Biology, ecology and management of the sweetpotato , puncticollis Boheman (Coleoptera: )

By Amin EL Zubeir Gubartalla Mohamed B. Sc. (Agric.) Hons., M. Sc. (Agric.) University of Khartoum

A thesis submitted in fulfillment of the requirements for the degree of Doctor of Philosophy

Supervisor: Prof. EL-Imam EL-Khidir Co-supervisor: Dr. Kamal Mowafi

Crop Protection Department Faculty of Agriculture University of Khartoum March 2005

1

DEDICATION

To the memory of my beloved late mother Rabaa

2 CONTENTS Pag e Dedication i Contents ii A knowledgements vi Abstract viii Arabic Abstract x 1. INTRODUCTION…………………………………… 1 ……. 2. REVIW OF 5 LITERATURE………………………………… 2.1 5 and distribution……………………………………. 2.2 7 Host range…………………………………………………. …. 2.3 8 Economic impact and damage……………………………….... 2.4 10 Biology………………………………………………… ……… 2.4.1 Description…………………………………………… 10 ………. 2.4.2 Life 11 history…………………………………………………

3 …

2.4.3 Effect of temperature on the development of the sweetpotato 14 weevil………………………………………………… ………. 2.5 Effect of sweetpotato root characters on the infestation of sweetpotato 15 weevil……………………………………………. 2.6 18 Influence of irrigation on sweetpotato weevil infestation…….. 2.7 Control………………………………………………… 21 ……… 2.7.1 21 Cultural control……………………………………………….. 2.7.1. 22 Crop 1 rotation………………………………………………… .. 2.7.1.2 Intercropping ………………………………………………… 23 2.7.1.3 Earthing up the soil (hilling)…………………………………. 23 2.7.1. 2 Sanitation and destruction of crop 4 4 residues…………………… 2.7.1. 2 Clean 5 5

4 cuttings…………………………………………………. 2.7.2 2 Host-plant 6 resistance…………………………………………. 2.7.3 3 Biological 0 control…………………………………………….. 2.7.4 3 Chemical 1 control……………………………………………… 2.7.5 Integrated pest management (IPM)…………………………… 3 5 3. 3 MATERIALS AND METHODS……………………………. 8 3.1 Survey………………………………………………………… 3 … 8 3.2 Laboratory experiments (first season 3 2001/02)…………………. 8 3.2.1 3 Life history of sweetpotato 9 weevil……………………………… 3.2.1. 3 Duration of development of immature 1 9 stages…………………... 3.3 Field experiments (first season 4 2001/02)……………………….. 0

3.3.1 The influence of irrigation intervals and sweetpotato clones on sweetpotato weevil infestation (autumn transplanting 4 experiment) 1

5 3.3.2 The influence of irrigation intervals and sweetpotato clones on sweetpotato weevil infestation (winter transplanting 4 experiment) 4 3.3.3 Sweetpotato weevil 4 management…………………………….…... 4 3.4 Laboratory experiments (second season 4 2002/03)……………….. 6 3.4.1 4 Life history of sweetpotato weevil, Cylas puncticollis 6 Boh……… 3.4.1. Duration of development of immature 4 1 stage……………………... 6 3.4.1. Preoviposition 4 2 period…………………………………………….. 6 3.4.1. Oviposition 4 3 rate…………………………………………………... 6 3.4.1. Sex 4 4 ratio…………………………………………………………... 7 3.5 Field experiments (second season 2002/03)…………………….. 47

3.5.1 The influence of irrigation intervals and sweetpotato clones on sweetpotato weevil infestation (autumn transplanting 47 experiment)... 3.5.2 The influence of irrigation intervals and sweetpotato clones on sweetpotato weevil infestation (winter transplanting 48 experiment) 3.5.3 Sweetpotato weevil 48

6 management…………………………….……. 4. 49 RESULTS………………………………………………………….. 4.1 49 Survey………………………………………………………………. 4.2 Laboratory experiments (first season 49 2001/02)…………………… 4.2.1 Life history of sweetpotato weevil, Cylas puncticollis 49 Boheman….. 4.2.1.1 Duration of development of immature 49 stages………………………… 4.3 Field experiments (first season 55 2001/02)…………………………. 4.3.1 The influence of irrigation intervals and sweetpotato clones on 55 sweetpotato weevil infestation (autumn transplanting experiment)... 4.3.2 The influence of irrigation intervals and sweetpotato clones on 77 sweetpotato weevil infestation (winter transplanting experiment)… 4.3.3 Sweetpotato weevil 92 management……………………………….. …. 4.4 Laboratory experiments (second season 94 2002/03)…………………... 4.4.1 Life history of sweetpotato weevil, Cylas puncticollis 94 Boheman.…..

