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In Egypt, Culex pipiens L. is the primary vector for bancroftian
filariasis (Southgate, 1979) and Rift valley fever (Meegan, 1980) .
Culex pipiens , therefore, is the main target in control programs against
these diseases, Culex pipiens larvae breed in different kinds of water
bodies as wet pit latrines, septic tanks, cesspits, cesspools, drains and
canals containing stagnant water polluted with organic waste. They also
breed in polluted water associated with home industries, such as cocnut
husk pits. Other breeding sites are pools and unused wells used for
dumping garbage (Zayed et al. , 2015) .
Repetition of using conventional insecticides as organophosphates
and pyrethroids led to the development of insecticide resistance in several
mosquito species (Cui et al. , 2006) . Also, harmful impacts to hum an
health, non -target organisms, environment and mutagenic occur. These
problems forced to search for safe and specific compounds as Photoactive
dyes which have potential as pesticides. These compounds become active
in sunlight compared with other pesticides that are quickly inactivated by
sun light.
The photoactive dye has been shown to have no carcinogenic
effects in either rats or mice based on long -term dietary studies
(Lipman, 1995) . Laboratory tests have shown the dye to have little
toxicity to beneticial insects (Dowell, 1997) . At the same time, the
photosensitized inactivation of yeasts and bacteria is used for the
decontamination of microbially polluted waters by sunlight
(Merchat et al ., 1996) .
The photodynamic action is happened when organic molecules are
illuminated by light in the presence of O 2 causes toxic effect on living



cells. It has been shown to function by one of two mechanisms
Heitz and Downum (1995) . In type one mechanism the dye absorbs a
photon of light rises the first to singlet exited state and then drops to the
exited tripled stat e. The energy of the photon is then added to the target
substrate molecule, making an activated form substrate. The activated
molecule then adds to ground state oxygen or their oxygen radicals and
becomes oxidized in the process, in type two mechanisms the dye again
absorbs a photon of light as the first step in the process. The dye rises first
to the exited singlet state and then to the excited triplet state. The excited
dye molecule then gives the energy to ground state oxygen thereby rising
the oxygen to the exited singlet state. Finally, the excited oxygen adds to
the target substrate and oxidizes it. So t he combined effect of the three
elements, light, photosensitizer and oxygen, has been termed
photody namic action (Blum, 1941) .
Well – known photosensitizers include several families of aromatic
and heterocyclic compounds such as pyrenes, xanthenes, phenothiazines,
porphyrins, and chlorins (Kohen et al. , 1995) .
Xanthene derivatives and other photosensitizers undergo rapid
activation when exposed to light, leading to the formation of singlet
oxygen and superoxide anions (Heitz, 1995) . Therefore, when insects
in gest a photosensitizer and are then exposed to light their detoxifying
systems become overwhelmed and they consequently die. Xanthene dyes
represent a family of photosensitizers that have been extensively tested as
photo -insecticides on several dipteran adults (Heitz, 1987; 1995 and
1997) . Different halogenated xanthenes as Rose Bengal, phloxine B and
rhodamine B have proven to be effective photo -insecticides against at
least two -dozen insect species Heitz (1995) . Diptera are particularly



susceptible to the photodynamic action of dyes (Heitz, 1995; Ben Amor
and Jori, 0222 ).
Rose Bengal was prepared in 1882 by Ghnem as an analogue of
fluorescein (Walter, 2010) and it has been used for 50 years to diagnose
liver and eye cancer. Furthermore, is nontoxic photosensitizer, currently
used as food additives and insecticides (Capinera and Squitier, 2000;
Martin et al., 1998 ).
More specifically, the photoactive dye phloxine B , one of the
less toxic xanthenes, is considered an environmentally friendly substance
that is innocuous to mammals (Lipman, 1995) . Phloxine B is one of the
most studied of these pesticides. The insecticidal activity of the
halogenated xanthene dyes begins w hen the dye absorbs a photon of light.
This photon raises the dye first to an excited singlet state, and then to an
excited triplet state. The excited dye molecule gives up this energy to
ground state oxygen, producing oxygen in the excited triplet state.
Finally, the excited oxygen re acts with the target substrate. This
oxidation, and resulting cellular damage, is believed to cause the deat h of
the insect (Heitz , 5991 ). USA has found over last 30 years Phloxine B
was active against 24 pests as fire ants ( Solenopsis spp.) (David and
Heitz, 1978) , corn rootworm ( Diabrotica spp.) (Schroder et al. , 1998) ,
and Mexican fruit fly Anastrepha ludens (Moreno and Mangan, 1995) .
Phloxine B needed to be ingested to exert a toxic effect.
Rhodamine B is being tested for using as biomarker and in biology
as a staining fluorescent dye, also it used in biotechnology applications as
fluorescence microscopy, flow cytom etry and fluorescence correlation



Adjuvants used in present study which de fined as ingredients that
improve the properties of pesticide formulation. This includes wetting
agents, spreaders, emulsi fiers, dispersing agents , foam suppressants,
penetrants, and correctives (Ware , 1978) .
Likewise , the present study was conducted to evaluate the effect of
the selected dye on biochemical and histopathological parameters of
Culex pipiens .
This study revealed the role of proteins, carbohydrates and lipids
concentration changes on mosquito larval mortality during
photosensitization process.
Enzyme assay has been also used due to its rapid, simple and
sensitive method for identification of mechanisms underlying the
insec ticide resistance in mosquito population even at low frequencies
(Lee, 1990)
Histochemical study on insects is one of the most specific and
interesting types of investigation. The photoactive compound
accumulates within the insect, followed exposure to vis ible light, induces
damage of its cuticle, malpighian tubules and midgut wall, followed by
feeding inhibition and eventual death (Ben amor et al., 1998) . At the
cellular level, most photosensitizers are able to induce apoptotic cell
death (Eggen et al., 2005)



? Aim of work:
1- Evaluation of some photosensitizer s and determination of median
lethal concentrations and median lethal time against 4th instar larvae
of Culex pipiens .
2- Synergistic effect o f some additives on photosensitizer performer.
3- Identify and understand the mode of action of photosensitizer on
insect’s main metabolites using biochemical assays on suspected
tissues of m osquito larvae, where determined total carbohydrate,
lipids ; protein content s; digestive and detoxification enzymes.
4- Investigate the histopathological and ultra -structural changes of
certain tissues (integument, muscle and midgut) by transmission
electron microscope in treated larvae of Cule x pipiens with
photosensitizer to detect which cellular targets were affected .


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