage to cassava chips caused by storage insects. Cassava chips were stored for 5 months in mud silos and 50 adults of T. nigrescens were added when the stores were first filled. Stores where no predator was released were monitored as controls. The main storage insects observed were Prostephanus truncatus and Dinoderus spp. Initial chip weight varied between 102 and 246 g with no difference between treatments. Chip weight and number of holes on chips initially differed between treatments after 2 months of storage. After 3 months of storage, losses reached 40-50% without T. nigrescens and 30-40% when cassava chips were stored with T. nigrescens. A farmer can increase his profit by 1437 Fcfa/100 kg (1$=560 Fcfa, 1£=968 Fcfa; 1€=656 Fcfa, as on 2 December 2005) through the use of T. nigrescens because losses are reduced by 11%. Data analysis showed that there were significant differences (P<0.0001) between the two treatments for the number of holes, number of insects, weight of each chip as well as damage. There were twice as many P. truncatus and holes on chips in stores where T. nigrescens was not released. The addition of the predator to farmers’ stores is an economic option for controlling losses due to insects in cassava chips.     

The flight activity of Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae) and Teretrius nigrescens Lewis (Coleoptera: Histeridae) in Kenya

The invasive storage pest, the larger grain borer (LGB) Prostephanus truncatus (Horn), was introduced into the maize-deficit, semi-arid areas of the eastern region in Kenya in the early 1980s. In spite of containment efforts and the introduction of the predator Teretrius nigrescens Lewis from Mexico, LGB has spread to the main maize production zone in western Kenya during the past five years. The present work presents results from a 28-month monitoring effort of LGB and its predator, using pheromone traps at five locations along an east-west transect across Kenya. LGB occurred in all regions with highest trap catches in the high potential maize production zones in Western Kenya. T. nigrescens had not spread to western Kenya and trap catches were very low and mostly zero in Eastern Kenya, even in the area where it was released during the 1990s, suggesting that it became locally extinct after initial establishment. LGB flight activity was closely related to relative humidity, temperature and vapour pressure deficit. A model based on climatic factors accurately predicted seasonal trends of LGB flight behaviour in Kakamega and Mombasa but not in Kitale and Thika. It was concluded that models that rely on the direct effect of climate cannot predict LGB flight accurately enough to allow assessment of the impact of T. nigrescens on a regional basis. It is suggested that other factors such as the availability of stored grain and thus the indirect effect of climate via enhanced or reduced crop production play a major role in the flight activity of LGB and T. nigrescens.     

Partial characterization of a chymotrypsin-like protease in the larger grain borer (Prostephanus truncatus (Horn)) in relation to activity of Hyptis suaveolens (L.) trypsin inhibitor

Hyptis suaveolens trypsin inhibitor (HSTI) inhibits, in vitro, most of the trypsin-like serine proteases present in the gut of Prostephanus truncatus (Horn), the larger grain borer. In order to measure its in vivo effectiveness, different doses of the purified HSTI were incorporated into artificial seeds to measure their effects on the growth of P. truncatus larvae and pupae. Results showed that this protease inhibitor had no significant effect in vivo. Consequently, we investigated, identified, and partially characterized an inhibitor-insensitive protease that could explain the growth of P. truncatus on diet containing HSTI. This protease had an apparent molecular mass of 31 kDa, an optimum pH of 7.0, and an activity range extending from pH 6.0 to 8.0, which would allow activity in the gut of P. truncatus. This enzyme could be one of the physiological mechanisms in P. truncatus that allow the species to avoid the adverse effects of trypsin-like protease inhibitors present in the normal diet.     

