Increasing evidences indicate that male haploid are more susceptible to parasites than female diploid(workers,alate females and queens)although the generality and reasons causing such susceptibility are still under debate.The male haploids in eusocial Hymenoptera are perfect for examining the susceptibility assumption and unveiling the molecular mechanisms of this assumption.In the present study,the males,workers and alate females of red imported fire ants(Solenopsis invicta)were challenged with entomopathogenic fungus Metarrhizium anisopliae.By measuring the LC50 values of M.anisopliae against different castes of S.invicta,we found that haploid males suffered from reduced disease resistance than diploid workers and alate females,a proof that haploid susceptibility was diminished in S.invicta.In this study we also examined the assumption that males invest less in innate immunity contributing to haploid susceptibility based on the transcript levels of genes encoding antimicrobial peptides(AMP)with quantitative reverse transcription-PCR(qRT-PCR).We found that infection increased the mRNA levels of hymenoptaecin in females(workers and alate females),but not in males;no significant difference was found in the mRNA levels of defensin,transferrin or crustin between infected ants and control ants in each sxe/castes.However,this study suggested that any resistance traits like behavioral and other immunological responses,are contributing to haploid susceptibility.
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