Based on surveys of winter roost sites, the eastern migratory population of the monarch butterfly (Danaus plexippus) in North America appears to have declined in the last 20 years and this has prompted the implementation of numerous conservation strategies. However, there is little information on the survivorship of first-generation monarchs in the core area of occupancy in Texas, Oklahoma, and Louisiana where overwinter population recovery begins. The purpose of this study was to determine the survivorship of first-generation eggs to third instars at a site in north Texas and to evaluate host plant arthropods for their effect on survivorship. Survivorship to third instar averaged 13.4% and varied from 11.7% to 15.6% over three years. The host plants harbored 77 arthropod taxa, including 27 predatory taxa. Despite their abundance, neither predator abundance nor predator richness predicted monarch survival. However, host plants upon which monarchs survived often harbored higher numbers of non-predatory arthropod taxa and more individuals of non-predatory taxa. These results suggest that ecological processes may have buffered the effects of predators and improved monarch survival in our study. The creation of diverse functional arthropod communities should be considered for effective monarch conservation, particularly in southern latitudes.

Introduction: Eastern migratory monarch butterflies (Danaus plexippus) have declined over 80% in recent years, but little is known about fall reproduction in the southern U.S. where monarchs may compete with queen butterflies (Danaus gilippus). Aims/Methods: We provide data on the survival to third instar, associated arthropods, and phenology of fall breeding monarchs and queens in Texas. Results: Monarch and queen survival was high, but varied among years. Oleander aphids (Aphis nerii), jumping spiders (Salticidae), and red imported fire ants (Solenopsis invicta) had minor negative effects on survival. The abundance of monarchs and queens on the study site peaked three to four weeks before the main passage of monarchs in the area. Queens had similar phenology and exhibited a migratory pattern similar to monarchs but on a smaller scale. Discussion: Survival of fall monarchs is high and likely to be important for winter roost recruitment. Fall egg survival was not greatly affected by any particular arthropod taxon, but may be affected by precipitation. Fall reproduction is a response to available host plants and likely adaptive. The timing of oviposition enables pupae to eclose in time for successful migration to winter roosts. Implications for Insect Conservation: Management of Asclepias viridisand other native milkweeds to facilitate fall reproduction is important for the recovery of monarchs because it buffers variable productivity occurring further north and contributes significantly to overwintering populations. Management should use mowing and burn schedules that promote high quality host plants. Populations of queens should be monitored for their potential to compete with monarchs especially in response to the potential impacts of parasite resistance and climate change.

The eastern migratory population of the monarch butterfly (Danaus plexippus) has shown evidence of declines in recent years. During early spring, when the population is at its smallest, red imported fire ants (RIFA) (Solenopsis invicta) have been implicated as having devastating effects on monarch egg and larval survival, but there are no conclusive experimental data to support this contention. The purpose of this study was to determine the effect of RIFA on the survival of spring monarch eggs to third instar larvae. Three treatments were analyzed: control plots, RIFA-suppressed plots, and RIFA-enhanced plots. Other host-plant arthropods were also documented. In control plots, monarch survival was unrelated to RIFA abundance on or around the plants. For both years combined, RIFA suppression had little impact on monarch survival. In one of the two years, higher survival occurred in the suppressed treatment, but confidence in this difference was low. In control plots, monarch survival increased with increasing numbers of other arthropods (not including RIFA) on the host plant. Predator pressure did not vary relative to arthropod abundance, and RIFA only occupied plants in large numbers when large numbers of other arthropods were also present. The presence of RIFA did not affect predator pressure. RIFA artificially drawn onto host plants created artificially high predator pressure, and monarch survival was low. Long-term use of bait to control RIFA may not be cost-effective provided surrounding biodiversity is high. Efforts to promote spring monarchs should focus on promoting biodiversity in addition to planting milkweed.

Introduction Eastern migratory monarch butterflies (Danaus plexippus) have declined over 80% in recent years, but little is known about fall reproduction in the southern U.S. where monarchs may compete with queen butterflies (Danaus gilippus). Aims/methods We provide data on the survival to third instar, associated arthropods, and phenology of fall breeding monarchs and queens in Texas. Results Monarch and queen survival was relatively high, but varied among years. Oleander aphids (Aphis nerii), spiders, and red imported fire ants (Solenopsis invicta) had minor negative effects on survival. The abundance of monarchs and queens on the study site peaked three to four weeks before the main passage of monarchs in the area. Queens had similar phenology and exhibited a migratory pattern similar to monarchs but on a smaller scale. Discussion Survival of fall monarchs is relatively high and potentially important for winter roost recruitment. Fall survival was not greatly affected by any particular arthropod taxon, but may be affected by precipitation. Fall reproduction is a response to available host plants and its timing enables pupae to eclose in time for migration to winter roosts. Implications for insect conservation Management of Asclepias viridis and other native milkweeds to facilitate fall reproduction could facilitate recovery of monarchs if it buffers variable productivity further north. Management should use mowing and burn schedules that promote high quality host plants. Populations of queens should be monitored for their potential to compete with monarchs especially in response to the potential impacts of parasite resistance and climate change.