Neonate carob moth larvae are cream-white or light pink and about 1 mm long. They have yellow to brown head capsules. Larger larvae are light pink with a brown head capsule, and measure about 18 mm in length, in the final instar (Morland 2015). Neonate FCM larvae are about 1.4 mm long and are white with a black head capsule (Stofberg, 1948).
With age, the body becomes pinkish red, generally darker than that of carob moth. The mature larva is 15 – 20 mm long (Moore 2002), the larvae of both species being slender and elongated with distinct head capsules and legs. This is unlike the fly larvae that can infest citrus fruit (fruit flies and vinegar flies). General appearance and biology of the larvae of the two species are summarised in Table 1.
Infestation and damage patterns in citrus fruit usually differ somewhat between the two species. FCM can be considered a primary pest of citrus. Female moths will lay their eggs on the fruit surface, usually singly, and hatching larvae will penetrate directly through the rind, but often through the navel end in Navel oranges.
Larvae will feed in the albedo of the fruit, just under the rind, or tunnel through into the central column of the fruit to feed. Larvae will not exit the fruit at all until they are ready to pupate (Newton 1998).
On the other hand, carob moth is often a secondary pest of citrus, being attracted to mealybug residues or those of other honeydew-producing insects. They can also attack fruit that is already damaged or move into a citrus orchard from an adjacent preferred host, such as pecans, pomegranates, or acorns.
Feeding is usually superficial, with larvae often exiting and re-entering fruit. That said, there seem to be increasing cases presenting little difference in the feeding patterns between carob moth and FCM (Honiball and Catling 1998).
FCM is a regulated quarantine pest for several export markets, especially the European Union (EU), which is the biggest export market for Southern African citrus, whereas carob moth only has quarantine status for a handful of Far Eastern markets. For the EU, a risk management system for FCM is implemented, which is based on stringent inspections from orchard to packhouse to post-packing (Hattingh et al., 2020).
FCM infestation threshold exceedance can lead to stricter shipping conditions or even rejection of fruit for export. Consequently, it is important that lepidopteran larvae infesting fruit are correctly identified as either carob moth or FCM.
There are several features that can be used to accurately differentiate carob moth and FCM larvae from one another (Morland 2015). However, for simplicity in on-farm application, only key diagnostic differences are provided here. Firstly, carob moth does not have an anal comb (Fig 3a), whereas FCM does (Fig. 3b). However, this only appears in the later instars and is often difficult to find in the folds of an imperfect specimen.
By far the clearest and most reliable morphological difference between the larvae of the two species, is the presence of a dark sclerotised patch on the first thoracic segment (T1) of carob moth (Fig 4a) and the presence of a much paler unsclerotised patch on FCM (Fig 4b).
Furthermore, the sclerotised patch is anterior to (in front of) the first spiracle in carob moth and dorso-anterior (below and protruding forwards) to the unsclerotised patch in FCM.
The patch in FCM also has a very distinct shape, which is consistent from larva to larva. Finally, in carob moth there are two setae (hairs) associated with the patch, whereas in FCM there are three. However, these may not be sufficiently clear if the specimen is not in very good condition and magnification is not adequate.
Another useful feature is the presence of a dark circle around the seta of the eighth abdominal segment (A8 – third last segment from the back) in carob moth (clearly visible in Fig 2a). This dark circle is missing in FCM (Fig 2b).
If a larval sample is in good condition and the larva is not too small, it should be possible to reliably observe the described characteristics of the T1 patch, using a handheld magnifying glass (10 X magnification). However, a stereoscopic microscope will help to improve the reliability of the identification. If there is any doubt at all about the identification, the default should be to list it as FCM, rather than carob moth, as the repercussions of an error in the other direction would be more dire.
If you would like to register for an online workshop to learn more about identification of moth larvae that are of economic significance to fruit crops in SA, please contact Caro Kapp at Stellenbosch University: ckapp@sun.ac.za. If you are at all uncertain about the identification of a larva found in a citrus fruit, please contact Dr Tammy Marsberg at CRI: mailto:tammy@cri.co.za.
References
Hattingh, V., S.D. Moore, W. Kirkman, M. Goddard, S.R. Thackeray, M. Peyper, G. Sharp, P. Cronjé, and K. Pringle. 2020. An Improved Systems Approach as a Phytosanitary Measure for Thaumatotibia leucotreta (Lepidoptera: Tortricidae) in Export Citrus Fruit from South Africa. Journal of Economic Entomology, 113, 700-711.
Honiball, F., and H.D. Catling. 1998. Carob moth. In: Citrus pests in the Republic of South Africa. Second edition. Bedford E.C.G., M.A. Van den Berg, and E.A. de Villiers (Eds.) Agricultural Research Council, South Africa. pp. 164-170.
Moore, S.D. 2002. The Development and Evaluation of Cryptophlebia leucotreta Granulovirus (CrleGV) as a Biological Control Agent for the Management of False Codling Moth, Cryptophlebia leucotreta, on Citrus. Ph.D. Thesis, Rhodes University, Grahamstown, South Africa.
Morland, G. 2015. The morphology and ecology of the carob moth (Ectomyelois ceratoniae) (Zeller) in citrus orchards of the Western Cape, South Africa. Doctoral dissertation. Stellenbosch, South Africa: Stellenbosch University. 1-122. https://scholar.sun.ac.za/items/282f7c7f-36ea-44c5-bbb9-920dc14f9886
Newton, P.J. 1998. False codling moth Cryptophlebia leucotreta (Meyrick). In Citrus Pests in the Republic of South Africa; Bedford, E.C.G., M.A. Van den Berg, E.A. De Villiers, Eds. Dynamic Ad: Nelspruit, South Africa; pp. 192-200.
Stofberg, F.J. 1948. Larval structure as a basis for certain identification of false codling moth (Argyroploce leucotreta, Meyr.) larvae. Journal of the Entomological Society of southern Africa 11: 68-75.