Prey-specific contact kairomones exploited by adult and larval Teretrius nigrescens: A behavioural comparison across different stored-product pests and different pest substrates

Prostephanus truncatus is a serious exotic beetle pest of stored maize and cassava in Africa. Teretrius nigrescens is a classical biological control predator of this pest that was released into Africa in 1991. In previous work it was shown that adult T. nigrescens are arrested in the presence of dust and frass produced by P. truncatus feeding on maize, and both adult and larval T. nigrescens are arrested by solvent extracts of this dust/frass when presented on filter paper. The current study used these two complementary bioassay approaches to test crude dust/frass and then solvent extracts of the same materials. Results demonstrate that T. nigrescens adults are arrested more strongly by the dust/frass of P. truncatus than the dust/frass of six other beetle pests of stored grain. Similar behaviours are observed for responses of both adults and larvae to solvent extracts. However, extract of dust/frass from Sitophilus zeamais is repellent to adults and larvae of T. nigrescens. Collections of dust/frass from P. truncatus cultured on maize, cassava and an artificial maize substrate previously stripped of all hexane extractable compounds, are all shown to arrest adult T. nigrescens when presented in their crude form and to arrest both adults and larvae when presented as solvent extracts. These experiments demonstrate that P. truncatus produces a species-specific kairomone that is independent of the food or tunnelling substrate. Findings are discussed in the context of prey location, particularly in natural habitats.     

Resistance in maize to the Larger Grain Borer, Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae)

Host plant resistance in maize can be a useful component of Integrated Pest Management (IPM) of the Larger Grain Borer (LGB), Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae). The germplasm bank of the International Maize and Wheat Improvement Centre (CIMMYT) has more than 14,000 maize accessions from all over the world. In 1993, from the seed regeneration nursery of Caribbean land races, 105 land races were selected using good plant type as the criterion. When grains of these land races were infested with LGB in the laboratory, 19 showed resistance as evidenced by the low amount of powder (chewed uneaten maize plus feces) formed 140 days after the infestation. Through a series of infestation, selection and inbreeding (self-pollination of land races) over four generations, S₃ maize ears were generated. These ears showed a high level of resistance as indicated by a low powder production relative to the susceptible control. The LGB reproduction was adversely affected on resistant ears as indicated by the small size of adult populations. Thus, antibiosis could be the mechanism of resistance operating within the S₃ progenies of selected land races. Such sources of resistance can be very useful in developing maize populations/hybrids for use in IPM of LGB.     

Optimising pheromone lures and trapping methodology for Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae)

Male Prostephanus truncatus release an aggregation pheromone, attractive to both sexes, consisting of two components, Trunc-call 1 (T1) and Trunc-call 2 (T2). Synthetic T1 and T2 are used as the lure in flight traps to catch the beetle; the standard commercial lure is a polythene capsule loaded with 2 mg of 1:1 mixture of the compounds. However, laboratory comparison of 1:1 and 2:1 loadings showed that capsules with the higher T1 ratio release a blend that is closer to the mean natural ratio. Field testing of alternative weights and ratios of pheromone components demonstrated that capsules with the 2:1 mixture lured more beetles, improving catch by 17-29%. This improvement is probably not great enough to justify a change in practice for routine monitoring in situations where the presence of the pest is already well known. But there may be potential for adopting the new ratio in situations where higher trap sensitivity is required.The lures were supplied in sealed foil sachets and when they were first exposed a very high ‘flash-off’ of pheromone was observed. The flash-off was largely completed within 4 h of exposure and by 24 h pheromone output was more or less steady. For experimental studies comparing different treatments over short periods of time, it may be important to avoid testing during this flash-off period. In these circumstances, pheromone capsules should be aired for at least 1 day before being placed in traps.     

Effect of wood ash and conidia of Beauveria bassiana (Balsamo) Vuillemin on mortality of Prostephanus truncatus (Horn)

A series of experiments was carried out to investigate the effect of treating maize with wood ash and entomopathogenic fungus on the mortality of the larger grain borer Prostephanus truncatus. Jars of maize were treated with ash and/or conidia of Beauveria bassiana at doses of 0.0005, 0.005, 0.05 and 0.2 g conidia/g ash/100 g maize. Adult P. truncatus were placed on the maize and numbers of live and dead insects were assessed weekly.Ninety-five per cent mortality of P. truncatus was observed after 1 week and 100% mortality after 2 weeks in maize treated with the highest dose of conidia with ash (0.2 g/g). Mortality of P. truncatus in all ash with conidia treatments was significantly higher than untreated controls over a 4-week period, except the lowest dose of conidia at week 4. The three highest concentrations of conidia per gram of ash resulted in significantly (1% level) higher mortality of P. truncatus than ash alone.In an experiment to investigate the possible synergy of ash and conidia, there were no significant differences in mortality of P. truncatus between treatments with the same concentration of conidia regardless of whether the conidia were mixed with ash or applied alone. Larval populations of P. truncatus were observed in all treatments without ash, but only one larva was observed in one replicate of a treatment containing ash suggesting that ash has an important effect in preventing the establishment of a second generation of insects.     

