A. Manta; C. ValenteA. Manta; C. Valente

Departamento de Engenharia Florestal, ISA, Lisboa, Portugal

T. T. Calv�oCalv�o

M. Branco; H.M. Branco; H. SantosSantos

Effect of Biodiversity in Eucalyptus Pests and their potential biocontrol agents

Faculdade de Ci�ncias e Tecnologia, UNL, Monte da Caparica, Portugal

RAIZ, Aveiro, Portugal

Outline:Outline:1. Rationale1. Rationale2. Objectives2. Objectives3. Methods3. Methods4. Results4. Results5. Conclusions5. Conclusions

Efect of Biodiversity in Eucalptus Pestsand their potential biocontrol Agents

Forest comprise 38% of Portuguese land area

1. Rationale

The major part of Eucalyptus plantations are pure stands (71%)

Eucalyptus plantations, comprise about 672 thousands hectares, i.e. 21% of the forest areas.

Eucalyptus occur in Portugal for more than 150 years, the most common species is E. globulus.

Being an exotic species until 20 years agoEucalyptus plantations were healthy forest types, regarding pests and pathogens.

Problems with pests and pathogens increased during the last two decades.

Phoracantha semipunctata, arrived during the eighties

Gonipterus scutellatus, arrived during the nineties

Problems with pests and pathogens in Eucalyptus plantations (cont.)

Mycosphaerella spp. leaf fungi, exhibited increasing damage during the last five years

Ctenarytaina eucaliptii, was introduced during the eighties andCtenarytaina spatulata, in 2002. The latest is particularly important.

Eucalyptus plantations also brought environmental concerns, in particular flora and fauna biodiversity and water management.

Vegetation layer in eucalyptus plantations is represented mainly by the genera Ulex (35%), Erica (30%), Cytisus (9%), Pterospartontridentatus (11%) Cistus (25%), Thymus and Lavandula (11% ) and Rubus (10%) (DGRF, 2001)

Considered in general low, however vegetation diversity vary in eucalyptus according to site and stand management

There is a common belief that forest biodiversity positively influences forest health, in the sense of its resistance to pests and pathogens.

Insect predation and parasitism by natural enemies

Host finding and host selection

Pathogen dispersion

A functional relationship between forest biodiversity, both in the sense of composition and structure, and forest health, could be explained by some ecological processes such as:

2. Objectives

Analyse the influence of changes in Eucalyptus plantation biodiversity at understorey vegetation level and landscape diversity in:

• Abundance of herbivorous insects

• Tree damage by herbivorous insects

• Abundance of specialised natural enemies

• Rates of mortality by specialist parasitoids

3. MethodsStudied areas: Six eucalyptus stands were used. Within each stand, 6 plots were chosen with discernible different biodiversity considering understorey vegetation and landscape variability.

Plots were classified in two types:

… high diversity.

low …

and

3. Methods (cont.): Understorey vegetation

In each sampling point two stratified continuous line transects, 10 meters long each, were carried out. All plants in the transect were identified and their canopy length measured.

Plant diversity was estimated using:Species Richness (S)Shannon’s Diversity Index (H), being species abundance, ni, the length of each plant canopy along the line.

3. Methods (cont.): Landscape biodiversity and complexity (for two stands only)

Edge Analysis: Mean Patch Edge in m (MPE)Total Edge in m (TE) Edge Density in m/ha (ED)

At distances:250, 500, 750 and 1000 m

Estimations:Richness, Shannon’s Diversity Index,

Landscape Diversity was calculated:

3. Methods (cont.): Gonipterus scutellatusG. scutellatus was surveyed in 2 young Eucalyptus plantations, about 2 years old, in April, May, September and October, 2004.

50 egg masses were collected to determine the parasitism by Anaphes Nitens.

In each plot, 10 trees were randomly selected, the number of adult weevils wascounted and defoliation evaluated.

Egg masses were kept in laboratory (24�C) until emergence of parasitoids. Rate of parasitism was determined.

3. Methods (cont.): Phoracantha semipunctata

The populations of the longhornedbeetle and egg parasitism byAvetianella longoi were assessed by using freshly cut log traps, 1 m in length. Traps were assessed after 1 week.

P. semipunctata was surveyed monthly in 3 mature Eucalyptus plantations, between June and September 2004

All egg masses were collected and kept in laboratory at room temperature for 30 days. The sterile eggs, P. semipunctata larvae, eggs parasitized by A. longoi and number of parasitism per egg was counted.

Avetianella longoi

4. Results: Gonipterus scutellatus

05

1015202530354045

April May April June September November

Sesmarias Ervideiro

Stand and date

Adu

lts p

er tr

ee

Low diversity plotsHigh diversity plots

a a

a

ab

a

a

a

a a a

b

Average number per tree �SE of adults of G. scutellatus in relation to type of plot in two stands: Sesmarias and Ervideiro

4. Results: Gonipterus scutellatus

0,0

0,5

1,0

1,5

2,0

2,5

3,0

April May April June September November

Sesmarias Ervideiro

Stand and date

Deg

ree

of tr

ee d

efol

iatio

n

Low diversity plotsHigh diversity plots

bba

a

aa

aa

ab

Average degree of tree defoliation �SE by G. scutellatus in relation to type of plot in two stands: Sesmarias and Ervideiro

4. Results: Gonipterus scutellatus

Average number of Anaphes nitens per egg

mass � SE by in relation to type of plot.

