The effects of the presence of stored product pests on the microfauna of a flour community

Optimization of a cultivation procedure to selectively isolate lactic acid bacteria from insects

AIMS

Natural niches and transmission routes of lactic acid bacteria (LAB) are highly versatile. Proposed routes of transmission to food fermentations are from plant material via insects or vice versa. This study aimed to establish a method for the selective isolation of LAB from insects.

METHODS AND RESULTS

Varied parameters that influence growth and selectivity are temperature, type of carbohydrate and atmosphere. Additionally, effects of antibiotics to suppress non-LAB species were evaluated. A model consortium consisting of 12 species representing different lifestyles was inoculated in growth medium to identify conditions for highest diversity and recovery rate. The method was applied to isolate LAB from Drosophila melanogaster, Sitotroga cerealella, Tribolium castaneum and Tenebrio molitor. Isolated species were Leuconostoc mesenteroides, Paucilactobacillus vaccinostercus and Lactiplantibacillus plantarum from D. melanogaster and L. mesenteroides, Pediococcus pentosaceus and Latilactobacillus curvatus from T. molitor. No LAB could be isolated from T. castaneum and S. cerealella. 16S rDNA amplicon sequencing of DNA obtained from insects corroborated part of our results.

CONCLUSION

A combination of different enrichment conditions ensures a high probability to isolate LAB species from insects and can be helpful above already known non-cultivation methods.

SIGNIFICANCE AND IMPACT OF THE STUDY

The novel method allows to selectively isolate LAB from insects and the strategy of the method is of interest to study other niches.

Biology, Ecology, and Control of Lasioderma serricorne (F.) (Coleoptera: Anobiidae): A Review

The cigarette beetle, Lasioderma serricorne(F.) (Coleoptera: Anobiidae), is an important pest in the food and tobacco industry in many regions of the world. Despite a great deal of research, control of this pest still relies on the use of phosphine fumigation, which is becoming less effective as the insect develops resistance to this compound. In addition, series of other nonchemical methods used to control the insect have given mixed and irregular results. This review summarizes and discusses information on important aspects of the biology and ecology of the cigarette beetle, and its control. The topics covered include a taxonomic discussion of the cigarette beetle, which includes a discussion of other anobiid species of economic importance. The mating behavior of the insect and conditions favorable for pest development were described. The review also includes a discussion of the life stages of the insect, its feeding habit, and economic damage. Important aspects of its chemical ecology and a discussion on the association between this species and its microorganisms, and major natural enemies, were presented. A summary of its flight behavior, including the factors governing flight initiation and temporal and seasonal flight activity were reviewed. Finally, the control methods currently used in the management of the insect were described. The review also identifies potential areas of further research on L. serricorne and gives an analysis of the control methods worthy of further investigation in the search for practical and sustainable methods for the management of this pest.

Social cues trigger differential immune investment strategies in a non-social insect, Tenebrio molitor

Social immunization (SI) is a horizontal transfer of immunity that protects naive hosts against infection following exposure to infected nestmates. While mainly documented in eusocial insects, non-social species also share similar ecological features which favour the development of group-level immunity. Here, we investigate SI in Tenebrio molitor by pairing naive females with a pathogen-challenged conspecific for 72 h before measuring a series of immune and fitness traits. We found no evidence for SI, as beetles who cohabited with a live pathogen-challenged conspecific were not better protected against bacterial challenge. However, exposure to a heat-killed-bacteria-challenged conspecific appeared to increase pathogen tolerance, which manifested in differential fitness investment. Our results together suggest that T. molitor do respond to immune-related cues in the social environment, despite not showing a classic immunization response as predicted.

Health Hazards Associated with Arthropod Infestation of Stored Products

Insects and mites are common inhabitants and accidental invaders of food, including durable commodities, and their presence can have both direct and indirect effects on human health. The most common direct effect is contamination of food with arthropod fragments and related contaminants, which may be allergenic or even carcinogenic. The most important indirect effect is that their presence can change the storage microenvironment, making durable products suitable for the rapid development of fungi and other microorganisms. Some of these fungi can produce toxins (e.g., aflatoxins) that endanger human health. Insects may actively or passively contribute to the spread of microorganisms, increasing product contamination, and they may host bacteria that have developed antibiotic resistance, contributing to their spread in food. Several species also may host, attract, or transmit tapeworms, predators, or parasitoids that may affect health. This review synthesizes research on these topics and suggests directions for future research.

Endogenous egg immune defenses in the yellow mealworm beetle (Tenebrio molitor)

In order to survive microbe encounters, insects rely on both physical barriers as well as local and systemic immune responses. Most research focusses on adult or larval defenses however, whereas insect eggs are also in need of protection. Lately, the defense of eggs against microbes has received an increasing amount of attention, be it through endogenous egg defenses, trans-generational immune priming (TGIP) or parental investment. Here we studied the endogenous immune response in eggs and adults of Tenebrio molitor. We show that many immune genes are induced in both adults and eggs. Furthermore, we show that eggs reach comparable levels of immune gene expression as adults. These findings show that the eggs of Tenebrio are capable of an impressive endogenous immune response, and indicate that such inducible egg defenses are likely common in insects.

