indoor arthropod communities and distributions in us homes

429 Pages·2017·5.78 MB·English

17
Proceedings of the Ninth International Conference on Urban Pests
Matthew P. Davies, Carolin Pfeiffer, and William H Robinson (editors) 2017
Printed by Pureprint Group, Crowson House, Uckfield, East Sussex TN22 1PH UK
INDOOR ARTHROPOD COMMUNITIES AND
DISTRIBUTIONS IN U.S. HOMES
1MATTHEW A. BERTONE, 2MISHA LEONG, 1KEITH M. BAYLESS,
3,4ROBERT R. DUNN, AND 2MICHELLE D. TRAUTWEIN
1Department of Entomology and Plant Pathology, North Carolina State University, Raleigh, NC, USA
2California Academy of Sciences, San Francisco, CA, USA
3Department of Applied Ecology, North Carolina State University, Raleigh, NC, USA
4Center for Macroecology, Evolution and Climate, Natural History Museum of Denmark, University of
Copenhagen, Copenhagen, Denmark
Abstract By furthering our understanding of biodiversity in urban landscapes, we can advance our understanding
of urban pests. We investigated the complete arthropod community of the indoor biome in 50 houses (located in
and around Raleigh, North Carolina, USA). We discovered high diversity, with a conservative estimate range of
32 to 211 morphospecies, and 24 to 128 distinct arthropod families per house. However, the majority of these
arthropods are not considered urban pests. We found arthropods within homes are both diverse and prevalent, and
are a mix of closely synanthropic species and a great diversity of species that enter homes accidentally. Despite
being found in the majority of homes, several arthropod groups such as gall midges (Cecidomyiidae) and book lice
(Liposcelididae) remain unfamiliar to the general public. The diversity of arthropods was non-random with respect
to location within the house; for instance, certain families, such as camel crickets (Rhaphidophoridae) and isopods
(Armadillidiidae) were particularly abundant in basements. On a landscape scale, the indoor arthropod community
conformed to the “luxury effect,” with houses located in higher income neighborhoods having higher arthropod
richness, even when accounting for house size and local vegetation. These findings present a new understanding
of the diversity, prevalence, and distribution of the arthropods in our daily lives.
Key words Landscape ecology, biodiversity, urban ecology.
INTRODUCTION
Humans have lived with animal associates (both invited and uninvited) for thousands of years. The
most diverse group of organisms on Earth is made up of arthropods (insects, arachnids, myriapods,
crustaceans, etc.), and while many species are known to live closely with humans (Robinson, 2005),
very few studies have assessed the entire community of arthropods that dwell with people, except
for a few noteworthy pest species. To better understand the diversity of arthropods found in homes
we comprehensively sampled specimens from houses located in and around Raleigh, NC, USA. We
identified the types of arthropods and where they were found in homes, using these data to describe what
arthropod diversity in houses look like and other aspects of the indoor arthropod community.
MATERIALS AND METHODS
Full methods (including a map of the study area) for this study can be found in Bertone et al. (2016) and
Leong et al. (2016). Briefly, 50 free-standing, volunteer homes were randomly selected in and around
Raleigh, NC, USA. Trained entomologists visited these homes and hand-collected all arthropods,
living and dead, from all visible surfaces of all rooms. Only attics and crawl spaces were sampled less
thoroughly, for safety reasons. All specimens were collected into vials of ethanol each labeled according
to house, room type and other characteristics (floor type; windows and doors to the outside). Specimens
18 M. A. Bertone, M. Leong, K. M. Bayless, R. R. Dunn, and M. D. Trautwein Indoor Arthropod Communities and Distributions in U.S. Homes
were identified by MAB and KMB as specifically as possible, with arthropod family as the major
taxonomic unit. In each group, the number of morphospecies (i.e. those that appeared to be different
species) was also documented per room. Some difficult to identify groups (based on current knowledge)
and/or specimens (due to physical damage precluding identification) were identified to the most specific
taxon possible. We classified rooms into six categories based on their similarities: attics, basements
(including finished and unfinished basements, and crawl spaces), bathrooms (including bathrooms and
laundry rooms), bedrooms (including bedrooms, offices, and libraries), common rooms (including living
rooms, dining rooms, and attached hallways), and kitchens (including kitchens and pantries); rooms not
conforming to one of the categories were classified as “other” and were excluded from analysis. We
estimated diversity of families based on the complete list of families acquired over each sampled house
using the Chao2 Estimator with 1,000 randomization runs in EstimateS (Colwell, 2013). For analyses
related to neighborhood income and arthropod diversity, see Leong et al. 2016.
