Population Dynamics and Economic Losses Caused by Zeuzera Pyrina, a Cryptic Wood-Borer Moth, in an Olive Orchard in Egypt

Agricultural and Forest Entomology (2014), DOI: 10.1111/afe.12075 Population dynamics and economic losses caused by Zeuzera pyrina, a cryptic wood-borer moth, in an olive orchard in Egypt

∗ ∗∗ Esmat Hegazi ,FredrikSchlyter†, Wedad Khafagi‡, Atwa Atwa§¶, Essam Agamy and Maria Konstantopoulou†† ∗Department of Entomology, Faculty of Agriculture, Alexandria University, 542245, Aflaton Str., Alexandria, Egypt, †Unit of Chemical Ecology, Department of Plant Protection Biology, Swedish University of Agricultural Sciences, PO Box 102, SE-230 53 Alnarp, Sweden, ‡Biological Control, Plant Protection Research Institute, 3236, Bacoos, Alexandria, Egypt, §Plant Protection Research Institute, 77688, Nadi El Seid Str., Cairo, Egypt, ¶King Abdul-Aziz University, Jeddah, Kingdom of Saudi Arabia, ∗∗Department of Entomology, Faculty of Agriculture, Cairo University, Cairo, Egypt, and ††Chemical Ecology and Natural Products Laboratory, NCSR ‘Demokritos’, 15310, Paraskevi Str., Attikis, Greece

Abstract 1 The leopard moth Zeuzera pyrina L. (ZP) is an invasive pest from Europe of increasing significance in North Africa, in particular for olive cultivation. We followed the temporal dynamics by combined light/pheromone trapping over a 10-year period (2002–2011) in a 240-ha olive farm in Northern Egypt. 2 The ZP had an annual cycle with one or two peak flights, from late April until October. Time series analysis showed a 2-year cycle of trap catch. This cycle is likely related to the ‘on/off’ bearing pattern of the olive, where years of high and low yield are observed to alternate. 3 Larval damage in both ‘on’ and ‘off’ years in the infested trees gave fruit yield losses of 37–42%. The loss was estimated to 2.1–4.8 t/ha among susceptible varieties. The relative losses were the same during on and off years. 4 Infestation of four susceptible and five resistant olive cultivars in different cropping systems varied within and between adjacent plots. The results suggest less infestation by intercropping of resistant varieties, which could assist in ZP management. 5 Both temporal and spatial dynamics strongly influence population dynamics and the dynamics are related to variation in the moth host plant. Keywords ARIMA, leopard moth, olive, periodic oscillations, population dynamics, Zeuzera pyrina.

Introduction et al., 2006). Newly-established olive orchards suffer the great- est damage, including the death of young trees. In nurseries, the The olive tree (Olea europea L.) plays an important part in the damage can be particularly extensive (Liotta & Giuffrida, 1967; lives of Mediterranean people. Its role is multiple: nutritional, Castellari, 1986). In Egypt, damage caused by ZP led to uproot- social, cultural, economic and political. The key insect pests ing of olive groves by growers (E. Hegazi, unpublished data). of Mediterranean olives are the olive fruit fly Bactrocera oleae The damage caused by the larval tunnels in structurally critical (Gmelin), the olive moth Prays oleae (Bernard), and the black wood can be extremely serious to a tree already bearing a fruit scale Saissetia oleae (Olivier). However, another insect pest, the load; it causes ordinary branches to break under a medium load, leopard moth Zeuzera pyrina L. (ZP) (Lepidoptera: Cossidae), whereas it may cause complete death of young trees with a heavy has become of increasing impact in North Africa in the last load as a result of damage to the major branches and trunk. Monitoring and control of this cryptic moth is extremely few decades (Katsoyannos, 1992). Little is known of its ecol- difficult because the larvae bore deep into twigs, branches and ogy in this new context. The larvae of ZP are cryptic wood- trunks. Visual inspection of larval activity has been used as borers affecting a wide variety of trees and shrubs, comprising main method of monitoring this pest (Kutinkova et al., 2006). over 150 plant species from 20 genera (Balachowsky & Mesnil, However, night-active adult moths are difficult to observe in the 1935; Carter, 1984; Castellari, 1986; Gratwick, 1992; Kutinkova field. Many moth pests of agricultural importance are commonly monitored using pheromone traps (Durant et al., 1986; Delisle, Correspondence: Esmat Hegazi. Tel.: +2 (3) 5908497; fax: +2(3) 1992), although other monitoring techniques such as black-light 5922780; e-mail: [email protected] traps are also used (Steinbauer, 2003; Szabo et al., 2007).