Detection and identification of species-specific bacteria associated with synanthropic mites

Internal bacterial communities of synanthropic mites Acarus siro, Dermatophagoides farinae, Lepidoglyphus destructor, and Tyrophagus putrescentiae (Acari: Astigmata) were analyzed by culturing and culture-independent approaches from specimens obtained from laboratory colonies. Homogenates of surface-sterilized mites were used for cultivation on non-selective agar and DNA extraction. Isolated bacteria were identified by sequencing of the 16S rRNA gene. PCR amplified 16S rRNA genes were analyzed by terminal restriction fragment length polymorphism analysis (T-RFLP) and cloning sequencing. Fluorescence in situ hybridization using universal bacterial probes was used for direct bacterial localization. T-RFLP analysis of 16S rRNA gene revealed distinct species-specific bacterial communities. The results were further confirmed by cloning and sequencing (284 clones). L. destructor and D. farinae showed more diverse communities then A. siro and T. putrescentiae. In the cultivated part of the community, the mean CFUs from four mite species ranged from 5.2 × 10(2) to 1.4 × 10(3) per mite. D. farinae had significantly higher CFUs than the other species. Bacteria were located in the digestive and reproductive tract, parenchymatical tissue, and in bacteriocytes. Among the clones, Bartonella-like bacteria occurring in A. siro and T. putresecentiae represented a distinct group related to Bartonellaceae and to Bartonella-like symbionts of ants. The clones of high similarity to Xenorhabdus cabanillasii were found in L. destructor and D. farinae, and one clone related to Photorhabdus temperata in A. siro. Members of Sphingobacteriales cloned from D. farinae and A. siro clustered with the sequences of "Candidatus Cardinium hertigii" and as a separate novel cluster.

Stored-product insects carry antibiotic-resistant and potentially virulent enterococci

A total of 154 enterococcal isolates from 95 stored-product insects collected from a feed mill, a grain storage silo, and a retail store were isolated and identified to the species level using PCR. Enterococcus casseliflavus represented 51% of the total isolates, followed by Enterococcus gallinarum (24%), Enterococcus faecium (14%), Enterococcus faecalis (7%), and Enterococcus hirae (5%). Many isolates were resistant to tetracycline (48%), followed by streptomycin (21%), erythromycin (14%), kanamycin (13%), ciprofloxacin (12%), ampicillin (4%), and chloramphenicol (<1%). Enterococci carried genes coding for virulence factors, including the gelatinase gene gelE (26% of isolates), an enterococcal surface protein gene esp (1%), and the cytolysin gene cylA (2%). An aggregation substance (asa1) gene was detected in six out of 10 E. faecalis isolates and five of these were positive for the aggregation substance. Enterococci were positive for hemolytic (57% of isolates) and gelatinolytic (23%) activity. The filter-mating assay showed that the tetracycline resistance gene, tetM, was transferable among E. faecalis by conjugation. These data demonstrated that stored-product insects can serve as potential vectors in disseminating antibiotic-resistant and potentially virulent enterococci.

Survival of Enterococcus faecalis OG1RF:pCF10 in poultry and cattle feed: vector competence of the red flour beetle, Tribolium castaneum (Herbst)

Laboratory experiments were designed to determine the survival of Enterococcus faecalis OG1RF:pCF10 in poultry and cattle feed and its acquisition and transmission by adults of the red flour beetle, Tribolium castaneum (Herbst), to sterile feed. Adult T. castaneum beetles were introduced into poultry and cattle feed inoculated with E. faecalis OG1RF:pCF10 and incubated at 28 degrees C with 65% relative humidity for 7 days in a growth chamber. E. faecalis survived in both poultry and cattle feed during the 7-day test period. There was a logarithmic decrease in E. faecalis concentration in poultry and cattle feed and in and on the insects. E. faecalis persisted on the surface and within T. castaneum adults for 7 days when adults were released on E. faecalis-inoculated poultry feed and for only 5 days on E. faecalis-inoculated cattle feed. The concentration of E. faecalis decreased more slowly on poultry feed than on cattle feed, and this may explain why adult T. castaneum insects were more successful in acquiring and transferring E. faecalis from inoculated poultry feed to sterile poultry feed during the 7-day test period. However, T. castaneum adults reared on inoculated cattle feed were unable to contaminate sterile cattle feed on day 7. To our knowledge, this is the first report documenting T. castaneum to successfully acquire antibiotic-resistant enterococci from animal feed and transfer them to sterile feed. Management of T. castaneum through effective integrated pest management program is therefore important to prevent the spread of antibiotic-resistant and virulent enterococci in animal feed and feed manufacturing environments.

The Effects of a Naturally Produced Benzoquinone on Microbes Common to Flour

Many species of insects are known to produce and secrete benzoquinone derivatives. These compounds are usually defined as "defense chemicals." However, in many cases, it has not been determined what the chemicals are meant to defend against. Tribolium beetles produce up to three benzoquinones, but their specific function is not known. In this experiment, one of the derivatives, methyl-1,4-benzoquinone (MBQ) was tested for its effectiveness for one of its purported functions as an antimicrobial. Methyl-1,4-benzoquinone was added in three concentrations (0.3, 30, and 150 microg/ml) to the liquid media of three species of Bacillus bacteria and eight species from four genera of yeasts, and the effect on their growth was monitored. The presence of MBQ altered growth in all species. The bacteria responded more negatively than the yeasts. All bacteria species showed reduced growth at all levels of MBQ. Yeasts were more tolerant to the presence of the chemical, and two species, Saccharomyces microellipsoides and Pichia burtonii, actually showed increased growth at the lowest level of MBQ.