Projecting distribution and dispersal of subtropical tamarisk beetles, Diorhabda sublineata, towards habitat of the endangered southwestern willow flycatcher

The subtropical tamarisk beetle (Diorhabda sublineata) was introduced on the Rio Grande near Presidio, Texas in 2009 for biological control of tamarisk (Tamarix ramosissima/T. chinensis), and it is rapidly dispersing and defoliating extensive areas of tamarisk in the TransPecos region. This beetle might adversely affect habitat of the federally endangered Southwestern Willow Flycatcher (Empidonax traillii extimus) in New Mexico and Arizona where tamarisk is a significant component of nesting habitat and is often used as a nest substrate. Envelope Score continental species distribution models, incorporating topoclimatic indices, are coupled with MIGCLIM-R cost-distance dispersal models that incorporate landscape functional connectivity for tamarisk beetles. The resulting dispersal models are used in least dispersal time cost path analyses to project the timing and route of dispersal of subtropical tamarisk beetles into flycatcher critical habitats in New Mexico and Arizona. A calibrated dispersal model projects beetles will travel north from El Paso along the Rio Grande and arrive in the largest extant flycatcher habitat on Elephant Butte Reservoir, NM by 2014. Arrival in tamarisk dominated flycatcher habitats on the middle Gila River, AZ is projected for 2017 as beetles travel west from Las Cruces, NM. Willow restoration in these flycatcher habitats should be implemented now in order to mitigate potential flycatcher habitat loss from beetle defoliation.