RESULTS AND DISCUSSION
Overall Metrics
Houses in the study ranged from 840 to 4,833 square feet in area (mean = 2,072; median = 1,720)
and were from seven to 94 years old (mean = 41.35; median = 30.5). During the course of sampling 554
rooms in the 50 homes, over 10,000 specimens were collected and identified. These specimens represented
all four subphyla (Chelicerata, Myriapoda, Crustacea, and Hexapoda), as well as six classes, 34 orders and
304 families of arthropods (for a complete list of taxa see Tables 1 and S1 in Bertone et al. 2016). While we
could not determine the exact number of morphospecies, there were at least 579 morphospecies based on our
most conservative estimates (calculated by summing the maximum number of morphospecies for each family
ever found in a single room).
We collected 24–128 families from each house, resulting in an average of 61.84 (s.d. = 23.24) distinct
arthropod families per house and a total gamma diversity (across houses) of 304 families (Figure 1A). One
hundred and forty-nine (149) families were rare, collected from fewer than 10% of homes, 66 of which were
found in just a single home. The number of families collected in a home was correlated with house size (r2 =
0.3, p = < 0.001). Conservative species estimates by home ranged from 32 to 211, with an average of 93.14
(s.d. = 42.34) morphospecies per house (Figure 1B). Our conservative species estimate assumes that rooms
with the greatest number of morphospecies by family included all species from other rooms (which is almost
certainly untrue), thus this number is likely much lower than the true number of species per house.
Taxon Specific Observations
While overall diversity was high, 12 frequently found families were identified in at least 80% of
homes (Figure 4 in Bertone et al. 2016). Four families were identified from 100% of houses sampled:
cobweb spiders (Theridiidae), carpet beetles (Dermestidae), gall midge flies (Cecidomyiidae) and ants
(Formicidae). Book lice (Liposcelididae) and dark-winged fungus gnats (Sciaridae) were found in 98%
and 96% of homes, respectively. Nearly half of all families (five of 12) found in over 80% of homes were
true flies (Diptera): fungus gnats (Sciaridae); mosquitoes (Culicidae); scuttle flies (Phoridae); non-biting
midges (Chironomidae); and gall midges (Cecidomyiidae).
Typical household pests were found in a minority of the homes, such as German cockroaches
(Blattella germanica: 6% of houses), subterranean termites (Rhinotermitidae: 28% of houses), and
fleas (Pulicidae: 10% of houses); bed bugs (Cimex lectularius) were not found during the study.
Larger cockroaches (Blattidae), such as smoky brown (Periplaneta fuliginosa) and American
cockroaches (Periplaneta americana) were found in the majority of houses (74%). However, the
American cockroach (which is the species considered a true pest) was only recovered from three
homes; smoky brown cockroaches made up the vast majority of large cockroaches collected. All pest
species were less common than other more inconspicuous arthropods such as pillbugs (Armadillidiidae,
78%) and springtails (Entomobryidae, 78%). In addition to those listed above, many of the same
pests we recovered were also found in archaeological sites (see discussion in Bertone et al. (2016).
