This review is looking at the way Musca domestica defends itself against harmful molecules. One of the most notable enemies is against oxidative stress. Over the years there were reports that indicated the development of resistance on range of pesticides that are used against the flies. Researches have demonstrated that there are several functional protein molecules which contribute directly or indirectly as a response to oxidative stress and resistance against insecticides. As currently, the whole genome sequencing of the organisms has enabled future study to be conducted in evaluating the behaviour of the targeted protein/enzyme in response to oxidative stress and intake of insecticides in the flies.
- Musca domestica
- oxidative stress
- insecticide resistance
An estimated 150,000 of species of Diptera have been described , and houseflies (
M. domesticaresponse towards insecticide
Naturally houseflies’ main ecosystem role is to decompose and recycle organic material. Houseflies are synanthropic insect in urban areas where high densities of human waste are their food source [10, 11]. It has been known to be vectors of various diseases of over 30 bacteria, protozoan, viruses and helminth eggs . It also transfers viruses such as polioviruses  and
The types of insecticides used to control houseflies on field are adulticides and larvicides (www.flycontrol.norvatis.com). Adulticides are carbamates (e.g. propoxur and methomyl), organophosphates (e.g. fenitrophon, azamethiphos and dimethoate), pyrethroids (e.g. cyfluthrin, deltamethrin and permethrin) and recently neonicotinoids (e.g. imidacloprid, thiamethoxam). Larvicides are insect growth regulators (IGRs) (e.g. triflumuron, diflubenzuron, cyromazine , and novaluron and juvenile hormone synthetic analogues (e.g. methoprene, fenoxycarb, pyriproxyfen  (www.flycontrol.novartis.com). Since the first case of DDT resistance is reported on the housefly , resistance of adult
In the United Kingdom, a resistance risk assessment done by  showed that although farmers claimed they had reduced using insecticides (a measure to reduce selective stress on field housefly strains), there was no sign of decrease of housefly resistance towards piperonyl butoxide synergized pyrethrins. Flies with high fenitrothion and dimethoate resistance were also discovered in Denmark . In 1997, an increase in pyrethroid-resistant strains and widespread of azamethiphos-resistant strains in 21 different farms all over Denmark were confirmed . In Argentina, a first insecticide survey was reported . Several
In Malaysia,  resistance of housefly from a garbage dump, poultry farm and agricultural farm was evaluated. It was shown that garbage dump and poultry farm fly samples were more resistant than agricultural farm. It was also shown that two poultry farms in the state of Penang against malathion, propoxur and DDT, with resistance ratio, have been found with strong correlations against relative humidity, which is a first in field discovery . However, on housefly larvae, resistance assessment has been relatively scarce with only a handful of feeding and toxicity tests done. A report on an increase in diflubenzuron resistance and new-found cyromazine resistant strain was also obtained . A dip test-emergence test of
3. Impact of oxidative stress-induced resistance
In an oxidative stress-induced insecticide resistance research, rats [38, 39, 40], humans , fresh water fish
In cytochrome P450,  it was revealed that three P450 genes, CYP4D4v2, CYP4G2, and CYP 6A38, were up-regulated in response to permethrin treatment on permethrin-resistant ALHF strains. By using PCR technology, constant overexpression of CYP 6A1, CYP 6D1 and CYP 6D3 in neocotinoid-resistant strains in Denmark during thiomethoxam challenge was demonstrated . CYP6D1 was also found to be implicating more than 5000-fold of cypermethrin resistance in Learn pyrethroid-resistant strain found in New York . Significant increase in non-specific esterases and glutathione S-transferases activities were also evaluated . A remarkable drop on GST activity has been reported on a DDT-resistant strain 698ab . Point mutation was reported as the cause of insecticide sensitivity in the case of acetylcholinesterases (E.C 126.96.36.199) . As far as metabolic-based resistance is concerned, there are still much more questions to be addressed. A study  stated that there is very little knowledge about the mechanism of the pyrethroid resistance (monooxygenase/CYP450), although pathways have been elucidated via genomic means. There was a significant correlation between kdr allele (i.e. genes reducing the sensitivity of the nervous system to pyrethroids) frequencies and the levels of knockdown resistance by deltamethrin via a PCR-based assay . It was also demonstrated that a behavioural resistance might be playing a role in contributing such resistance and such traits are still being inherited in the field . The upregulation mediated by changes to transacting factors reveals that these mechanisms were underlying in some cases of resistances of P450, GSTs, and acetylcholinesterases [56, 57].