7 4.4.1.1Duration of development of immature 94 stages……………………… 4.4.1.2 Preoviposition 99 period………………………………………….. … 4.4.1.3 Oviposition 99 rate……………………………………………………. 4.4.1.4 Sex 99 ratio…………………………………………………………… 4.5 Field experiments (second season 99 2002/2003)………………………. 4.5.1 The influence of irrigation intervals and sweetpotato clones on sweetpotato weevil infestation (autumn transplanting 99 experiment) 4.5.2 The influence of irrigation intervals and sweetpotato clones on sweetpotato weevil infestation (winter transplanting 11 experiment) 7 4.5.3 Sweetpotato weevil 13 management………………………………..….. 4 5. 13 DISCUSSION…………………………………………………….. 7 … 5.1 Laboratory 13 experiments……………………………………………… 7 5.2 Field 13 experiments……………………………………………………. 9 5.2.1 Autumn transplanting season experiment (2001/2002) and 13

8 (2002/2003)………………………………………………………. 9 5.2.2 Winter transplanting season experiment (2001/2002) and 14 (2002/2003)………………………………………………………. 5 5.2.3 Sweetpotato weevil management(2001/2002) and 15 (2002/2003)…. 0 6. 15 REFERENCES…………………………………………………… 2 … Appendices 17 ………………………………………………………………. 0

9 AKNOWLEDGEMENTS

I would like to express my profound gratitude and appreciation to my supervisor Prof. EL-Imam EL-Khidir for his interest, expert guidance and his relentless effort to make me produce an outstanding work. I wish to thank my co-supervisor Dr. Kamal Mowafi in particular for his advice during the course of this study, his friendly constructive comments have been highly valuable.

The author is deeply indebted to a number of people who played key roles in the development of the research programme. First and foremost is Dr. Ali Khalafalla, Dr. Ensaf Sheihk Idris and Mr. Salah Muzamil, Agricultural Research Corporation, Shambat Station who provided me with sweetpotato clones and insecticides. My appreciation would be incomplete without recognizing Dr. Georg Georgen, International Institute of Tropical Agriculture (IITA), Biological Center for Africa/ Museum and Mr. Yakubu Adedigba Head, library and documentation services (IITA), Nigeria who sent for me valuable information and scientific papers at the early stage of the research. The financial contribution of the Third World Academy of Sciences (TWAS) Italy, International Potato Center (CIP) and PARAPACE-Kampala offices were of paramount importance in execution of an advance training on sweetpotato weevil in Uganda. Without assitance of Dr. Benson Odongo, Dr. Robert Mwanga, Mr. Charles Niringiye, Mrs. Justine Nanteza and all members of sweetpotato programme of Namulonge Agricultural and

10 Production Research Institute (NAARI) Uganda, it would have been futile to expect fruitful training. My thanks and appreciation are extended to Dr. El-Tom EL-Sadig and DR. Abdul-Wahab Hassan Abdalla, Department of Crop Production Faculty of Agriculture University of Khartoum for their help in data analyzing.

The author is appreciative to the University of Zalengei for funding the work. Needless to say, I would like to express my gratitude and appreciation to my family, my father, brother, sisters and in particular to my wife Itimad for boosting my morale during my stay aboard.

A number of other people efforts, Abdul El Hameed Mohamed Ahamed, Sabah Mohamed Abdul-Wahab and Hanan Abdul El Rahaman who spent countless hours in typing the thesis are greatly aknowledged. Sincere thanks are also expressed to my colleagues who supported me in one way or anther.

11 ABSTRACT

The biology of the developmental stages of the weevil, Cylas puncticollis Boheman a pest of sweetpotato storage roots was carried out for two years under laboratory conditions-at ambient room temperature and relative humidity and at a constant temperature of 30°C and 65% relative humidity (RH). Also field experiments were conducted for two years (2001/02 and 2002/03) to study the influence of irrigation intervals and type of sweetpotato clones on this weevil infestation. A trial to test some integrated pest management (IPM) techniques to improve sweetpotato yield and reduce weevil damage was also run. Average preoviposition period under room conditions was 4.33 ± 1.23 days. Eggs incubation period on average was similar under ambient room conditions and the controlled temperature and relative humidity experiment (3.00 ± 0.71and 3.00 ± 0.58 days-second year also gave close figures). The duration of the larval period under room conditions took less days (10.37 ±1.06 and 10.82 ± 1.57 days in the first and second year, respectively) than under constant temperature and RH conditions (13.83 ± 0.96 and 11.96 ± 0.76 days in the first and second year respectively); pupal period was also the same under ambient room conditions (3.15 ± 0.14 and 3.26 ± 0.27 days) and the constant temperature and RH (3.64 ± 0.22 and 3.98± 0.18 days). The methods of rearing (disturbed and undisturbed) was found to affect the developmental period seriously as there was a highly significant difference in the duration of the total life cycle of the weevil between the disturbed and the undisturbed rearing methods. Also, a significant difference with respect to the total life cycle existed between rearing

12 under room conditions and the constant temperature and RH conditions. The oviposition rate on average was 3.90 ± 1.67 eggs/female/day, sex ratio 1: 0.9 (female to male). Field experiments covered four seasons, two autumns and two winters in the years indicated to assess the effects of different irrigation intervals 7, 14, and 21 days gap and three types of clones TIS2544 (exotic), Baladi yellow (BY) and Baladi red (BR) (local) on the weevil infestation. The influence of harvesting time was also evaluated. Among the factors tested in relation to weevil build up or infestation, it was found that the irrigation intervals had a remarkable influence on infested storage root weight and percentage of infested storage roots in winter transplanting crop especially at late harvest time. Twenty one days irrigation interval (DII) treatment was more seriously infested than 7 DII and 14 DII; it had also affected percentage of infested stems. This result confirmed the hypothesis that water-stressed sweetpotatoes suffer higher level of insect damage than un-stressed ones. With respect to clone type and characters, the exotic type TIS2544 with the largest storage root girth (diameter) produced the largest storage root weight and also showed the maximum percentage of infested storage roots. Other clones showed less storage root weight, also girth, hence less percentage of infested storage roots. According to these findings storage root girth, total storage root weight and infested storage roots weight were positively correlated with sweetpotato weevil infestation. Late harvesting times 6 to 7 months after transplanting with respect to the different clones showed more sweetpotato weevil damage.

