Molecular applications available for everyone – a cheap tool to monitor parasitism rates of invasive agricultural pests

Daniela Sint


Project description

Leafmining flies (LMF) of the genus Liriomyza (Diptera: Agromyzidae) are an important pest in

agricultural and horticultural crops where they can induce severe damage and yield losses. Their

origin is in South and North America, but during the last decades they are spreading worldwide

(Scheffer, Lewis et al. 2006 and citations therein). Although Liriomyza can cause also severe losses in

regions where it occurs naturally, there it is attacked by a rich community of natural enemies (Mujica

and Kroschel 2011). The lack of these antagonists and hardly any native parasitoids attacking invasive

LMF are probably the reason why the most wide spread and polyphagous species L. huidobrensis, L.

trifolii (both also known from Austria where their occurrence is subject to report; AGES 2012) and L.

sativae can reach pest status shortly after introduction. Due to high morphological similarities

between Liriomyza species and absence of host plant specificity, it remains often unclear which of

the mentioned species actually induced the damage (Scheffer 2000; Scheffer and Lewis 2005).

In Nepal L. huidobrensis was introduced very recently and severe damage was observed on potato

plants (Paneru and Giri 2011). Leafmining flies cannot be well controlled with common insecticides,

as the larvae feed inside the leaf and pupation takes place in the soil – both protecting the LMF from

direct contact with the pesticide. On the contrary, application of insecticides often enhances LMF

outbreaks as the enemy community is totally destroyed by the pesticide (Murphy and La Salle 1999).

To overcome these problems methods of classical biological control are applied. This means

parasitoid species known to regularly attack Liriomyza in their native habitat are introduced, mass

reared and released in infested regions. Ideally the introduced parasitoid establishes stable

populations in the new habitat and provides this ecosystem service continuously, reducing costs and

health risks related to pesticide use for the farmers. This is especially desirable in developing

countries, where resources are limited and often no protection of humans against hazardous

chemicals is applied. Up to now no native Nepalese parasitoids seem to control the invasive L.

huidobrensis, thus it is thought to import parasitoids from South America as biological control agents

like it was already done in Kenya.

Monitoring programs accompanying biological control measures are essential to a) verify that

invasive LMF are attacked by the introduced parasitoids and b) the parasitoids will not harm

indigenous non-pest insects. This monitoring can be done via rearing of LMF larvae from infested

leaves and subsequent counting and identifying adult LMF and parasitoids (Mujica and Kroschel

2011), which does not only require excellent taxonomic skills but is also time and space consuming

and suffers regularly from difficulties during rearing. Nowadays the application of molecular methods

is a common alternative (e.g. Traugott, Bell et al. 2008), but an application in developing countries is

often “out of reach” due to limited resources.

In the proposed project we want to adapt and optimise a multiplex PCR system (MP-system) that was

developed within the project “Sustainable potato pest management in the Hindu Kush-Himalaya

region” financed by the Austrian Developmental Agency (

forschung/potato_pest.html.en). This system allows detection of economically important Liriomyza

species and tracking their most important parasitoids. Thus it will provide a possibility to rapidly

identify Liriomyza species that cause damage and yield loss in agricultural fields. At the same time

parasitism rates can be determined, helping to find strategies in combating these pests. The system

will be optimized in a way that it delivers robust results and can be applied also at a low cost level,

making it available for developing countries. In a second step the MP-system will be implemented

and tested in Peru, where Liriomyza is native, and a developing country that suffers from invasive

LMF and where parasitoids from South America were introduced to control the outbreaks. As up to

now no such parasitoids were released in Nepal, Kenya will serve as a pilot region. To evaluate the

implementation and detection rates generated in Kenya and Peru, field samples will be collected in

the respective country and half of the samples will be analysed there and half of them in Innsbruck.


Aims and objectives

Molecular methods proved to be a fast, sensitive and valuable tool to investigate trophic interactions

(e.g. Macfadyen, Gibson et al. 2009; Sint, Raso et al. 2012) and allow identification of morphologically

similar species (e.g. Staudacher, Pitterl et al. 2011) placing them among standard practices in high

developed countries. On the other hand the application of these methods is rarely possible in

developing countries due to a lack of resources and knowledge. Within this project we want to

develop a molecular detection system for pests and their natural enemies that is robust and cheap

and thus can also be useful for not so high-end equipped laboratories. The also proposed approach

of comparison between laboratories allows us to detect any problems or weaknesses in the

developed PCR system to make it a useful tool for low budget applications and the co-operating

laboratories in Kenya and Peru get the feedback and confidence that the implementation of the new

method was successful and that reliable data is generated.

The opportunity to directly compare parasitism rates of native and invasive Liriomyza populations

will help to better understand the effectiveness of classical biological control to regulate these pests.

Furthermore the results of this project provide help to decide if and if yes, which South American

parasitoids should be introduced to Nepal to control Liriomyza outbreaks.


There are three objectives within this proposed project

· To develop a cheap and robust molecular detection system that allows identifying the pest

species (L. huidobrensis, L. trifolii, L. sativae) and tracking their most abundant parasitoids

· To evaluate the implementation and application of the system in two pilot regions via field

collected samples that will partly be analysed in Innsbruck, Kenya and Peru respectively

· To investigate whether the relative importance of common parasitoids and their parasitism

rates of Liriomyza differ between the origin region (Peru) and invasive populations in Kenya