3[7] Amblypelta [EIFS

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This leaflet is produced by the Ministry of Agriculture & Livestock, Solomon Islands, with support
from IPPSI: Improved Plant Protection in Solomon Islands, a project financed by ACIAR, the
Australian Centre for International Agricultural Research, Canberra. Authors: Helen Tsatsia &
Grahame Jackson, TerraCircle Inc.

Extension Fact Sheet 19:

Cassava Shoot Dieback

Common name: Cassava shoot dieback and Coconut premature nut fall

Scientific name: Amblypelta cocophaga and other species.

Hosts: Coconut, causing premature nut fall; shoot-tip dieback of Eucalyptus deglupta
and cassava, and cocoa pod distortion.

Damage

As Amblypelta feeds it injects a poison. In coconuts, the young fruit (buttons or nuts)
fall; in Eucalyptus and cassava, the shoot wilts and dies, and cankers form on the
stems (photo, left); in cocoa, sunken black spots occur and young pods become
distorted as they grow.

Early or premature nut fall of coconuts in Solomon Islands has been a major problem
in some parts of the country, and has been investigated since the 1930s by a number
of entomologists. The islands of Guadalcanal, Malaita and Nggela are those most
affected. Loss of coconuts was estimated to be between 10 and 20%, but that on
individual farms on Malaita and Nggela losses were devastating. It is difficult to be
accurate as nut fall is patchy, depending on the distribution of various ant species and
their interaction with Amblypelta. Also, coconut has a natural fruit drop of over 60%.

Another problem occurred in the 1980s. Amblypelta dieback was seen on Eucalyptus,
threatening the success of forest replanting schemes on Kolombangara, in particular.
Amblypelta caused death of the leading shoot. After a while, other shoots developed,
but these, too, were attacked and the trees became hedge-like.

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Biology and Life Cycle

The body is about 20 mm long, the legs are pale green, while the wings are pale-
brown (photo, above right). Females lay eggs on or near the host plant. Nymphs hatch
a few days later. They are dark brown with long legs and antennae; they look like
adults without wings. Nymphs feed in the same way as adults, and on the same plants
using needle-like mouthparts. It is not known if nymphs inject poison, but it is likely.
Wings develop when nymphs become adult, 3-4 weeks after emerging from the egg.

Management

Natural enemies

In 1937, four egg parasites were collected in Indonesia and released in Solomon
Islands against A cocophaga. However, these did not control the pest. Later, a
Tachnid fly was introduced from Queensland, but this, too, was unsuccessful. A
Braconid wasp was found on Kolombangara infecting late stage nymphs.

Amblypelta is found at low numbers on coconuts and probably other hosts. The
damage caused by one adult is significant, so it is unlikely that parasites could reduce
numbers enough to prevent economic losses.

Manipulation of ant species

Attempts over many years to control premature nut fall have tried to encourage some
species of ant whilst removing others. Mostly, this means removing Pheidole
megacephala and Iridomyrmex cordatus and encouraging Oecophylla smaragdina.
The idea is to have ant species that discourage Amblypelta from feeding on the young
coconuts. Oecophylla invades the palm in search of food and at the same time chases
Amblypelta away.

Removal of P megacephala using herbicide and insecticide applied to the base of the
trunk is possible. Once removed, soursop trees are planted among the coconuts, the
fruits of which readily become colonised by mealybugs, which are ‘farmed’ by
Oecophylla for their honeydew. The success of this strategy was patchy, however, as
the ant populations keep changing. Also, removal of I cordatus is difficult as it makes
its home in the crown of the palm, not in the ground.

In more recent years, a fire ant, Wasmannia auropuntata, has become established
throughout Solomon Islands. This ant is capable of protecting palms against
Amblypelta as well as displacing I cordatus and probably P megacephala.

Chemical control

A number of insecticides applied as sprays or as trunk injections from different
chemical groups have been tested against premature nut fall. Some are effective;
however, the height of coconut palms prohibits easy application, and it is unlikely that
such treatments are economic. To be effective, they would need to be applied
frequently, perhaps 8-10 times a year.