13 In the trial conducted to test some integrated pest management (IPM) techniques to reduce damage by the weevil, earthing (hilling) up the soil and earthing up coupled with application of insecticides deltamethrin (Decis) and carbofuran (Furadan) resulted into a significant crop yield increment and low weevil attack.

14 ﻣﻠﺨﺺ اﻷﻃﺮوﺣﺔ

ﺃﺠﺭﻴﺕ ﺘﺠﺎﺭﺏ ﻤﻌﻤﻠﻴﺔ ﻟﺩﺭﺍﺴﺔ ﺘﺎﺭﻴﺦ ﺤﻴﺎﺓ ﺴﻭﺴﺔ ﺍﻟﺒﻁﺎﻁﺎ (ﺍﻟﺒﺎﻤﺒﻲ) Cylas puncticollis Boheman ﺨﻼل ﻋﺎﻤﻴﻥ ﺘﺤﺕ ﻅﺭﻭﻑ ﺍﻟﻤﻌﻤل ﺍﻟﻁﺒﻴﻌﻴﺔ ﻭﺘﺤﺕ ﺩﺭﺠﺔ ﺤﺭﺍﺭﺓ ﻭﺭﻁﻭﺒﺔ ﻨﺴﺒﻴﺔ ﺜﺎﺒﺘﺔ 30°ﻡ ﻭ65%، ﻜﻤﺎ ﺃﺠﺭﻴﺕ ﺘﺠﺎﺭﺏ ﺤﻘﻠﻴﺔ ﺨﻼل ﺍﻟﻌﺎﻤﻴﻥ (02/2001 ﻭ03/2002) ﻟﺩﺭﺍﺴﺔ ﺃﺜﺭ ﻓﺘﺭﺍﺕ ﺍﻟﺭﻱ ﻭﺃﻨﻭﺍﻉ ﻤﻥ ﺍﺼﻨﺎﻑ ﺍﻟﺒﻁﺎﻁﺎ ﻋﻠﻰ ﺍﻹﺼﺎﺒﺔ ﺒﻬﺫﻩ ﺍﻟﺤﺸﺭﺓ. ﻜﺫﻟﻙ ﺃﺠﺭﻴﺕ ﺘﺠﺭﺒﺔ ﻟﻤﻌﺭﻓﺔ ﺠﺩﻭﻯ ﺒﻌﺽ ﻋﻭﺍﻤل ﺍﻟﻤﻜﺎﻓﺤﺔ ﺍﻟﻤﺘﻜﺎﻤﻠﺔ ﻋﻠﻰ ﺘﺤﺴﻴﻥ ﺇﻨﺘﺎﺝ ﺍﻟﺒﻁﺎﻁﺎ ﻭﺘﻘﻠﻴل ﻨﺴﺒﺔ ﺍﻟﺘﻠﻑ ﺒﻬﺎ.

