Biological Performance of Potato Tuber Moth on Leaves of Tomatoes

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1 iologial Performane of Potato Tuber Moth on Leaves of Tomatoes 1 Ethiopian Institute of Agriultural Researh, P.O. ox 23, Addis Ababa, Ethiopia 2 Faulty of Agriultural, Food and Environmental Quality Sienes, Hebrew University of Jerusalem, P.O. ox 12, Rehovot 761, Israel Abstrat Lower population buildup of potato tuber moth (PTM) in tomatoes, when ompared with potato, during vegetative growth period was observed. The present study was made to investigate on whether the lower PTM buildup in tomatoes was due to poor performane of PTM larvae on tomato leaves. Leaf feeding bioassays were arried out on three tomato ultivars in omparison with potato. Potato and tomato leaves were taken at preblossom and blossom plant stages and assayed under fully ontrolled ondition. Aording to the results, the survival of PTM larvae reared on leaves taken at the preblossom stage was higher on herry (87.%) than other tomatoes and potato. Whereas, the survival on leaves taken at the blossom stage was higher on potato than tomatoes. Moreover, larval and larva adult development times were signifiantly shorter on potato than tomatoes leaves at both plant stages. Therefore, the higher level of survival and signifiantly shortened larval and larva-adult development times on potato than the tomato leaves showed that tomato leaves were poor quality food soure to the PTM ompared with potato. Thus, the in-situ lower PTM population buildup on tomato leaves was attributed to poor performane of its larvae. Hene, any attempt to ontrol the PTM on tomatoes should use this opportunity and fous on the post-flowering period. Key words: potato tuber moth, performane, potato, tomato, feeding bioassay Introdution Although tomato leaf serves as one of the feeding sites for potato tuber moth (PTM) larvae, it is mainly before tomato plants set fruits and the borne fruits start to mature that PTM larvae live on tomato leaves by bloth mining (ayeh 23). Nevertheless, the buildup of PTM on tomato leaves has been too slow in omparison with potato leaves and resulted in small population inrease over the vegetative growth period of tomatoes (ayeh 23). Instead, PTM larvae population in tomatoes peaked during the fruiting period (ayeh 23). This ontrasting effet of leaves and fruits of tomatoes on PTM entails that tomato leaves might provide less quality food for larvae of the PTM than the fruits. esides this larvae feeding in tomato fruits get a proteted feeding nihe (Coll and ayeh 23, ayeh and etre 24, and ayeh et al., 24) than those feeding in the leaves. These imply that onsuming tomato leaves might affet the biologial performane of PTM larvae more than the fruits do. Therefore, onsidering the inreasing importane of PTM on tomatoes, its biologial performane on tomatoes needs to be well understood. Performane is a omposite term for survival, growth, development, reprodution and longevity (Thompson 1988). The biologial performane of the PTM in fruits of tomatoes was onfirmed to be influened by the size, maturity and -tomatine ontent of the fruits. Tomato ultivar with big fruits and trae amount of -tomatine provided the best feeding nihe, whih was found to be partiularly the ase in the ripening fruits (ayeh et al. 26). The present study was Pest Mgt. J. Eth. 11:61 67 (27)

