Isolation and efficacy of entomopathogenic fungus (Metarhizium anisopliae) for the control of Aedes albopictus Skuse larvae: suspected dengue vector in Pakistan

Possible Synergistic Effect of Combined Metarhizium anisopliae and Fenitrothion for Control of German Cockroach (Blattella germanica) as a Novel Approach

Background

Cockroaches are one of the most common pests in many residential areas. In this study, the simultaneous effects of fungi, Metarhizium anisopliae and fenitrothion-coated baits on the mortality rate of the German cockroach nymphs were investigated.

Methods

To determine the lethal level of fenitrothion insecticide, a bioassay test was performed on the last instar nymphs of the German cockroach reared at insectarium conditions. Various toxic concentrations of fenitrothion (0.1%, 0.3%, 0.5%, 0.7%, 0.9%, 1.5%, and 2%) were used. Different concentrations of M. anisopliae (1×10⁴, 1×10⁵, 1×10⁶, 1×10⁷, 1×10⁸ Conidia/ml) were also applied to nymphs. Eventually, we combined the effective dose of fenitrothion (0.93%) with the effective concentration of M. anisopliae (6.6 ×10⁶ Conidia/ml) to provide the fungus-coated bait to attract insects. Mortality was recorded 24-96 hours after exposure to the toxic bait. The resulting data were subjected to Probit analysis.

Results

The results of applying M. anisopliae spores with fenitrothion composition showed that the mortality rate of German cockroach nymphs was significant. Therefore, the optimal dose of fenitrothion used in combination with M. anisopliae seems essential to reduce the German cockroach nymphs.

Conclusion

The results of this study can be considered a suitable method as a mixture with low cost and minimal damage to the environment and other organisms.

Identification of locally isolated entomopathogenic Fusarium species from the soil of Changa Manga Forest, Pakistan and evaluation of their larvicidal efficacy against Aedes aegypti

Dengue fever vectored by the mosquito Aedes aegypti is one of the most rapidly spreading insect-borne diseases. Current reliance of dengue vector control is mostly on chemical insecticides. Growing insecticide resistance in the primary mosquito vector, Aedes aegypti, limits the effectiveness of vector control through chemical insecticides. These chemical insecticides also have negative environmental impacts on animals, plants and human health. Myco-biocontrol agents are naturally occurring organisms and are found to be less damaging to the environment as compared to chemical insecticides. In the present study, entomopathogenic potential of local strains of fungi isolated from soil was assessed for the control of dengue vector. Local fungal isolates presents better alternative to introducing a foreign biocontrol strain, as they may be better adapted to environmental conditions of the area to survive and may have more entomopathogenic efficacy against target organism. Larvicidal efficacy of Fusarium equiseti and Fusarium proliferatum was evaluated against Aedes aegypti. Local strains of F. equiseti (MK371718) and F. proliferatum (MK371715) were isolated from the soil of Changa Manga Forest, Pakistan by using insect bait method. Larvicidal activity of two Fusarium spp. was tested against forth instar larvae of A. aegypti in the laboratory, using concentrations 105, 106, 107 and 108 conidia /ml. LC50 values for F. equiseti after 24h, 48h, 72h and 96h of exposure were recorded as 3.8x 108, 2.9x107, 2.0x107, and 7.1x106 conidia /ml respectively while LC50 values for F. proliferatum were recorded as 1.21x108, 9.6x107, 4.2x107, 2.6x107 conidia /ml respectively after 24h, 48h, 72h and 96h of exposure. The results indicate that among two fungal strains F. equiseti was found to be more effective in terms of its larvicidal activity than F. proliferatum against larvae of A. aegypti.

Scorpion neurotoxin AaIT-expressing Beauveria bassiana enhances the virulence against Aedes albopictus mosquitoes

To improve the insecticidal efficacy of this entomopathogen Beauveria bassiana, the fungus was genetically modified to express an insect-specific scorpion neurotoxin AaIT. The virulence of the recombinant B. bassiana strain (Bb-AaIT) against Aedes albopictus adults (which occurs via penetration through the cuticle during spore germination or by conidia ingestion), and the larvae (by conidia ingestion) was measured with bioassays. The median lethal concentration (LC50) of Bb-AaIT against A. albopictus larvae was 313.3-fold lower on day 4 and 11.3-fold lower on day 10 than that of the wild type (WT). Through conidia feeding or body contact, Bb-AaIT killed 50% of adult female mosquitoes at 3.9- or 1.9-fold reduced concentrations on day 4 and at 2.1- or 2.4-fold reduced concentrations on day 10. Compared with the results for the WT, the median lethal time (LT50) of Bb-AaIT was reduced by 28.6% at 1 × 107 conidia ml-1 and 34.3% at 1 × 106 conidia ml-1 in the larvae bioassay by conidia ingestion, while it decreased 32.3% at 1 × 107 conidia ml-1 by conidia ingestion and 24.2% at 1 × 108 conidia ml-1 by penetrating through the cuticle in the adult bioassay. All the differences were significant. Our findings indicated that Bb-AaIT had higher virulence and faster action than the WT in killing the larval and adult mosquitoes, and therefore, it is valuable for development as a commercial mosquito pesticide.

Dengue: An Analysis of Epidemiological Pattern Over a Six Year Period

INTRODUCTION

Dengue is an arboviral infection transmitted among humans by Aedes aegypti, the urban vector and Aedes albopictus as a maintenance vector in sub-urban and rural areas. The diagnosis is routinely established by detection of NS1 antigen and/or by IgM antibodies testing. Dengue infects 50-100 million cases per year worldwide with atleast half million serious cases needing hospitalization. Therefore, it is necessary to keep the surveillance ongoing to timely look out for changes occurring in disease pattern over a geographical area.

AIM

To study the epidemiological patterns of dengue virus infection in our region over a period of six years.

MATERIALS AND METHODS

The present retrospective study was undertaken in the Department of Microbiology, Government Medical College Hospital, Chandigarh during time period January 2010 to December 2015 on 10,774 serum samples from patients clinically suspected to be suffering from dengue infection. Samples were selected as per World Health Organization (WHO) criteria. All the samples were processed for the presence of dengue IgM antibodies by μ anti-body-capture Enzyme Linked Immunosorbent Assay (ELISA), MAC ELISA and/or NS1Ag by ELISA as per the instructions of the manufacturer. The data was analysed from the data sheets available.

RESULTS

During the time period, a total of 10,774 samples were processed and 2,449 (22.7%) samples came out to be positive for dengue virus infection. Marked seasonal variation was noted with 0-2 cases presenting during month of January to July but positivity peaked in post monsoon season in October (>70%) and tapered till December every year. The adult age group (16-45 yrs) showed maximum positivity (83.5%) with males affected more than females.

CONCLUSION

The present study clearly shows that our region is endemic for the dengue virus infection and there is need to continuously monitor the transmission of the disease in the community, to plan effective measures, to control the spread of dengue virus infection timely.