Methods of monitoring ZP adults by using pheromone-baited Each quadratic plot was divided into 10 sectors or ‘strips’, traps have been investigated (Tonini et al., 1986; Pasqualini each comprising approximately 30 trees. Each strip combined et al., 1992; Pasqualini & Natale, 1999). There are, however, three lines of one cultivar alternating with another strip of three some limitations with respect to using light (Blomberg et al., lines of the second cultivar, and so on, in a ‘strip intercropping 1976; Baker & Sadovy, 1978) or pheromone traps (Malo et al., system’. Thus, the width of each strip was similar. It was 2001) alone. Light traps are less competitive than calling females established in 1996, drip irrigated and not in close proximity to an with respect to capture males, whereas pheromone traps do not apple plantation or other known host plants of ZP grown within capture females. The available data on the flight phenology and 15 km, and only palm trees and naturally occurring wild plants biology of ZP in Egypt are scarce and often contradictory (Ismail were nearby. et al., 1992). Hence, we have used trapping stations combining No chemical control was applied on monitoring or experimen- pheromone and black light trapping (Hegazi et al., 2009) tal plots during the experimental period. The arid climate (data In our study area, a major outbreak of ZP occurred in July to for 2006–2009) comprised rainy seasons lasting from Novem- October 2001, causing massive damage. Of the 240-ha planta- ber /December to January/February with a mean annual rainfall tion, 12 ha were severely infested by ZP and the owner had a of 9.2 mm. The mean monthly minimum temperature varied from plan to uproot this area. Initiation of insect outbreaks is poorly 10.2 ∘C in January to 23.9 ∘C in August and the mean monthly understood. Factors causing such outbreaks remain enigmatic as maximum temperature varied from 18.9 ∘C in January to 35.6 ∘C a result of the requirement for many years of data, as well as the in July. The mean relative humidity ranged from 47.8% in April examination of detailed mechanisms (Maron et al., 2001; Nel- to 63.8% in January. son et al., 2013). In addition, the olive has a strong year-to-year deviation cycle in yield, known as ‘on/off’ years (Lavee, 2007). This alternate bearing is highly dependent on the climate in Detection of infested trees, natural enemies and larval each growing region (Morettini, 1950; Hartmann, 1951). These phenology distinct ‘on/off’ years in the host tree are expected to co-vary Infestations were recognized (Fig. 2) by the presence of (i) cylin- with the population dynamics of the moth, although no details drical yellowish to brown excrement pellets in bark crevices, are known. around the entrance of larval tunnels and on the ground; (ii) pro- In the present study, we aimed to investigate relevant aspects truding empty pupal skins on the infested parts by ZP, indicating of the population dynamics and the impact of this upcoming the emergence of moths from larval tunnels; (iii) several partly pest in North Africa, leading to an improved integrated pest broken branches as a result of fruit load and wind mechanical management of this invasive pest. damage with dead brown foliage hanging in tree crowns, char- We document the population dynamics on seasonal and yearly acteristic of heavy infestation; and (iv) secreting gum near the scales by full season pheromone and black light trapping (Hegazi infested parts. In September 2007 and 2009, we collected lar- et al., 2009) for the months of April to November over 10 years, vae during this larval monitoring for quantification of parasitoid including five pairs of ‘on/off’ years. The dynamics are modelled incidence. by an autoregressive integrated moving average (ARIMA) time Phenology of larvae was investigated by careful field dissection series. Intensive damage records (visual) and loss estimates of branches, twigs and trunks of heavily-infested trees in the late (grower’s data) were recorded for 2 years for estimates of and early 2010 and 2011 olive seasons, respectively, to estimate economic loss, in addition to a 1-year study of infestation at larval abundance in relation to spring flight period of the moths. different scales of variety intercropping.

Trapping for temporal variation Materials and methods To study the population cycles, the flight phenology of the adult Experimental ﬁelds leopard moth was studied for 10 consecutive seasons with an The present study was conducted in a commercial olive farm ultraviolet–light pheromone sticky trap combination (Fig. 1C) (Fig. 1) with drip-irrigation, located in the arid growing area (Hegazi et al., 2009). Five traps (one trap every 3 ha) were used between Alexandria and Cairo (30∘51′21′′E; 30∘08′27′′N), per season in plots that combined susceptible olive varieties 177 km south of Alexandria, 60 km north of Cairo. The farm (Toffahi, as well as Sennara or Sennara and Hamed). Each trap (240 ha, 336 trees/ha) is divided into 88 plots (3.0–3.5 ha, each was baited with pheromone dispenser (Fersex ZP; SEDQ, Spain). comprising two varieties/plots) isolated by windbreak hedges. The main components of the product are: (E,Z)-2,13-octadecenyl The olive trees were 11–12 years old, 3–4 m in height, planted acetate and (E,Z)-3,13-octadecenyl acetate. For each trap, a at a distance of 5 m along the row and 6 m between rows. hollow metal stake was placed in the ground of the selected The principal cultivars of table olives at the orchard (61 774 area. A wooden pole of a slightly smaller diameter than the olive trees) were Picual representing approximately 27.2%, hollow metal stake was cut to the appropriate height and slipped Manzanello representing approximately 26.1% and Toffahi inside the metal stake. The trap was mounted on the top of the representing approximately 12.4%. Less than 10% were found wooden pole. The hollow metal stakes acted as rat guard (i.e. for six cultivars; Kalamata, Akss, Sennara,Dolcie,Hamed and to prevent rats from climbing up to the trapping insects). Trap Shami, representing approximately 8.1%, 6.2%, 5.8%, 5.3%, height was adjusted to 50–100 cm above the level of the canopy. 4.7% and 4.2%, respectively, of the total bearing. Varieties Light was run from sunrise to sunset only. The distance between considered as susceptible (Hegazi & Khafagi, 2005) are shown traps was >200 m. The position of the traps was switched in italics. at each visit to minimize the possible effects of microhabitat

