RESISTANCE TO INSECT HERBIVORY OF COTTON LINES - QUANTIFICATION OF RECOVERY CAPACITY AFTER DAMAGE

This study investigated the degree of variability among cotton (Gossyp ium spp.) lines in their ability to recover after damage from insect h erbivory. Recovery capacity of 25 lines was assessed in a glasshouse e xperiment in which shoot dry weight (W) and leaf area (L) of undamaged controls (c) and damaged plants (d, apical bud removed manually) were measured 18 days after the treatment. Indices of recovery (R) were ca lculated based on W, i.e. R-W = W-d/W-c, or L, i.e. R-L = L-d/L-c. Rec overy capacity among lines varied widely, as indicated by the ranges f or R-W (0.37 to 1.79) and for R-L (0.46 to 1.49). Data from field expe riments including 12 to 19 lines were used to explore the association between these recovery indices and yield losses due to naturally occur ring insect pests. Yield of unprotected crops (Y-d) subjected to damag e by the naturally occurring pests and yield of control crops protecte d with insecticides (Y-c) were measured in four field experiments wher e main herbivore insects included Lepidoptera (Helicoverpa spp.), and sucking mirid bugs (Creontiades dilutus and Campylomma livida). Across experiments, the effect of insect pests varied from an almost complet e yield loss (Y-d/Y-c = 0.07) to a slight yield increase (Y-d/Y-c = 1. 11). Yields of protected crops and recovery indices were unrelated. A positive association was found between yield of unprotected crops and R-L, and the magnitude of this association increased with increasing l evel of insect damage. These results indicate that variation in recove ry capacity could be an important component of the variation in resist ance to insect herbivory in cotton. (C) 1997 Elsevier Science B.V.