Plant Protection based write up on entomology

1. 15/07/29 Clint Willemse
Plant Protection A
ND: Horticulture
Dr F Nchu
Plant Pest:
Abstract
Here in contains information captured for the topic of researched insects for Plant Protection A,
using taxonomic order and the interaction with host plants. No reference to any specific plant specie
is made. A look into the phylum 'Arthropoda', Sub-phylum 'Hexapoda', Mandibulata, Insecta super
groups will be made, with the orders being Thysanoptera, Hemiptera, Homoptera and Lepidoptera.
Insects
There are many plant pests known to man which ravish plant stock in all environmental habitats.
Plants that come in contact with insects beyound physical control are referred to as an 'infested
plant'. This is detrimental in crop production whereby, Infected plants may display gradual
'necrotic'*1
symptoms leading to death through various methods that insects deposit through its
interaction with plants. Insects are referred to as an 'vector'*2
carrier, whereby pathogens, viruses,
bacteria etc. are often a result of this contact. Insects may too be beneficial to an garden
environment like the common 'Centepede' class 'Diplopoda', sub-phylum Myriapoda. Insects are
commonly found a hindrance in greenhouses, ornamental displays in landscapes, turf culture,
vegetable and herb production etc. As more species of insects co-exist compared to any other group
of animals and plants put together.*3
In order to better understand species of all kinds, naming systems are studied to ensure proper
classification of insects belonging to the phylum Arthropods. Figure 2 shows the largest class of
insects with 30 million species and are the most successful of all animals. See Figure 1. There are
750 000 recorded species in the phylum Arthropods consist of nine orders, of which we are
discussing the four (beetles, flies, butterflies, bees, true bugs) pg. 666 'Biology 8th
Edition' Raven,
Johnson, Logos, Mason, Singer; Mc Graw Hill 2008. All arthropods have an strong cuticle
exoskeleton made of chitin*4
- a tough resistant nitrogen containing polysaccharide that forms the
cell walls of certain fungi, exoskeleton of arthropods, and the epidermal cuticle of other
invertebrate’s. Insects typically possess three regions; a thorax, head and abdomen usually with
antennae.
Thysanoptera:
Are usually garden pests that attack all types of vegetation as “Thrips” and possess a minute
characteristic, slender shape with brightly coloured at larvae stage and yellow, brown or black at
maturity with asymmetrical mouth parts and narrowed set of wings. Refer to figure 3. Damaging
crops is typified in its feeding in multitudes. Thrips may position itself underside a leaf, in vegetable
crop or in between flower petals, carrying potentially tomatoe spotted wilt virus, etc. Distributed
worldwide in both harshful dessert and arctic regions this species cause galls on plants, while others
are found in decomposed plant material. “Thrips population may increase dramatically in a short
space of time when particularly abundant in wheat and Lucerne crop” further investigation revealed
how, “they rasp the tissues of plants to suck sap” (Diseases and Pest of Ornamental Plants: 5th
Ed.
1907). It remains an serious pest in cultivated cosmopolitan crop (readily utilized vegetables) and
transmit virus and disease whilst feeding on plant tissue*5
*7
. The order Thysanoptera comprises of
8 sub-orders with an paler appearance; naming a number of thrips; Thripidae, Aeolothripidae,
Heterothripidae and Merothripidae compared to the darker brown to black appendages on
Phlaeothripidae in the sub-order Tubulifera. According to online citation from “World
Thysanoptera” Phlaeothripidae feed on fungal hyphae, whereby transportation of fungus onto crop
maybe eminent and maybe be found in flowers.*6

