Figure 1. Fate of injected viable Escherichia coli bacteria in honey bee larvae.
(A, C) Number of colony-forming units (CFU) recovered from the haemolymph of infected larvae. Four-day-old worker larvae (n = 4) (A) and six-day-old drone larvae (n = 3) (C) were challenged with ∼105 E. coli cells and haemolymph was collected at the indicated times post-injection (p.i.). Aliquots of the haemolymph were spread onto agar plates to estimate the number of surviving bacteria. Each point represents the mean number of CFUs ± standard deviation. Separate analyses of covariance testing for CFUs recovered at different times post-injection revealed significant effects for worker larvae at 0.5 h, 6 h and 24 h p.i. (p<0.0001) as well as for drone larvae at 0.5 h (p = 0.0108), 24 h, 48 h and 72 h (p = 0.0106). (B, D) Inhibition-zone assay for the detection of antimicrobial activities in the haemolymph of infected larvae. Haemolymph aliquots derived from larvae examined in (A, C) were applied onto agar plates together with Micrococcus flavus as indicator bacteria. The original area of application is encircled.