Ability of naturally occurring parasitoids to suppress the introduced pest Prostephanus truncatus (Horn) (Coleoptera, Bostrichidae) in traditional maize stores in Togo

Beneficial parasitoids associated with traditional maize stores in southern Togo were collected during three storage seasons (1988–1990) at different sites to investigate their relationship to the introduced pest, Prostephanus truncatus. Two parasitoids, Anisopteromalus calandrae and Theocolax elegans were observed regularly and in higher numbers in the samples and were therefore studied for their relationship with P. truncatus. Correlation analysis of population densities observed in stores showed that correlation coefficients for numbers of both parasitoids and P. truncatus were mainly negative and very close to zero, but positive and greater in value for the parasitoids and Sitophilus zeamais. Glass jar trials were carried out with A. calandrae and T. elegans on loose maize. A. calandrae reduced numbers of P. truncatus by 70.1% in the single species culture after 8 weeks, whereas T. elegans had no impact. In double species culture A. calandrae had an effect on both populations; P. truncatus was reduced by 61.3% and S. zeamais by 22.5%. T. elegans only had an influence on S. zeamais.     

Laboratory studies on behavioural interactions of Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae) with conspecifics, synthetic pheromone and the predator Teretriosoma nigrescens (Lewes)(Coleoptera: Histeridae)

A bioassay method was devised to test the responses of adult Prostephanus truncatus (Horn) to conspecific adults or synthetic pheromone and to observe the response of the predator Teretriosoma nigrescens (Lewes) to adult or larval P. truncatus or the synthetic pheromone of this species.

The results confirmed earlier observations that male P. truncatus are the source of a pheromone attractive to both males and females, P. truncatus adults (in this case virgin females) are disinclined to leave food in response to the pheromone and maize itself is relatively unattractive to P. truncatus. For the first time it has been demonstrated that males are not attracted to females, females repel or avoid each other and males are less attracted to the naturally produced pheromone secretion than are females. In view of the fact that unmated females will not leave food to locate a calling male it was concluded that the female response to the pheromone is primarily a means of locating a food source, rather than a sexual partner. In contrast, males release their secretion to attract females.

When adult P. truncatus were tested against grains treated with the synthetic pheromone the response of males and females was apparently identical, in contrast to the lower response of males when tested against conspecific males. It seems probable that the amounts of pheromone used when testing the synthetic mixture are greater than would be produced naturally by a calling male and that this may mask the apparently lower sensitivity of males to the natural pheromone.

The pheromone of P. truncatus is known to be a kairomone for T. nigrescens, but in the bioassay this species was not attracted to synthetic pheromone and responded more strongly to empty maize grains than to adult or larval P. truncatus. It would appear that when walking, adult T. nigrescens are unwilling to approach closely to P. truncatus. The possible significance of this is discussed.     

Distribution of and association between the larger grain borer Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae) and the maize weevil Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae) in maize stores

Interspecific interactions between the larger grain borer Prostephanus truncatus and the maize weevil Sitophilus zeamais were studied during two storage seasons in maize stores, in Bénin. Maize ears, randomly sampled from farmers’ grain stores, were ‘reared out’, i.e., kept for 4 weeks under controlled conditions for F₁ to emerge, and periodically sampled, in order to examine colonisation patterns of P. truncatus and S. zeamais. For both storage seasons, P. truncatus and S. zeamais populations were sparsely aggregated and not associated with each other. The degree and strength of association increased with each monthly sampling occasion with the Ochiai, Jaccard and Dice indices of association. By the fourth sampling occasion, P. truncatus was found on most ears and on some ears in very high numbers (>300 insects). Almost all ears with P. truncatus contained at least a few S. zeamais individuals, but many ears with S. zeamais contained no P. truncatus.     