Indoor Arthropod Communities and Distributions in U.S. Homes 19
Figure 1A (top): Number of
morphospecies collected
from homes ranked by
house size. The bottom limit
is the minimum or
conservative estimate of
morphospecies by house
which was calculated by
taking the maximum
number of morphospecies
from the room containing
the highest number of
morphospecies, for each
family, and summing the
total The upper limit is the
maximum possible of
morphospecies within a
house, with the assumption
that each set of
morphospecies within each
room were unique from
other rooms. Figure 1B
(bottom): Estimated
diversity of families. The
mean, along with 95%
Figure 1 A. Number of morphospecies collected from homes ranked by house size. The bottom
lower and upper confidence
limit is the minimum or conservative estimate of morphospecies by house which was calculated by
intervals, was calculated
taking the maximum number of morphospecies from the room containing the highest number of
morphospecies, for each family, and summing the total The upper limit is the maximum possible based on the complete list of
of morphospecies within a house, with the assumption that each set of morphospecies within each families acquired over each
room were unique from other rooms. sampled house using the
Chao2 Estimator with 1,000
randomization runs in
Arthropod Distribution within the Home
EstimateS (from Bertone et
Arthropods were found on every level of the home and in all room types. Only 5 rooms (non-attics)
al. 2016)
had no arthropod specimens collected (four bathrooms, one bedroom). Six arthropod orders dominated
houses, comprising 81% of the diversity in an average room: Diptera (true flies, 23%), Coleoptera

(beetles, 19%), Araneae (spiders, 16%), Hymenoptera (predominantly ants, 15%), Psocodea (book
lice, 4%), and Hemiptera (true bugs, 4%) (Figure 2). Eight additional orders made up another 15%
of the diversity (Blattodea, Collembola, Lepidoptera, Isopoda, Zygentoma, Polydesmida, Orthoptera,
and Acari), while all remaining orders comprised a total of 4% of the overall diversity (Figure 2). The
percentage of rooms in which an arthropod was collected varied among taxa, as did their presence in
rooms of different types (Table 1 in Bertone et al., 2016).
We found that although many groups were common throughout a home, some were more
restricted to certain room types than others. After ranking the prevalence of different families by room
type, many common groups change rank drastically between rooms. Isopods (Armadillidiida e) and
camel crickets (Rhaphidophoridae) ranked as commonly found in basements, but did not make it into
the top ten (or even top 20 in most cases) for any other room type. This is expected, as these arthropods
are typically limited to dark, damp environments not usually found homes except in basements.
Figure 1A (top): Number of
morphospecies collected
from homes ranked by
house size. The bottom limit
is the minimum or
conservative estimate of
morphospecies by house
which was calculated by
taking the maximum
number of morphospecies
from the room containing
the highest number of
morphospecies, for each
family, and summing the
total The upper limit is the
maximum possible of
morphospecies within a
house, with the assumption
that each set of
morphospecies within each
room were unique from
20 M. A. Bertone, M. Leong, K. M. Bayless, R. R. Dunn, and M. D. Trautwein Indoor Arthropod Communities and Distributions in U.S. Homes
other rooms. Figure 1B
(bottom): Estimated
diversity of families. The
mean, along with 95%
lower and upper confidence
intervals, was calculated
based on the complete list of
families acquired over each
sampled house using the
Chao2 Estimator with 1,000
randomization runs in
EstimateS (from Bertone et
al. 2016)

Figure 1B. Estimated diversity of families. The mean, along with 95% lower and upper
confidence intervals, was calculated based on the complete list of families acquired
over each sampled house using the Chao2 Estimator with 1,000 randomization runs in
EstimateS (from Bertone et al., 2016).
FiguFrieg u2r.e P2:r oPprooprotritoionnaall diversi-
diversity of arthropod
ty of arthropod orders across all
orders across all rooms.
rooms. Average morphospecies
Average morphospecies
composition calculated across
composition calculated
all roaocrmos st yaplle rso.o mPh tyoptoess. Amlol dified
fromp Bhoetortso bnye M eAt Bal.. , 2016.
(modified from Bertone
et al. 2016)

Figure 3: Rank
abundance of families by
room type. These are lists
of the 20 most commonly
collected families for
each room type.
Indoor Arthropod Communities and Distributions in U.S. Homes 21
Arthropods and the Luxury Effect
The “luxury effect,” in which wealthier neighborhoods are more biologically diverse, has been observed
for both plants and animals including birds (Luck et al., 2013), lizards (Ackley et al., 2015), and bats (Li
and Wilkins, 2014). However, where indoor environments are concerned, there is a general perception
that homes in poorer neighborhoods harbor more indoor arthropods (Cohn et al., 2016; Wang et al.,
2007).