2. 15/07/29 Clint Willemse
Apart of causing spotting on leaves and flowers many as 12 different viruses (eg. Iris yellow spot
virus) are transmitted by 'Eabaci' thrips on cosmopolitan crop (onions, tobacco, tomatoes, cotton
etc) in Southern Africa. Onion thrips (Thrips tabaci) damage onion leaves with spotting by piercing
and sucking as well as cucumber leaves and carnation petals*8
. Causing much of the blemishes on
citrus fruits are the Indigenous 'Citrus thrips' Scirtothrips aurantii, which feed on superficial cells
around the stem end of still growing pea shaped green fruit*7
.
Hemiptera:
This class of half membranous insect is best equiped with 2 pair of wings whereby the fore wings
are thickened at base and are comprised by doing damage with its piercing and sucking mouth parts
eg. Aphids, lace bugs, chinch bug, waterboatmen*9
. According to 'Insects of Southern Africa', the
structure of the mouthparts render efficient for extracting liquidified content from plants or animals
(obtaining amino acids from vascular tissue)*10
. The secretions left behind by a majority of Scale
and Aphids (Hemiptera Coccoidea and Aphidoidea); a by product of sap feeding habit known as
'honey dew' is exudated. This honey dew is an sybiotic process shared with ants, whereby ants
forage the exudates for reproduction. Homopterans are protected by ants in this regard. ('Insects of
Southern Africa: Scholtz C.H, Holm E, 1986). With this secretions comes intracellular bacterial
symbionts and as much as 78% of amino acids incorporated with nitrogenous wastes that may be
transformed from non essential amino acids to essential amino acids to the vascular tissue.
However because of the periodic nature of this parasite that continually feed on the vascular tissues
of the xylem and phloem, the aphid will regulate the amino acid composition from the non essential
to essential by secreting honey dew in quantity it can handle*11
. Also determined as aphids saliva is
belived to be linked to gall, necrosis, chlorotic lesions and morphological changes. This also
determines the phloem composition with an increase in amino acid concentration in the leaf tissue
causing senesence and increased translocation of amino acids resulting from break down of leaf
proteins*11
. Figure 5.
The most familiar types of aphid are 'potatoe aphid' Macrosiphum euphorbiae or 'rose aphid'
Macrosiphum rosae which attack early spring and former aphids migrate during summer to other
plants eg. Aster, cosmos, dahlias, gladiolus, hollyhock, iris, sweet pea, zinnia etc.*12
A clear
understanding of aphids breeding is not misunderstood as mentioned in ''Diseases and Pests of
Ornamental plants; 5th
Edition'' (1907) [pg 61], 'dark-green to black eggs are layed on the tips of the
rose bush leaves over winter, but a spray of lime sulphur kills least resistant eggs since it is difficult
to kill'...'a usual spray of malathion in summer will aid recovery of an infected plant'. 'Root aphids'
Brachycaudus spp, typically attack roots of ornamentals eg. Browallia, buttercup, calendula,
primrose, cosmos, dahlia, aster, sweet pea'. Some species live through summer on host plant as fir,
then migrated by ants to roots of plant. Autumn ants gather eggs and keep them over winter caring
for them and are returned to surface in spring to stems and leaves. Application of Diazinon will be
necessary.
Homoptera is an sub-order to Hemiptera (very similar and close to Thysanoptera) but belongs to
Exopterygota group meaning outside crawling with an gradual metamorphosis. The young are
called nymphs and the papal stage is not an metamorphic attribute.*13
Homoptera:
This leafhopper group finds itself varied with more aphids, leafhopper, cicadas, white flies, psyllids,
mealybug, scale; distinguished by 4 wings and well adapted mouthparts for piercing and sucking.
The species of scale maybe armoured or unarmoured (soft scale)- emerging two weeks before
spring compared to armoured crawlers. Many of the insects in this group cover themselves with
white waxy secretion, under which young develop, while some members deposit its eggs into the
host.*14