Analysis of free fatty acids in food substrates and in the dust and frass of stored-product pests: Potential for species discrimination?

The larger grain borer, Prostephanus truncatus, is a serious beetle pest that tunnels extensively to produce large quantities of dust and frass. The natural enemy Teretrius nigrescens is an important biological control beetle which is known to exploit at close-range solvent-extractable chemical cues in the dust and frass. The objective of the current study was to analyse quantitatively and qualitatively, the free fatty acid mixtures in different food-substrate materials both before and after insect attack by a range of stored-product pests in order to ascertain whether differences in these mixtures could explain the T. nigrescens selectivity to P. truncatus dust/frass over that of other species irrespective of food substrate. By TLC, GC and GC-MS we found triglyceride and five free fatty acids were the most abundant chemicals in dust/frass (palmitic acid (C16:0), stearic acid (C18:0), oleic acid (C18:1), linoleic acid (C18:2) and linolenic acid (C18:3)). In maize flour, Sitophilus species did not significantly change free fatty acid concentrations whereas with P. truncatus, Rhyzopertha dominica and Dinoderus minutus there were 4-6-fold increases, and, for Tribolium species there were over 20-fold increases. These differences provide interesting insights to tunnelling/feeding habits and are correlated with known feeding preferences within grain. Principal component analysis (PCA) demonstrated that free fatty acid ratios in dust/frass of different species are most linked to the food substrate and confer little discriminatory information that could be used to distinguish between the different species. Although increases in free fatty acid concentrations are good indicators of pest infestation and this may contribute behaviourally in an additive or synergistic way, we conclude that other chemical(s) are present and are key to T. nigrescens recognition of P. truncatus on different substrates.     

Protection of farm stored maize against infestation by Prostephanus truncatus (Horn) and Sitophilus species in Tanzania

Large scale trials were undertaken in Tanzania in order to assess the effectiveness of spray applications of insecticide as protectants of maize cobs against infestation by Prostephanus truncatus (Horn) and Sitophilus oryzae (L.) and S. zeamais Motsch. In general, protection of cobs was not as effective as the protection afforded to insecticide-treated grain. However, in simulated farm stores excellent protection was obtained either by applying permethrin as a dilute dust to grain or by applying it as a spray to cobs with sheathing leaves intect. Paddy husk ash also provided good protection when applied to maize grain. The treatment of maize cobs by spraying may provide the small scale farmer with a viable and more traditionally compatible alternative to the currently recommended practice of shelling maize and treating it with a dilute insecticide dust.     

Laboratory studies on predation by Teretriosoma nigrescens Lewis (Col.: Histeridae) on Prostephanus truncatus (Horn) (Col.: Bostrichidae) infesting maize cobs in the presence of other maize pests

Over 14 weeks at 27°C, 70% r.h., the mean rate of increase of three pairs of Prostephanus truncatus (Horn) was reduced by a factor of ten or four by the addition, after 3 or 6 weeks respectively, of four adult Teretriosoma nigrescens Lewis. The effect of the predator on Tribolium castaneum (Herbst) and Sitophilus zeamais Motschulsky populations was not as great: the mean rate of increase ofT. castaneum was approximately halved; and S. zeamais was not affected by the presence of the predator. T. castaneum had no significant effect on the numbers of P. truncatus or the numbers and predatory ability of T. nigrescens. Selective predation of P. truncatus by T. nigrescens did not encourage significant increases in populations of S. zeamais or T. castaneum.     

Infestation of maize cobs by Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae)—Aspects of biology and control

The initial attack and subsequent development of Prostephanus truncatus on maize cobs, with husk intact, was investigated at 27°C and 40, 50 and 70% r.h. The beetles showed a strong tendency to attempt infestation by first boring into the maize cob cores although they eventually gained access to the grain via the apex of the cob by walking between the grain and husk. At 50 and 70% r.h., the rate of oviposition over the first 2 wk was particularly high, while at 40% r.h. the rate was more or less constant. Some F₁ generation completed their development within 32–39 days at 50 and 70% r.h. and within 39–46 days at 40% r.h. Under all three moisture conditions, adult dispersal from the cobs was first detected at the end of the sixth week.

