The size and geographic distribution of Coccinella novemnotata Herbst populations have been decreasing rapidly across North America closely following the establishment, spread, and population growth of the invasive seven-spotted lady beetle, Coccinella septempunctata L. To determine whether intraguild predation and competition for prey may be partially responsible for the decline, we paired first-instar larvae of two populations of C. novemnotata (eastern and western) with first-instar C. septempunctata at low or high aphid densities. Survival of both C. novemnotata populations was significantly lower when larvae were paired with C. septempunctata, and western C. novemnotata exhibited significantly lower survival compared with the eastern population. This relationship depended on aphid density with the greatest survival of both C. novemnotata populations occurring at the high aphid density. Both male and female C. novemnotata weighed less on the day of eclosion when paired with C. septempunctata as compared with pairings with conspecifics. In a second test, C. septempunctata and C. novemnotata instars were varied at the start of the trial and C. novemnotata survival to adulthood in the presence of C. septempunctata was dependent of the instar of C. novemnotata used to initiate the experiment. C. novemnotata exhibited higher rates of survival and weighed significantly more on the day of eclosion when C. novemnotata was older than its C. septempunctata partner. These results suggest that interspecific competition including intraguild predation by C. septempunctata may contribute to C. novemnotata population declines, but that the intensity of this impact may vary across C. novemnotata populations.

Populations of the native ninespotted lady beetle, Coccinella novemnotata Herbst, have undergone precipitous declines in North America following the establishment of the exotic sevenspotted lady beetle, Coccinella septempunctata L. Recent volunteer efforts have made it possible to establish colonies of the now-rare C. novemnotata and test mechanisms contributing to its decline. We evaluated the relative frequencies of intraguild predation and cannibalism of eggs between these two species. A single C. novemnotata or C. septempunctata adult was exposed to conspecific and heterospecific eggs in either the presence or absence of pea aphids. The study revealed two expected results: 1) eggs of C. novemnotata were consumed more frequently than eggs of C. septempunctata by both species, and 2) egg consumption was higher when aphids were absent, independent of predator and egg species. There were also two unexpected results from the study: 1) the asymmetry between egg predation rates was higher when aphids were present, and 2) higher predation rates on C. novemnotata eggs in the absence of alternate prey was due to a relatively higher rate of intraspecific cannibalism. This implies that C. novemnotata would have suffered higher egg mortality rates before the invasion of C. septempunctata, but even though the aggregate rate of egg predation on C. novemnotata eggs is lower post-invasion, it is still significantly higher than the aggregate rate of predation of C. septempunctata eggs. This differential pattern of asymmetric predation could contribute to habitat compression and the overall decline of C. novemnotata.

Mosquitoes use many cues to assess whether a habitat is conducive for reproduction, possibly including the presence of stimuli from aquatic macrophytes. The effect of water infusions of water hyacinth (Eichhornia crassipes), water lettuce (Pista stratioles), parrotfeather (Myriophyllum aquaticum), and water pennywort (Hydrocotyle umbellata) on mosquito oviposition and attraction was investigated. Gravid Culex quinquefasciatus deposited significantly more egg rafts in water hyacinth, water lettuce, or Bermuda hay (positive control) infusions compared to water, while water pennywort and parrotfeather infusions did not differ from water. In‐flight attraction responses of Cx. quinquefasciatus, Aedes aegypti, and Anopheles quadrimaculatus were evaluated. The strongest attraction of gravid Cx. quinquefasciatus and Ae. aegypti occurred in the presence of volatiles from infusions of water hyacinth and water lettuce, which were equal in attractiveness to hay infusion. Water pennywort and parrotfeather infusions were not attractive. Gravid An. quadrimaculatus were not attracted to aquatic plant volatiles. The results suggest that water hyacinth and water lettuce emit volatile chemicals that attract two of three mosquito species tested and stimulate oviposition by Cx. quinquefasciatus, demonstrating that the level of attraction of aquatic plant volatiles varies among species in ways that may have relevance to bait‐based detection and control methods.