ﺍﺴﺘﻐﺭﻗﺕ ﻓﺘﺭﺓ ﻤﺎ ﻗﺒل ﻭﻀﻊ ﺍﻟﺒﻴﺽ ﻓﻲ ﺍﻟﻤﺘﻭﺴﻁ 1.23±4.33 ﺘﺤﺕ ﻅﺭﻭﻑ ﺍﻟﻤﻌﻤل ﺍﻟﻁﺒﻴﻌﻴﺔ ﻭﺘﺴﺎﻭﺕ ﻓﺘﺭﺓ ﺤﻀﺎﻨﺔ ﺍﻟﺒﻴﺽ ﺘﺤﺕ ﻅﺭﻭﻑ ﺍﻟﻤﻌﻤل ﻭﺘﺤﺕ ﺩﺭﺠﺔ ﺍﻟﺤﺭﺍﺭﺓ ﻭﺍﻟﺭﻁﻭﺒﺔ ﺍﻟﺜﺎﺒﺘﺔ ﻓﻲ ﺍﻟﺴﻨﺔ ﺍﻷﻭﻟﻰ (0.71±3.0 ﻭ 0.5±3.0 ﻴ ﻭ ﻤ ﺎﹰ ﻋﻠﻰ ﺍﻟﺘﻭﺍﻟﻲ) ﻜﻤﺎ ﺃﻋﻁﺕ ﻨﺘﺎﺌﺞ ﺍﻟﺴﻨﺔ ﺍﻟﺜﺎﻨﻴﺔ ﺃﺭﻗﺎﻡ ﻤﺘﻘﺎﺭﺒﺔ. ﺍﺴﺘﻐﺭﻗﺕ ﻓﺘﺭﺓ ﺍﻟﻁﻭﺭ ﺍﻟﻴﺭﻗﻲ ﺘﺤﺕ ﻅﺭﻭﻑ ﺍﻟﻤﻌﻤل ﺃ ﻴ ﺎ ﻤ ﺎﹰ ﺃﻗل (1.06±10.37 ﻭ 1.57±10.82 ﻴ ﻭ ﻤ ﺎﹰ ﻓﻲ ﺍﻟﺴﻨﺔ ﺍﻷﻭﻟﻰ ﻭﺍﻟﺜﺎﻨﻴﺔ ﻋﻠﻰ ﺍﻟﺘﻭﺍﻟﻲ) ﻋﻥ ﺘﻠﻙ ﺍﻟﺘﻲ ﺘﺤﺕ ﺩﺭﺠﺔ ﺍﻟﺤﺭﺍﺭﺓ ﻭﺍﻟﺭﻁﻭﺒﺔ ﺍﻟﺜﺎﺒﺘﺔ (0.76±11.96 ﻭ 0.96±13.83 ﻓﻲ ﺍﻟﺴﻨﺔ ﺍﻷﻭﻟﻰ ﻭﺍﻟﺜﺎﻨﻴﺔ ﻋﻠﻰ ﺍﻟﺘﻭﺍﻟﻲ)، ﻜﻤﺎ ﺘﺴﺎﻭﺕ ﺘﻘﺭﻴﺒﺎ ﻓﺘﺭﺓ ﻨﻤﻭ ﺍﻟﻌﺫﺭﺍﺀ ﺘﺤﺕ ﻅﺭﻭﻑ ﺍﻟﻤﻌﻤل ﺍﻟﻁﺒﻴﻌﻴﺔ ﺨﻼل ﺍﻟﻌﺎﻤﻴﻥ (0.14±3.15 ﻭ 0.27±3.26 ﻴ ﻭ ﻤ ﺎﹰ) ﻭﺘﺤﺕ ﺩﺭﺠﺔ ﺍﻟﺤﺭﺍﺭﺓ ﻭﺍﻟﺭﻁﻭﺒﺔ ﺍﻟﺜﺎﺒﺘﺔ (0.22±3.64 ﻭ 0.18±3.98 ﻴ ﻭ ﻤ ﺎﹰ). ﻜﺫﻟﻙ ﺃﻅﻬﺭﺕ ﻁﺭﻴﻘﺔ ﺘﺭﺒﻴﺔ ﺍﻟﺤﺸﺭﺓ ﺩﺍﺨل ﺍﻟﺠﺫﻭﺭ ﺒﺤﺎﻟﺘﻬﺎ ﺍﻟﻁﺒﻴﻌﻴﺔ ﺃﻭ ﺘﺭﺒﻴﺘﻬﺎ ﻋﻠﻴﻬﺎ ﻜﺸﺭﺍﺌﺢ ﺃﻭ ﻗﻁﻊ ( Disturbed and un-disturbed) ﺘ ﺄ ﺜ ﻴ ﺭ ﺍﹸ ﺒ ﻠ ﻴ ﻐ ﺎﹰ ﻋﻠﻰ ﻓﺘﺭﺍﺕ ﻨﻤﻭﻫﺎ ﻤﻥ ﻁﻭﺭ ﺍﻟﻴﺭﻗﺔ ﺤﺘﻰ ﺍﻟﺤﺸﺭﺓ ﺍﻟﻜﺎﻤﻠﺔ ﺤﻴﺙ ﻭﺠﺩﺕ ﻓﺭﻭﻕ ﻤﻌﻨﻭﻴﺔ ﻋﺎﻟﻴﺔ. ﻭﻜﺎﻨﺕ ﺍﻟﻔﺭﻭ ﻗﺎﺕ ﺍﻟﻤﻌﻨﻭﻴﺔ ﺃﻴﻀ ﺎﹰ ﻭﺍﻀﺤﺔ ﺒﻴﻥ ﺘﺭﺒﻴﺔ ﺍﻟﺤﺸﺭﺓ ﺘﺤﺕ ﻅﺭﻭﻑ ﺍﻟﻤﻌﻤل ﻭﺘﺭﺒﻴﺘﻬﺎ ﺘﺤﺕ ﺩﺭﺠﺔ ﺍﻟﺤﺭﺍﺭﺓ ﻭﺍﻟﺭﻁﻭﺒﺔ ﺍﻟﺜﺎﺒﺘﺔ. ﺒﻠﻎ ﻤﻌﺩل ﻭﻀﻊ ﺍﻟﺒﻴﺽ ﻟﻠﺤﺸﺭﺓ ﻓﻲ ﺍﻟﻴﻭﻡ ﺍﻟﻭﺍﺤﺩ 1.67±3.90 ﻭﻨﺴﺒﺔ ﺍﻟﺫﻜﻭﺭ ﻟﻺﻨﺎﺙ 1:0.9 .

ﺃﺠﺭﻴﺕ ﺘﺠﺎﺭﺏ ﺤﻘﻠﻴﺔ ﻷﺭﺒﻌﺔ ﻤﻭﺍﺴﻡ. ﻓﺼﻠﻲ ﺨﺭﻴﻑ ﻭﻓﺼﻠﻲ ﺸﺘﺎﺀ ﺨﻼل ﺍﻷﻋﻭﺍﻡ ﺃﻋﻼﻩ ﻟﺘﻘﻴﻴﻡ ﺃﺜﺭ ﻓﺘﺭﺍﺕ ﺍﻟﺭﻱ 7، 14 ﻭ 21 ﻴ ﻭ ﻤ ﺎﹰ ﻭﺜﻼﺙ ﺍﺼﻨﺎﻑ ﻟﻠﺒﻁﺎﻁﺎ ﺼﻨﻑ ﻤﺴﺘﻭﺭﺩ TIS 2544 ﻭﺼﻨﻔﺎﻥ ﻤﺤﻠﻴﺎﻥ ﺍﻟﺒﻠﺩﻱ ﺍﻻﺼﻔﺭ ﻭﺍﻟﺒﻠﺩﻱ ﺍﻻﺤﻤﺭ ﻋﻠﻰ ﺍﻹﺼﺎﺒﺔ ﺒﺴﻭﺴﺔ ﺍﻟﺒﻁﺎﻁﺎ. ﺃ ﻴ ﻀ ﺎﹰ ﻗﻴﻡ ﺃﺜﺭ ﺯﻤﻥ ﺍﻟﺤﺼﺎﺩ ﻤﺘﺄﺨﺭﺍ ﺃﻭ ﻤﺒﻜﺭﺍ ﻋﻠﻰ ﺍﻹﺼﺎﺒﺔ.