Estimates were made of the rate of increase of P. truncatus under each of the three moisture conditions. The population increased most rapidly at 70% r.h. and was at its peak between the eighth and twelfth weeks during which time grain damage and weight loss had effectively reached 100%. At 50% r.h., this stage was reached between the twelfth and sixteenth weeks while by this time at 40% r.h. the grain weight loss was only 40%.

Two novel techniques were tested for protecting maize cobs from infestation by P. truncatus. The exposed ends of maize cob cores were dipped into permethrin, 0.1% w/v aqueous dispersion or 0.5% w/w dilute dust, or untreated cobs were kept with permethrin-treated expanded-polystyrene blocks which acted as alternative refuges. Such treatments were examined at two beetle population densities. Dipping of the maize core was particularly effective in the prevention of infestation at low population density. This technique should be the subject of a field trial and if successful will offer important advantages over currently recommended control procedures.     

Fumigant properties of physical preparations from mountain big sagebrush, Artemisia tridentata Nutt. ssp. vaseyana (Rydb.) beetle for stored grain insects

Vapors released from foliage of mountain big sagebrush, Artemisia tridentata Nutt. ssp. vaseyana (Rydb.) Beetle, through a patented process, were hypothesized to have an insecticidal time of action (24 h or less after time of exposure) similar to the fumigant methyl bromide. Patented preparations were more effective from plants harvested from a relatively wet site in mid to late summer (5 July to 11 September). Bioassays with the lesser grain borer, Rhyzopertha dominica (F.), 0–3 days after adult emergence indicated an LT₅₀ of 7.0±1.2 h for the volatiles generated from only 30 mg dry processed plant material (=0.56 mg active ingredients) per ml headspace. Hatching of eggs of the Indian meal moth, Plodia interpunctella (Hübner), was completely suppressed when exposed 4–20 h after oviposition to a concentration of 7 mg processed plant material per ml headspace (=0.14 mg active ingredients) in a container that allowed passive diffusion and from which the terpenes disappeared by 48 h. Adult red flour beetle, Tribolium castaneum (Herbst), had an LT₅₀ of 40.7±1.2 h when exposed to 29 mg processed plant material per ml headspace. Gas chromatography/mass spectrometry (GC/MS) analyses of the headspace above this processed plant material revealed five major peaks, all non-chlorinated and non-brominated. The two main volatiles, 1,8-cineole and camphor, occurred initially in a mean ratio of 1:3.2, gradually shifting to 1:2.4 over 24 h. The μg/ml headspace of each detectable compound in a sealed container was followed intensely (0.25, 1, 2, 12, 24, 48, and 72 h) for 72 h and at less frequent intervals for 60 days. The active compounds released by the plant material in a closed, but not airtight container, were no longer detectable after 24 h based on GC/MS analysis. Fumigative studies with the same ratio of the two main compounds generated synthetically indicated that embryos of P. interpunctella and adults of R. dominica were as sensitive to the synthetic mixture as they were to the processed plant material. Although one could apply the precise commercial terpenes in the same ratio, the plant material provides a natural formulation that is conveniently diluted (formulated) to levels safe for handling. Therefore, this preparation method and plant material shows good potential as an alternative to methyl bromide for protection of stored grain, commodity, and space fumigations. No residues are detectable in the headspace of aerated commodity, milled product, or in fumigated space.     

The effect of grain stability on damage caused by Prostephanus truncatus (Horn) and three other beetle pests of stored maize

In an experiment where grain was presented to Prostephanus truncatus (Horn), Rhyzopertha dominica (F), Sitophilus zeamais Motsch, and Tribolium castaneum (Herbst) in four different ways, it was found that on simulated maize cobs P. truncatus caused much more damage than on loose maize, whereas the reverse was true for the other species. Damage was measured as percentage weight loss over a 6 week period, starting with adult beetles. It is suggested that such differences in the biology of the pests should be taken into account when investigating the inherent susceptibility to infestation of different maize varieties.     

