Biological Control of Insect Pests: Southeast Asian Prospects - EcoPort

156 Biological Control of Insect Pests: Southeast Asian Prospects
was possibly due to its requirement for large numbers of hosts, since 7 larvae
consumed over 100 medium to large sized hosts during the last half of their
larval lives. In Guatemala it is highly parasitised by two species of chalcidid
wasps. Carter (1935) regarded it as a promising species for biological
control.
Vincentodiplosis pseudococci Dipt.: Cecidomyiidae
This midge is native to Mexico and was established in Hawaii in 1950. In
neglected, weedy pineapple plantations in Hawaii, where the ant Pheidole
sp. was less reliant on mealybug honeydew, the midge was sufficiently
effective in controlling D. brevipes as to almost completely eliminate the
mealybug from the fruit. Many fruit were covered with the old webs
produced by midge larvae, but there were no live mealybugs. The midge is
rarely found on leaves, but its larvae are commonly found attacking large
mealybugs at the base of the fruit (Carter 1935, 1944).
Comments
It is very likely that D. brevipes evolved in South and/or Central America
and there is, therefore, a prima facie case to consider it as a candidate for
classical biological control in Southeast Asia and the Pacific. Indeed, there
are 2 parasitoid species (Anagyrus ananatis and Hambletonia
pseudococcina: both Eulophidae) and 2 predator species (Vicentodiplosis
pseudococci: Cecidomyiidae and Pseudiasta nebulosa: Diastadidae) that are
capable of reducing the mealybug to subeconomic levels. However, when
any one or more of a number of ant species attends the mealybug it is largely
protected from natural enemies and is able to build up to damaging numbers.
In the absence of both ants and natural enemies the unharvested honeydew it
produces leads to heavy growth of sooty moulds and there is transmission of
pineapple mealybug wilt. Since apparently suitable natural enemies are
available for introduction, the key to D. brevipes control is to deal with the
attendant ants. There are several ant baits that have been used successfully
for this purpose, but these are no longer registered for use in USA and,
hence, cannot be recommended. No doubt suitable replacements will soon
emerge. When extensive plantings of pineapples are made on areas where
the soil has been worked to kill weeds, very few ant colonies survive.
Recolonisation of the planted area occurs as colonies move along the rows
towards the centre of the crop. One cultural method recommended to delay
this spread is to plant several peripheral rows parallel to each boundary. Ants
will then move along these, rather than into the crop and control measures
can be concentrated on these rows (Rohrback et al. 1988). Promising results
obtained with the integrated management of D. brevipes in Hawaii suggest
that it would be well worth exploring similar methods elsewhere.