Diversity and Abundance of a Pollinator
Group: Hawkmoths (Lepidoptera:
Sphingidae) in Forests and Surrounding Farmlands, East Usambara Mountains, Tanzania
Adelaide E Sallema1 and Shabani S Selemani1,2*
1Department of Collection, National Museum and House of Culture, National Museum of Tanzania, Tanzania
2Biological and Marine Sciences Unity, Marian University College, Tanzania
Submission: September 22, 2022; Published: October 03, 2022
*Corresponding author: Shabani S Selemani, Biological and Marine Science Unity, Marian University College, P. O. Box 47, Bagamoyo, Tanzania
How to cite this article: Adelaide E S, Shabani S S. Diversity and Abundance of a Pollinator Group: Hawkmoths (Lepidoptera: Sphingidae) in Forests
02 and Surrounding Farmlands, East Usambara Mountains, Tanzania. Int J Environ Sci Nat Res. 2022; 31(1): 556307. DOI 10.19080/IJESNR.2022.31.556307
Pollinators are now facing a drastic biodiversity fall in various parts of our world. In Africa data to measure and monitor their biodiversity trend is still inadequate and concentrated more on some insect pollinator groups, especially bees and butterflies. In this study, hawkmoth diversity and abundance in East Usambara Mountains were assessed. Data collection was conducted from three different habitat types that included thick vegetation assemblage with canopy cover, edges of the forest, and farmlands between 2017 and 2019. Hawkmoths were captured using a UV-light trap 250W mercury bulb in 12 sampling sites. A total of 35 hawkmoth species and 991 individuals belonging to the family Sphingidae were identified. The highest hawkmoth abundance was recorded from forest edges (p < 0.05). Canopy cover and farmlands showed lower hawkmoth abundance. Accordingly, higher Shannon Weiner diversity indices were recorded from canopy cover and forest edges (p < 0.05). Farmlands had the lowest Shannon Weiner diversity index. Differences in diversity and abundance of hawkmoths among three habitat types suggest that accelerating anthropogenic factors has led to the destruction of natural habitats. Meanwhile, natural habitat destruction has often been found to exert adverse effects on biodiversity. Moreover, the decline in biodiversity of pollinator insects like hawkmoths hinders the vital pollination service to both crops and wild flora. East Usambara Mountains are still an important refuge for many species that become restricted to different environments due to climate change and anthropogenic pressure, hence calling for regular pollinator conservation and monitoring. This study will provide the baseline data on hawkmoth species richness, abundances and diversity for potential conservation and monitoring programs.
Insect pollinators contribute greatly to plant pollination compared to other pollinator groups but sadly they are now facing drastic declines in various parts of our world [1-3]. In Africa, data to measure and monitor their trend is still inadequate and concentrated more on some insect pollinator groups especially bees neglecting other groups such as hawkmoths. Hawkmoths provide vital ecosystem services as pollinators of both crops and wild flora . They are insects from order Lepidoptera family Sphingidae. They pollinate many plants like pawpaw (Carica papaya and Asimina triloba), coffee (Coffee spp.), kapok (Ceiba pentandra) and Sphingophilous flowers which include Lantana spp., Lonicera spp., and Silene spp. [4-6]. There are about 4% of all the plants in Kenya, including pawpaw, and many different African orchids such as aerangoid orchids which are pollinated by hawkmoths [7,8]. A study conducted in South Africa by Johnson & Raguso , together with the findings of Martins & Johnson  in East Africa, demonstrates the existence of a guild of African plants that appears to rely almost exclusively on the long-tongued convolvulus hawkmoth Agrius convolvuli for pollination.
Hawkmoths comprise about 1,602 species and 205 genera worldwide . About 70% of these species occur in the Africa and the New World [12,13]. Most species are crepuscular and nocturnal, except for some strictly diurnal hawkmoths, such as species of Aellopos, Hemaris and Macroglossum . Hawkmoths are generally composed of nectarivorous species with little exclusion which makes them a very important pollinator group . Apart from hawkmoths, insect pollinator groups include
bees, flies, butterflies, moths, wasps, beetles, and thrips, among
others [5,16]. It has been estimated that animal pollinators are
considered necessary for the reproduction of 90% of flowering
plants and one-third of human food crops . Abundant and
healthy populations of pollinators can enhance fruit set, quality,
and size, then ultimately in farming increase production per acre,
and in the wild, biodiversity and wildlife food sources increase
. In the United States year 2005 the value of honey bee and
non-honey bee pollination services was worth an estimated US $
15 billion and $ 5-6 billion respectively per year .