The effect of sub-zero temperatures on different lifestages of Lasioderma serricorne (F.) and Ephestia elutella (Hübner)

The effect of sub-zero temperatures on different lifestages of Lasioderma serricorne and Ephestia elutella was investigated as a means of disinfesting stored tobacco. Eggs, unacclimated cocoons and acclimated cocoons of L. serricorne were exposed to −10 °C, −15 °C and −20 °C in insulated boxes. There was no adult emergence from eggs or unacclimated cocoons following exposure to the respective temperatures for 4 h, 2 h and 1 h. With acclimated cocoons there was no adult emergence after 2 h at −15 °C and 1 h at −20 °C, but at −10 °C, there was adult emergence after 8, 12 and 24 h exposures.In field-scale experiments, cold acclimated fourth-instar larvae of L. serricorne were inserted into cases of leaf tobacco and boxes of finished product, put into commercial freezers and exposed to minimum temperatures of −10 °C, −18 °C or −25 °C. Critical temperatures were measured at the core of the commodity. No adults emerged from the commodity when exposed to at least −18 °C for periods ranging between 3.75 h and 39.25 h or when exposed to at least −25 °C for between 2.4 h and 3.7 h. At a minimum of −10 °C, 3 live adults emerged after 24 h exposure.With E. elutella, diapausing larvae were inserted into small scale tobacco bales and exposed to −10 °C, −13 °C, −15 °C or −20 °C. No emergence of adults and no larval survival was achieved after 21 d, 3 d and 2 h exposure at −10 °C, −15 °C and −20 °C respectively. At −13 °C, there was no adult emergence after 2 and 5 d exposure, but live larvae remained after 24 weeks incubation at 25 °C.Minimum conditions of −18 °C for 24 h and −25 °C for 4 h are recommended for the control of L. serricorne and −20 °C for 24 h for the control of E. elutella in stored tobacco (to fit with operational logistics).     

Determining thermotolerance of fifth-instar Cydia pomonella (L.) (Lepidoptera: Tortricidae) and Amyelois transitella (Walker) (Lepidoptera: Pyralidae) by three different methods

Thermotolerances of codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae), and navel orangeworm, Amyelois transitella (Walker) (Lepidoptera: Pyralidae), were determined using two water-immersion methods and one dry-heat method. The two water-immersion methods were: 1) directly immersing screen tubes containing test insects in hot water (direct immersion method) and 2) immersing in hot water solid copper tubes containing insects submerged in tap water (tube immersion method). The dry heating method involved heating insects in computer-controlled heating blocks (heating block system, or HBS). Each test insect was treated at three temperature-time combinations and exposures were adjusted so that each method received the same equivalent accumulated lethal time. In five of the six tests, the HBS provided the lowest mean insect mortality among the three methods, although no statistically significant differences were observed between the direct immersion and the HBS methods. The mean insect mortality obtained with the tube immersion method was significantly higher than that from the direct immersion method and the HBS in four and three of the six temperature-time combinations, respectively. When compared with the two water-immersion methods, the HBS method yielded lower mortality data with less variation at the same mortality level, resulting in more conservative treatment recommendations.     

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.     

Proteomic assessment of resistance to the fumigant phosphine in the lesser grain borer, Rhyzopertha dominica (F.)

A previous publication compared a strain of the stored-grain pest beetle, Rhyzopertha dominica, resistant to the fumigant phosphine, with a susceptible strain using two-dimensional polyacrylamide gel electrophoresis. Certain proteins appeared to differ and the authors proposed that arginine kinase in particular might be used as a marker for the rapid monitoring of resistance in this species and other pests of stored grain. Here an expanded set of susceptible and resistant strains is surveyed using the two-dimensional fluorescence difference gel electrophoresis (2D-DIGE) system. Of hundreds of spots only two showed a significant difference between the resistant and susceptible strains and the magnitudes of those differences were less than three-fold. Arginine kinase spots were identified but they did not differ significantly. The proposal that certain abundant proteins of R. dominica might be used as markers of phosphine resistance was not supported by the present study.