(A) (C)

(B)

Figure 1 (A) The olive farm from satellite view. (B) Close up of part of the olive farm from satellite. A and B imagery from Google Earth (http://www.google.com/earth/). (C) The pheromone-light trap. structure between the plots and rebaited with fresh dispensers 2002) as the difference between the actual yield by the infested every 40 days. Trapping was initiated in mid-April and ended trees and the potential yield or, more precisely, as the yield in the second week of November of each season. Trap captures that would have been obtained in the absence of the pest of male and female moths of ZP were counted every other day under study, estimated from ‘apparently uninfested trees’. Two, during which the sticky pad was changed. Data are presented as 3-ha naturally badly infested olive plots with leopard moth mean catches/trap per week or per month for additional detail. planted with the same susceptible local varieties/plot (Sennara Females were carefully dissected to determine their reproductive and Toffahi) were selected to study the economic loss caused state. by the pest for two successive years (2006 & 2007). All trees/variety/sector were checked every other week from July Yield and economic losses until late September to record the presence of active tunnels of ZP larvae, the number of broken branches bearing fruit and the In 2006 and 2007, efforts were made at the experimental farm to observed tunnels marked. In each inspection, fruit weight/broken ensure uniform ZP infestation plots by using highly susceptible branches (infested) was also recorded. At harvest time, trees local varieties (Toffahi and Sennara/plot) and adjusting both the were classified into infested and apparently uninfested. Severely time of fertilizer application and irrigation, keeping the exper- (i.e. with extensive signs of injury) or moderately injured trees imental plots free of chemical or mechanical insect control to (three to six broken limbs) as a result of ZP larvae were document the level of damage by an unmanaged ZP infestation. considered as infested. Dead or fruit-free trees (9%) were The design could use only two naturally severely injured olive not included. At harvest time, the fruit yield of three trees plots with ZP with plantings of susceptible local olive varieties of both infested and apparently uninfested/sector (i.e. each, (Sennara & Toffahi) exactly similar to those available in this part 3trees× 5 sectors = 15 trees/variety/plot = 120 trees/season) was of the olive farm in the 2006 and 2007 olive seasons. There is a selected randomly to estimate the real fruit yield/tree. drawback to this design because only two plots were included, The real fruit yield (Y ) = yield of infested trees + yield of although the 15-fold sampling of each variety and the natural r uninfested trees. presence of infested and uninfested trees ensured sufficient and The theoretical or ‘potential yield’/sector (Yp) = number of some degree of independent variation of observations. However, trees/sector × mean of fruit weight/uninfested tree of the same only the effect of the infested/uninfested categories can be for- sector. mally tested without pseudoreplication (Hurlbert, 2009) and not The difference between real and theoretical yield gives the crop the direct effects of the different susceptibility of varieties. loss weight (L ): Economic losses as a result of ZP were measured based W on actual yield losses. Crop loss can be defined (de Groote, Yp – Yr = Lw (1)

(A) (B) (C)

(D) (E) (F) (G) (H)

Figure 2 (A) Badly infested tree by Zeuzera pyrina (ZP). (B) Larval tunnel in broken branch. (C) Branch of susceptible tree containing 21 ZP larvae. (D) Protruding empty pupal skins indicating the emergence of ZP moth. (E) Secreting gum near the infested parts. (F) Emergence hole of larval tunnel. (G) Yellowish to brown faecal pellets. (H) Low fruiting yield of infested tree.

Multiplication of crop loss with the price of olive fruits per (RR- or SS-types) on yield loss in target plots that had at least weight ($W) gives the economic loss (LE) of ZP per area one resistant variety (R + RorR+ S). The restriction of pos- (Table 1): sible contrasts was a result of the paucity of target plots with

Lw × $W = LE (2) S-varieties present.

Statistical analysis Spatial variation of infestation and yield Trapping counts were analyzed for cyclic patterns at different After making informal observations during 2006 and 2007 multi-annual levels by ARIMA time series algorithms (Yaffee & indicating a possible lower infestation in susceptible-variety McGee, 2000) using ibm spss, version 19 (IBM Corp., Armonk, plots near resistant-variety plots, we made a small study of New York) with procedures TSMODEL and TSPLOT. This spatial variation of infestation. In 2009, six target plots, each type of model is only a statistical fitting to data and does not comprising 3-ha naturally-infested olive plots with ZP planted address any biological detail of the population dynamics such with olives varying in their tolerance to ZP, were selected to as rates of birth or deaths as in a population dynamics-based study the possible effects of variety intercropping [i.e. some were model (Turchin, 2013). ARIMA time series models are the most susceptible (S) and some were resistant (R)] (i.e. variety mixtures general class of models for forecasting a time series that can in target plots as S + S, S + R, R + R). In addition, each treatment be stationarized by transformations such as differencing and plot had ‘pure’ neighbouring plots of only resistant (RR) or logging (Yaffee & McGee, 2000). This type of model can be susceptible (SS) trees on both sides (Table 2). All trees of each seen as a fine-tuned version of random-walk models, where target plot were inspected for activity of the cryptic larvae every the fine-tuning consists of adding lags of the differenced series other week, as described above. At harvest time, trees of each plot and/or lags of the forecast errors to the prediction equation, as were classified into apparently uninfested, moderately infested needed to remove any last traces of autocorrelation from the (less than six broken branches/tree) and severely (more than eight forecast errors. The numerical outputs of the ARIMA models broken branches/tree) infested trees. The fruit yield of six trees are not given in the results; instead, only the corresponding of each category for each variety/target plot was harvested and auto-correlation function (ACF) and partial ACF (PACF) plots weighed. are provided, which give visual information on the best supported The number and combination types of resistant and suscep- population cycle lengths obtained from the data by the models. tible varieties pairs did not allow for a full factorial analysis We included an estimate of the yearly trapping total for the first of variance (anova), testing for both the effect of the identity ‘outbreak’ in 2001 to gain an 11-year series allowing analysis of varieties inside target plots and the influence of resistant of somewhat longer cycles. The added conservative estimate for or susceptible neighbours on the infestation rate (Table 2). 2001 was found by rounding up to the one-significant digit higher However, without resorting to pseudoreplication (Hurlbert, value compared with the 2009 total, because 2001 was observed 2009), we could contrast the influence of neighbouring plots to have a clearly higher damage magnitude.

