Transcript Document

Growing mahogany sustainably through conservation and augmentation of the weaver ant,
a biological control agent of mahogany pests
Grace T. Lim1&2, Scott M. Salom1, Laurence G. Kirton2, Loke T. Kok1,
1Entomology Dept, Virginia Tech, 2Entomology Unit, Forest Research Institute Malaysia
Introduction
Mahogany is among the most valuable tropical hardwoods in the world
and has been harvested to commercial extinction. Numerous
reforestation efforts worldwide with mahogany species, e.g.,Swietenia
macrophylla and Khaya ivorensis (Meliaceae) have been foiled by the
mahogany shoot borers (Hypsipyla spp., Lepidoptera: Pyralidae) found
throughout the tropics. Eight decades of research spanning 23 countries
has yet to come up with a reliable, cost-effective and environmentally
sound solution to this problem.
Hypsipyla robusta, the Shoot Attacker
Below L-R: The adult female lays eggs on a leaf axil
or new shoot that a newly emerged larva will burrow
into. The larva later migrates to the terminal shoot;
which dies as the pith is consumed; and the tree
develops multiple leaders as a result
Assessing Food Preference of the Ant
• Data analysis: Kruskal-Wallis & Friedman’s tests
Results
• The ants preferred live mealworms (Fig 1.a) but
accepted fish when no choice was given (Fig 1.b).
• The ants did not consume much liquid food.
Discussion
• Established colonies may get enough honeydew
from trophobionts but relocated colonies have few
trophobionts and may need ‘high-carb’ supplemental
foods. Thus, ‘high-carb’ weaver ant formula and
‘high-protein’ mealworms chosen for next study.
Oecophylla smaragdina, the Shoot Protector!
It is an aggressive predator of
arthropods,
including
H.
robusta (R).
It vigilantly patrols its host
plant, which includes K.
ivorensis (L), building nests
from young leaves.
• The ant also tends ‘trophobionts’, e.g.,mealybugs (Hemiptera), in
exchange for ‘honeydew’ excreta, an important food of the ant.
• The leaf nests of this ant can be ‘harvested’ from other trees and
introduced to mahogany plantations to protect them.
• Protection is needed for the first three years until an unbranched height
of 8 m is achieved.
International collaborative research by Virginia Tech’s Entomology
Department and the Forest Research Institute of Malaysia (FRIM) is
currently focusing on conservation and augmentation as biological
control approaches to enhance the performance of the weaver ant
against the shoot borer.
Rationale
A weaver ant colony relocated to new host plants can be conserved and
augmented in a ‘two-pronged’ approach:
1. Short term: Direct food supplementation to meet energetic needs
until it is self-sufficient, i.e., has cultivated enough trophobionts.
2. Long term: Indirect food provision and additional nesting sites in a
more stable and diverse mixed-plantation.
Therefore, the objectives of this research program were to identify:
1. Preferred foods of the ant that aid colony conservation. These foods
should be cheap and practical to apply.
2. A preferred alternate host plant species of the ant that can be easily
grown with mahogany as a second crop.
Surveys for Host Plants of the Ant
nest
Methods
• A choice and no-choice study used mature weaver ant colonies at FRIM
• Choice test (R): 6 ant colonies had ad libitum access to 4 foods: fish, live
mealworms, liquid ‘weaver ant formula’ (with body-building protein
powder) and honey solution. Food amounts taken recorded daily for 7 d.
• The no-choice test was similarly conducted, but gave only one of the 4
foods to a total of 12 colonies.
Choice Test
The weaver ant, Oecophylla smaragdina (Hymenoptera: Formicidae),
inhibits infestation of mahogany by the shoot borer, Hypsipyla robusta,
which attacks mahoganies in Asia, Australia and the Pacific Islands.
Conclusions
Major Studies and Results
(a)
nest
string
treatment
No Choice Test
(b)
Ants!
Honey
Food
Mealworms
Fish
0
5
10 15 20
Weight of food taken (g)
-5
Results
• Four host plant species were particularly ant-abundant: Morinda
citrifolia (Rubiaceae), Talipariti tiliaceum (Malvaceae), Bruguiera spp.
(Rhizophoraceae), Acacia auriculiformis (Fabaceae).
control
Weaver ant formula
-5
Methods
• Four
Malaysian habitats, including
mangroves (R), were surveyed for host
plants of the ant.
• All vegetation within 3 m of trail borders
along a 1 km line transect was examined for
weaver ant nests .
0
5
10 15 20
Weight of food taken (g)
Figs. 1.(a-b). The average amount of four foods taken daily by O. smaragdina
in the choice test (left) and no-choice test.(right) (± SEM, n = 6 and n = 3 for
the choice and no-choice tests, respectively)
Screening Host Plant Candidates
Methods
• Three favored host plant species from the previous study were tested: M.
citrifolia, T. tiliaceum and Bruguiera spp, plus non-host Avicennia
officinalis (Acanthaceae) as the control.
