Photos from the WFIWC Archives:
Mexico
Fig. 1. A. Dendroctonus rhizophagus has a distinctive antennal club and black body differing from D. valens (B).
Fig. 2. David Cibrián examining a young Pinus engelmannii killed by D. rhizophagus near Mesa del Huracan, Chih.
Dendroctonus rhizophagus. This exclusively Mexican species is superficially similar in appearance to the sympatric red terpentine beetle, D. valens (Fig. 1 A,B). However, it only infests young pines, especially Pinus engelmannii in its juvenile "grass stage" (Fig. 2), whereas D. valens normally infests mature pines throughout much of North America. It was described from Chihuahua and Durango by Thomas and Bright (1970) and placed in synonymy under D. valens by Wood (1974). This is an account of cooperative work with David Cibrián of the University of Chapingo leading to reinstatement of D. rhizophagus as a valid species.
As mentioned in a previous account, I had met David at a WFIWC meeting in 1976. We went on a subsequent (1977) field trip to Chihuahua to collect Douglas-fir beetles. Our association continued and I was invited to participate in the 1st National Symposium on Forest Parasitology, in Urapan in 1980. In Mexico, forest pathology and forest entomology are integrated under the term "Parasitology." Because of that, I met Frank Hawksworth there. He was the authority on dwarf mistletoes (Fig. 3 A,B). Through various circumstances, we three made an extended field trip in my camper truck through northern Mexico and southwestern USA in 1981. Relevant here is our visit to Mesa del Huracan, Chih., from where D. rhizophagus was described.
Fig. 3. Frank Hawksworth examining a mistletoe, Arceuthobium globosum, on the trunk of a pine. Chihuahua, Mexico.
Fig. 4. Oscar Estrada studied the biology and control of D. rhizophagus while a student at University of Chapingo. The beetle causes great economic damage to pine plantations as exemplified by this Pinus arizonica, which he is examining. Had the tree lived a few more years it would have outgrown susceptibility to the beetle.
There, we met Oscar Estrada (Fig. 4), a student at University of Chapingo who was studying the biology and control of D. rhizophagus (then a synonym of D. valens). It was causing great economic damage to newly planted pine plantations in this area, 40% of which were susceptible P. engelmannii. One or two females create a gallery at ground level. Larvae mine downward in the root and excavate weevil-like pupal cells that deeply score the wood (Fig. 5). Curiously, all host species of pines usually out-grow susceptibility by the time that they are 1.5 meters tall.
Our trip continued through other Mexican states and then back to the USA. Frank left us in Phoenix and David and I continued to Brigham Young University, Provo, Utah, to confer with Steve (S.L.) Wood concerning our comparative studies that showed D. rhizophagus to be a valid species. Wood was well underway toward publication of his monograph on Scolytidae of North & Central America (Wood 1982). We were anxious that rhizophagus should not remain a synonym in that monumental publication!
Fig. 5. The D. rhizophagus egg gallery extends a short distance below ground level. The larvae mine downward in the root and excavate pupal chambers that score the sapwood (arrow).
Now, I must back-track. The particulars reside in my files but the jist of it is that a few years earlier, David and I agreed to conduct comparative biological and anatomical studies of rhizophagus and valens, which we had reason to believe were, indeed, distinct species. Consequently, his associate, Rodolfo Campos, and I examined adults with SEM and light microscopy at Moscow (Furniss & Campos Bolaños 1982) while David and Oscar gathered biological information in the field (Estrada Murrieta & Cibrián Tovar1982).
Thus it was that, on May 12, 1981, I dropped-off David to visit Steve Wood in the Monte L. Bean Museum while I found a parking place. I had some reservation about the matter at hand, not knowing how our case might be received by the Master of scolytid taxonomy. So, maybe I did drive around the lot a few times to give David a head start. But I need not have worried. After presenting our findings, Steve agreed and D. rhizophagus gained species status in his monograph (although too late to have been included in the species key!).
Fig. 6. The antennal club of D. rhizophagus (left) is rather angular whereas that of D. valens is more rounded. They also differ in color as noted in the narrative.
So, what were the adult characters separating these beetles? We listed 10 such characters of the adult. Of these, the one that I find to be both definitive and easily seen involves the shape (Fig. 6) and color of the antennal club. That of rhizophagus is somewhat angular and the basal segment is black while the distal segments are light reddish brown; that of valens is more rounded and uniformly reddish brown. Also, the body of rhizophagus is invariably black (Fig. 1 A) while that of valens is generally reddish brown. -- Photos and text by Malcolm M. Furniss
References
Estrada Murrieta, O, and D. Cibrián Tovar. 1982. Biologia del descortezador del renuevo de pino Dendroctonus rhizophagus Tomes y Brighten en la region de Mesa del Huracan, Chihuahua. Proc. 2nd Nat'l. Sympos. For. Parasitology, Cuernavaca, Mexico Feb. 17-20, 1982. Secretaria de Agricultura y Recursos Hidraulicos Publicación Especial No. 46.
Furniss, M. M. and Campos Bolaños, R. 1984. Anatomia comparativa de adultos de poblaciones simpatricas de Dendroctonus rhizophagus Thomas and Bright, y Dendroctonus valens Le Conte, en Chihuahua, Mexico. p. 97-105. Proc. 2nd Nat'l. Sympos. For. Parasitology, Cuernavaca, Mexico Feb. 17-20, 1982. Secretaria de Agricultura y Recursos Hidraulicos Publicación Especial No. 46.
Thomas, J.R., and D.E. Bright. 1970. A new species of Dendroctonus (Coleoptera: Scolytidae) from Mexico. Can. Entomol. 102: 479-483.
Wood, S. L. 1982. The bark and ambrosia beetles of North and Central America (Coleoptera: Scolytidae), a taxonomic monograph. Great Basin Nat. Mem. No. 6.
Wood, S.L. 1974. New synonymy and records of North American bark beetles (Coleoptera: Scolytidae). Great Basin Naturalist 34: 277-290.
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