Mortality of the leaf-mining , Aristaea thalassias (Gaertn.) F. Muell (: Myrtaceae), a biological control agent of Leptospermum laevigatum

Thembelihle Mlokoti*, Fiona Impson, John Hoffmann and Candice Lyons

Fynbos Forum, Swellendam, 2017 Introduction

 Leptospermum laevigatum originates from Australia

 It was introduced into South Africa in the 1800’s to stabilise dunes

 It poses threat to the fynbos biome in the Western Cape and Eastern Cape

 Two biological control agents Dasineura strobila and Aristae thalassias were introduced to supress the weed in the 1980s Aristae thalassias

 The leaf – mining moth lays eggs on the adaxial and abaxial surfaces of newly formed leaves at the tip of stems of L. laevigatum

 The early instar larvae feed on parenchyma within the leaf, forming serpentine mines which become broader as the larvae grow

 Eventually all of the parenchyma is consumed at which stage the hollow leaves become air-filled and puffy and soon after they fall from the plant

Aristae thalassias

 Three life stages:

 ―Mined leaves‖ – mining stage characterized by visible mines

 ―Puffy leaves‖ - pre-pupal stage

 ―Rolled leaves‖ - pupal stage Questions

 What are the causes of mortality in the different immature life stages of the moth?

 Which life stages are most prone to mortality and what are the levels of mortality?

 How does mortality vary seasonally? Methodology

 Study site- Walshacres farm, near Stanford and Agricultural Research Council, Plant Protection Research Institute (ARC- PPRI)in Stellenbosch

 The investigation took place between July 2015 and Feb 2017

 Sample collection- mined, puffy and rolled leaves (30 each type) were collected on a weekly basis in the field.

 Dead and live pre-pupae and pupae were recorded via means of dissection

 For possible causes of mortality, intraspecific competition, presence and absence of parasitoids and mites was inspected

• Percentage mortality of larvae and Results pupae was high, but highest in rolled

100 leaves ± 90

80 70 • There was no difference in mortality Mined(L) 60 discernible between seasons Puffy(L) 50

Pre-pupae(L) S.E.) 40 Pupae • Mortality of larvae in mined leaves 30 showed a slight increase in winter, 20 10 while mortality in rolled leaves was % mortality of ( and pupae of larvae mortality % 0 highest in summer and autumn Summer Autumn Winter Spring

Fig. 1: Mortality of A. thalassias larvae and pupae at different • Mortality attributed to parasitism was seasons and percentage mortality due to parasitism. low: Autumn= 20% and Spring = 10%

100

S.E.) 90 ± 80

70

60 Mined(L) 50 Puffy(L) 40 30 Rolled(L) 20 Pupae 10 0 Summer Autumn Winter Spring

% mortality % of larvae andpupae (

Results 100 100 90 90 80 80 • Percentage mortality of 70 70

60 60 larvae due to intraspecific

50 50

40 40 competition showed a slight

30 30 larvae larvae

competition increase from January to 20 20 10 10 March. 0 0

Jan Feb Mar Apr May June Jul Aug Sep Oct Nov Dec % Mortality dueMortality % intraspecfic to

of containing leaves multipleof

% % Months

Fig. 2: percentage larval mortality due to intraspecific competition in mined leaves

Discussion

 The current drought situation, in place since 2015, may be impacting mortality of the moth in the early life

 Leaf age is important in the development and survivorship of phytophagous , with feeding damage concentrated on young foliage

 Weather is an important force that limits the length of time that

the food resources are available, affecting insect populations Discussion

 Predation is another possible cause for the high rate of mortality of pre- pupae and of the pupal stage. Natural enemies are more likely to limit phytophagous insect populations.

 Mortality attributed to parasitism was low, contrary to other studies that parasitism is a major source of mortality in most leaf–mining insects.

 Intraspecific competition is another possible cause for high mortality

of leaf-miners. Conclusion

 Mortality is high at all stages but the pupal stage is the most prone to mortality

 Causes of mortality were not readily determinable but predation, intraspecific competition and desiccation might be contributing factors—especially at the pupal stage Acknowledgements

 Agricultural Research Council and University of Cape Town

 My supervisors

 My colleagues

 DEA: NRMP

THANK YOU