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1. Agricultural Research Council, Plant Protection Research Institute, South Africa

Currently this is the only project world-wide that is investigating the host range and efficacy of new biocontrol agents. The project is conducted from Cedara, KZN (insects) and Stellenbosch, Western Cape (pathogens). The project concentrates on insects which will be compatible with the SA biotype of chromolaena and those which will tolerate prolonged dry periods and fire. All attack different parts of the stem. Those currently under investigation are:

  • Lixus aemulus Petri (Coleoptera: Curculionidae)
  • Conotrachelus reticulatus Champion (Coleoptera: Curculionidae)
  • Dichrorampha odorata Brown & Zachariades (Lepidoptera: Tortricidae)
  • Carmenta n.sp. (Lepidoptera: Sesiidae)
  • Recchia parvula (Lane) (Coleoptera: Cerambycidae)
  • Melanagromyza eupatoriella Spencer (Diptera: Agromyzidae)
  • Pathogens


1.1 Lixus aemulus Petri (Coleoptera: Curculionidae)

This weevil, collected in western Brazil off a hairy form of chromolaena, lays single eggs into mid-sized stems of chromolaena, and larvae bore down stems for up to 30cm, reducing growth and sometimes causing stem death (Kluge & Zachariades, 2006). Pupation occurs in the stem. Host range testing was completed in the early 2000s (Zachariades et al., 2002) and permission was obtained from the South African Department of Agriculture for release. However, a permit from the Department of Environmental Affairs and Tourism is still pending. It is expected that the weevil will survive seasonally drier conditions better than the two leaf feeders (P. insulata and C. eupatorivora) already established in South Africa. Rearing this agent is easy, although fairly slow.

Availability: Available from SA immediately, if import permits have been obtained from country of introduction.


L. aemulus adult


 

L. aemulus oviposition holes in the stem of
C. odorata. The female drills an inspection hole with her rostrum and if the stem is suitable she inserts the egg into the
stem and plugs the hole

 
Adult L. aemulus exit hole from
C. odorata stem. Stem probably
killed by larval feeding

 

1.2 Conotrachelus reticulatus Champion (Coleoptera: Curculionidae) 


Adult C. reticulatus on C. odorata.
Photo: Oona Delgado, UCV-MIZA

 

C. reticulatus eggs are laid on the leaf next to a vein, after a small hole has been cut through the leaf, and therefor covered with trichomes. Hatching larvae bore down the vein and through the petiole to the node, where they create a gall


A mature C. reticulatus gall. The larva may have already left the gall to pupate in the soil

 
Adult C. reticulatus
A young C. reticulatus gall on
C. odorata in Venezuela

The larvae of this weevil form gall-like swellings in the upper nodes of the plant, preventing or reducing further growth and probably acting as a nutrient sink

Larvae exit the galls and pupate in the soil; the insect is thus suitable for seasonally dry and fire-prone areas. The insect has a wide geographic range (Brazil to Venezuela and probably Colombia).

A culture was imported from Venezuela into South African quarantine in the late 1990s, cultured, and partial host range testing completed, which indicated high specificity (Zachariades et al., 2007).

However, the culture was eventually lost, and due to concerns over the compatibility of the weevil with the SA biotype it was not re-imported. Further host range studies (both in the field and cages) have been conducted under contract by Universidad Central de Venezuela – MIZA in Venezuela and the insect appears specific.

The plan is to re-import C. reticulatus into South African quarantine within the next few years and test it for biotype compatibility. No plant-insect matching problems are expected with the AWA biotype of chromolaena.

Availability: Needs to be re-collected in Venezuela through cooperation with Universidad Central de Venezuela.

 

1.3 Dichrorampha odorata Brown & Zachariades (Lepidoptera: Tortricidae)

This small moth has larvae which form galls in the shoot tips of chromolaena. It has recently been described from Jamaica (Brown & Zachariades, 2007) but is also known from Cuba.

A culture was successfully imported into SA quarantine in 2005, and the insect has several attributes which make it promising as a biocontrol candidate.

It has a high rate of increase, short life span, is easy to breed and to test for host range, and so far appears specific to chromolaena. Being from Jamaica, there should be no insect-plant compatibility issues with regards the SA biotype.

However it does not have a distinct diapause period and may thus not be suitable for the driest areas invaded by chromolaena.

Availability: Host range testing should be completed in 2010. 


Adult D. odorata


Mature D. odorata larva in
C. odorata
stem-tip gall

 
D. odorata gall on C. odorata. A pupation chamber is visible
on the right-hand leaf. The larva exists the gall to pupate,
cutting a leaf crescent, folding it over and sewing it with silk


1.4 Carmenta n.sp. (Lepidoptera: Sesiidae)
 


Female Carmenta n.sp. adult


Shoot of C. odorata
with older Carmenta n.sp.
damage, Venezuela
   

Shoot of C. odorata recently attacked by
Carmenta n.sp. larva; Venezuela

Emergence window cut by Carmenta n.sp. larva prior to pupation. The enclosing adult pushes the pupal case partially out of this window. Photo: Oona Delgado, UCV-MIZA

This day-flying moth lays eggs on leaf petioles near the top of the stems of chromolaena plants. Larvae bore into the shoot tip and kill it, causing characteristic wilting shoot-tips (not to be confused with the similar-looking damage of the fly Melanagromyza eupatoriella which causes spiral tunnels in shoot-tips – see below) before moving down the stem 20-30cm, where they pupate.

