Research and IPM

Refine integrated pest management strategies for pitch canker by determining the risk that wood infesting insects carry the pathogen.

We have trapped and determined the phoresy rate of two species of phloem-feeding engraver beetles (Ips mexicanus and Ips plastographus), two species of sapwood-infesting beetles (Asemum nitidum, longhorned beetle, and Gnathotrichus retusus, ambrosia beetle), and at least two species of twig beetles (Pityophthorus setosus and P. carmeli) occurring in central coastal California in 2003 to 2005. We also determined the spore load of I. mexicanus, I. plastographus, P. setosus and P. carmeli. As far as we know, this is the first report of the number of spores of F. circinatum carried by an insect.

All these insects have a wide host range, and A. nitidum is known to colonize Douglas-fir and Pinus species.

We have also collected symptomatic Monterey pine branches to rear Pityophthorus spp. We determined the phoresy rate and spore load of these beetles. Phoresy rate and spore loads of beetles reared from F. circinatum-infected branches were several-fold higher than those beetles trapped using semiochemicals, suggesting that beetles emerging from the infected host material have a great potential to vector F. circinatum in nature. We successfully demonstrated transmission of F. circinatum by two species of twig beetles, P. carmeli and P. setosus in nature.

We have strong evidence that both sexes of I. mexicanus, I. plastographus, P. setosus and P. carmeli carry propagules of pitch canker, thus both sexes are potentially important in introducing the fungi into host tissue. Natural spore loads on these beetles and their ability to transmit the pitch canker pathogen are important factors in predicting the future distribution of this disease on other hosts in California and elsewhere.

We captured a total of 8,821 beetles from 11 species in five families in 2003.

We have determined natural propagule load for I. mexicanus and P. setosus trapped in June and August 2003. This is the first report of the number of propagules of F. circinatum carried by an insect. Presently we are determining the natural propagule load of these and other insects from the remaining monthly sampling dates (June-November 2003).

We set up additional traps in the southern most population of native Monterey pines in Cambria, and sampling was initiated for the early April collection and will continue monthly until the end of November.

Recent attempts to isolate and determine the number of propagules of F. circinatum on various species of bark and wood boring beetles have been successful for Ips mexicanus and two species of longhorned beetles in 2004.

We have evidence that males of Ips spp. and some Pityophthorus species initiate galleries and excavate nuptial chambers, whereas females excavate egg galleries only. We have evidence that both male and female P. setosus initiate entrance tunnels. Phoresy rates (proportion of individuals carrying the pathogen) for males and females are different for some species of Pityophthorus, i.e. P. carmeli, males have [a] higher phoresy rate than females, P. setosus and P. nitidulus females have a higher phoresy rate than males.

Natural propagule loads on these insects and their ability to transmit the pitch canker pathogen are important factors in predicting the future distribution of this disease on other hosts in California and elsewhere. The relative importance of the different vector species will enable efforts to reduce spread of the pathogen to be focused on the key vectors.