Insects of medical and veterinary importance especially Culex pipiens and Musca domestica are nuisance pests and vectors of hundreds of diseases. Twenty years after synthetic insecticides were enthusiastically entrenched in ‘modern’ agricultural production; they induce widespread environmental contamination, toxicity to non-target organisms, development of resistance against insecticides, and adverse effects on animal and human health. Hence, there is a pressing need to explore and utilize naturally occurring products for fighting such pests. Several materials as three essential oils, two insect growth regulators, a bacterium, and three fungi, 2 of them were isolated for the first time in Egypt, were applied against early 3rd larval instars of M. domestica as well as late 3rd larval instars and early 4th larval instars of C. pipiens.
Nigella, Nigella sativa, onion, Allium cepa, and Sesame, Sesamum indicum essential oils induced larvicidal effect and adversely affect pupation and adult emergence rates and induce abnormalities during the development of insects at sublethal concentrations.
At 16 x104 ppm, such oils induced 93.3%, 91.7, 86.2%, respectively, larval mortalities and induced 100% pupal mortalities against M. domestica. The LC50 values were 5.87 x104, 5.49 x104, and 4.45 x104. On the other hands, the LC50 values of such oils against field and laboratory strains of C. pipiens were 247.99 and 108.63; 32.11 and 2.87; and finally, 673.22 and 143.87 ppm, respectively.
Treatment of M. domestica and C. pipiens with pyriproxyfen (Sumilarv®, Somitomo Co.) as a juvenile hormone analogues (JHA) hinders normal metamorphosis and induced several developmental abnormalities as larval-pupal intermediates which do not survive; lower concentrations significantly prolonged larval and papal durations, 10.5 and 11 days (at concentration 0.1 ppm) and 9.9 and 15.1 days (at concentration 4 ppm), respectively, than those of the control group (3, 5.7 days and 3.9, 1.1 days, respectively). Diflubenzuron (Dimilin®, El –Delta Company, Egypt) as a chitin synthesis inhibitor (CSI) is effectively controlled mosquitoes than house flies. LC50 values were 1.26 and 1000 ppm, respectively. Treated larvae of C. pipiens (concentrations: 0.04 - 40 ppm) were in due course died because Dimilin® prolonged the larval durations (11.9 days vs. 4 days in the control group) and increased larval abnormalities (46.7%). Such anomalies include larvae with transparent cuticle, a splitting of the cuticle, and pharate pupae. It also brings about pupal abnormalities. Likewise, treatment of M. domestica with the same product (at 1ppm) induced larval and pupal malformations reached 23.3 and 56.5%, respectively, and reduced adult emergence (66.7%). malformations of M. domestica include small, shrunken, macerated larvae, larvae with week cuticle, distorted puparia, and failure of adult emergences.
The entomopathogenic bacterium, Bacillus thuringiensis israelensis, Bti (VectoBac®, 12 AS, Wady El- Niel for agricultural development Co., Egypt) is highly effective against C. pipence than M. domestica, LC50 values were 1x10-5 and 3.86 x103 spores/ml, in that order, and LC 90 values were 0.04 and 37.28 x 103 spores/ ml, respectively. All survived mosquito larvae died as pupae. A commercial strain of the fungus, Beauveria bassiana (Biosect®, Kafr El Zayat - KZ Chemicals, Egypt) was used to control larvae of both M. domestica and C. pepiens. The LC50 an LC90 values were 29.2 x107 and 9.97 x108 spores/ ml for house flies and 1.2x107 and 4.17x109 spores/ ml, for mosquitoes, respectively. The whole larval mortalities of mosquitoes were approximately 100%, a small number of the survived larvae died as pupae. At the lowest concentrations, Larval and pupal malformations were 30% and 45%. Symptoms of mycosis after treatment with the three fungi were revealed.
Lagenidium spp. is an aquatic fungus famous for being survive in unpolluted water , but it was isolated for the first time, during this work, form C. pipiens larvae infesting a polluted creak with biological matters in Miet El- Attar, a village near Benha city, 50 Km north Cairo, Egypt. Such fungus was propagated on SDA medium and Peptone yeast glucose (PYG) for sporulation. Five concentrations (5 x105- 1.6 x107) were used to infect C. pipiens late 3rd larval instars in vitro and the biological parameters had been reported on till emergence of adults. LC50 and LC90 values were 2.79 x106 and 3.94 x108 spores/ ml, correspondingly. At the lowest concentration, larval duration reached 8.3 days in contrast to 3.6 days in the control group. The morphological changes (symptoms of mycosis) reached 66.7%. All stay alive larvae died as pupae; accordingly, this isolated strain of Lagenidium spp. inhibited adult emergence.
All available previous literature mentioned that Entomophthora muscae is a pathogenic fungus of adult M. domestica. In this PhD work, this strain of fungi was isolated for the first time in Egypt, from Moshtohor, Toukh, Qlubia governorate, 35 Km north Cairo, and has a unique ability to infect larvae of house flies for the first time during this work. The isolated fungus was replicated on Sabouraud Dextrose Agar (SDA) medium for hyphenation and on liquid medium for laboratory – scale Entomophthora’ hyphal production for enhancement of zoosporogenesis. Moreover, a bioassay was prepared using early 3rd larval instars of house flies infected In vitro by adding different concentrations of E. muscae (from 25 to 16 x 102 spores/ml) to the breeding medium of larvae and followed up until adult eclosion. LC50 and LC90 values for larval mortalities reached 2.19 x 102 and 20 x 102 spores/ ml, respectively. At lower concentrations, larval durations were prolonged (7.2 days) than that of the control group (2.6 days). Larval abnormalities were larval pigmentation, black, red- pinpoint pigmentation, ulceration, maceration, in addition to larval-pupal intermediates. Mortality and morphological changes of pupae including symptoms of mycosis were 100% at 8 x 102 spores /ml. Adult mortalities, deformity, and emergence reduction rates elevated as the concentrations increased (79.3%, 60%, 98.2%, respectively, at 4x102 spores/ ml). Adult malformations include failure of adult eclosion, small adults, and deformed wings and legs. Furthermore, E. muscae manipulates the behavior of infected host for its own dissemination as the apparently normal adults displayed the characteristic position of Entomophthora spp as adults died in elevated positions, with the proboscis extended and attached to the substrate, legs spread, the abdomen angled away from the substrate, and the wings rose over the thorax. The conidial shower reached 3-9 cm, depending on the size of the cadavers. Conidia are forcibly expelled from conidiophores that emerge most profusely from the intersegmental membranes on the insect’s abdomen. As a result, this conspicuous posture enhances dispersal of conidia and the prevalence of infection with this fungus.
According to LC50 values, the relative potency of the used biological control agents indicated that Vectobac (Bti), and Lagenidium spp. were 12x1011 and 4.3 times, respectively, more effective than the fungal product Biosect®, B. bassiana. As fungi have the ability to be self- propagated, they could be cost-effective control agent against house flies and mosquitoes. The previously mentioned results indicated that the applied materials especially onion oil, Vectobac®, Sumilarv®, and E. muscae were effectively controlled M. domestica and/ or C. pipiens and could be applied in the fields as eco-friendly solution for controlling such serious insects of medical and veterinary importance.