Host Acceptance Behavior of Pear Psylla (Homoptera: Psyllidae) Affected by Plant Species, Host Deprivation, Habituation, and Eggload

Abstract

The interactive effects of plant species, host deprivation (amount of time deprived of the host), and mature egg complement (eggload) on host acceptance activities of pear psylla, Cacopsylla pyricola Foerster, were monitored in laboratory bioassays. Plant species included a natural host, ‘Bartlett’ pear, Pyrus communis; an Asian pear, P. calleryana, currently of use in breeding programs; and the nonhost apple, Malus domestica. Plan species differed primarily in their effects on oviposition-related activities; settling-probing activity was similar among species. Increased duration of host deprivation resulted in increased time spent in oviposition activities, egg-laying rates, and eggload; fraction of oviposition-related activities that failed to result in an egg being deposited decreased with increasing deprivation. Largest differences among plant species in their effects on oviposition activities occurred at the longest deprivation level. On ‘Bartlett’ pear, oviposition activity and probability of oviposition increased with increasing eggload, whereas settling-probing activity decreased. On the Asian pear, significant relationships between eggload and activity were noted only at one deprivation level; the patterns were similar to those on ‘Bartlett’ pear. On apple, settling-probing activity decreased with increasing eggload at a single deprivation level. On all plant species, oviposition activities increased with time spent in contact with the leaf; for nonhosts, this result suggests that psylla habituated to novel species. First-order transitions between pairs of behaviors were quantified. Psylla rarely initiated oviposition activities immediately upon leaf contact. Rather, oviposition activities tended to be preceded by settling-probing activity. We interpret these results as evidence that plant cues received on initial contact were insufficient to release oviposition activity but that plant cues received during settling-probing activity released oviposition activities. Oviposition activity on P. calleryana and apple was ended before egg deposition with higher frequency than on ‘Bartlett’ pear. This result suggests that plant cues received during oviposition activities affected ultimately whether the egg was deposited.