The Pacific Oak Twig-girdler
Journal of Economic Entomology 13(5): 379-384
The Buprestid, Agrilus angelicus, Horn, causes serious damage to oaks (Quercus agrifolia) in California. It also attacks interior live oak (Q. wislizeni), leather oak (Q. durata), canyon live oak (Q. chrysolepis), mesa oak (Q. engelmanni), California black oak (Q. californica) and tan oak (Q. densiflora.) It is found from a few feet above sea-level to an altitude of 6, 000 ft. The eggs are generally laid singly on the smooth bark of the twig near the end of the last year's growth at the end of June or beginning of July. They hatch in from two to three weeks, and the larvae begin boring under the bark. The complete life-cycle requires about two years. By the middle of the first winter the mine extends down the small twigs for about one to three inches. Some of the larvae may reach the wood, whilst others still remain in the bark. Mining is continued in the following spring and summer, the length of the burrow being increased to from 6 to 12 inches. The winter is passed in the centre of the branch. In the succeeding spring the burrow is lengthened by an inch or two, after which the larva turns and retreats for several inches before entering the wood to form the pupal cell, usually about the middle of May. The adults remain for several days in the pupal cell before emerging in May and June. The natural enemies of this beetle include the following Hymenopterous parasites: - Cryptohelcostizus rufigaster, Cushm., Cryptoideus fasciatus, Ashm., Doryctes muculipennis, Rohw., Callihormius sp., Ptinobius agrili, Rohw., reared from the larvae, Metapelma spectabilis, Westw., which may be a hyperparasite, Tetrastichus anthracinus, Ashm., of which as many as 17 larvae have been found in one larval host, and Dinotus agrili, Rohw. The remedial measures advocated include pruning about April before the beetles emerge. These prunings should be placed in a box or barrel covered with a 16 mesh wire screen to permit the escape of the parasites. Poison and contact sprays exercise a certain amount of check by poisoning the beetles as they feed, but not sufficient to warrant their use against this beetle only.