2 AYEH ET AL. made to investigate on the biologial performane of PTM larvae in tomato leaves through leaf feeding bioassays. Materials and Methods Fully expanded young leaves from three tomato ultivars: a herry (v. Series), proessing (v. Serio) and fresh market (v. Marglobe) types and the preferred host potato were olleted randomly from plots planted for the purpose. An exised leaf was plaed in separate plasti box and stored in iebox on ie ubes until use. Assays were performed in sterilized Petri dishes (Ø 9m) lined with moistened Whatman filter papers. A leaflet was transferred into eah Petri dish and its ut end was immediately overed with water soaked otton ball. The assays were arried out on leaves taken from plants at preblossom and blossom stages. One neonate larva, less than 24 hr old, was then plaed on the leaflet. Eighty larvae were initially used per ultivar at eah growth stage of the tomatoes. The test larvae were taken from the ulture established in the laboratory. All Petri dishes were transferred to a limate hamber set at 26 o C, a photoperiod of 12L: 12D and 7% RH. The arrangement in the hamber was ompletely randomized. The Petri dishes were heked at 14x magnifiation 24 hr later, in order to determine whether the introdued larvae had settled and started to feed. Thereafter, all Petri dishes were examined daily for larval ativity, and the ut ends of the leaflets were watered daily. This was ontinued until the developing larva in eah leaflet died or stopped feeding and displayed typial prepupation wandering behavior. ody weights of wandering larvae were measured, and the larvae were afterwards transferred individually into gelatin apsules to allow pupation. Capsules were examined twie a day and pupation time was reorded. Pupae were removed from the gelatin apsules several hours later, after their utile had hardened, and their body weight was measured. They were then transferred into individual glass vials and plaed in the limate hamber to omplete pupal development. During the ourse of the study, the following data were olleted on eah test larva: survival in the different stages of development until adult emerged, development time of eah larval instar and of the pupal stage, body weight of wandering larvae, and weight of pupae. Larval survival rate on eah ultivar was determined based on the initial 8 larvae. The follow up was ontinued until the last adult moth emerged from the last viable pupa. Larval instar was determined based on head apsule size and, when possible, by loating the molted head apsules from between the leaf sheathes. Oviposition preferene Free oviposition hoie trial was onduted among the three tomato ultivars and potato in laboratory ages using exised leaves. Fully expanded young leaves were olleted from field-grown tomato plants from plants of eah tomato ultivar and potato. They were plaed in the four orners of Plexiglas ages (.6 m X.6 m X.6 m) by dipping eah of their rahis in tap water filled plasti bottle. A pair of newly emerged PTM adults was introdued into eah age and provided sugar solution as soure of food and water. The adults were removed from the ages after three days and the number of oviposited eggs and their loation were reorded. There were a total of 3 repetitions made using leaves from eah ultivar. Statistial analysis Rior to the ondut of analysis of variane, the olleted data were tested for normality. Then after, on data obtained from the leaf feeding assays, two-way ANOVA were run on the effet of ultivar and plant phenology on both the development and growth performane data. The survival dataare

3 PERFORMANCE OF PTM ON TOMATOES Larval Larva-adult 1a Larval Larva-adult 1b A A A b ab a A A a a b Figure 1. Mean ± SE larval and larva-to-adult development time of PTM on leaves of the herry (CH), proessing (PR), a fresh market (FM) tomatoes and the potato (P) at preblossom (1a) and blossom (1b) stages. Table 1. F-ratios and P-values on within ultivar omparisons of larval performane, on leaves of tomatoes and potato, between preblossom and blossom stages Leaf soure ultivars Cherry Proessing Fr. Market Potato Fitness parameters F P F P F P F P Development time (L) NS NS ody weight (L) (mg) ody weight (P) (mg) Development time (L-A) L = larva, P = pupa and A = adult, F = F-ratio and P = probability values, Fr = fresh reported as mean perentage values per ultivar and plant stage. On the oviposition data, one-way ANOVA was done. Mean values for development, growth and oviposition were ompared for differenes between ultivars using Tukey-Kramer honest signifiane differene test (P <.). Moreover, orrelation analysis was done between oviposition and the three performane measurement variables for the respetive tomato ultivars and the potato (JMP In Statistial Software, version.1). Results Survival of PTM larvae At preblossom stage, 87.% of the larvae reared on the herry leaves survived to reah the adult stage. Whereas on the proessing and fresh market tomatoes leaves, 67.% of the larvae survived, while on potato only 6% survived and reahed the adult stage. At the blossom stage, the highest survival was on the potato leaves (78.7%). Whereas, on the tomatoes, 3.7%, 1.2% and 38.2% survived to reah the adult stage on the herry, proessing and fresh market tomatoes, respetively.

4 AYEH ET AL. Development time for PTM larvae There were signifiant interations between the rop ultivars and the two plant phenologies (preblossom and blossom) in affeting total development times (DT) (F 3,4 = 4.92, P <.2) i.e. from neonate larvae to adult moths. Total larval DT at the preblossom stage was signifiantly shorter on potato and longer on the proessing followed by the fresh market, in whih it did not differ from the herry tomato (F 3,236 = 3., P <.1) (Figure 1a). At the blossom stage, total larval DT was signifiantly longer on the herry and fresh market ultivars and shorter on the potato (F 3,2 = 62, P <.1) (Figure 1b). Pupal DT was not signifiantly different between the tomato ultivars and potato at preblossom stage (F 3,227 = 2.26, P <.8); but it was signifiantly longer in potato at blossom stage (F 3,174 = 82., P <.1). Larva-to-adult DT at preblossom stage was signifiantly shorter on potato than the tomatoes (F 3,226 = 7.24, P <.1) (Figure 1a). At the blossom stage, it was longer on the herry and shorter on the potato and the proessing tomato (F 3,174 = 4.14, P <.2) (Figure 1b). Growth of PTM larvae There were signifiant interations between the plant phenologial stages and the rop ultivars in affeting body weights of larvae Larval Larva-adult A A A b ab a 1a Larval Larva-adult 1b A A a a b Figure 1. Mean ± SE larval and larva-to-adult development time of PTM on leaves of the herry (CH), proess (PR), and fresh market (FM) tomatoes and the potato (P) at preblossom (1a) and blossom (1b) stages. Table 2. Pair wise orrelations between oviposition preferene of the potato tuber moth and different biologial performane measuring parameters Eggs/ leaf DT (days) LW (g) PW Survival (%) Crop varieties branh (g) Cherry tomato Proessing tomato Fresh market tomato Potato Correlations of oviposition with (P-value) (.26) (.7) (.13) (.6) DT = development time, LW = larval body weight and PW = pupal body weight, Sur.= Survival