Average egg mass parasitized by A. nitens � SE in relation

to type of plot.

0,0

0,2

0,4

0,6

0,8

1,0

Ervideiro Sesmarias

Stand

Ana

phes

nite

ns /

egg

mas

s

Low diversity plotsHigh diversity plots

a

a a

a

a

0,0

0,2

0,4

0,6

0,8

1,0

Ervideiro Sesmarias

Stand

egg

mas

s pa

rasi

tised

(%) Low diversity plots

High diversity plots

ab

a a

4. Results: Phoracantha semipunctata

0

100

200

300

400

500

600

High Low High Low High Low

Ameixoeira Barrocal Couto dos Pelados

Stand / plot biodiversity

Num

ber

of e

ggs

per

trap

Number of eggs per trap

Eggs parasitised per trapa

a

a

ba

b

a

a

a

ba

a

Average number of eggs of P. semipunctata and eggs parasitized by Avetianella longoi �SE in relation to type of plot in three stands:

Ameixoeira, Barrocal and Couto dos Pelados.

4. Results: Relationship with vegetation layerRelationship between the diversity of understorey vegetation (H) and both the abundance of P. semipunctata and parasitism by the parasitoid Avetianella longoi (Pearson correlation, r, n=6)

** - significant at α =0.01* - significant at α =0.05

Stand Total number of eggs per

plot

Eggs parasitized

(%)

Egg mortality

(%)

Ameixoeira -0,92** -0,35 0,26

Couto dos Pelados -0,83* 0,01 -0,41

Barrocal -0,88* -0,06 0,29

Relationship between the abundance of P. semipunctataand eggs parasitized by Avetianella longoi

Stand Ameixoeira C. dos Pelados Barrocal

Pearson, r 0,93**, n=20 0,75**, n=18 0,84**, n=24

Relationship between the diversity of understorey vegetation (H) and the abundance of Gonipyterus scutellatus and the parasitism by the egg parasitoid Anaphes nitens (Pearson correlation, r, n=6)

Stand Number of adults per

tree and plot

Egg masses parasitized

(%)

Number of Anaphes nitens per egg mass

Ervideiro -0,75 -0,11 0,11

Sesmarias -0,68 -0,70 -0,42

4. Results: Relationship with vegetation layer

Stand Ervideiro Sesmarias

Pearson, r (n=6) -0,12 0,75

Relationship between the abundance of G. scutellatusand eggs parasitized by Anaphes nitens.

4. Results: Landscape analysis

Relationship between the diversity of landscape diversity (H) and the abundance of Phoracantha semipunctata (Pearson r,

n=6), stand of Barrocal

** - significant at α =0.01* - significant at α =0.05

Distance(m)

Shannon’sdiversityIndex H

Shannon’s Evenness Index E

Edge density(m/ha)

Mean Patch edge (m)

Total edge size (m)

250 -0,53 _ -0,53 -0,53 -0,53

500 -0,18 -0.95** -0,13 -0,98** -0,13

750 0,18 -0.33 0,30 -0,72 0,30

1000 0,37 0.33 0,46 -0,65 0,46

Relationship between the diversity of landscape diversity (H) and the abundance of Phoracantha semiunctata (Pearson r,

n=6), stand of Ameixoeira

** - significant at α =0.01* - significant at α =0.05

Distance(m)

Shannon’sdiversityIndex H

Shannon’s Evenness Index E

Edge density(m/ha)

Mean Patch edge (m)

Total edge size

(m)

250 -0.78 -0.86* -0.82* 0.71 -0.82*

500 -0.51 -0.84* -0.56 -0.42 -0.56

750 -0.14 -0.02 -0.28 -0.52 -0.28

1000 -0.64 -0.01 -0.61 0.40 -0.61

4. Results: Landscape analysis

5. Conclusions:

The plots with lower vegetation diversity, showed a tendency tocontain higher densities of herbivorous insects.

This tendency was more evident for P. semipunctata.

Consistently, the relationship between vegetation diversity (H) and pest abundance was negative in all cases. However, correlations were significant for P. semipunctata only.

The fact that G. scutellatus was surveyed in young stands, with low understorey diversity and less contrasting plots in comparison of the mature stands selected for P. semipunctata may in part explain this result.

5. Conclusions (cont.) :

Higher plot diversity did not lead to a higher rate of parasitism by the specialist parasitoids: Avetianella longoi and Anaphes nitens.

The density response to host species may be more relevant to explain parasitism success.

High landscape diversity and complexity can explain a reduction in pest density, significant until 500m radius.

The effect of understorey and landscape diversity in the abundance of these pests, in particular P. semipunctata, might be explained by a higher pressure of natural enemies such as generalist predators.