The Asian tiger mosquito, Aedes albopictus, is an anthropophilic aggressive daytime-biting nuisance and an efficient vector of certain arboviruses and filarial nematodes. Over the last 30 years, this species has spread rapidly through human travel and commerce from its native tropical forests of Asia to every continent except Antarctica. In 2011, a population of Asian tiger mosquito (Aedes albopictus) was discovered in Los Angeles (LA) County, California. To determine the probable origin of this invasive species, the genetic structure of the population was compared against 11 populations from the United States and abroad, as well as preserved specimens from a 2001 introduction into California using the mitochondrial cytochrome c oxidase 1 (CO1) gene. A total of 66 haplotypes were detected among samples and were divided into three main groups. Aedes albopictus collected in 2001 and 2011 from LA County were genetically related and similar to those from Asia but distinct from those collected in the eastern and southeastern United States. In view of the high genetic similarities between the 2001 and 2011 LA samples, it is possible that the 2011 population represents in part the descendants of the 2001 introduction. There remains an imperative need for improved surveillance and control strategies for this species.

In 2011, a thriving population of Aedes albopictus (Skuse), the Asian tiger mosquito, was discovered within three cities in Los Angeles County over an estimated 52-km2 urban area. Two years later in 2013, Aedes aegypti (L.), the yellow fever mosquito, was detected within several urban areas of Madera, Fresno, and San Mateo counties. State and local vector control agencies responded with an aggressive effort to eradicate or interrupt the spread of these two invasive mosquitoes; however, known populations continued to expand outward and new infestations were identified at an accelerated pace in central and southern California. By the end of 2015, one or both species had been detected within the jurisdictional boundaries of 85 cities and census-designated places in 12 counties. Herein we report on the discovery and widespread establishment of Ae. aegypti and Ae. albopictus in urban areas of coastal, central, and southern California between 2011 and 2015 and discuss the subsequent rapid changes to the activities and priorities of vector control agencies in response to this unprecedented invasion.

Sixty-two questing adult Rhipicephalus sanguineus (Latreille) ticks were collected by direct removal from blades of turfgrass and adjacent concrete walkways at a suburban home in Riverside County, CA, and tested for the presence of Rickettsia, Bartonella, and Ehrlichia DNA. Polymerase chain reaction (PCR) was used to amplify fragments of the 17-kDa antigen gene and the rOmpA gene of the spotted fever group rickettsiae. One male tick contained R. rickettsii DNA; its genotype differed from R. rickettsii isolates found in Montana and Arizona that cause Rocky Mountain spotted fever and from Hlp#2 and 364D serotypes. One male tick and one female tick contained B. henselae DNA. No Ehrlichia platys or Ehrlichia canis DNAs were detected using nested PCR for their 16S rRNA genes. These findings extend the area where Rickettsia rickettsii may be vectored by Rh. sanguineus. Rh. sanguineus also may be infected with Bartonella henselae, a human pathogen that is typically associated with fleas and causes cat scratch disease.

Cat fleas, Ctenocephalides felis (Bouché), were reared at different temperatures to examine further the effects on egg-to-adult development and emergence of adults from cocoons. Three different temperatures (26.7, 21.1, and 15.5 degrees C) were used to rear fleas. Emergence of adults from cocoons was monitored using 2 experimental designs-cocoons maintained in groups and cocoons individually isolated. At cooler temperatures, cocoons kept in groups had a higher incidence of late-emerging adults than did individual cocoons. At 15.5 degrees C, adults continued to emerge from grouped cocoons up to 80 d after all had emerged from individual cocoons. Developmental time of prepupae and pupae was determined by inhibiting cocoon formation of late 3rd instars. Male prepupae and pupae developed approximately 20% slower than did females. Comparisons between emergence of adults from cocoons and from naked pupae indicate that a large percentage of adults emerge from cocoons soon after molting. The possible association of developmental temperatures and emergence from cocoons with overwintering populations is discussed.

The first breeding populations of Aedes aegypti (Linnaeus) were identified in California in 2013, and have since been detected in 13 counties. Recent studies suggest two introductions likely occurred, with genetically distinct populations in the central and southern regions of the state. Given the threat of dengue, chikungunya, and Zika virus transmission, it is imperative to understand if these populations harbor genes that could confer resistance to pyrethrin-based insecticides, known as pyrethroids, the most commonly used class of adulticides in the state. In 2017, the California Department of Public Health initiated a pesticide resistance screening program for Ae. aegypti to assess the presence of specific mutations on the sodium channel gene (V1016I and F1534C) associated with knockdown resistance to pyrethroids. Mosquitoes collected between 2015 and 2017 from 11 counties were screened for mutations using real-time polymerase chain reaction assays. Results revealed distinctly different resistance profiles between the central and southern regions. The central population displayed nearly fixed resistant mutations at both loci, whereas the southern population was more variable. The relative proportion of resistant alleles observed in sampled mosquitoes collected in southern California increased each year from 2015 through 2017, indicating potential increases in resistance across this region. The presence of these mutations indicates that these mosquitoes may be predisposed to surviving pyrethroid treatments. Additional biological and biochemical assays will help better elucidate the mechanisms underlying insecticide resistance in California Ae. aegypti and prompt the use of pesticides that are most effective at controlling these mosquitoes.