Systematics Most closely related to Phymatopus behrensii and P. hectoides (Wagner, 1989)
Biology Larvae of Phymatopus californicus tunnel in woody stems of shrubs or externally on roots. Tunnels in bush lupine usually occur 0.5-0.75 m above ground, and most are in lower boles or decumbent stems in contact with leaf litter and soil. Tunnels were usually in the living woody tissues but sometimes in dead stems. Most tunnels have a single opening but some have two. Tunnels may extend up or down from the opening, and often occur at a branch axil. The tunnel entrance is plugged by a mixture of frass, wood shavings and silk. Larvae feed exclusively on the xylem and did not leave the tunnels to feed on bark or callus tissue around the tunnel entrance. Several larvae were in tunnels almost the same length as the body, suggesting that some construct more than one tunnel. Wandering late instar larvae were observed at night on three occasions (Wagner, 1985).
First and early instar larvae were not observed in above ground tissues and Wagner (1985) suggested that they may be feeding on rootlets or leaf litter on the ground. Under laboratory conditions first instar larvae of P. californicus were fed on the tubers of several plants as well as synthetic spruce budworm and codling moth diets. They were also observed to feed on fungal hyphae and spores that grew on sliced carrots and the synthetic media. These larvae did not tunnel, but fed under a sparse tent of silk and frass (Wagner, 1985).
Research at the Strong Lab (University of California, Berkeley) has shown that the soil nematode Heterorhabditis marelatus has a significant impact on P. californicus populations (Strong et al. 1995). Nematodes release a symbiotic bacterium that kills P. californicus larvae. Nematodes feed on the bacteria and digested host tissues and reproduce inside the larvae (Strong et al., 1996)