3. 15/07/29 Clint Willemse
As mentioned in 'Diseases and Pests of Ornamental Plants’ Firth Ed on page 57 pertaining to the
honey dew secretions by aphids and scale may result in growth of black mould on leaves and stems.
“Many carry viruses; whereby introduced as food is sucked out”.
*14
The 'citrus mealybug', Planococcus citri is one which damage citrus plants. It is broadly
elliptical in shape with short bristles or filamentts all around the margin. The female deposits 300
eggs in a compact, cotton waxy sac hatching within 10 days. See figure 6. Young are at first smooth,
later developing leg like marginal filaments. Pseudococcus longispinus, easily distinguished by two
long and some what shorter appendages. Long tailed mealybug is covered with a mass of wooly
substance and does not move about so often like the short tailed variation. Infestation depends upon
proximity and amount on host plant, but do contribute to loss of plant vigor in weakening or loss of
leaves, buds and flowers (sucking up plant tissue)*15
. Honey dew is secreted as shared in the
members of 'Hemiptera'. Unlike apids mealy bugs/ scale is not host specific. Pseudococcus fragilis
'citrophilus mealybugs' latch onto shrubs and trees, while others are known to attack roots
(underground parts). Scale may not display any body parts or appendages in its design. Application
of organic based phosphates malathion provides effective control.
Lepidoptera:
This unique order from Hymenoptera comprises of butterflies (Rhopalocera) and moths
(Heterocera) and have adapted as flowers did so are crucial for pollination. Wings and the body are
surrounded by dust-like scale. However these majestic creatures are injurious to plants at a young
stage, caterpillars and not at the adult stage. The mouth parts suck sap and borers may live inside
plant tissue (stem and leaf blades). The eggs are attached on leaves and stems but caterpillars are
highly destructive.*17
Eg cutworms, tent caterpillars, leaf rollers, and leaf tiers. The antennae
distinguishes the butterflie from the moths where the butterflies antennae is clubbed and thinned.*16
There are considerable traits in solving infestation when it comes to insects for example usage of
Cedar and Juniper woods or lavender may repel moths. 'White fly' Trialeurodes vaporariorum
plagues ornamentals like Fuchsia, Lantana, Coleus and may be delt with an synthetic pyrethroid,
Resmethrin. 'Cutworms' Peridroma saucia and Agrotis ipsolon lay eggs atop grass and weed
surfaces then burrow into the ground for winter. Moths emerge in June, July or August. When they
are fully grown they form pupae in the soil. However the destruction Is at night as they are
nocturnal feeders in turf culture. This results in wilted plants, quick destruction of flowers and
foliage; plant results in eventual death. Application spray of Diazinon, Dursban, Dyloz, Proxol and
Sevin.
Conclusion:
Understanding Biodiversity through the study of plants, ecology or insects alike is so importantly
diverse and broad that it leads Horticultaralists, Entomologist, Foragers etc, to the appreciation of
all insects and the role insects play in keeping the interconnected quality in nature in mind. As we
noted the symbiotic connection with Aphids and Ants with the connection being hony dew, or the
flying insects that act as pollinators shows one the grattitude we should all hold. The plague of
crops; invasive insects are ones carefully mitigated with organic practices or daily observations as
one cannot forget the harshful implications of inorganic practices.
References:
• *1
Resulting from Necrosis; mechanism of 'apoptosis'. “Cells that die due to injury typically
swell and burst, releasing their contents into the extracellular fluid.” This form of cell death
is called 'necrosis', in contrast, “cells programmed to die shrivel and shrink in a process
called apoptosis, meaning falling away, and their remains are taken up by surrounding
cells” pg. 388 ['Biology 8th
Edition' Raven, Johnson, Logos, Mason, Singer; Mc Graw Hill
2008]