The insect is able to spend the dry season in diapause in the stems. Females appear to favour tall, large shrubs in sunny positions for oviposition. The insect was discovered in Venezuela and is currently being described (Eichlin et al., 2009).

A culture was successfully imported into South African quarantine in 2005, and has been partially tested for host range, indicating high specificity so far. A preliminary field host range survey in Venezuela did not find any other plants being attacked by the moth. Because Carmenta n.sp. was collected off a different form of chromolaena, there may be compatibility issues with the SA biotype, even though these are not apparent in the laboratory.

Availability: Host-range tests are several years from being completed.


1.5 Recchia parvula (Lane) (Coleoptera: Cerambycidae) 

This univoltine insect lays eggs in the shoot tips of chromolaena and larvae bore right down to the root crown, cutting off the plant at its base (Zachariades et al., 2007).

It is thus highly damaging and should be able to tolerate seasonally dry conditions and burning. It was collected in Argentina and imported into SA quarantine in 2002.

Preliminary host range tests indicate good specificity. It is likely to have been collected from Chromolaena hookeriana but breeds successfully in the laboratory on C. odorata.

Availability: Several years, if adequate host specificity is shown.

Two R. parvula adults with feeding damage to stem tip.

Typically, an egg is inserted into the stem tissue just below the damaged section


Mature R. parvula larva in stem, Argentina.
Photo: Daniel Gandolfo, USDA-SABCL

At the end of the summer the R. parvula larva has reached the crown and cut off the stem, leaving a stump

 

 

1.6 Melanagromyza eupatoriella Spencer (Diptera: Agromyzidae)

M. eupatoriella ovipositing under a young C. odorata leaf. The larva bores down the petiole and into the stem tip

​The larvae of this fly create a spiral mine in the shoot tip, thereby killing it.

The fly was recorded by Cruttwell (1974) in Trinidad but because it could not be reared, was not considered at the time as a biocontrol candidate. However it has been mentioned over the years as a possible candidate in various publications, and was studied in the 1990s in Trinidad by CABI.

It has been imported several times into quarantine in SA, from several neotropical countries, but the culture could not be sustained over more than two generations. It is currently the subject of a study in Jamaica to assess its field host range. Biotype incompatibility seems unlikely because the fly is found throughout the native range of chromolaena. Similar mines are found in the stem tips of several Asteraceae in the field in Jamaica. If these are M. eupatoriella, the fly may have too wide a host range for use as a biocontrol agent.

Availability: Not currently available


C. odorata shoot recently attacked by
M. eupatoriella larva. The characteristic spiral mine is visible.

Shoot with older M. eupatoriella damage. The fly pupates in the stem: the adult emergence window is visible below the damaged section of the stem

 


1.7 Pathogens


Septoria leaf spot on C. odorata


Possible pathogen attacking leaves of C. odorata in Jamaica

Numerous pathogens, including the leaf-spot pathogens Septoria ekmaniana Petr. & Cif. (Deuteromycotina: Coelomycetes), Pseudocercospora eupatorii-formosani (Sawada) J.M. Yen (Deuteromycotina: Hyphomycetes), Mycovellosiella perfoliata (Ellis & Everh.) Munt.-Cvetk (Deuteromycotina: Hyphomycetes) and Anhelia niger (Viégas) Arx (Ascomycotina: Ascomycetes: Myriangiales) and the rust fungus Cionothrix praelonga (Wint.) Arthur (Basidiomycotina: Urediniomycetes: Uredinales) have been collected from chromolaena in the field in its native range since the 1980s (Elango et al., 1993; Barreto & Evans, 1994), but very few have successfully been inoculated onto SA biotype plants in the laboratory, and those that have were not highly virulent (den Breeyen, 2002). Little work has been conducted in quarantine on suitable pathogens for the AWA biotype. SA biotype plants have now been planted out into the field in Jamaica to act as trap plants for compatible pathogens, which will be harvested and isolated in the quarantine laboratory in South Africa.

Availability: No compatible, virulent pathogens for the SA biotype found so far. Trap plants set up in Jamaica.

2. Australian Centre for International Agricultural Research

Australia became concerned with the threat of invasion by C. odorata into its tropical and subtropical northern regions (Queensland and Northern Territory) in the late 1980s, especially as Indonesia, PNG and East Timor contained heavy infestations of the weed. In the 1990s and 2000s ACIAR thus initiated and funded C. odorata biological control projects in several countries in South-East Asia and Oceania, including Indonesia, PNG and the Philippines. The most recent ACIAR projects, on biocontrol of chromolaena in PNG (July 1997 – March 2007) and East Timor (July 2004 – February 2009), have ended. Work is still progressing in both countries to assess the impact of the gall fly Cecidochares connexa. Another project in East Timor could be started using new agents for chromolaena, especially those such as C. reticulatus that are likely suited to seasonally drier areas where the gall fly is unlikely to be as effective.