Table 1 Economic losses in local susceptible olive cultivars caused by Zeuzera pyrina in two plots estimated under natural infestation in ‘high-fruiting year’ 2006 and ‘low-fruiting year’ 2007

Infested trees Apparently uninfested trees Losses/hac Trees Limb fruit Fruit yield Trees Yield Real yield Theoretical a b Plot Variety Number loss(t) Total (t) Per tree (kg) Number Total (t) Per tree (kg) (Y r) (t) yield (Y p) (t) LW (t) LE ($) Season 2006 1 Sennara 163 1.3 5.6 34.9 ± 1.7 227 12.5 56.7 ± 4.8 18.1 22.1 3.1 1800 Toffahi 239 2.3 7.4 31.6 ± 2.1 151 8.2 55.0 ± 3.5 15.7 21.4 4.8 3200 2 Sennara 127 0.6 4.5 35.2 ± 2.8 263 15.8 61.0 ± 3.9 20.3 23.8 2.8 1700 Toffahi 119 0.8 4.3 37.1 ± 2.8 271 16.1 59.5 ± 3.3 20.5 23.2 2.3 1500 Season 2007 1 Sennara 161 0.6 4.8 29.6 ± 1.5 229 11.7 51.0 ± 1.3 16.4 19.9 2.9 1700 Toffahi 162 0.8 4.5 28.5 ± 2.2 228 10.8 47.1 ± 1.8 15.3 18.4 2.6 1700 2 Sennara 143 0.6 3.9 27.7 ± 2.8 247 11.9 48.6 ± 1.5 15.9 18.9 2.6 1500 Toffahi 134 0.7 4.0 28.7 ± 2.6 256 12.1 47.3 ± 1.2 16.0 18.4 2.1 1400 aThe harvest of infested and non-infested trees, based on the samples of 15 trees/variety/plot. b The theoretical or potential yield (Y p) is calculated as number of trees × mean yield of uninfested trees (per variety and plot). c Weight of crop loss (LW) and economic loss (LE) is the difference between Yp and Yr and the product of LW and price per weight ($W), in accordance with Eqns 1 and 2, respectively (see Materials and methods).

Table 2 Infestation rate (%) and yield losses in target olive plots and the effect thereon of neighbouring plots with different combinations of susceptible and resistant olive trees in 2009

Target plot fruit yield/tree (kg) Target plot’s Infestation rate Apparently Moderately Severely Olive cultivars of cultivarsa (%)b non-infested infested infested Mean/infested tree Loss (t/ha) neighbouring plotsc

Picual (R) 0.0 49.0 ± 4.3 0.0 0.0 0.0 0.0 RR ‘Dolcie & Shami’ Manzanello (R) 0.0 59.0 ± 4.3 0.0 0.0 0.0 0.0 Dolcie (R) 0.0 80.0 ± 3.5 0.0 0.0 0.0 0.0 RR ‘Dolcie & Kalamata’ Kalamata (R) 0.0 26.4 ± 2.7 0.0 0.0 0.0 0.0 Picual (R) 8.2 37.6 ± 2.5 10.2 ± 1.6 0.7 ± 0.3 5.4 ± 1.7 0.9 SS ‘Toffahi & Sennara’ Manzanello (R) 10.3 45.0 ± 3.5 13.0 ± 2.1 0.6 ± 0.4 6.8 ± 2.3 1.3 Shami (R) 9.1 55.0 ± 3.5 18.6 ± 1.9 2.8 ± 0.9 10.7 ± 2.8 1.4 SS ‘Hamed & Sennara’ Toffahi (S) 18.9 81.0 ± 4.3 26.4 ± 2.7 0.0 13.2 ± 4.6 4.3 Kalamata (R) 11.1 26.6 ± 2.6 11.0 ± 1.2 0.0 5.5 ± 1.9 0.8 SS ‘Toffahi & Sennara’ Toffahi (S) 17.5 75.0 ± 3.5 20.2 ± 1.8 1.1 ± 0.6 10.6 ± 3.3 3.8 Sennara (S) 25.3 67.0 ± 4.6 19.4 ± 1.7 3.6 ± 1.2 11.5 ± 2.8 4.7 SS ‘Toffahi & Sennara’ Hamed (S) 39.8 16.0 ± 1.4 3.6 ± 0.8 0.1 ± 0.1 1.8 ± 0.7 1.9 aType of variety in plot: S, susceptible; R, resistant. bTarget plots are sorted by mean target plot infestation rate of the two target plot cultivars. cType of variety of neighbouring plots: SS, both cultivars susceptible; RR, both cultivars resistant.

