We have developed an equipment-free biosensor for visual pesticide residue (acetamiprid) detection with high sensitivity and selectivity. The target acetamiprid associates with an aptamer sequence and releases trigger DNA to initiate the cyclic signal amplification process. An ingeniously designed hairpin DNA probe was employed as the sensing element, which contains the same sequence as the trigger DNA in the stem part of the hairpin and a G-rich sequence in the loop part of the hairpin. An exonuclease III (Exo III)-mediated target recycling strategy was utilized to achieve quadratic amplification. This two-step cyclic signal amplification results in the generation of numerous G-quadruplex DNAzymes that can catalyze the H2O2-mediated oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to generate a colored signal readout, thus providing the amplified colorimetric detection of the target. This assay is ultrasensitive, enabling the visual detection of acetamiprid at concentrations as low as 10 pM without instrumentation. Our proposed sensing system also displays high selectivity and can be applied to determine acetamiprid residues in food samples. Moreover, the assay does not involve any chemical modification of DNA, which is simple and low-cost. This sensing platform provides a promising approach for on-site detection of target molecules in resource-constrained regions because of the easy and straightforward readout of results without the use of sophisticated apparatus.