Elachistidae: Agonoxeninae: Agonoxenini

Palm Moths, Grass-Miner Moths

BIOSECURITY ALERT

This Family is of Biosecurity Concern

This family occurs in Australia.

Palm moths are a small group of 31 genera that belong to the Agonoxeninae, a sub-family of the family Elachistidae (grass-miner moths). This sub-family is divided into two tribes the Agonoxenini and the Blastodacnini, twenty species of which are native to Australia. Agonoxenini are globally known as pests of palms, and consist of, and typified by, the four species belonging to the genus Agonoxena: A. argaula, A. phoenicia, A. pyrogramma and A. miniana. The Australian native representative of this genus is Agonoxena phoenicia (palm moth), which feeds on Alexandra or northern bangalow palm (Archontophoenix alexandrae).

The taxonomy of this group has recently undergone major changes from studies incorporating new molecular and morphological data. Firstly, the former family Blastodacnidae was retained under the Agonoxenidae (Hodges, in Kristensen 1999), and then the latter treated under the Elachistidae to become the subfamily Agonoxeninae (Heikkilä et al. 2014, Sohn et al. 2016), relegating the Blastodacnidae and the Agonoxena group to tribal status, Blastodacnini and Agonoxenini respectively.

Palm moths are the only members of the Elachistidae, currently considered to be of biosecurity importance to northern Australia.

Diagnostic Features of Agonoxenini (Palm Moth Caterpillars)

1. Secondary setae present. Agonoxena argaula has numerous secondary setae that are much smaller than the primary setae. However, A. pyrogramma only has secondary setae on the prolegs and A10 but it is still likely that secondary setae are characteristic of Agonoxena (see Agonoxena diagnosis and description below). Caterpillars in the Blastodacnini also have secondary setae, but they are much more abundant, over the entire body, than most of Agonoxena at least (Stehr et al. 1987).  On this characteristic, Agonoxeninae (Agonoxenini and Blastodacnini) caterpillars are similar to the Pterophoridae (plume moth) larvae. However the two groups of larvae differ on the following features:
   1. Palm moth caterpillars do not have secondary setae grouped into verrucae, or the like (some pterophorids do).
   2. Palm moth caterpillars have a single SV seta on T1 and T2, whereas pterophorids have two. (Note: the SV setae may be difficult to distinguish from secondary setae in A. argaula).
2. Agonoxenini caterpillars differ from those of Blastodacnini by having the L group of T1 included in the prothoracic shield.
3. Prolegs with crochets in a uniordinal circle. In Blastodacna curvilineela, crochets form a mesoseries.

THE FOLLOWING SPECIES IS OF BIOSECURITY CONCERN TO NORTHERN AUSTRALIA

Agonoxena argaula (palm moth) (Elachistidae: Agonoxeninae: Agonoxenini)

The main palm moth of biosecurity concern to northern Australia is coconut flat moth or coconut leaf moth (Agonoxena argaula), which is a pest of coconut and other palms (Fig. 1). Damage is principally exerted on young palms. The species is spread through artificial means and often by commerce.

Agonoxena pyrogramma is considered to be of relatively minor concern as a pest of palms that causes much less damage than A. argaula. However A. pyrogramma occurs geographically closer to Australia as it has been introduced into Papua New Guinea.

 Biology and Feeding Damage

• Feeding occurs in the epidermis on the leaf underside, underneath webbing.
• The feeding scar is long and narrow when the larva is small and immature, developing into characteristic long, thin, grey patches of damage as the caterpillar becomes larger (Fig. 2).
• Infestations may be heavy with at least several thousand larvae feeding in a single palm tree.
• Caterpillars become active when disturbed and may drop to the substrate below on silk threads. Both species are more active in dry weather.
• The caterpillar pupates beneath a close, elongated, white web on the leaf surface (either the upper or lower) of the host plant or understorey. 

Key to species of Agonoxena larvae

This key has been adapted from Bradley (1966).

1. 1. Tergal (suranal) plate of A10 truncate caudally, setae somewhat appressed anterior puncture Aa of epicranium posteriad of A2; mesonotum without spiculi ... miniana
   2. Tergal (suranal) plate of A10 obtusely rounded, setae erect; anterior margin of mesonotum with spiculi; epicranium with puncture Aa mesad, antero-mesad or postero-mesad of A2 ... 2
2. 1. Thoracic and abdominal segments with numerous secondary setae; mesonotum with dense band of spiculi; puncture Aa mesad of A2; suranal plate of A10 obtusely rounded, setae erect … argaula
   2. Thoracic and abdominal segments without numerous secondary setae, at most just on prolegs and A10; mesonotum with two small patches of spiculi, or a weak and comparatively indistinct band; puncture Aa antero-mesad or postero-mesad of A2 … 3
3. 1. Mesonotum with elliptical patches of spiculi anteriad of setae D1 and D2; puncture Aa antero-mesad of A2 ... pyrogramma
   2. Mesonotum with a weak band of spiculi; puncture Aa posteromesad of A2 ... phoenicia

Diagnosis and Description of Agonoxena caterpillars       

Diagnosis

This diagnosis is based on the description of Agonoxena larvae provided in Bradley (1966) and Hodges (1999).