After model testing, we found that indoor arthropod diversity was best predicted by models that
take into consideration not only house square footage, local ground vegetation cover and diversity, but
also mean neighborhood income. To better understand the impact of vegetation on indoor arthropod
diversity, we further explored the interactions between income and our house-level vegetation variables.
The interaction term revealed that for houses whose yards have limited ground vegetation cover, being
located in a higher income neighborhood had a strong positive effect on indoor arthropod diversity
(Figure 3). Yet for houses that have yards with high ground vegetation cover, neighborhood income did
not influence indoor arthropod diversity. We suspect that in higher income neighborhoods, enhancements
at the neighborhood scale (including higher vegetation overall, as found in Hope et al., 2003; Kinzig et
al., 2005; Grove et al., 2006; Clarke et al., 2013) can compensate for limited vegetation in the yard of an
individual house. Thus, simply being located in a higher income neighborhood may provide ecological
benefits to outdoor and indoor biodiversity. This suggests that vegetation at the scale of neighborhoods
can be predictive of indoor arthropod diversity at the scale of individual houses. It matters, in short,
not only how much vegetation you have in your yard, but how much is present in the yards and other
habitats nearby (Goddard, 2010).
Figure 4: Interaction plot.
For houses with low and
medium levels of
vegetative ground cover,
neighbourhood income
had a strong influence on
number of arthropod
families. (modified from
Leong et al. 2016)

Figure 3. Interaction plot. For houses with low and medium levels of vegetative ground
cover, neighbourhood income had a strong influence on number of arthropod families.
(modified from Leong et al. 2016)
22 M. A. Bertone, M. Leong, K. M. Bayless, R. R. Dunn, and M. D. Trautwein Indoor Arthropod Communities and Distributions in U.S. Homes
CONCLUSIONS
Our results show indoor communities of arthropods in the Southeastern U.S. are a mixture of both
synanthropic species (i.e. those that rely on human dwellings for shelter and breeding sites) and accidental
visitors from the outdoors that become trapped inside. We also found the majority of arthropods in homes
are not typical pest species, though pests were collected. Although almost all parts of a home can be occupied
by arthropods, some arthropods are associated with certain room types more than others. Lastly, houses in
neighborhoods with higher income appear to have more diversity of arthropods entering homes.
REFERENCES CITED
Ackley, J.W., J. Wu, M.J. Angilletta Jr., S.W. Myint, and B. Sullivan. 2015. Rich lizards: How
affluence and land cover influence the diversity and abundance of desert reptiles persisting in
an urban landscape. Biol. Conserv. 182, 87–92. doi:10.1016/j.biocon.2014.11.009
Bertone, M.A., M. Leong, K.M. Bayless, T.L.F. Malow, R.R. Dunn, and M.D. Trautwein. 2016.
Arthropods of the great indoors: characterizing diversity inside urban and suburban homes.
PeerJ 4:e1582 https://doi.org/10.7717/peerj.1582
Clarke, L.W., G.D. Jenerette, and A. Davila. 2013. The luxury of vegetation and the legacy of
tree biodiversity in Los Angeles, CA. Landsc. Urban Plan. 116, 48–59. doi:10.1016/j.
landurbplan.2013.04.006
Cohn, R.D., S.J. Arbes, R. Jaramillo, L.H. Reid, and D.C. Zeldin. 2006. National prevalence and
exposure risk for cockroach allergen in U.S. households. Environ. Health Perspect. 114,
522–526.
Colwell, R.K. 2013. EstimateS: statistical estimation of species richness and shares species from
samples. Version 9. User’s Guide and application. Available at http://purl.oclc.org/estimates
Goddard, M. A., A.J. Dougill, and T.G. Benton. 2010. Scaling up from gardens: biodiversity
conservation in urban environments. Trends Ecol. Evol. 25, 90–98. doi:10.1016/j.
tree.2009.07.016
Grove, J.M., A.R. Troy, J.P.M. O’Neil-Dunne Jr., W.R. Burch, M.L. Cadenasso, and S.T.A.
Pickett. 2006. Characterization of Households and its Implications for the Vegetation of
Urban Ecosystems. Ecosystems 9, 578–597. doi:10.1007/s10021-006-0116-z
Hope, D., C. Gries, W.X. Zhu, W.F. Fagan, C.L. Redman, N.B. Grimm, A.L. Nelson, C. Martin,
and A. Kinzig. 2003. Socioeconomics drive urban plant diversity. Proc. Natl. Acad. Sci. U.
