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.