The field surveys were conducted using a complete random- the growing season until mid-November (i.e. moths were present ized block design and data were subjected to anova (SAS, all season). The population trends of ZP showed one annual 2000). Data are presented as the means of moth catches and fruit peak in some years (2005, 2008 and 2009) and two peaks in yield/tree. Means were normalized using log(x + 0.5) transfor- most years. Moth emergence takes place from late April to mation to increase variance homogeneity. For the infestation rate, mid-November. The highest number of trapped moths occurred we had to use nonparametric statistics as a result of the many zero in September or August to September (Fig. 3). The flight period values. of the minor peak was only observed during May (2005) or June (2002, 2004, 2010 and 2011). Field dissection of infested wood showed that a large number of larvae of different ages remained Results in a dormant stage over the 2010 winter, whereas, in the spring of 2011, they started feeding and boring into the tree. A cohort Trapping study: within and between years variation of larger ones (10–28% of total larvae) become full-grown in Moth catches and larval phenology. Monthly catches in late spring and could change to pupal stage and these may create light-pheromone traps for ZP, over the period 2002–2011, the minor flight. Most of the ZP larvae were much smaller, are presented in Fig. 3. The first capture occurred during late continuing to feed throughout the season and become fully April or early May and then continuously from May throughout grown only in the late summer, creating the larger peak.

(A)80 (B) 80 2002 2004 70 "on" 70 "on" 2003 2005 60 "off" 60 "off" 50 50

40 40

30 30

20 20 Moths/Trap/Month

10 10

0 0

10 50

0 0

(E) 80 20102010" 70 "on"on" 2011 60 "off"

20 Moths/Trap/Month

Month

Figure 3 (A–E) Monthly number of Zeuzera pyrina captured/trap in pheromone-light traps during the 2002–2011 olive seasons. Vertical bars represent the mean ± SD.

The yearly total season-long capture of leopard moths is shown confidence interval of no effect, the first lag peak (Fig. 4C). This in Fig. 4(A). Generally, higher numbers of ZP moths were first lag (t = t − 1) corresponds to a 2-year cycle (a previous year trapped in ‘off’-years versus smaller ones in ‘on’-years. A 2-year is the most different, or in other words; years that are 2 years cycle can be seen directly in raw trap counts for 2002–2011 apart are the most similar). From the original 10-series data, (Fig. 4A). This is supported by time series analysis, as indi- no longer cycles, corresponding to higher lags, were discernible cated by the ACF plot in Fig. 4(B) showing yearly alternating (Fig. 4B,C). peaks. All seven of these were significant by a Ljung–Box test When we included an estimate of trapping level for the (P < 0.05). However, PACF, which removes effect of correlation first ‘outbreak’ in year 2001, an 11-year series with two large to intermediate lag years, contains only one peak crossing the ‘outbreak’ peaks is clearly seen (Fig. 4D). The ACF plot for this

(A) (D) 6.5

) 6.0 y

5.5

Trap catch ln( 5.0

4.5

2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 Year Year

(B) 1.0 (E) 1.0

0.5 0.5

0.0 0.0 ACF ACF

−0.5 −0.5

−1.0 −1.0

1 2 3 4 5 6 7 1 2 3 4 5 6 7 8 Lag Number (C) Lag Number (F) 1.0 1.0

0.5 0.5

0.0 0.0 Partial ACF Partial ACF

−0.5 −0.5

−1.0 −1.0

1 2 3 4 5 6 7 1 2 3 4 5 6 7 8 Lag Number Lag Number

Figure 4 Full season counts of captured Zeuzera pyrina moths during the 2002–2011 olive seasons. (A) Yearly catches for 10 years of trapping, 2002–2011, transformed by ln(x). •, ‘on’ years with high fruiting. (B) Autocorrelation function (ACF) plot among years for the 10-year series at different lags (past years). The series was differentiated by 1 year to achieve stationarity (constant mean and variance over time). (C) Partial ACF plot (which removes the effects of intervening years) for the 10-year series. (D) Yearly catches with an added, conservative estimate of catch for 2001 based on the outbreak level observed that year, giving a 11-year series [transformed by ln(x)]. (E) ACF for the 11-year series, differentiated by 1. (F) Partial ACF for the 11-year series. In (A) and (B), the horizontal line is the mean of the series. In (B), (C), (E) and (F), solid lines give the 95% conﬁdence limits for coefﬁcients.