Currently, there is a persistent decline in the abundance and
diversity of Lepidopterans in some countries such as Tanzania and
the United States [20,21]. Furthermore, pollinating hawkmoth
declines of eight species had been reported in the Northeastern
United States which may have ecological effects on both the
plants pollinated by these species and vertebrate predators of
the moths . In Tanzania, quantification of Lepidopterans
to check their diversity trend is at an insufficient level even in
the areas where the biodiversity hotspots of the world such as
the East Usambara Mountains. Unfortunately, East Usambara
Mountains have been under considerable pressure as a result
of expanding human population and demands for arable land
[23-25]. These activities have led to the clearance of a large part
of the forests as well as fragmentation and hence a decrease in
biodiversity [26,27]. Moreover, the fragmentation of forests leads
to the decline of pollinator diversity of endangered plant species
found in the East Usambara Mountains such as Mesogyne insignis
. The study by Notø  showed anthropogenic disturbance
in the East Usambara Mountains affecting the abundance and
diversity of fruit-feeding butterflies (Lepidoptera; Nymphalidae).
It is recently reported that the abundance of some Lepidoptera
pollinating families at farmlands in East Usambara Mountain is
significantly dwindling compared to woodland .
Data is required to understand how these threats affect
the pollinator groups and how to manage agricultural and wild
landscapes to secure pollination in such circumstances. Data is
needed to provide information for the management and decisionmaking
agencies about various pollinator groups. These key
knowledge gaps are targeted focusing on hawkmoths. Sampling
took place in a key ecosystem area, the East Usambara Mountains.
Forests and the agroecosystems surrounding the forests were
sampled for the hawkmoth species as little information exists on
the diversity, abundance, and status of this pollinator group in
forests and the surrounding farmlands.
A sampling of hawkmoths was conducted in the East Usambara
Mountains situated in northeastern Tanzania about 40km from the
town of Tanga region between 4º45′-5º20′S and 38º26’-38º48′E (Figure 1), with an altitudinal range of 130m to 1506m [24,31].
The rainfall distribution of East Usambara Mountains is bi-modal,
peaking between March and May and between September and
December . The dry seasons are from June to August and
January to March, however, precipitation occurs in all months
. Rainfall is greatest at higher altitudes and in the southeast of
the mountains, increasing from 1,200 mm annually in the foothills
to over 2,200mm at higher altitudes .
A total of 12 sampling sites located in 3 different habitat types
including thick vegetation assemblage with canopy cover, forest
edges, and farmlands were sampled between 2017 and 2019
(Figure 1). The study sites were georeferenced using Garmin eTrex
30x GPS and validated with google Maps (Table 1). The dominant
crops found in the farmlands were Camellia sinensis, Elettaria spp.,
Amomum spp., Cinnamomum spp., Saccharum spp., Musa spp.,
Piper nigrum, Artocarpus heterophyllus, Syzygium aromaticum, and
Dioscorea spp. The dominant vegetation compositions in canopy
cover were tree species such as Cephalosphaera usambarensis,
Leptonychia Usambarensis, Allanblackia stuhlmannii, and Annickia
kummeriae. Meanwhile, at the edges of the forest, the dominant
vegetations were grassy verges such as Cynodon spp., Pennisetum
purpureum, Lantana camara, Clidemia hirta, and tree species such
as Eucalyptus spp., and Maesopsis eminii.
Sampling took place for the period of 60 days during long rain
(April-June) and short rain (November-December). Hawkmoths
were sampled with the help of a UV-light trap consisting
of 250W mercury bulbs. Lamps were connected to a 250V
generator to ensure stable voltage output. Lamps were placed
1.5m above ground in front of a 3 x 2m white sheet which was
attached vertically to two wooden poles. This installation was
placed at each site with a white sheet facing only the particular
sampling site. The techniques used to sample hawkmoths almost
resemble those described in Kingstone & Nummelin , Ferro &
Romanowski , and Lourido et al. . All three habitat types
were surveyed between 18:00 and 24:00 hours, 5 days each.
Hawkmoths attracted to the light trap were captured by direct
handling or with an insect net. Sampled specimens were killed
and then placed in envelopes for later preparation and species
identification in the Biology laboratory at the National Museum
of Tanzania. Identifications were made to species level from keys,
illustrations, and guides [4,38,39].
Species diversity was calculated using Shannon-Wiener
diversity index (H’) [40,41]. The Shannon-Wiener diversity index
is given by the formula:
While Where Pi is proportional to species ith relative to the total number of species R. n is the number of individuals in a
species, and N is the total number of individuals in a sample.
Pielou’s evenness index was used to measure species evenness
of the hawkmoth species in a habitats type  Pielou’s evenness
was computed using the following formula:
Where J 'is Pielou’s evenness index, H ' is a Shannon-Wiener
index and S is species richness.
Sørensen index of similarity was used to measure the
similarity of species communities among pairs of habitats .