3.1 Enzymatic removal of cellular hydrogen peroxide
It was suggested that aerobic organisms survive due to their evolved antioxidant capability . Catalase (EC 188.8.131.52) was discovered in tobacco extracts . Catalase detoxifies H2O2 into water and oxygen . Catalase is one of the well-described enzymes, and it is a class of enzyme including the iron-heme enzyme, catalase-peroxidases and a small group of manganese enzymes . Superoxide dismutase (EC 184.108.40.206) is a well-known enzyme against oxidative stress. SOD1, the first superoxide dismutase to be identified, uses free radical as a substrate . A metalloenzyme, superoxide dismutase catalyses the dismutation of superoxide anion (O2−) to hydrogen peroxide and oxygen, as the first defence line against oxidative stress . They are also known to exhibit additional peroxidase activity when hydrogen peroxide level is at its large. It has been suggested that the removal of superoxide anion will reduce SOD alternate toxic behaviour . Copper-zinc and manganese SODs scavenge and dismutate superoxide anion in mitochondrial electron transport systems. It was demonstrated that a manganese superoxide dismutase-deficient yeast thrived in hyperoxia conditions (95% oxygen, 5% carbon dioxide) under the removal of electron transport system . A copper-zinc SOD1 in baker’s yeast was characterized at the intermembrane space of mitochondria .
Glutathione peroxidase (EC 220.127.116.11) utilizes reduced glutathione (GSH) to decompose hydrogen peroxide [66, 67, 68]. This enzyme was discovered  and identified as selenocysteine enzymes at first , better known as GPx1. Later, more selenocysteines were identified such as GPxs-GPx2, GPx3, and GPx4 . It was also found in mammals [68, 71]. Later, a catalytic cysteine residue on rat was discovered , known as GPx5, and followed by GPx6  which is a selenocysteine proteins in humans but not in rats or mice . Mammalians GPx7 and GPx8 were the last to be elucidated but have a low GPx activity .
Peroxiredoxins (EC 18.104.22.168) are another group of enzymes worth mentioning when discussing about oxidative stress in cellular organisms. Peroxiredoxins are a family of antioxidant enzymes . Highly specific in reducing hydrogen peroxide , its cysteine residue makes up the active site of peroxiredoxins, which in turn are being oxidized into sulfenic acid and recycled back to thiol, via sulfiredoxins . They also control cytokine-induced peroxide levels which, in turn, mediate signal transduction in mammalian cells .
4. Oxidative stress-related proteins in
There are several possible candidates of oxidative stress defence proteins. Those are superoxide dismutase, catalase, glutathione peroxidase, glutathione S-transferases, GSSG reductase, thiol transferases, gamma-glutamylcysteine synthetase, and glucose-6-phosphate dehydrogenase. Oxidative stress hypothesis is evident on aging and has always been raising questions from researchers.
GST gene family and their isoforms have been discovered to participate in oxidative stress pathway. Overexpression and peroxidase activity of GSTs in peroxide treatment were observed . Other than oxidative stress resistance, GSTs detoxify xenobiotics, protect from tissue damage, participate in Jun-kinase signaling pathway and act as non-catalytic carrier proteins (ligandins) in the intracellular transport of hydrophobic compounds [3, 4, 5]. Glutathione synthetase (GSHs) are responsible in the antioxidant defence as the dominant non-protein sulphhydryls in the cell  forming conjugates non-enzymatically or more by the catalysis and mediation of GSTs. H2O2 oxidizes thiolate group in cysteine residues (-S-) into thiols (-SOH), which is present in the exposing active site. Reaction against peroxidants is also energy-consuming due to the inhibition of oxidative phosphorylation  and deprives energy to maintain the recycling of NADPH during pentose phosphate pathway and glucose 6-phosphate dehydrogenase, making cells hyperglycaemic  and able to topple the condition of cell redox levels in levels of lactate/pyruvate ratio . Most of the cases above were investigated towards organophosphates and pyrethroids. In cadmium ion treatment, concentration ranging from 0.2 to 5 mM in the medium, widely known to enhance reactive oxygen species in cell, increases the levels of superoxide dismutase . Lowering the intake of selenium via diet increases the events of a peroxidative injury. The group further purified the selenium-independent glutathione peroxidase  and suggested this enzyme and the related pathways should be in the picture during the investigation of insect antioxidant defence system. There was no direct research work on peroxiredoxins with relation to houseflies, and its mechanisms and activities in vivo are not much of knowledge. However, it was discovered that there was no increase in catalase activity even though the diet of selenium in
Despite such remarkable immunity and rising insecticide tolerance exhibited by
The work has been funded by the University of Malaya Postgraduate Research Fund (PPP: PV091/2011A) and Ministry of Higher Education under the Fundamental Research Grant (FRGS: FP052-2014A).