© 2014 The Royal Entomological Society, Agricultural and Forest Entomology, doi: 10.1111/afe.12075 8 E. Hegazi et al. new 11-year series again shows many strong values, passing the 70 Infestation 95% confidence lines at a lag of 1 and at a lag of 7 and 8 (Fig. 4E), Apparently unifested indicating that there might be both a 2-year cycle (peak years Infested tree are 2 years apart) and a possible 8- or 9-year cycle (peaks are 60 8 or 9 years apart) (Fig. 4E). However, the partial ACF strongly supports only a signature of cycles at lag 1 (corresponding to a 50 2-year cycle), just as the original data set of only 10 years does (Fig. 4F). 40

Female catches and natural enemies. Female catches were very small. However, during the whole trapping season, of all trapped 30 leopard moths (218 and 505 moths/trap) in ‘off’-years of 2007 and 2009, only 10% and 13% were female, respectively. In ‘on’-years of 2008 and 2010, females represented 4.1% and 95% CI Yield/tree (kg) 20 2.9%, respectively. Almost all females caught in the trap were already mated and gravid, bearing approximately 500–2000 10 eggs at various developmental stages. Very few leopard moths were females during April to June of the trapping season. From August until late October, the trapped females laid their 0 eggs on the sticky sheet of the trap (400–950 eggs/female). 2006 High fruiting 2007 Low fruiting On 3 September 2007, 245 mid- to large-sized leopard moth Year larvae were dissected from heavily-infested trees. We deter- mined that 1.2% of larvae were parasitized by an ecto-parasitoid Figure 5 The fruit harvest in two badly infested plots by Zeuzera pyrina, wasp (Hymenoptera: Eulophidae: Hyssopus sp.), 1.6% were in a 2006 season ‘on’ year and 2007 season ‘off’ year (mean ± SEM). Infestation and year are both very highly signiﬁcant factors by analysis of infected by the entomopathogenic fungus Beauveria bassiana, > > variance at P 0.0001 (F1,12,both 50) (***) but not the interaction of 1.2% were infected by Metarhizium anisopliae and only one infestation × year (F = 2.9, P > 0.10) (not signiﬁcant; NS). larva was infected with entomopathogenic nematodes (Stein- 1,12 ernema sp.). On 15 September 2009, we dissected 155 ZP larvae, although only 1.9% were infected by M. anisopliae, the low fruiting year of 2007, the infestation near harvest time whereas ants were seen to be busy collecting newly-hatched ZP was 34–41%. The average annual crop loss corresponded to larvae. economic losses of some 1400–1700 $/ha (Table 1).

Yield and economic losses Spatial variation of infestation and yield with variety intercropping Figure 5 shows the fruit harvest/tree of apparently uninfested and ZP infested trees in year 2006 (a ‘high fruiting year’) and We observed the response of five pairs of different olive vari- 2007 (a ‘low fruiting year’). A very significant difference as a eties with two different cropping systems, namely adjacent plots result of infestation was clear, with a much higher fruit yield with a pair of either susceptible or resistant varieties (Table 2). from uninfested trees compared with infested ones (P < 0.0001). Losses of yield (t/ha) for the susceptible varieties were sim- However, not only the infestation factor (infested tree/apparently ilar to those in Table 1, although much less in the resistant uninfested), but also the year was a very significant factor varieties (Table 2). The three first rows of Table 2, all with in yield (P < 0.0001), whereas there was no interaction at all resistant varieties in the target plots (R + R), show the clear- (P > 0.10, factorial anova) for infestation × year. This means est pattern. When the olive trees neighbouring the first two of that the relative importance of infestation by ZP was the same, these plots were resistant olive cultivars (only RR-type), infes- irrespective of the fruiting level of the host tree (Fig. 5). The tation and losses were at zero levels. By contrast, for the plot data in Table 1 summarize the economic loss in two plots with Picual (R) + Manzanello (R) as the third row, with the of a cropping system [Sennara (S) + Toffahi (S)] caused by susceptible olive cultivars of Toffahi and Sennara as neigh- ZP under a natural infestation (n ≈ 390 trees/variety/plot). The bouring plots (SS-type plots), infestation was 8–10% in the two varieties appeared to have very similar yields within each target plot (R + R). When two partly resistant cultivar mixes category of infestation and year (Table 1). Crop losses in weight (S + R) were surrounded by SS-type plots, infestation appeared

[LW in Eqn 1] were a function of the final infestation and the to be higher, 9–19%, and, with all cultivars susceptible (S + S olive yield of the year. In 2006, the final infestation near harvest with SS-type neighbour plots), achieved 25–40% (Table 2, last time varied between 30% and 61% for different varieties and rows). plots. The average annual crop losses (LW) were calculated as In target plots that had at least one resistant cultivar (R + R between 2 and 5 t/ha, respectively, implying economic losses or R + S; n = 10), the influence on infestation rate by the two

[LE in Eqn 2] of some 1500 and 3200 $/ha. The average losses types of neighbouring plots [RR- or SS-types, mean ± SE; of fruits on broken branches reached up to 8 and 6 kg/infested 0.0 ± 0.0% (n = 4) and 12.5 ± 1.9% (n = 6), respectively] was tree for Sennara and Toffahi trees, respectively (Table 1). In quite significant (Mann–Whitney U = 24, P = 0.010).