ﻤﻥ ﺒﻴﻥ ﺍﻟﻌﻭﺍﻤل ﺍﻟﻤﺨﺘﺒﺭﺓ ﻟﻤﻌﺭﻓﺔ ﺩﺭﺠﺔ ﺍﻹﺼﺎﺒﺔ ﻭﺍﻟﺯﻴﺎﺩﺓ ﺍﻟﻤﻀﻁﺭﺩﺓ ﻟﻠﺤﺸﺭﺓ، ﻭﺠﺩ ﺃﻥ ﻓﺘﺭﺍﺕ ﺍﻟﺭﻱ ﻟﻬﺎ ﺘﺄﺜﻴﺭ ﻭﺍﻀﺢ ﻋﻠﻰ ﻭﺯﻥ ﻭﻨﺴﺒﺔ ﺍﻟﺠﺫﻭﺭ ﺍﻟﻤﺼﺎﺒﺔ ﻭﺨﺎﺼﺔ ﻓﻲ

15 ﻤﻭﺴﻡ ﺍﻟﺸﺘﺎﺀ ﻭﻋﻨﺩ ﺘﺄﺨﻴﺭ ﺍﻟﺤﺼﺎﺩ. ﺃﺒﺎﻨﺕ ﻓﺘﺭﺓ ﺍﻟﺭﻱ ﻋﻠﻰ ﻤﺩﻯ 21 ﻴ ﻭ ﻤ ﺎﹰ ﺇﺼﺎﺒﺔ ﺃﻜﺜﺭ ﻋﻥ ﻓﺘﺭﺍﺕ ﺍﻟﺭﻱ ﺍﻷﺨﺭﻯ 7 ﻭ 14 ﻴ ﻭ ﻤ ﺎﹰ. ﻜﺫﻟﻙ ﺍﺯﺩﺍﺩﺕ ﻨﺴﺒﺔ ﺍﻟﺴﻴﻘﺎﻥ ﺍﻟﻤﺼﺎﺒﺔ ﻋﻨﺩ ﻫﺫﻩ ﺍﻟﻔﺘﺭﺓ ﺃ ﻴ ﻀ ﺎﹰ. ﻫﺫﻩ ﺍﻟﻨﺘﻴﺠﺔ ﺘﺅﻜﺩ ﺼﺤﺔ ﻓﺭﻀﻴﺔ ﺃﻥ ﺍﻟﻨﺒﺎﺘﺎﺕ ﺍﻟﺘﻲ ﺘﺘﻌﺭﺽ ﻟﺸﺢ ﺍﻟﻤﺎﺀ ﺃﻜﺜﺭ ﻋﺭﻀﺔ ﻟﻺﺼﺎﺒﺔ ﺒﺴﻭﺴﺔ ﺍﻟﺒﻁﺎﻁﺎ.

ﺒﺎﻟﻨﺴﺒﺔ ﻟﻸﺼﻨﺎﻑ ﻭﺼﻔﺎﺘﻬﺎ ﻨﺠﺩ ﺃﻥ ﺍﻟﺼﻨﻑ ﺍﻟﻤﺴﺘﻭﺭﺩ TIS 2544 ﻟﻪ ﺠﺫﻭﺭ ﻏﻠﻴﻅﺔ (ﻜﺒﻴﺭﺓ ﺍﻟﻘﻁﺭ) ﻭﺃﻋﻁﻰ ﺃﻜﺒﺭ ﻭﺯﻥ ﻟﻠﺠﺫﻭﺭ ﻭﻜﺎﻥ ﺃﻜﺜﺭ ﻋﺭﻀﺔ ﻟﻺﺼﺎﺒﺔ ﻤﻥ ﻏﻴﺭﻩ. ﺒﻴﻨﻤﺎ ﺃﻅﻬﺭ ﺍﻟﺼﻨﻔﺎﻥ ﺍﻵﺨﺭﺍﻥ ﺃﻗل ﻨﺴﺒﺔ ﻭﻭﺯﻥ ﻟﻠﺠﺫﻭﺭ ﺍﻟﻤﺼﺎﺒﺔ. ﻤﻥ ﻫﺫﻩ ﺍﻟﻨﺘﺎﺌﺞ ﻨﺠﺩ ﺃﻥ ﻗﻁﺭ ﺠﺫﺭ ﺍﻟﺼﻨﻑ ﻭﻭﺯﻨﻪ ﺍﻟﻜﻠﻲ ﻭﻭﺯﻥ ﺠﺫﻭﺭﻩ(tubers) ﺍﻟﻤﺼﺎﺒﺔ ﻴﺭﺘﺒﻁ ﺍ ﺭ ﺘ ﺒ ﺎ ﻁ ﺎﹰ ﻤ ﻭ ﺠ ﺒ ﺎﹰ ﻤﻊ ﺍﻹﺼﺎﺒﺔ ﺒﺴﻭﺴﺔ ﺍﻟﺒﻁﺎﻁﺎ. ﻭﺠﺩ ﺃﻴﻀﺎ ﺇﻥ ﺍﻟﺤﺼﺎﺩ ﺍﻟﻤﺘﺄﺨﺭ 6 ﻭ 7 ﺸﻬﻭﺭ ﺒﻌﺩ ﺍﻟﺯﺭﺍﻋﺔ ﻟﻸﺼﻨﺎﻑ ﺍﻟﻤﺨﺘﻠﻔﺔ ﻴﻌﺭﻀﻬﺎ ﻻﺭﺘﻔﺎﻉ ﻨﺴﺒﺔ ﺍﻟﺘﻠﻑ.

