BACKGROUND Changes in plants induced by one species have indirect effects on interactions with other species, thus shaping their abundances. The root‐feeding beetle Longitarsus bethae released as a biological control agent for Lantana camara has established at a few sites in South Africa. Lantana camara plants infected with the root‐knot nematode Meloidogyne javanica often exhibit an increase in L. bethae abundance, suggesting that nematode‐infected plants could be enhancing the development of the beetle. This study investigated the interaction between L. bethae and M. javanica. RESULTS The study showed that galling by M. javanica occurred at the highest inoculation of 300 eggs of L. bethae per plant. Longitarsus bethae performed over twofold better on M. javanica‐infected L. camara roots compared with healthy roots, and 275 adult L. bethae progeny, with slightly larger body size, emerged from M. javanica‐infected compared with 167 adults that emerged from healthy plants. Fresh gall weight from treatments where both L. bethae and M. javanica were combined was 36% higher than that from M. javanica only, suggesting that the combination of both species induces more galling than the nematode does alone. The total biomass of plants with M. javanica only, L. bethae only, and the two species combined was reduced by 48%, 24% and 50%, respectively. CONCLUSION Meloidogyne javanica improves the performance of L. bethae, and combination of the two species has an additive negative effect on L. camara. The interaction between M. javanica and L. bethae could enhance the biological control of L. camara. © 2019 Society of Chemical Industry