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The following examples of agents tested for control of Mimosa pigra illustrate the testing procedures for different agents according to the behaviour of adults, mobility of larvae and availability of the host plant part to be tested and emphasise careful interpretation of results.
 | The stem-boring moth Carmenta mimosa Eichlin and Passoa
(Lepidoptera: Sesiidae) develops in stems of
M. pigra. Females are indiscriminate when ovipositing under laboratory conditions, often placing eggs on the frame and gauze of the cage. Choice oviposition tests therefore could not be carried out. Instead larval development tests were
made in which eggs or first instar larvae were inserted into stems and development observed. It was shown that although larvae developed beyond the first instar on a few closely related plants, none completed development on any plant other than
M. pigra. As a result of these tests C. mimosa was released in Australia and later in Thailand
(Forno et
al. 1991).
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| Some tests have to be conducted on portions excised from the whole plant. This was the case with
Coelocephalapion pigrae (Coleoptera: Apionidae), which develops in the flower-buds of
M. pigra. The host test list includes many trees which will not produce flower buds when the plant is growing in a pot and the only option was to test flower-buds on cut foliage. Fortunately,
C. pigrae accepted excised flower-buds of M. pigra and fed and reproduced normally. Results of choice tests showed that
C. pigrae preferred M. pigra for oviposition and feeding but occasional oviposition occurred on the weed, Mimosa
pudica, and the native plant, Neptunia dimorphantha. In no-choice tests, the level of oviposition on
M. pudica and N. dimorphantha was greater than in choice tests but was still less than that on
M.
pigra. Development was completed on these three species but survival of immature stages was lower on
M. pudica and N. dimorphantha than on M. pigra. This, together with their low acceptance for
oviposition, indicates that neither plant could sustain populations of C.
pigrae. Furthermore, populations of N. dimorphantha are disjunct from current and projected populations of
M. pigra. The results of these tests were accepted by the regulatory authorities and
C.pigrae was released in Australia in May 1994 (Heard and Forno
1996).
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| Sibinia fastigiata (Coleoptera: Curculionidae) oviposits in the pods of its host plant. Adults feed on the nectar and pollen from open flowers and so do not damage the plant. We combined elements of choice and no-choice
tests to design a testing method for this insect. We alternated pods of the normal host with the choice of pods of test plant species. The time spent with the normal host gives information on the fecundity of the insects. The test plants are then assessed for their acceptibility in a choice design.
We provided flowers continuously to maintain healthy fecund adults (Heard
et al. 1997).
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| Adults of the leaf beetle Syphrea flavipes nr. cardiaca
(Coleoptera: Chrysomelidae) feed on leaves but the larvae feed on roots of the host plant. Adults would not oviposit in the laboratory, therefore oviposition tests could not be done. Larvae developed on excised roots but their survival was poor, therefore larval development tests could not be done. Adults fed on excised leaves in containers and so adult feeding trials could be performed. These trials showed that the adults fed on many species of legumes. Thus we were able to reject this agent before spending resources on developing oviposition and larval development tests. |
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Tim Heard
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