S. A. 100, 8788–8792. doi:10.1073/pnas.1537557100
Kinzig, A.P., P. Warren, C. Martin, D. Hope, and M. Katti. 2005. The effects of human
socioeconomic status and cultural characteristics on urban patterns of biodiversity. Ecol.
Soc. 10, 23.
Leong, M., M.A. Bertone, K.M. Bayless, R.R. Dunn, and M.D. Trautwein. 2016. Exoskeletons and
economics: indoor arthropod diversity increases in affluent neighbourhoods. Biol. Lett. 2016
12 20160322; DOI: 10.1098/rsbl.2016.0322. Published 2 August 2016.
Li, H. and K.T. Wilkins. 2014. Patch or mosaic: bat activity responds to fine-scale urban
heterogeneity in a medium-sized city in the United States. Urban Ecosyst. 17, 1013–1031.
(doi:10.1007/s11252-014-0369-9)
Luck, G.W., L.T. Smallbone, and K.J. Sheffield. 2013. Environmental and socio-economic
factors related to urban bird communities. Austral Ecol. 38, 111–120. doi:10.1111/j.1442-
9993.2012.02383.x
Robinson, W.H. 2005. Urban insects and arachnids: A handbook of urban entomology. Cambridge:
Cambridge University Press.
Indoor Arthropod Communities and Distributions in U.S. Homes 23
Wang, C., M.M.A. El-Nour, and G.W. Bennett. 2007. Survey of Pest Infestation, Asthma, and
Allergy in Low-income Housing. J. Community Health 33, 31–39. doi:10.1007/s10900-007-
9064-6
25
Proceedings of the Ninth International Conference on Urban Pests
Matthew P. Davies, Carolin Pfeiffer, and William H Robinson (editors) 2017
Printed by Pureprint Group, Crowson House, Uckfield, East Sussex TN22 1PH UK
REVIEW OF CLIMATE CHANGE IMPACTS ON URBAN PESTS
PARTHO DHANG
Independent Consultant, 2410 Belarmino Street, Bangkal, Makati City 1233, Philippines
Abstract Urban centres amplify both abiotic and biotic parameters favouring pest life history. In absence of
natural enemies in urban areas, these parameters often are directly proportional to growth and population of these
pests. Under the influence of climate change and global warming, these centres will act as favourable spots for
pests in multiple ways, thus posing far reaching consequences, affecting human lives. Insects are cold-blooded
organisms and are unable to regulate their body temperature and it is believed that the effect of temperature
on insects largely overwhelms the effects of other environmental factors. Evidence of climate change and its
impact are now apparent in many parts of the world, such as reports of insect vectors and vector borne diseases
in previously unrecorded elevations, pest damages in uncited latitudes and pest activity in unexpected seasons.
Its influence on aspects such as building materials, quality of urban structures, non-vectors, nuisance pests and
prevention are now under examination. Increased urbanization and people’s choice of urban life has made this a
very relevant subject and this article reviews impact of climate change on various aspects of pest dynamics as well
as its influence on a number of tools and methodologies which are used to control and manage them.
Key words Climate change, global warming, urban pests, urban heat island.
INTRODUCTION
Consequences of climate change on humans is mostly unknown, but its impact is slowly being realised.
Among many, some could be challenges caused purely by urban and public pests (Dhang, 2016). The
impact of climate change on vectors for disease pathogens (mosquitoes, ticks, blackflies, fleas, etc.)
and other medically important arthropods (stinging insects, spiders, and bed bugs) is a topic of great
concern (Sims and Appel, 2016). Climate change can modify pest life history, resulting in increased
diversity and density of pests, consequently posing significant risk to humans. It is also notable that
climate change impacts could be amplified in urban centres much different from natural areas due to the
creation of urban heat island, making most urban areas warmer than surrounding areas (Douglas and
James, 2015). This phenomenon in certain latitudes could influence pests, by increasing their activity
and also by making non pest species to move into these warmer centres and become pests as evident by
examples described by Douglas and James, (2015). A number of comprehensive reports are available
discussing the effects of climate change on public pests in both indoor and outdoor conditions (Dhang,
2016; USEPA, 2010; CIEH 2008; Epstein, 2005; Patz et al., 2003).
