J. Lerin et K. Koubaiti, MODELING WINTER OILSEED RAPE PLANT INFESTATION BY BARIS-COERULESCENS (COLEOPTERA, CURCULIONIDAE), Environmental entomology, 26(5), 1997, pp. 1031-1039
Baris coerulescens Scopoli is a pest attacking the tap root of winter
oilseed rape. Females lay eggs in the root crown for >3 mo. The slow a
ccumulation of eggs in plants poses problems in defining cohorts for m
odeling larval development under fluctuating temperatures. The total n
umber of immature individuals per plant was assessed throughout the wh
ole reproduction period during a 4-yr study. Two supplementary data se
ts were collected in 1994 and 1996. Total insect population density pl
otted against degree-days (in base 10) differed among years. The speed
at which the population maximum was reached was steeper during wet ye
ars than during dry years. The hypothesis was that the differences in
slopes were caused by drought stresses, which were known to influence
egg laying from experiments in controlled conditions. A model based on
the Weibull distribution and describing the growth of insect populati
on density per plant from the beginning of egg laying to maximum densi
ty is proposed. The insect population density is expressed as the cumu
lative proportion of individuals found in plants, varying in the inter
val (0,1). The initial degree-day scale is corrected by a coefficient
linked to the upper soil water content. This correction ensured a good
concordance among years and places. The model predicted correctly the
dynamics of plant infestation under variable climatic conditions.