Host plant resistance to blackmargined aphids on pecan

The blackmargined aphid is a major insect pest of pecan. Host plant resista nce to this insect was tested in two NPACTS (National Pecan Advanced Clone Testing System) tests in California in 1998. Number of aphids per leaf were determined 16 times at weekly intervals. 'Pawnee: which had been shown to be resistant in Texas and Georgia, also demonstrated resistance in Californ ia. Aphid populations varied greatly, with the Lagomarsino Test averaging 4 .10 aphids per leaf for the season, and the Clark Test averaging 8.52. Temp oral variation in each test was great, with significant clone X date intera ctions. Level of host plant resistance in clones was generally unpredictabl e, based upon parentage. In pecan breeding programs, this makes testing of potential clone releases imperative, since predictability of performance ba sed on pedigree has limitations.