MATERIALS AND METHODS
Journal articles were retrieved from library, online sources and personal collection using the key words
mentioned elsewhere in this article. A relatively small number of studies exist on the topic, so reference
list provided in relevant articles were reviewed in detail to find additional articles. The final information
was reviewed to check for completeness towards the theme before being written.
26 Partho Dhang Review Of Climate Change Impacts On Urban Pests
RESULTS AND DISCUSSION
Climate Change In Urban Areas
The urban environment is a complex of wholly or partially anthropogenically-influenced habitats created
from natural areas, sometimes via the intermediate state of agricultural land (Robinson, 2005). In the
context of the urban environment, ‘urban’ comprises not just the city centre, but also the surrounding
suburbs, urban green space, industrial areas, and the rural-urban fringe (Robinson, 2005). Urban areas
present unique composition unlike natural. The main driver of an urban ecosystem is human, his
activates and behaviour. Urbanity presents concentrated human population, accumulated resources such
as food and water, variety of niches such as micro-habitats, diversity of flora and fauna, climate control
options, varied ideology etc. to be called unique. However one of the most significant features which is
experienced in urban areas is heat island.
An urban heat island (UHI) is an area/city warmer than its surrounding natural areas due to
human activities. The main cause of the urban heat island effect is from the modification of land surfaces
(Solecki, 2004; USEPA, 2015) and waste heat generated by energy usage is a secondary contributor
(LI and Zhao, 2012). Thus urbanization causes regional increases in temperature that exceed those
measured on a global scale, which are as much as 12°C warmer than their surroundings (Angilletta et
al., 2007). It is obvious, animals and plants living in urban area will deferentially respond to altered
conditions in comparison to natural world. This makes urban areas to amplify both abiotic and biotic
parameters often favouring pest life history, and in absence of natural enemies, these parameters often
are directly proportional to population of these pests (Dhang, 2016).
Urban heat island also bring permanent changes in the physiology of the species when compared
to their natural populations, favouring a step towards evolution of a group which can be now be called
“truly urban”. It is observed that leaf-cutter ants, Atta sexdens colonies in urban heat islands have an
increased heat tolerance at no cost (Angilletta et al., 2007). It is expected that species that are good at
colonizing can invade to utilize favourable conditions provided by urban heat islands to thrive in regions
outside of their normal range. Examples of this include Pteropus poliocephalus, a flying fox, and the
house gecko Hemidactylus frenatus, (Warren, 2005).
Urban areas around the world are known to harbour common pests due to their close dependence
on humans. Roy et al. (2009) predicted the effect of climate change on nuisance insect species in the
United Kingdom. The report highlights the nuisance insect species that are unlikely to be affected by
environmental warming are Blattella germanica (German cockroach), Cimex lectularius (bed bug),
Monomorium pharaonis (Pharaoh ant), Anobium punctatum (wood-worm), Ctenocephalides felis (cat
fleas), Lyctus brunneus (powderpost beetle), Hylotrupes bajulus (house longhorn), Tineola bisselliella
(common clothes moth), Dolichovespula media (media wasp) and Vespa crabro (European hornet).
The ten species most likely to increase with climate warming are Tinea riaalternata (moth fly), Lasius
neglectus (invasive garden ant), Thaumetopoea processionea (oak processionary moth), Linepithema
humile (Argentine ant), Reticulitermes grassei (Mediterranean termite), Culex pipiens molestus (urban
mosquito), Culex pipiens pipiens (mosquito), Aedes vexans (mosquito – wetland), Ochlerotatus cantans
(mosquito – woodland) and Musca domestica (house fly). The study further predicted that the ten species
most likely to increase with changes in precipitation patters are the same as for increasing temperature
with the exception of Musca domestica, but included Phlebotomus mascittii (sand fly).
