Fate of injected viable <i>Escherichia coli</i> bacteria in honey bee larvae.

<p>(<b>A</b>, <b>C</b>) Number of colony-forming units (CFU) recovered from the haemolymph of infected larvae. Four-day-old worker larvae (n = 4) (<b>A</b>) and six-day-old drone larvae (n = 3) (<b>C</b>) were challenged with ∼10⁵<i>E. coli</i> 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. (<i>p</i><0.0001) as well as for drone larvae at 0.5 h (<i>p</i> = 0.0108), 24 h, 48 h and 72 h (<i>p</i> = 0.0106). (<b>B</b>, <b>D</b>) Inhibition-zone assay for the detection of antimicrobial activities in the haemolymph of infected larvae. Haemolymph aliquots derived from larvae examined in (<b>A</b>, <b>C</b>) were applied onto agar plates together with <i>Micrococcus flavus</i> as indicator bacteria. The original area of application is encircled.