Discussion living wood during the off-year is of a high ‘nutritional quality’ that accelerates larval growth, leading to a decline in natural We have clearly shown temporal variation in a yearly cycle larval mortality, an increase in female fecundity and, in turn, and a 2-year cycle of population dynamics. In addition, the an increase in the annual trapped ZP moths in the subsequent corresponding economic damage was quantified in detail for off-year season. different varieties. We also observed a spatial variation in damage related to intercropping of resistant/susceptible varieties, indicating a possible associational resistance. Outbreaks. Initiation of insect outbreaks is poorly understood Subsequent to early 1995, nine olive cultivars have been and the factors involved in the initiation of insect outbreaks planted in monoculture mixing olive varieties in desert area remain enigmatic (Maron et al., 2001; Myers & Cory, 2013). near Cairo. In this area, an outbreak of the leopard moth ZP There is a general asuumption that insect outbreak risk is higher was observed in 2001. One approach for understanding the in plant monocultures than in natural and more diverse habi- ZP population cycle comprises performing experiments on tats, although empirical studies investigating this relationship are long-term insect density during the initiation phase of a natural scarce (Jactel & Brockerhoff, 2007; Dalin et al., 2009). Other outbreak (Myers, 1988; Krebs, 1991). Accordingly, we per- explanations have been reported, including changes in food-plant formed long-term monitoring 1 year after the outbreak of the quality (Schultz & Baldwin, 1982; Mattson & Haack, 1987; leopard moth ZP. When studying normal annual cycling of this Rossiter, 1992), favourable weather (Martinat, 1987) and reduc- insect in 2002–2011, we observed a new outbreak in 2009. The tions in predation, parasitism or disease (Myers, 1988; Walsh, strict isolation of this area, not in proximity to apple plantations 1990), although satisfactory tests are difficult to employ. The or any other known host plants of ZP and surrounded by sand interaction of ZP with the parasitoids–pathogens observed in desert habitat, makes it ideal for studying a local population the present study area appears to be too low to cause population without biotic influence from landscape scale. cycles. However, the results provide strong evidence of periodic behaviour in population densities. It appears that the bearing pattern (food-plant quality) in the monoculture farm may generate Temporal variation herbivore periodic oscillations. Annual. The trapping study indicated that the ZP has an annual There is no apparent reason why large numbers were recorded biological cycle in olive trees in Egypt. Captures show the in most traps in 2009. Most studies of the population dynamics occurrence of an early-season flight that continued throughout of forest-defoliating insects suggest outbreak cycles ranging the growing season and into the autumn and the beginning of from 8 to 12 years (Liebhold & Kamata, 2000). The gradual harvest. The largest flight of the year began near the end ofthe reduction of infestation of forest tree by lepidopteran insects season. The observation of a large number of larvae of different is the manifestation of a 9-year cycle that includes 3 years of sizes in a dormant stage over the winter of 2010 indicates a cohort population increase, 3 years of population at high levels and of larger individuals becoming full-grown in late spring resulting 3 years of population decline (Myers, 1988). It is reasonable to a minor peak, whereas the smaller individuals become full grown speculate that outbreak cycles of ZP are within 8–9 years. in late summer and create the major flight peak. In both cases, this constitutes a single yearly cycle of reproduction. Thus, the number of flight peaks appears to depend on the population age Spatial variation structure of ZP larva, which is likely dependent on multi-year Entomological studies on interplanted perennial crop plants are temperature patterns. scarce but indicate an effect of lower herbivore damage at a higher tree diversity and the effects of specific semiochemicals The 2-year cycle. Our data and ARIMA time series analysis known as nonhost volatiles (Jactel & Brockerhoff, 2007; Jactel clearly show a 2-year cycle in total catches. When attempting to et al., 2011). The present data are interesting in terms of rep- explain such annual trends in trapping the leopard moth, records resenting the first estimate of losses in olive yield caused by can be associated with alternative bearing in some fruit trees. ZP. The observed trend suggests that mixing olive cultivars can Olive (Olea europea) has very high tendency for year-to-year assist in pest control and provide yield advantages. Neighbour- deviation in yield (Lavee et al., 1996; Seyyednejad et al., 2001; ing olive varieties can also influence the rate of ZP colonization. Lavee, 2007). Studies on changes in carbohydrate components The results suggest that focal plants may gain protection from of leaves from ‘on’ (bearing) and ‘off’ (nonbearing) years cycle herbivores because of their proximity to neighbouring plants and have shown that sugars are much higher at the beginning of an thereby be defended by neighboring plants’ anti-herbivore phys- on- than of an off-year yield (Lavee et al., 1996; Seyyednejad ical or chemical traits (Baraza et al., 2006; González-Teuber & et al., 2001; Lavee, 2007; Erel et al., 2013). Also, the degree Gianoli, 2008), forming a case of associational resistance (Bar- of alternate bearing is highly dependent on the environmental bosa et al., 2009). conditions and might be very different in accordance with the The present study is not intended to provide a generalized climate in each growing region (Morettini, 1950; Hartmann, definition for the attack threshold at which action should be 1951; Sadok et al., 2013; Turktas et al., 2013; Yanik et al., taken against ZP but rather indicates that the intercropping of 2013). The depletion of stored carbohydrates during the on-year insect-resistant crop varieties among the susceptible varieties in (high yield) (Bustan et al., 2011) and environmental conditions olive orchards is economically, ecologically and environmentally may affect the availability and quality of living wood as food advantageous. Ecological and environmental benefits arise from material for ZP larvae (Hoch et al., 2013). Thus, it appears that increases in species diversity in the agroeco-system, in part