Evidence of Climate Change Impacts on Urban Pests
Evidence of climate change and its impact are now visible in many parts of the world. Examples of
this can be had from changes in distribution, density or behavioural patterns of pests. Reports of new
pest occurrence, such as reports of insect vectors and vector borne diseases in previously unrecorded
elevations in eastern and central Africa, Latin America, and Asia are now attributed to climate change
Review Of Climate Change Impacts On Urban Pests 27
(Dhang, 2016). In addition to mosquitoes, other pest species such as flies, lice, ticks, fleas, bats, rodents,
snails and termites could significantly increase their distribution range and contribute to spread of
diseases and damages to humans, influenced by changes in climate. This is evident in one of the WHO
reports which highlights the linking of climatic factors such as temperature, precipitation, and sea level
rise, to the lifecycles of infectious diseases, including both direct and indirect associations via ecological
processes (Patz et al., 2003).
Mosquito and its link to climate change has recently under close scrutiny with the increased
incidence of malaria in highland urban cities, such as Nairobi, and rural highland areas of Papua New
Guinea (Reiter, 2008). Similarly vector of Dengue, Chikungunia and other zoonotic disease Aedes
aegypti, once limited by temperature to approximately 1000 m in elevation, has recently been found at
1700 m in Mexico and 2200 m in the Colombian Andes (Epstein, 2004). A study conducted by Culler
(2015) on artic mosquitoes Aedes nigripes conclusively show that warmer spring temperatures caused
the mosquitos to emerge two weeks earlier and shortened their development time through the larval and
pupal stages by about 10 percent for every 1°C increase in temperature. Warming increased the number
of mosquitoes being eaten by diving beetles, but the mosquitoes accelerated growth in their vulnerable
juvenile stages lessened their time with aquatic predators, which ultimately increased their chance of
surviving to adulthood. With a 2°C warming scenario, the model predicted the mosquito’s probability of
survival will increase by 53 percent.
A number of studies such as by Easterling et al., 2000; Greenough et al., 2001; Pall et al., 2011,
also link climate change to mosquito outbreaks. The studies point out that mosquitoes belonging to
the species, Culex tritaeniorhynchus and Culex tarsalis, vectors for the Japanese and Western Equine
Encephalitis viruses respectively, are floodwater species and may increase in abundance in the urban
environment during and after flooding events, which are predicted to increase with climate change.
Increase in geographic range of mosquitoes following warm temperature gradients into previously
unknown territories in USA (Rochlin et al, 2013), serves as another good example how temperature can
influence urban pest dynamics.
Evidence of other species showing influence of climate are being increasingly reported. Sims
and Appel (2013) reported weather-influenced effects on pests from St. Louis area of USA. They
reported termite swarming unusually early in the year, following the extremely mild winter of 2011-
12. The mild winter was followed by a very warm and dry summer and this was also associated with a
significant increase in houses invaded by brown recluse spiders that normally reside outdoors. Quarles
(2007) suggested temperature increases in the USA to favour warm weather pests such as ants, termite
pests, clothes moths, flies, mosquitoes, fleas, stored product moths, wood boring beetles, and bed bugs.
It is observed that termite distribution and abundance is closely linked to distribution and abundance
of rainfall gradient (Wood and Johnson, 1986), temperature and relative humidity (Cabrerra, 1994).
Termite foraging patterns are linked to key abiotic parameters (Haagsma and Rust 1995; Mesenger
and Su 2005; Moura et al., 2006). Evidence of termites in previously unrecorded latitudes are also
coming to light now. Reports of tropical species, such as Coptotermes gestroi, becoming established in
the subtropics (Grace, 2006); and subtropical species Coptotermes formosanus expanding their range
northwards into more temperate areas (Jenkins et al., 2002) substantiate the role climate could play in
pest distribution.
In colder areas of North America such as Wisconsin and southern Canada, populations of
Reticulitermes flavipes appear to be gradually expanding their range and even swarming under natural
outdoor conditions (Arango et al., 2014, Scaduto et al., 2012). However, colony growth and slow
dispersal without the need for swarming has been associated with these northern colonies on the fringe
of their range (Arango et al., 2014). Swarming events can occur in all months of the year. With
increasing temperatures, both the total yearly number of swarms and frequency of swarms in cooler
months can be expected to increase.