1. Size.  The mature caterpillars of A. argaula are significantly larger than the other three species in the genus. Size 16–18 mm long (Fig. 1). A. phoenicia is 7-8 mm; A. pyrogramma is 10-12 mm; A. miniana is 10-11 mm.
2. Mid-dorsal line.  Only A. argaula and A. miniana have a brown mid-dorsal line along the body (Fig. 1).
3. Secondary setae.  Numerous, short secondary setae that are much shorter than the primary setae, are on all thoracic and abdominal segments of A. argaula (Bradley 1966). Although Bradley goes on to state that secondary setae are absent in the other species, Stehr et al. (1988) noted that secondary setae are present on all the prolegs of A. pyrogramma and surmised that they may also be present in the other two species and thus be characteristic of the genus.
4. Two flattened setae at apex of tarsus.
5. Mandible.  The medial ‘teeth’ on the mandible of A. miniana are relatively larger and better developed than the other species.
6. T2 dorsal band of spicules.  In A. argaula and A. pyrogramma, T2 has a dense transverse band of small spines or spiculi on the mesonotum, divided into two separate patches, anterior of the D setal group. In A. miniana and A. phoenicia, the band is shorter and narrower with no spiculi (miniana) or minute spiculi (phoenicia).
7. Head chaetotaxy.
   1. Adfrontal seta AF2.  In A. argaula the adfrontal seta AF2 is slightly above the apex of the apotome.  In A. pyrogramma and A. miniana it is level or nearly level, but it is much higher in A. phoenicia and about the same distance above the apex of apotome as AF1 is below.
   2. Adfrontal puncture AFa. The adfrontal puncture AFa is usually directly below AF2 but in A. phoenicia, AFa lies approximately midway between AF2 and AF1 because AF2 is relatively more dorsal.
   3. Distance from F1 to AF1 This is about the same as from AF1 to AF2 in A. argaula, but in A. pyrogramma and A. miniana AF1 is nearer to AF2, but its position is variable in A. phoenicia).
   4. Puncture Aa.  The puncture Aa is mesad of A2 in A. argaula but is antero-mesad in A. pyrogramma, posteriad in A. miniana and postero-mesad in A. phoenicia). 

Current Distribution

Oceania and Australasia

Agonoxena argaula

• Fiji
• Guam
• New Hebrides
• Hawaii
• Tonga
• Samoa
• Ellice
• Wallis
• Futuna
• the Palmyra Atoll
• Tokelau

Agonoxena miniana

• Java

Agonoxena phoenicia

• Northern Queensland, Australia.

Agonoxena pyrogramma

• Guam
• Federated States of Micronesia
• Java
• Northern Mariana Islands
• New Britain
• Papua New Guinea
• Solomon Islands
• Indonesia

Caterpillar Host Plants

• golden cane palm, areca palm, yellow palm, butterfly palm (Dypsis lutescens)
• coconut (Cocos nucifera)
• loneliest palm (Hyophorbe amaricaulis) 
• Kentia palm or thatch palm (Howea forsteriana)
• fan palms (Pritchardia)

Australian Centre of International Agricultural Research (ACIAR) (2017) Pacific Pests and Pathogens - Fact Sheets. Coconut flat moth (065) http://www.pestnet.org/fact_sheets/coconut_flat_moth_065.htm

Bradley, J. D. (1966). A comparative study of the coconut flat moth (Agonoxena argaula Meyr.) and its allies, including a new species (Lepidoptera, Agonoxenidae), Bulletin of Entomological Research, Volume 56, Part 3, pp. 453-472.

Heikkilä, M., Mutanen, M., Kekkonen, M. & Kaila, L. (2014) Morphology reinforces proposed molecular phylogenetic affinities: a revised classification for Gelechioidea (Lepidoptera).Cladistics, 30,563–589. Herbison-Evans, D. and Crossley, S. (2013) Agonoxena phoenicia Bradley, 1966, Palm Moth, Agonoxenidae, Gelechioidea. http://lepidoptera.butterflyhouse.com.au/agon/phoenicia.html updated March 2015.

Hodges, R. W. (1999) The Gelechioidea. In: Kristensen, N.P. (Ed.), Handbook of Zoology. 4(35.1). De Gruyter, Berlin, New York.

Howard, F. W., Giblin-Davis, R., Moore, D., Abad R. (2001) Insects on Palms. CABI

Sohn, J., Regier, J. C., Mitter, C., Adamski, D., Landry, J. Heikkilä, M., Park, K., Harrison, T., Mitter, K., Zwick, A., Kawahara, A., Cho, S., Cummings, M. And Schmitz, P. (2016). Phylogeny and feeding trait evolution of the mega-diverse Gelechioidea (Lepidoptera: Obtectomera): new insight from 19 nuclear genes. Systematic Entomology, 41:112–132 DOI: 10.1111/syen.12143

Stehr, F.W., Martinat, P.J., Davis, D.R., Wagner, D.L., Heppner, J.B., Brown, M.E., Toliver, M.E., Miller, J.Y., Downey, J.C., Harvey, D.J., McFarland, N., Neunzig, H.H., Godfrey, G.L., Habeck, D.H., Appleby, J.E., Jeffords, M., Donahue, J.P., Brown, J.W. & Frack, D.C. (1987) Order Lepidoptera, pp 288–596. In Stehr, F. W. (Ed.), Immature Insects. Kendall/Hunt, Dubuque.

Byrne, CJ & Moyle, DI (2019). The Caterpillar Key Fact Sheet: Elachistidae (Agonoxeninae: Agonoxenini).