Ant-hemipteran mutualisms can have positive and negative effects
on host plants depending on the level of hemipteran infestation and plant
protection conferred by ants against folivory. Differential effects of such
mutualisms on plant survival are well documented in undisturbed and
ant-invaded systems, but few have explored how anthropogenic disturbance
affects interactions between hemipterans and native ant species and what
the consequences may be for recovering ecosystems. Within a fragmented
landscape in Costa Rica, restored tropical forests harbor a mutualism
between the native ant Wasmannia auropunctata and the scale insect
Alecanochiton marquesi on the abundant, early-successional tree Conostegia
xalapensis. I added A. marquesi scales to C. xalapensis seedlings and
either allowed or excluded W. auropunctata to investigate if this mutualism
leads to increased scale infestation, decreased scale mortality, and
decreased folivory. I also examined whether these effects are mediated by
the percentage of remnant forest cover in the landscape. I found that
seedlings with ants excluded had fewer scale insects and higher herbivory
than plants with ants present. Combined scale mortality due to fungi and
parasitism was also higher on ant-excluded vs. ant-allowed plants but only
at sites with high surrounding landscape forest cover. Together, these
results suggest that mutualisms between scale insects and native ants can
promote scale infestation, reduce folivory on native plant species, and
disrupt biological control of scale insects in recovering tropical forests.
Further, my experiment underscores the importance of remnant tropical
forests as sources of biological control in anthropogenically-disturbed
landscapes.
Data collected includes abundance data for A. marquesi in both March 2018 when the experiment began and June 2018 at the end of the experiment. Data also included mortality of A. marquesi due to fungi and parasitism, W. auropunctata abundance, and change in percent folivory on leaves of C. xalapensis after the end of the experiment in June 2018. Percent landscape forest cover at buffers out to 650 m are also included in the dataset.
Data was entered in Microsoft Excel 360 and processed in R Studio (Version 1.2.5019)
Data processing included creating new variables for difference in abundance of A. marquesi between March and June of 2018 (scale_abun_jun18 - scale_abun_mar18) and subtracting A. marquesi abundance based on ambient scale colonization of control treatments at the subplot (block) level.