4. 15/07/29 Clint Willemse
• *2 “
Allows propagation of recombinant DNA in a host which it is introduced.” ['Biology 8th
Edition' Raven, Johnson, Logos, Mason, Singer; Mc Graw Hill 2008]
• *3
Citation: pg 50 “Diseases & Pests of Ornamental Plants 5th
Edition”, Pascal P. Pirone 1907
• *4
G4, Glossary 'Biology 8th
Edition' Raven, Johnson, Logos, Mason, Singer; Mc
Graw Hill 2008
• *5
pg 177 “Insects of South Africa”, Scholtz, C,H., Holm, E. Butterworths, Durban 1986
• *6
“World Thysanoptera” Online citation 7/8/2015
http://anic.ento.csiro.au/thrips/identifying_thrips/Phlaeothripidae.htm
• *7
pg 177; 178 “Insects of South Africa” Clark H Scholtz. Erik Holm, Butterworths Durban,
1986
• *8
pg 207, 212 “Principles of Horticulture” 5th
Edition C.R Adams, K.M Bamford and M.P
Early 2008
• *9
Pg 54, Pirone P,P., 1907, ‘Diseases and Pests of Ornamental Plants’ Firth Ed. Publication
of, The New York Botanical Garden.
• *10
Quotation: pg 112 “Insects of South Africa”, Scholtz, C,H., Holm, E. Butterworths,
Durban 1986
• *11
Online Article- Arthropod-Plant Interaction (2011) “Aphid-host plant interaction: Does
aphid honey dew exactly reflect the host plant amino acid composition”. Springer
Science+Business Media B.V. 2011
• *12
Pirone P,P., 1907, ‘Diseases and Pests of Ornamental Plants’ Firth Ed. Publication of, The
New York Botanical Garden.
• *13
Wikipedia Online reference: 10/08/2015 Exopterygota
https://en.wikipedia.org/wiki/Exopterygota
• *14
Pg 62 Pirone P,P., 1907, ‘Diseases and Pests of Ornamental Plants’ Firth Ed.
Publication of, The New York Botanical Garden.
• *15
Online Mealybug reference: 10/08/2015 “American Orchid society”
https://www.aos.org/Default.aspx?id=511
• *16
Difference between moths and butterflies: Online citation
https://en.wikipedia.org/wiki/Moth
• *17
Page 63 Pirone P,P., 1907, ‘Diseases and Pests of Ornamental Plants’ Firth Ed.
Publication of, The New York Botanical Garden.
Picture and Diagram References:
Figure 1
Arthropoda’s 9 orders pg 666 'Biology 8th
Edition' Raven, Johnson, Logos, Mason, Singer; Mc
Graw Hill 2008

5. 15/07/29 Clint Willemse
Figure 2: “Classification of the arthropods and their allies sensu Snodgrass (1938).”
Online reference : 08/082015 Enhancement Chapter: Raven and Johnsons, 6th
Edition
http://www.mhhe.com/biosci/genbio/raven6b/graphics/raven06b/enhancementchapters/raven43_enh
ancement.html
Figure 3:
“Life stage of Gladiolus thrips” Ent 462 Order Of Hexapoda
http://entomology.osu.edu/bugdoc/Shetlar/462/462InsectOrders/Orders25.htm
Figure 4: Tomatoe spotted virus on potatoe emphasis on the dark broad chlorotic spots
Cornell University: Vegetable MD online Department of Plant Pathology
http://vegetablemdonline.ppath.cornell.edu/PhotoPages/Tomatoes/Tom_SpWilt/Tom_SpWiltFS15.h
tm

6. 15/07/29 Clint Willemse
Figure 5:
Left- Scale supplying nutritious honey dew to Argentinian ant
“Ornamental and Turf: Department of Entomology Insect Note, NC State University”
https://www.ces.ncsu.edu/depts/ent/notes/O&T/trees/note140/note140.html
Right-Ant milking aphid
"Ms. Taylor's Ecology Class at Wolcott High School” http://ctayloreco.weebly.com/gallery.html
Figure 6: 'Citrus mealubug' Planococcus citri
Emphasis on the fir created by female and the tiny scale eminating from
underwww.flickr.com/photos/gellerfipeter/4922289215/in/photostream/

7. 15/07/29 Clint Willemse
Figure 5:
Left- Scale supplying nutritious honey dew to Argentinian ant
“Ornamental and Turf: Department of Entomology Insect Note, NC State University”
https://www.ces.ncsu.edu/depts/ent/notes/O&T/trees/note140/note140.html
Right-Ant milking aphid
"Ms. Taylor's Ecology Class at Wolcott High School” http://ctayloreco.weebly.com/gallery.html
Figure 6: 'Citrus mealubug' Planococcus citri
Emphasis on the fir created by female and the tiny scale eminating from
underwww.flickr.com/photos/gellerfipeter/4922289215/in/photostream/