Effect Of Low-temperature Stress On Worker Capped Brood Development And Its Mechanism In Honey Bees(Apis Mellifera Ligustica)

Temperature is a fundamental ecological factor for honeybee development.In this study,different stages of worker capped brood in honey bees Apis mellifera ligustica were exposed to 20? for various cold duration in order to study effect of low-temperature stress on honeybee development.The transcriptome and emzyme activity were compared to explore the molecular mechanism underlying capped brood susceptibility to low temperature.The results will enrich the fundamental knowledge of ecology and developmental biology of honey bee,as well as improve strategies in bee keeping.The worker capped brood of 12 different developmental stages were exposed to 20? for 12,24,36,48,60,72,84 and 96 hours,followed by incubation at 35? until emergence.The effects of cold stress on capped brood were estimated by capped brood mortality,developmental duration,as well as ecolosed adult birth weight,longevity,morphological characteristics,wing vein.In addition,the differentially expressed transcritome and enzyme activity of stressed capped brood were estimated.Prepupae were more sensitive to low-temperature exposure than pupae stages.Prepupae with clod treatment led to higher mortality,shorten longevity,shorter length of femur,tibia and basitarsus,imperfection in wing veins including lost or additive veins.Peroxidase activity treated at 20? in prepupae was lower than that in control group.For transcriptomic RNAs,development and stress-related genes were up-regulated but proteolytic and metabolic-related genes were down-regulated during prepae cold treated for 4 h.Three pathway were enriched by KEGG:Phototransduction-fly?Wnt signaling pathyway and Facal adhesion in both CS group and CSR group.Medium-term pupae,8 and 9 days after capping,showed the highest resistance to low-temperature stress.They presented lowest capped brood mortality and the longest longevity among all cold duration exposure.There was nearly no difference in birth weight or morphology between cold treatment and control and few imperfection in wing veins was detected in emerged adults.Moreover,the peroxidase activity for stressed mid-pupae was higher than that in control group.Pupal misorientation inside cells was observed when capped larva were exposed to cold.Brood of 4-36 h tended to misorient under low-temperature stress leading to dead emerged adults which could not jaw their way out.A 10 m cold stress to capped larvae could result in misorientation and a 60 m cold stress caused higher misorientation.Brood aged 24 h exposed to cold for 36 h reached the highest misorientation to about 40%.Developmental duration of cold exposed capped brood was prolonged.The increased developmental duration(y)was positively correlated to cold duration(x).The linear regression equation for them were:y=0.037x+0.034,R2=0.9994,respectively.Trehalase activity was reduced in the sensitive stage and cold resistant stage treated at 20?,showing that low-temperature stress reduced the metabolic level.