• Ant preference was evaluated using a ‘relative ant abundance index’,
based on ratio of volume of nests : plant crown surface area.
• Data analysis: Kruskal-Wallis test.
Results and Discussion
• The ant was most abundant on M.
citrifolia, followed by T. tiliaceum and
Bruguiera spp. (Fig 2. below).
• Many ants aggregated on M. citrifolia
fruit, imbibing nectar (R). Trophobionts
tended by the ant on M. citrifolia posed no
pest risk.
• M. citrifolia was selected for next study.
4
3
2
Relative ant
abundance rank 1
(Kruskal-Wallis z- 0
value)
-1
-2
-3
Methods
• 12 ant colonies relocated to new mahogany host
plants at FRIM.
• Half the colonies received weaver ant formula and
mealworms (L-R) for 16 weeks.
• Ant activity monitored weekly on shoots, around the
foods and in nest-building.
• Data analysis: GLM ANOVA.
Results and Discussion
• Food-supplemented (F) colonies had greater colony sizes than the C
colonies receiving no food.
• For F colonies much weaver ant formula was consumed initially (wk 1-9)
then declined while ant activity on shoots and nest-building increased.
• F colonies may have ‘weaned off’ the foods after establishing.
• Relocated weaver ant colonies
can be conserved by short-term
food supplementation
• Live mealworms (L) and
weaver ant formula are
preferred foods that are cheap
and simple to apply
• Foods should be given for at
least 3 months to ensure colony
establishment
• M. citrifolia is a preferred host
plant of the ant that is easy to
grow and yields profitable
medicinal by-products.
Providing foods directly through supplemental feeding and
indirectly by planting alternative host plants with the main crop
may well prove to be a reliable approach to growing
environmentally-friendly mahogany in partnership with the
weaver ant.
Literature Cited
Bluthgen, N. & Fiedler, K. 2004. Preferences for sugars and amino acids and
their conditionality in a diverse nectar-feeding ant community. Journal of
Animal Ecology 73:155-166.
Griffiths, M.W. 2001. The biology and ecology of Hypsipyla shoot borers. Pp.
74-80 in Floyd, R.B. & Hauxwell, C. (Eds.). Proceedings of an International
Workshop on Hypsipyla Shoot Borers in Meliaceae. ACIAR Proceedings Series
No 97. Kandy, Sri Lanka, 20-23 August 1996. ACIAR, Canberra.
Lim, G.T. & Kirton, L.G. 2003. A preliminary study on the prospects for
biological control of the mahogany shoot borer, Hypsipyla robusta (Lep.:
Pyral.), by ants (Hymen.: Form.). Pp. 240-244 in Proc. of Intern. Conf. on
Forestry and Forest Products Research. Kuala Lumpur, 1-3 October 2001.
FRIM, Malaysia.
Way, M.J. & Khoo, K.C. 1991. Colony dispersion and nesting habits of the
ants, Dolichoderus thoracicus and Oecophylla smaragdina (Hymenoptera:
Formicidae), in relation to their success as biological control agents on cocoa.
Bulletin of Entomological Research 81(3):341-350.
Morinda
citrifolia
(9.3 ± 4.7)
Talipariti
Bruguiera spp. Avicennia
tiliaceum
(1.1 ± 0.5)
officinalis
(1.3 ± 0.7)
(0)
Plant species
(Relative nest volume ± SEM, cm3m-3, n = 4)
Effect of Food Supplementation on the Ant
A complementary series of studies was successfully conducted to
conserve and augment weaver ant populations.
Fig. 2. Relative ant abundance in relation to three host plant species and
one non-host plant species of O. smaragdina.
Future Work
A study is in progress to evaluate effects of mixed-planting M. citrifolia
with mahogany on establishment of food-supplemented ant colonies
(below). Please contact first author for additional information. E-mail:
[email protected]. Campus address: 216 Price Hall, Blacksburg VA 24061
Acknowledgements
We thank Ms. Saimas Ariffin, Mr. Saiful Azhari, Mr. Shaiful Amri, Ms.
Nurziah Ishak, Mr. Fadir Ishak (below), Ms. Hidaya, and Mr. Azmi
Mahyuddin (Entomology Section, FRIM) for assistance in conducting
the experiments, and Dr Ang Lai Hoe (Ecophysiology Section, FRIM)
for use of Hobos.
The plant species were identified by Mr Mohd. Asri and Mr Kamarudin
Saleh (Botany Section, FRIM). Identification of trophobionts was
provided by M. Kosztarab (Virginia Tech) S.H. McKamey and D.R.
Williams (USDA-ARS).
This project was supported by
the
Fulbright
Program
(administered by the U.S.
Department of State, the
Institute
of
International
Education, and the MalaysianAmerican
Commission
on
Educational Exchange), Virginia
Tech and FRIM.