A mathematical model for supermarket location problem with stochastic station demands

This paper aims to investigate the effect of station demands variations on supermarket location problem (SLP). This problem arises in the real-world assembly line part feeding (PF) context where supermarkets are used as the intermediate storage areas for stations. To this purpose a stochastic SLP model is developed to optimize the total cost of PF in terms of shipment, inventory and installation costs. The computational results over a real case as well as different test instances verify that the station demands variation has an effect on the SLP solutions.CC BY-NC-ND 4.0</p

The Effects of Nutrient Concentration, Addition of Thickeners, and Agitation Speed on Liquid Fermentation of Steinernema feltiae

Entomopathogenic nematode production in liquid fermentation still requires improvements to maximize efficiency, yield, and nematode quality. Therefore, this study was aimed at developing a more suitable liquid medium for mass production of Steinernema feltiae, by assessing the effects of nutrient concentration, thickeners (primarily agar), and agitation speed on infective juvenile (IJ) yield. Base medium (BM) contained yeast extract (2.3%), egg yolk (1.25%), NaCl (0.5%), and corn oil (4%). All media were inoculated with Xenorhabdus bovienii, and 2 d later, with 2-d-old S. feltiae juveniles. For the nutrient concentration experiment, we evaluated the base medium versus a modified base medium containing all the components, but with 33 concentrations of yeast extract (6.9%), egg yolk (3.75%), and corn oil (12%). The nematodes and bacteria were cultured in 150-ml Erlenmeyer flasks containing 50 ml of liquid medium at (258C) and 180 rpm on a rotary shaker incubator. To assess the effect of thickeners, IJs were inoculated in BM with agar (0.2%), carrageen (0.2%), and carboxymethyl cellulose (0.2% and 0.5%). The addition of 33 more nutrients relative to the BM resulted in a significantly lower yield of nematodes. For agar and agitation speed experiments, five levels of agar in the BM (0%, 0.2%, 0.4%, 0.6%, and 0.8% agar) and two agitation speeds (180 and 280 rpm) were evaluated for production. Increasing agitation speed from 180 to 280 rpm and higher levels of agar in the medium (. 0.2%) significantly increased the yield of bacteria. At the lower agitation speed, media amended with 0.4% and 0.6% agar produced higher nematode yields compared to media without agar. Media with 0.2% and 0.8% agar resulted in intermediate levels of nematode production. At the higher agitation speed, media supplemented with 0.8% agar resulted in the lowest yield of nematodes when compared to the other media tested.Results indicated that increasing nutrient concentration levels was detrimental to nematode production. Also, media containing agar (0.4% and 0.6%) increased nematode yields when cultures were grown at low agitation speed. When IJs were used as the inoculum,0.2% agar also enhanced recovery and nematode yield at the higher agitation speed

Indiscriminate ingestion of entomopathogenic nematodes and their symbiotic bacteria by Aedes aegypti larvae: a novel strategy to control the vector of Chikungunya, dengue and yellow fever

Third and fourth instar larvae of Aedes aegypti actively ingested entomopathogenic nematodes (EPNs) and their symbiotic bacteria, resulting in larval mortality. All six EPN species evaluated in this study were pathogenic to Ae. aegypti but varied significantly in their virulence. Heterorhabditis bacteriophora and Steinernema carpocapsae were most virulent, H. megidis and S. kraussei showed the least virulence, whereas H. downesi and S. feltiae had intermediate virulence. Larval mortality was dose dependent for all EPN species. When using a dose of 100 infective juveniles (IJs) per larva, H. bacteriophora and S. carpocapsae caused 90%-100% mortality, whereas H. downesi and S. feltiae caused only 40%-60% mortality. Even when using 200 IJs/larva, H. megidis and S. kraussei caused a maximum of 30%-40% mortality. Some of the invasive EPNs were melanized, suggesting a strong humoral defense response by the Aedes larvae. The degree of melanization was quite variable; some EPNs were totally enveloped in a melanin sheath while others were partially coated with melanin. Melanization did not stop the EPN from multiplying and killing the Aedes larvae. IJs released from infected larvae would have the potential to infect healthy mosquito larvae. Also, both bacterial supernatant and bacterial cell suspension of Xenorhabdus nematophila caused >91% larval mortality after 48 h, whereas only the bacterial cell suspension of Photorhabdus laumondii was effective against the mosquito larvae. These data provides useful information on the potential use of EPNs and/or formulated bacterial cell suspensions in the control of the important urban and container-breeding mosquito, Ae. aegypti, and are a starting point for future simulated and actual field studies

Natural occurrence and distribution of entomopathogenic nematodes (Steinernematidae, Heterorhabditidae) in Viti Levu, Fiji Islands

In Fiji, little or no attention has been given to entomopathogenic nematodes (EPNs) in biocontrol programs due to the lack of awareness about their occurrence and distribution in Fiji. A survey of EPNs was conducted for the first time in Fiji Islands in 2012 and 2013, throughout the eight provinces in Viti Levu to determine the occurrence and distribution across different habitat in Viti Levu. The soil samples from various habitats were collected and assayed for the presence of EPN using Galleria mellonella as baits. EPNs were recovered from five out of seven provinces with 35 positive sites (7.3%) out of 478 sites sampled. The only EPN genera encountered was Heterorhabditis. Steinernema was not isolated from any of the samples. Characterization of isolates was done by using morphometric and molecular examinations and isolates were identified as Heterorhabditis indica. H. indica isolates were primarily recovered from leeward side of the Viti Levu Island along the coastline and riversides, being more prevalent in lighter soil with pH > 6. Further, this study found significant association between habitat type, soil type, soil pH, average annual rainfall and EPN occurrence. This is the first record of naturally occurring EPNs in Fiji. The found nematodes will serve as the basis for efficacy screening with the ultimate aim of delivering effective, more sustainable and environmentally safe control for agricultural pests in Fiji

Steinernema biddulphi n. sp., a New Entomopathogenic Nematode (Nematoda: Steinernematidae) from South Africa

A new species of entomopathogenic nematode (EPN), Steinernema biddulphi n. sp., was isolated from a maize field in Senekal, Free State Province of South Africa. Morphological and molecular studies indicated the distinctness of S. biddulphi n. sp. from other Steinernema species. Steinernema biddulphi n. sp. is characterized IJs with average body length of 663 mm (606–778 mm), lateral fields with six ridges in mid-body region forming the formula 2,6,2. Excretory pore located anterior to mid-pharynx (D% = 46). Hyaline layer occupies approximately half of tail length. Male spicules slightly to moderately curved, with a sharp tip and golden brown in color. The first generation of males lacking a mucron on the tail tip while the second generation males with a short filamentous mucron. Genital papillae with 11 pairs and one unpaired preanal papilla. The new species is further characterized by sequences of the internal transcribed spacer (ITS) and partial 28S regions (D2-D3) of the ribosomal DNA (rDNA). Phylogenetic data show that S. biddulphi n. sp. belongs to the ''bicornutum'' clade within the Steinernematidae family