Abstract BACKGROUND The brown planthopper ( BPH ), Nilaparvata lugens (Staparvata luera: Delphacidae), is a serious rice pest that easily develops resistance to chemical insecticides and resistant rice varieties. This study evaluated the infectivity of the BPH fungal pathogen, Pandora delphacis , and developed a novel formulation as an alternative means of BPH control. RESULTS In a multiconidial concentration bioassay, P. delphacis ‐infected BPH cadavers were observed on day 4, but most occurred between days 5 and 8. BPH mortality depended on the inoculated conidial concentration. The cumulative mortality of adult BPHs reached 81.7% at 192 conidia mm −2 in 8 days. Inoculation with 40.9 conidia mm −2 was sufficient to induce 50% BPH death, based on analysis of a time‐concentration‐mortality model. A floatable P. delphacis ‐based formulation was made for use in paddy fields; mycelium‐containing pellets mimicking mycosed cadavers could produce 7–15.7 × 10 4 infectious conidia pellet −1 at 11–28 °C. In the laboratory bioassay, three floating pellets in a BPH ‐rearing jar caused 75.5% BPH mortality within 8 days, similar to the mortality level caused by direct conidial inoculation. CONCLUSION P. delphacis is a potential biocontrol agent of BPHs for further research, and the novel floatable formulation holds promise as a method for BPH control. © 2015 Society of Chemical Industry