Mesquite Biological Control: Sap-sucking Psyllid, Prosopidopsylla flava

Mesquite Home | Bioloical Control

Summary | Taxonomy and Origin | Lifecycle | Host Specificity | Mass-rearing and Release | Establishment, Damage and Impact | Current Research | References

Summary
This insect was released throughout Australia in 1998-2000. However, it has only tenuously established at two infestations, in north-west New South Wales and south-west Queensland, despite the release of over 180,000 insects. These infestations have not been resurveyed since 2001, so it is uncertain whether populations still remain. Available evidence suggests that ant predation, and possibly poor adaptation to climate in hotter regions, may be the key factor preventing establishment.

Taxonomy and origin
Prosopidopsylla flava is widely distributed through northern and central Argentina where it has been recorded from 10 provinces (Catamarca, Chaco, Cordoba, Formosa, La Rioja, Mendoza, Santiago del Estero, San Juan, San Luis and Salta).

Lifecycle
Prosopidopsylla flava is intimately associated with its host plant throughout its lifecycle. There are five nymphal instars. All five are relatively sedentary, moving only when the food supply is exhausted. Mating and oviposition all occur on the food plant and adults can only survive in the absence of their host for two to four days under laboratory conditions. Eggs are attached by a peduncle which is inserted into the plant tissue and they will not hatch if removed.

Unlike many psyllids, the nymphs do not excrete a protective covering. Their bodies are, however, dorso-ventrally flattened and fringed with hairs and so remain closely appressed to the substrate. Both adults and nymphs feed on leaves, rachi and stems, where they feed on the phloem (Taylor & Carver 1991). Salivary injection causes tissue breakdown with a subsequent release of soluble amino acids (Hodkinson 1974). Dispersal is probably primarily windborne as adults (Hodkinson 1974) and the mechanism of host-plant selection is probably chemo-gustatory (Hodkinson 1974).

Eggs can be laid on all parts of the vegetative plant foliage, although they are rarely attached to immature (i.e. still expanding) foliage. Eggs hatch from eleven days after oviposition and adults begin emerging after about 36 days.

Adults live for up to 36 days. Females begin ovipositing 3-5 days after emerging and continue ovipositing through their life. Individual females can produce over 200 eggs, with a peak production of over 37 eggs per day.

Host-specificity
Prosopidopsylla flava is highly specific to the genus Prosopis. Adults can survive for over five weeks on Prosopis compared with a maximum of four to six days on the 62 non-target plant species tested. Thus adult feeding is likely to be restricted to Prosopis. Egg production is also restricted to Prosopis, and is dependent on nutrients gained from adult feeding. Fecund females can oviposit into most plant species in no-choice laboratory trials. Oviposition in the field is, however, almost certainly restricted to the plant on which adults feed. Complete nymphal development is also restricted to Prosopis. Limited early nymphal development was recorded within 32 days of oviposition on two Neptunia species (N. gracilis and N. major), but no adults developed..

Mass-rearing and release
P. flava is relatively easy to mass-rear. Approximately 300-400 adults were placed into gauze cages together three to six potted mesquite plants (150 mm diameter pots or equivalent). Additional plants were added as required. Next generation adults were harvested 1-2 times a week directly into plastic containers using a hand-held vacuum aspirator. P. flava proved to be relatively difficult to transport because both adults and nymphs die quickly in the absence of their host plant and are sensitive to hot, dry conditions. Adults were therefore transported in insulated containers lined with absorbent paper and containing freshly cut foliage. They were released within 36 hours of harvesting. Releases were made on mesquite in six regions throughout northern Australia. Mostly adults were directly released onto trees that were isolated from the ground with stickem to prevent access by ants. Sometimes adults were first released into gauze sleeves attached to mesquite branches. Almost 183,000 live adults were released in Australia between October 1998 and June 2000.

Establishment, damage and impact
Prosopidopsylla flava failed to establish at most sites despite large-scale, multiple releases. Small numbers were recorded in north-west New South Wales and south-west Queensland at least 12 months after final releases were made suggesting that they are tenuously established there. However, no systematic surveys have been conducted since 2001 so their current status is unknown.

There are several possible reasons why the psyllid failed to establish and/or reach damaging densities (van Klinken et al. 2003). Strong circumstantial evidence suggests that ant predation may have been an important factor. Nymphs are free-living and have no apparent defence against ants, such as excretions. However, the necessary ant-exclusion trials have not been done to confirm this. There is also circumstantial evidence that climate may not have been optimal in regions where no establishment occurred.

Current research
None. Any future work on this insect would aim to test hypotheses as to why it failed to establish and/or result in impact, including climatic reasons, and predation, host quality, competition with Evippe (in the Pilbara), and inbreeding in laboratory cultures.

References

1. van Klinken, R.D. (2000). Host-specificity constrains evolutionary host change in the psyllid Prosopidopsylla flava. Ecological Entomology 25, 413-422.

2. van Klinken, R.D., Fichera, G. and Cordo, H. (2003). Targeting biological control across diverse landscapes: the release, establishment and early success of two insects on mesquite (Prosopis) in rangeland Australia. Biological Control 26, 8-20.