ﺸﻤﻠﺕ ﺍﻟﺩﺭﺍﺴﺔ ﺃ ﻴ ﻀ ﺎﹰ ﺍﺨﺘﺒﺎﺭ ﺒﻌﺽ ﻤﻜﻭﻨﺎﺕ ﺍﻟﻤﻜﺎﻓﺤﺔ ﺍﻟﻤﺘﻜﺎﻤﻠﺔ ﻋﻠﻰ ﺴﻭﺴﺔ ﺍﻟﺒﻁﺎﻁﺎ ﻓﻲ ﺘﺠﺭﺒﺔ ﺤﻘﻠﻴﺔ. ﺩﻟﺕ ﺍﻟﻨﺘﺎﺌﺞ ﻋﻠﻰ ﺃﻥ ﺭﺩﻡ ﺍﻟﺠﺫﻭﺭ ﺃﻭ ﺘﻐﻁﻴﺘﻬﺎ ﺃﻭ ﺇﺠﺭﺍﺀ ﻨﻔﺱ ﺍﻟﻌﻤﻠﻴﺔ ﻤﻊ ﺇﻀﺎﻓﺔ ﺍﻟﻤﺒﻴﺩﺍﺕ ﺍﻟﺤﺸﺭﻴﺔ ﻤﺜل (deltamethrin (Decis ﻭ(carbofuran (Furadan ﺃﺩﻱ ﻟﺯﻴﺎﺩﺓ ﺍﻹﻨﺘﺎﺝ ﻭﺘﻘﻠﻴل ﺍﻹﺼﺎﺒﺔ ﺒﻬﺫﻩ ﺍﻟﺤﺸﺭﺓ.

16 1. INTRODUCTION

Sweet potato (Ipomoea batatas (L.) Lam.) is considered the sixth most important crop in the world after wheat, rice, corn, white potato and barley (Vietmeyer, 1986). In a more recent ranking by F.A.O (1999) soybean, cassava appeared as number 6th and 7th . In the tropics it can be planted from vines not normally used for food at any time of the year. It is a low input crop that can almost always yield, and can be harvested at almost any time, from 4 to 6 months after planting. It is versatile in its uses and highly nutritious. Sweetpotato was domesticated more than 5000 years ago. There was still much debates to just where in the Americas this took place, South America or Central America, although recent evidence suggests that it was the latter.

Sweet potato is very widely adapted throughout temperate and tropical zones over almost 80 degrees of latitude and from sea level to over 2000 m altitude. Sweet potato grows best in regions of 750-1250 mm of rainfall per annum but, it responds well to irrigation in more arid regions, perhaps because of the increase in sunshine. The most suitable soils are well-drained, sandy loams or tropical peats but sweet potato can be grown on fairly poor soils if the ground is well cultivated. Heavy soil should be avoided as the tubers tend to be badly shaped and difficult to lift. There is almost no fresh storage of roots. Farmers practice in ground storage and piece meal harvesting (Smit and Odongo, 1995-96). Over 95 percent of the global sweetpotato crop is produced in developing countries, it has considerable unrealized potential.

17 Unfortunately, this crop is highly susceptible to over 40 insect species which attack it in the field and in storage. Among them three species of , commonly called sweetpotato weevils are the most destructive. These species are: (Fabricius), Cylas puncticollis Boh., and Euscepes postfaciatus Fairmaire. Although the Cylas species are widespread, they have identical food habits and ecological requirements (Talekar, 1987c). The sweetpotato weevil species found in East Africa, C. puncticollis and C. brunneus (Fabricius) are unique to the continent, but little or no published information is available on the biology and ecology of the African sweetpotato weevil species, basic studies revealed differences in the biology of the two weevil species (Smit and Odongo, 1995-96).

The weevil is monophagous to the extent that significant feeding, growth and reproduction only occur on Ipomoea spp. in the Convolvulaceae, I. batatas its preferred host. The damage is caused by feeding and egg laying punctures of the adults but is mostly caused by the feeding of larvae in the roots and tubers. Slight feeding may cause the potato to be unfit for human consumption because of the presence of larvae and the bitter flavour. It does feed on the above parts of the plant but this damage is insignificant as compared to the feeding in the root (Burns, 1999).

Weevils are generally more important under dry conditions and in traditional systems where tubers are harvested sequentially. Increasing the frequency of irrigation during the season not only tended to reduce weevil infestation but also reduce root yield. A proper balance between frequency of irrigation to reduce soil cracking to prevent access of the weevil to roots and allow roots to develop

18 adequately to get optimum yield should be established for each soil type and crop cultivar.

The weevil Cylas puncticollis is the only sweet potato pest which seems to have attracted major research attention among scientists. Studies commonly report between 50 and 100% yield loss due to complex of Cylas spp. weevils, especially under dry conditions. Losses due to complex of Cylas species occurring in East Africa have not been well quantified.

