July 2004. This moth is referred to as the cardamom shoot borer in the Himalayas and the yellow peach moth in Australia and elsewhere. It is thought to be the one that is attacking ginger in Sikkim. The eggs are laid on the leaves and the grubs burrow into emerging leaves and kill the shoots. The question asked was whether Tichogramma chilonis is likely to be effective against it. How could it be tested under rather basic lab conditions. At present, Trichogramma is mass-reared each year in Sikkim and released to control rice pests, leaf roller and the like.
There were interestig responses:
Members suggested caution before introducing Trichogramma spp. They are often generalists, in which case they will attack non-target hosts. If the sp./spp. being mass-releasing is/are polyphagous, the impact on non-target fauna is likely to be considerable.
It was then asked if it was possible to give some idea, in general terms, of the impact on non-target fauna from the mass rearing of Trichogramma. Are there articles or web site, etc, that could provide an introduction. It is likely that the impact of the scheme on the (beneficial) fauna has not been considered in Sikkim, and as several people there are members of PestNet, there will be much interest.
John Noyes has made a list – supplied by Dr Jo Berry, Hymenopterist with Landcare NZ – showing more than 100 species of lepidoptera (and the odd other insect) attacked by T chilonis. It is not recorded as a hyperparasitoid, which is a bonus.
It is hard to tell the impact of egg parasitoids. If large numbers are released in an area, and it is a generalist, it is likely to attack whatever it comes across, so an important point would be what lepidoptera are present adjacent to the release areas (beneficial lepidoptera, beautiful butterflies, etc.). Also, how far will the released parasitoids search and spread? If they attack a large proportion of eggs laid in one generation of a species in a locality, obviously they will have quite an impact on the next generation. Of course, this is how a biological control agent is used. It will also, probably, have a non-target impact on other natural enemies, such as larval parasitoids of that species.
Research on Conogethes on durian in Malaysia
Conogethes (Dichocrocis) punctiferalis also attacks durian (Durio zibethenus) and, thus, is known as the Durian fruit borer in Malaysia and neighboring countries. Incidentally, it is also known as the Yellow peach moth (obviously the host is peach) in Taiwan and Japan. Work is being done on its management in durian, especially on its ecology and the development of pheromones, which have been analysed and synthesised, but they have not proved to be effective in the field based on trap catches. In the lab it has been reared on zingerbers, but it is not a suitable host compared to starfruit (Averhoea carambola) and durian.
As for the parasitoids, there have not been any studies on parasitism of Conogethes eggs by Trichogramma. However, based on experience with trichogrammatids in crucifers and other pest systems, it will not be surprising to find Trichogramma, being a generalist, parasitising eggs of Conogethes, especially under lab conditions. The daunting issue, however, is the quantification of their impact under field conditions as host eggs are quite difficult to see and establishing a numerical response relationship is difficult. The discussion on the suitability of generalists such as Trichogramma as effective parasitoids/biocontrol agents against pests is an old and moot one. Incidentally, the level of parasitism of this pararsitoid in the field is done through transplant experiments, i.e., putting lab-reared eggs on cards and placing them in the field to assess natural levels of parasitism.
On the identification of Conogethes
The pest species may not be Conogethes punctiferalis. The species that attacks alpinias (also ginger family) in Darwin is C pluto. These species would be indistinguishable (without examining the male genitalia) apart from the fact that the male of C pluto is light brown rather than yellow. As a result, there is now some evidence that the Australian species known as Conogethes punctiferalis is a complex of species.
Molecular methods of identification of the species/strain of immature life stages of Conogethes punctiferalis and Phthorimaea operculella are being developed by Lincoln University, New Zealand.