Bacillus sphaericus in the adults of Culex quinquefasciatus mosquitoes emerged from treated larvae and its effect on development of the filarial parasite, Wuchereria bancrofti

Abstract

Bacillus sphaericus is a bio-control agent effective against Culex quinquefasciatus, the vector of bancroftian filariasis. Apart from its larvicidal effect, there are reports of reduced infection of filarial parasites in mosquitoes exposed to it. In the present study, adults of Cx. quinquefasciatus emerged from B. sphaericus treated larvae were fed on blood samples positive for microfilariae of Wuchereria bancrofti and examined at various time intervals to assess the infection level. The rate of infection was reduced from 95% on day 1 post-feeding to 75% on day 13, when fed with blood sample containing 41 mf/20 μl. The mean parasite burden was also reduced from 4.9 per mosquito on day 1 to 2.15 on day 13. When fed with another sample (30 mf/20 μl), the infection was reduced from 100% on day 1 to 80% on day 13. Reduction in parasite burden was 4.0 to 1.75. Abnormally developed second-stage larvae of the parasite were seen in treated mosquitoes. Thus, the results indicated adverse effect of B. sphaericus treatment on infection and development of the filarial parasite in mosquitoes. The possible reason for the parasite regulation was studied through the assessment of the carryover of the bacterium as well as its toxins to the surviving mosquitoes. The presence of B. sphaericus was determined through plating of homogenate of survived mosquitoes on NYSM agar. Toxic protein was detected through immunoblotting. The bacterium as well as its 41.9-kDa toxic protein was found to be transmitted from larvae to adults and affected the parasite development, directly by the toxin or indirectly by eliciting humoral immune response of the mosquito.

Transstadial immune activation in a mosquito: Adults that emerge from infected larvae have stronger antibacterial activity in their hemocoel yet increased susceptibility to malaria infection

“…Additionally, these findings are consistent with studies that focused on a single anopheline life stage, whereby a previous infection acquired as an adult can render those individuals better equipped to fight a later infection (Lowenberger et al, ; Rodrigues et al, ). Finally, these data support findings that environmental exposure of mosquito larvae—mainly culicine larvae—to different microorganisms can have a negative effect on adult‐acquired pathogens (Dickson et al, ; Kala & Gunasekaran, ; Mahapatra, Hazra, Rup, Acharya, & Dash, ; Moreno‐Garcia et al, ; Paily, Geetha, Kumar, & Balaraman, ; Ramirez et al, ). Taken together, larval exposure to certain microorganisms, be it in the gut or hemocoel, can boost the immune system of an adult mosquito.…”

Anopheles gambiae larvae mount stronger immune responses against bacterial infection than adults: evidence of adaptive decoupling in mosquitoes

“…First, because mosquitoes are holometabolous insects, studying the larval immune system could yield important insights into how immune responses change over the course of development [ 11 ]. Secondly, larval environmental factors, including food availability, temperature, population density, competition and chemical insecticide exposure [ 151 – 159 ], as well as exposure to bacterial and fungal pesticides [ 98 , 160 – 166 ], have all been shown to impact adult vector competence. Thirdly, many of the most widespread and effective mosquito control methods directly target the larval stages [ 167 – 169 ], and resistance to insecticides evolves more rapidly in larvae compared to adults, likely due to the stronger selection pressures at work in the larval stage [ 35 ].…”

Comparative structural and functional analysis of the larval and adult dorsal vessel and its role in hemolymph circulation in the mosquito Anopheles gambiae

“…Specifically, the data presented herein provide novel insights into larval circulatory physiology and describe numerous differences between the larval and adult dorsal vessel, providing a developmental perspective on this organ system. Larvae are a common target in mosquito control strategies (Fillinger and Lindsay, 2011) and many chemical and biological pesticides exert their effect at the larval stage after penetrating the cuticle or midgut and circulating throughout the hemocoel (Favia et al, 2007;OtienoAyayo et al, 2008;Paily et al, 2012). Furthermore, numerous mosquito-borne pathogens must complete an obligate migration from the midgut to the salivary glands that involves traversing the hemocoel, where they are subject to hemolymph flow currents (Hillyer et al, 2007).…”