The main producing areas of sweetpotato in the Sudan are New Halfa Scheme, Rahad Scheme, Damazein area, Gezira Scheme and Southern regions, the crop is grown twice a year in some parts of the Sudan, the autumn (kharif) and winter planting. Although the crop has great potential in the Sudan, it received little attention by research workers. Only few studies have been conducted on cultivars testing (El Hilo and Ahmed, 1966 and El Shafie, 1967) and cultural practices (Ali and Bushra, 1993a; 1993b and Ibrahim, 2000) and chemical constituents of the tubers (Alhag, 1998). The total area and the productivity were decreased from 10-13 thousand feddans to about 5- 8 thousand feddans and from 8-15 to 5-8 ton per feddan in 1995/96, respectively; one of the main reasons is devastative infestation by sweetpotato weevil, Cylas puncticollis (Ibrahim, 2000) which is a major pest of sweet potato in the Sudan (Schmutterer, 1969). No work was done in the Sudan about this pest, very meagre, if not entirely absent information on the biology and management of this pest.

Rapid increase in weevil damage in the Sudan obviated the need for assessment and characterization of the pest. First efforts must be concentrated on developing integrated pest management (IPM) and

19 filling some knowledge gaps in the biology and seasonal occurrence of the weevil. The aim of the present research project was to gain insight in the biology and ecology of sweetpotato weevil and based on this insight, develop pest management programme by achieving the following objectives:

1. To study some aspects of the biology of sweetpotato weevil, Cylas puncticollis Boh.

2. To relate the impact of irrigation interval on the infestation of sweetpotato weevil.

3. To investigate the susceptibility of some clones of sweet potato to natural infestation caused by sweetpotato weevil, Cylas puncticollis.

4. Describe the damage and type of losses caused by the weevil.

5. To introduce some integrated pest management measures to control sweetpotato weevil in the field.

20 2. REVIEW OF LITERATURE

2.1 Taxonomy and distribution

Cylas puncticollis was first described by Boheman in 1833 from Senegal; other name used Cylas compressus Hartmann, commonly known as sweetpotato weevil, African sweetpotato weevil and weevil, sweet potato. Traditionally Cylas has been placed in the tribe Cyladini of the family Apionidae. However, on the basis of adult and larval characters, both Thompson, (1994) and May (1994) placed this genus in the subfamily Cyladinae of the Brentidae, this subfamily was earlier placed under the (Borror and White, 1970). There are currently at least four un-described species. However, a number of available names are junior synonyms. Wolfe, (1991) estimated that in the conclusion of the systematic revision of Cylas, there will be approximately 25 valid species of Cylas, but he was unable to locate and examine the type specimen. However, he examined numerous specimens of C. puncticollis from West Africa and so far was unable to find a consistent set of characters to separate population at the subspecific level. All members of this species group are uniformly black with the eyes dorsally narrowly separated in males and require genitalic examination for conclusive identification.

The alimentary canal and the central nervous system were described and illustrated for 208 species of Curculionoidea representing 140 genera and 8 families and the results were compared with published data on related species. The alimentary canal and the nervous system of 4 genera, including Cylas, were described and the systematic position of these genera was discussed. It was concluded that on the basis of internal characters, the genus Cylas was now

21 placed in the Brentidae, may be allied to both the Brentidae and Apionidae (Calder, 1989).

Cylas puncticollis has a wide distribution in the tropics as it occurs in most countries where sweet potatoes are grown on large scale. In the Sudan, the insect was found in the Northern Province (Shendi), Khartoum Province, Kassala Province (Gedarif), Bahr Elghazal Province (Wau) and Equatoria Province (Juba, Yambio etc)(Schmutterer, 1969). The same author added that Cylas puncticollis resembles the closely related species C. formicarius (F) in appearance and bionomics. C. formicarius repeatedly recorded as a pest of sweet potatoes in the Southern part of the Sudan but seems to be less common than C. puncticollis.

The distribution of Cylas spp. weevils varies between regions, C. formicarius is the most widespread, being the only species found in Philippines, Indonesia and Thailand and in the Pacific countries such as Papua New Guinea. In East Africa, three species have been reported C. formicarius, C. puncticollis and C. brunneus, the former two species being the most common and the latter two being restricted to Africa (Lenne, 1991 and Smit et al., 2001). There are only two records of occurrence of C. formicarius in Africa: Msabaha in coastal Kenya and Natal Province in South Africa. In Kenya and Uganda C. puncticollis and C. brunneus are of equal importance (Smit, 1997). C. formicarius is widely distributed, it occurs in Africa, Asia, the Caribbean, in parts of North and South America and the Pacific, C. puncticollis is confined to Africa (Moyer et al., 1989).

Adult weevils fly freely during the warm part of the year and are capable of ranging at least one mile per season. Distribution of

22 sweetpotato weevil in fields is aggregated. Flight takes place primarily at night and during the day if the are disturbed. Flight activity tends to be more general on dark nights than on bright moon lit nights.

It is very clear that male weevils flew more actively than females, regardless of their age. This result supported direct observations from the field and laboratory and light trap records. Although there were big differences in the flight ability between sexes, flight ability of the weevils as a whole was low compared with other insects. Locomotion activity was also significantly higher in males than in females; however, the difference was much smaller than that of the flight activity, and no migratory movement (Moriya and Hiroyoshi, 1998).

From a taxonomic standpoint, C. puncticollis is the most problematic species within this species group (Wolfe, 1991).