5 PERFORMANCE OF PTM ON TOMATOES (F 3,446 = 6. and P <.1) and pupae (F 3,431 = 4.3 P <.3). The highest body weight (F 3,24 = 6.42, P <.3) was reoded for larvae reared at the preblossom stage on the fresh market tomato followed by the herry, on whih larval weight was not different from the potato and the proessing tomato. In ontrast, there was no signifiant differene in body weight of larvae reared on all the tomato ultivars and potato at blossom stage (F 3,26 = 1.84 P <.14). Pupal weight was signifiantly higher (F 3,234 =.942, P <.6) on the fresh market, followed by the potato on whih it was not signifiantly different from the herry and proessing tomatoes at the preblossom stage (Figure 2a). The differenes were not signifiant (F 3,197 = 1.74, P <.1) at the blossom stage (Figure 2b). The within ultivar omparisons, between the two plant phenologies, of larval performane were in general signifiantly higher for larvae reared on leaves at the preblossom stage (Table 1). Oviposition preferene Signifiantly more eggs were deposited on potato leaves than the three tomato ultivars (F 3,11 =22.3, P<.1). There was no signifiant differene among the three tomato ultivars in the number of eggs deposited on them (F 2, 87 =.6, P<.93). More than 9% of the eggs were laid on the lower surfaes of the leaves of all the ultivars. On this surfae, most of the eggs were laid in the ervies of the leaflets midribs and lose to the major veins radiating from the midribs. On the upper surfaes, eggs were found only in grooves loated at the posterior ends of the midribs of leaflets. Nevertheless, the orrelations between the number of eggs deposited on the leaves of eah ultivars and the orresponding values for the different biologial performane measuring parameters taken at the blossom stage were not statistially signifiant (Table 2). Disussion oth larval and larva adult development time on potato was signifiantly shorter than on the tomatoes, whih agrees with Lopes et al. (21) who reported that feeding on tomato leaves inreases PTM larval development time when ompared with potato leaves. On the other hand, the prolonged development time of PTM larvae on the fresh market tomato ultivar leaves, taken at the preblossom stage, was aompanied with signifiant body weight gain, although the total number of larvae survived feeding on the leaves of this ultivar was very low. On the other hand, in the foliages of the herry ultivar, although their development time was prolonged, more larvae survived to reah the adult stage. However, the body weight they were able to attain was signifiantly lower than on the fresh market tomato foliage, but was omparable with the proessing tomato and the potato ultivars. Therefore, shortened development time is probably one of the important parameters that has made potato a preferred host by the PTM. eause, when development time is shortened due to availability of suitable host plant and is aompanied with signifiant survival, the number of possible generations per year is more, resulting in higher population buildup on potato. Whereas, the effet is otherwise when development time is prolonged and survival is low. A host plant that may prolong larval development time has other onsequenes. It may expose herbivorous insets to their natural enemies for longer period (Prie 1986). ut for the PTM on tomatoes, although its development time was prolonged, it was onfirmed that these same tomato ultivars provided the PTM with natural enemy free spae (ayeh et al. 24). Hene, supporting the possibility, as stated by Thomas and Waage (1996), of the adverse effet a host plant might have both on herbivore inset and its natural enemies.