Sørensen index of similarity was calculated using the following
Where CS explains the coefficient of similarity, a is the number
of species found in habitat A; b is the number of species present
in habitat B and ab is the number of species shared by the two
Shapiro-Wilk normality test was used to test the normality of
the data by which the normal distribution of the data was verified (p > 0.05). The abundance of hawkmoths among habitats was
analyzed by One-way ANOVA test. Comparisons of abundance
between pairs of habitats were conducted by Dunn’s post hoc test.
A special t-test (diversity t-test) was used to compare the species
diversity between pairs of habitats. Paleontological Statistics
(PAST) version 3.20 was used for all mentioned above analyses
. The statistical significance level for accepting all null
hypotheses was 5% (α = 0.05). Results were summarized using
tables and graphic presentations.
In total, 991 hawkmoth individuals were collected belonging
to 35 species from all sites in three habitat types (Appendix 1).
The abundance and species richness of Sphingids was highest
in forest edges, followed by closed canopy cover, and lowest
in farmlands (Figure 2). The differences in abundance among
habitats were statistically significant (One-way ANOVA test, F =
5.531, p= 0.0052). Abundance comparisons between pairs of
habitats to check where statistically significant differences exist
by using Dunn’s post hoc test shown in Table 2 below:
Hawkmoth species sampled in the East Usambara Mountains
by this study represent about 63% of all Sphingid species
sampled on the lower slopes of the Uluguru Mountains located in
the eastern part of Tanzania . Moreover, this study includes
about 21% of all Sphingid species known from Tanzania .
The most common species were Euchloron Megaera, Coelonia
fulvinotata, Nephele argentifera, Nephele comma, and Temnora
elegans. 4 species were the least abundant and very uncommon among sphingid species detected in all sites. These species were
Centroctena imitans, Cephonodes hylas, Neoclanis basalis, and
Temnora atrofasciata (Appendix 1). On the other hand, Euchloron
Megaera and Nephele comma were recorded as among the most
common and abundant species by Kingstone & Nummelin 
and Kioko et al.  concordant with this present study. None
of the Sphingid species caught were endemic to Tanzania in this
study, although species such as Chaerocina livingstonensis and
Macropoliana scheveni are known to be endemic to Tanzania
The abundance and species richness of hawkmoths showed
a declining trend as one moves from the forest edges through
canopy cover to farmlands (Figure 2). Additionally, farmlands
had the lowest Shannon Wiener index of diversity compared to
those indices of the canopy cover and the forest edges (Figure
3). A study by Selemani  showed that farmlands in the East
Usambara Mountains had lower hawkmoth abundance compared
to woodland. These findings of the lowest species abundance,
species richness, and species diversity regarding farmlands,
indicate this habitat type experienced severe disturbance and
probably from anthropogenic pressure. Furthermore, farmland
disturbances have adverse impacts on both pollinators and
crop pollination, and this negatively affects crop production
and commodity markets . On the other hand, Forest edges
had a significantly higher abundance than canopy cover (Table
2). It might be due to a nectar source plant; Lantana camara, an
invasive plant species which was predominant at the forest edges.
This implies either declines of native nectar plants in the forest
canopies or higher competition shown by invasive nectar plants
against native nectar plants in pollination ecology. Hawkmoths
had been observed extending their forages on Lantana camara
and other introduced invasive species such as Tithonia diversifolia
in various African countries such as Madagascar and Kenya
[10,48]. Higher Sorensen indices of similarity between habitat
types propose a wide and almost even distribution of the majority
of hawkmoth species in the East Usambara Mountains recorded
by this study.
The findings of this present study showed that forest edges
and canopy cover were providing potential support to the
diversity and abundance of hawkmoths in the East Usambara
Mountains. Hence, attention should not only be given to these two
forest habitat types but also to the farmlands and other habitat
types to boost the diversity of various pollinator groups. Due to
the higher species similarities of the hawkmoths on farmlands
and forest habitat types, agroforestry should be encouraged.
This is because, if the farmlands are managed well, they could be
a valuable conservation asset in the difficult trade-off situation
between the conservation of biodiversity and the sustainability of
rural livelihood. The diversity of hawkmoths and all Lepidoptera
species, in general, is directly connected to the availability of
specific host plants and not every plant in a particular habitat
type. Therefore, for effective and efficient conservation of this
pollinator group, a study of the knowledge of hawkmoth host
plants should be conducted in the East Usambara Mountains.
The authors would like to thank Huruma Mtemela, Agnes
Robert and Rashid Njechele for their help with the field and
laboratory works. We thank the National Museum of Tanzania (NMT) management for the support of this study. We acknowledge
the Botanical Garden of Amani Nature Reserve and the Tanzania
Forestry Service Agency branch of Amani Nature Reserve for
allowing fieldwork to be conducted.
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