© 2014 The Royal Entomological Society, Agricultural and Forest Entomology, doi: 10.1111/afe.12075 10 E. Hegazi et al. because of reduced use of insecticide (Teetes, 1994). Many olive Barbosa, P., Hines, J., Kaplan, I. et al. (2009) Associational resistance and variety combinations are possible and each can have different associational susceptibility: having right or wrong neighbors. Annual effects on beneficial/harmful insect populations. For example, Review of Ecology, Evolution, and Systematics, 40, 1–20. the choice of tall resistant and short companion olives can Blomberg, O., Itämies, J. & Kuusela, K. (1976) Insect catches in a magnify these effects. blended and a black light-trap in northern Finland. Oikos, 27, 57–63. Bustan, A., Avni, A., Lavee, S. et al. (2011) Role of carbohydrate reserves In all trapping seasons, larger numbers of ZP males were in yield production of intensively cultivated oil olive (Olea europaea caught compared with females in combined pheromone-black L.) trees. Tree Physiology, 31, 519–530. light traps. We speculate that, because the females are Carter, D.J. (1984) Pest Lepidoptera of Europe with Special Reference to heavy-bodied, they might be extremely poor fliers. How- the British Isles. Dr W. Junk, The Netherlands. ever, the specific reason for the relatively higher female catch in Castellari, P.L. (1986) Zeuzera pyrina L. (Lep. Cossidae): biological an ‘off’-year compared with that in an ‘on’-year is not known investigations and field tests on the attractiveness of mixtures of and may need further investigation. These seasonal flights sex pheromone components. Bollettino dell’Istituto di Entomologia can be readily identified with pheromone-black light traps in ’Guido Grandi’ della Universita degli Studi di Bologna, 40, 239–270. naturally-infested susceptible olive cultivars, as indicated in the Dalin, P., Kindvall, O. & Björkman, C. (2009) Reduced population present study. control of an insect pest in managed willow monocultures. PLoS One, 4, e5487. Delisle, J. (1992) Monitoring the seasonal male flight activity of Choris- Conclusions toneura rosaceana (Lepidoptera: Tortricidae) in eastern Canada using virgin females and several different pheromone blends. Environmental The present data are interesting, providing the first detailed Entomology, 21, 1007–1012. estimate of heavy economic losses in olive yield caused by ZP. Durant, J., Manley, D. & Cardé, R. (1986) Monitoring of the Euro- Control with conventional insecticides in this pest is almost pean corn borer (Lepidoptera: Pyralidae) in South Carolina using impossible because it is cryptic for most of the life cycle and pheromone traps. Journal of Economic Entomology, 79, 1539–1543. the use of systemic insecticides is more or less impossible in a Erel, R., Yermiyahu, U., Van Opstal, J. et al. (2013) The importance of slowly maturing food crop. Integrated management, however, olive (Olea europaea L.) tree nutritional status on its productivity. allows both augmentation of beneficial and chemical ecology Scientia Horticulturae, 159, 8–18. González-Teuber, M. & Gianoli, E. (2008) Damage and shade enhance based management options such as mass-trapping (Hegazi et al., climbing and promote associational resistance in a climbing plant. et al. 2009), mating-disruption (Hegazi , 2010) and an increase Journal of Ecology, 96, 122–126. of semiochemical diversity by intercropping (Zhang & Schlyter, Gratwick, M. (1992) Crop Pests in the UK: Collected Edition of MAFF 2003). As shown in the present study, the most directly appli- Leaflets. Chapman & Hall, U.K. cable method for this invasive pest comprises the monitoring of de Groote, H. (2002) Maize yield losses from stemborers in Kenya. Insect distribution and population levels by pheromone traps. A more Science and its Application, 22, 89–96. detailed and replicated study of the spatial variation of damage Hartmann, H.T. (1951) Time of floral differentiation of the olive in in relation to the composition of olive tree varieties and the quan- California. Botanical Gazette, 112, 323–327. tification of volatiles released from foliage is now under way. Hegazi, E.M. & Khafagi, W.E. (2005) Varietal sensitivity of olive trees to the leopard moth, Zeuzera pyrina L. (Lepidoptera: Cossidae). IOBC/WPRS Bulletin, 28, 121–131. Acknowledgements Hegazi, E., Khafagi, W., Konstantopoulou, M. et al. (2009) Efficient mass-trapping method as an alternative tactic for suppressing popu- We appreciate the constructive criticism of the referees. A critical lations of leopard moth (Lepidoptera: Cossidae). Annals of the Ento- reading of an earlier draft by Dr S. Hagenbucher improved mological Society of America, 102, 809–818. clarity. We gratefully acknowledge grower-collaborator Mr M. Hegazi, E., Khafagi, W., Konstantopoulou, M. et al. 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