6 AYEH ET AL. There was signifiant temporal differene in the suitability of the leaves of the tomato ultivars to the PTM where relatively better larval performane was reorded at the preblossom than the blossom stage. The inreased mortality of PTM larvae on the herry leaves at the blossom stage might be due to loss of nutritional quality of its foliage, probably due to the inreasing shift of the sink to the reprodutive strutures whih might have rendered the herry tomato leaves to be poor quality food to the PTM. On the other hand, in the fresh market and proessing tomato ultivars, it seems that there are a number of fators inplanta besides the loss of nutritional quality that affeted PTM larval performane, partiularly larval survival and development time. Although the oviposition differene between the tomato ultivars, in the free hoie trial onduted using exised leaves in laboratory age, was not signifiant, more eggs were laid on the leaves of the herry ultivar. esides, in another free hoie trial, performed in an exlusion field age on atively growing tomato plants, signifiantly higher leaf infestation was sustained by the herry ultivar (ayeh Mulatu 23). These give indiations that PTM prefers the foliages of the herry ultivar to the others, whih is supported by the observed better larval performane on the herry ultivar leaves at preblossom stage in the urrent study. Thompson (1988) stated that for a herbivorous inset, relationships between oviposition preferene and various omponents of performane of offspring on different plant speies range from good to poor orrespondene. However, the relationships between preferene and performane are still inompletely known (Thompson 1988). In this partiular study, the lak of signifiant orrespondene between oviposition preferene and PTM progenies performane ontributed to the unknown. ased on the results disussed above, it seems two distint life history strategies that PTM, on the three tomato ultivars, whih showed differential suitability, uses to insure its survival in tomatoes: (i) in the poor quality leaves of the fresh market tomato, prolonging development time yet gaining signifiant body weight by the few survived larvae and (ii) in the relatively good quality leaves of the herry ultivar, at the preblossom stage, inreasing survival of larvae by ompromising body weight gain to survival. In general, from the results of the leaf feeding bioassays, it ould be onluded that the leaves of the tomatoes are suboptimal hosts and are poorly preferred by the PTM. Thus, the in-situ lower PTM population buildup in tomato leaves is the result of poor performane of its larvae. Thus during vegetative growth period tomato growers should fous only on monitoring for PTM presene in their tomato fields. No ontrol measures should be taken before flowering period. On the other hand, during the flowering and fruit development period, appliation of insetiides ould provide effetive ontrol of the pest. This will help tomato growers in plaes where PTM is a serious problem to redue the use of insetiides, hene ontributing both to the farmers eonomi gain and the environment. Aknowledgements We sinerely thank Damtew Nigatu for handling the routine field work. The researh was supported by a grant from USAID-CDR program (TA-MOU ). Referenes Lopes, M.T-do-R.; Vendramim, J.D. and Lopes, M.T-do-R. 21. Resistane of potato genotypes to the potato tuber moth Phthorimaea operulella (Zeller). Sientia Agriola 8: ayeh Mulatu. 23. Tritrophi level interations in Ethiopian tomato systems: effet of plants on potato tuber moth, Phthorimaea operulella (Zeller) (Lepidoptera:

7 PERFORMANCE OF PTM ON TOMATOES Gelehiidae) and its parasitoids. PhD Thesis, The Hebrew University of Jerusalem. ayeh Mulatu and etre Tadesse,. 24. iologial and Cultural Fators Contributing to the importane of Potato Tuber Moth on Tomatoes in Ethiopia. Pest Management Journal of Ethiopia 8: ayeh Mulatu, Applebaum S. W., Moshe Coll. 24. A reently aquired host plant Provides an oligophagous inset herbivore with enemyfree spae. Oikos 17: ayeh Mulatu, Applebaum S. W., Kerem, Z. and Moshe Coll. 26. Tomato fruit size, maturity and -tomatine ontent influene the performane of potato tuber moth larvae. ulletin of Entomologial Researh 96: Prie, P.W Eologial aspets of host plant resistane and biologial ontrol: Interation among three trophi levels. In: D.J. oethel and R.D. Eikenbary (eds.), Interation of plant resistane and parasitoids and predators of insets. John Willey and Sons, New York. Thomas, M. and Wagge, J Integration of biologial ontrol and host plant resistane breeding: a sientifi and literature review. CTA, Wageningen, The Nehterlands. Thompson, J.N Evolutionary eology of the relationship between oviposition preferene and performane of offspring in phytophagous insets. Entomolgia Experimentalis et. Appliata 47: 3-14.

Experiment Station. Department of Soil and Crop Sciences

Experiment Station. Department of Soil and Crop Sciences Tehnial Bulletin TB06-03 August 2006 Ag riultural Experiment Station College of Agriultural Sienes Department of Soil and Crop Sienes Western Colorado Researh Center Organi Alternatives for Weed Control