An experimental and theoretical study is presented of the ${\mathrm{B}}^{+}$(1${\mathit{s}}^{2}$2pnl, n=4 and 5) doubly excited states. Experimentally, low-energy electron emission spectra of ${\mathrm{B}}^{+}$, excited by ${\mathrm{B}}^{+}$+He, ${\mathrm{B}}^{+}$+Ar, and ${\mathrm{B}}^{+}$+C-foil collisions, have been recorded with a zero-degree electron spectrometer setup. Several autoionizing states of ${\mathrm{B}}^{+}$ have been observed between 1 and 3 eV in the projectile emitter frame. The observed resonances, namely, (1${\mathit{s}}^{2}$2p4s) $^{3}$P \ifmmode^\circ\else\textdegree\fi{}, $^{1}$P \ifmmode^\circ\else\textdegree\fi{}, (1${\mathit{s}}^{2}$2p4p) $^{3}$D${,}^{1}$D, (1${\mathit{s}}^{2}$2p4d) $^{3}$F \ifmmode^\circ\else\textdegree\fi{}, $^{1}$F \ifmmode^\circ\else\textdegree\fi{}, (1${\mathit{s}}^{2}$2p4d) $^{3}$P \ifmmode^\circ\else\textdegree\fi{}, and $^{1}$P \ifmmode^\circ\else\textdegree\fi{} do not appear in any previous data. The observations also suggest that the population of triply excited states in B is not important in the excitation process. Theoretically, five-state (2s,2p,3s,3p,3d) close-coupling calculations using impact have been performed to determine positions, widths, and partial collision strengths for 22 of the lowest ${\mathrm{B}}^{+}$(1${\mathit{s}}^{2}$2pnl) resonance states. Excellent agreement between theoretical and experimental energy positions is obtained.