2.2 Host range

Cylas puncticollis can affects seedling stage, vegetative growing stage and post harvest and feeds on leaves, roots and stems. It feeds on herbaceous Convolvulaceae, but especially Ipomoea spp. It has also been reported on sesame in Uganda, Cassia actifolia (C. senna) in Sudan and cowpea in Nigeria (Nonveiller, 1984). The primary host is Ipomoea batatas (sweet potato). Secondary hosts are Coffea sp. (coffee), Zea mays (maize), Vigna unguiculata (cowpea), Sesamum sp. (sesame), and Ipomoea panduratea (morning glory).

Jayaramaiah, (1975a) working under laboratory conditions, succeeded in breeding Cylas formicarius on Dacus carota (Umbilleferae), Manihot ultissima (Euphorbiaceae) and Ipomoea campanulata. Ranjith, (1985) recorded the infestation of black pepper,

23 Piper nigrum by the apionid Cylas formicarius for the first time from observations in Kerala, India in 1983-1984.

2.3 Economic impact and damage

Cylas puncticollis is of the most important biotic factors limiting sweet potato production in Africa, notably Uganda, Rwanda, Kenya and Cameron (Pfeiffer, 1982; Chalfant et al., 1990; Smit and Matengo, 1995). Adults attack the leaves of sweet potatoes but, larvae are more injurious, boring into the stems and causing serious mortality to seedlings (Daiber, 1994). Allard et al., (1991) reported on serious larval infestations disrupting sweet potato nurseries in Ethiopia. On established plants the larvae feed on the tubers and stems, producing larval tunnels and latter, pupal chambers. Stem damage is believed to be the main reason for yield loss, although damage to the vascular system caused by feeding, larval tunneling and secondary rots reduce the size and number of roots. Severe infestations render the crop unpalatable and therefore inedible to humans. Pest damage usually continues during storage, therefore, infested tubers cannot be stored for along time. In conjunction with other pests C. puncticollis can completely destroy sweet potato plantations (Geisthardt and van Harten, 1992). The developing larvae of the weevil tunnel in the vines and tubers causing significant damage. In response to damage, tubers produce terpenephytoalexins which render tuber inedible at low concentrations and low levels of physical damage. Feeding inside the vines causes malformation, thickening and cracking of the affected vine. Foliage may become pale green in colour and the growth and vigour of the plant can be affected. Heavy infestation in the vines have been correlated with high damage levels in tubers and reduction in

24 total yields and tuber size although, there is evidence that this is not always the case (Talekar, 1982). In some 75 lines, infestation of the crown and roots of plants by C. formicarius elegantulus appeared not to be correlated (Jones et al., 1978).

The low weevil densities may cause devastating crop losses of up to 60-100% (Chalfant et al., 1990). The crop losses from C. formicarius damage range from 5-80% with duration of the crop in the field being the most significant factor exacerbating the pest damage. In Hawaii damage increased sharply between 24 and 30 weeks after planting (Sutherland, 1986a). In Papua New Guinea Sutherland, (1986c) demonstrated that at low population levels the relationship between damage and time was positive and linear between 20 and 26 weeks. In Kerala, India this insect can cause yield loss of 19-54% (Palaniswami, 1989), where as in Malaysia, Ho, (1970) reported a yield loss of up to 80% and in Philippine C. formicarius reduces sweet potato yield by 50% (Gapasin, 1989). Similar losses are found in other Asian and Pacific countries. In Kenya, data from an area where subsistence farmers practice piecemeal harvesting, indicate loss on the order of 10% (Smit and Matengo, 1995). In Uganda, commercial farmers sustain losses as high as 57% and losses in experimental fields range from 6 to 42% (Smit, 1997).

Sweetpotato yield was higher in the dry season, but the incidence of pests and diseases affecting the roots was also greater (Braun and van de Fliert, 1999). In Sudan Ibrahim, (2000) stated that all tested clones were infested by weevils. The damage caused by weevils varied from 0.74 to 4.26% in clone TIS 2544 and from 4.0 to 14.4% in clone TIS9265.

25 In a survey in Japan in 1988 the damage caused by C. formicarius to sweet potatoes was observed to start above ground and spread to the tubers, and to spread from the edges to the centre of the field. Damage was greatest at the edges of the field. The number of punctures of feeding adults per tuber was correlated with the degree of damage to the tubers caused by larval feeding (Setokuchi and Nakao, 1991).

The cryptic feeding of the sweetpotato weevil larvae and nocturnal activity of adults make it difficult to detect sweetpotato weevil infestation. Crop loss of sweet potato caused by insect damage is the most important problem in the field. Although the importance of pest species varies regionally, sweetpotato weevil (Cylas spp.) are the most important threat worldwide. Production loss often surpasses 60% and can reach 100% (Zhang et al., 1995-96).

2.4 Biology

2.4.1 Description

The egg is oval, and yellowish-white and the larva was briefly described and figured by Schmutterer, (1969). According to Allard, (1990) the head of the various larval instars ranged from 0.25 to 1.00 mm. Body elongate, slightly curved, tapered at posterior, entirely covered with very short setae. Schmutterer, (1969) described pupa as white and approximately 5-6 mm in length and also provided detailed description. The adults entirely black, with a faint, metallic blue luster. Body length 6-8 mm. Rostrum extremely short and blunt. Antennae distinctly sexually dimorphic; length of male antennal club equal to or greater than combined length of all preceding segments. Eyes close together in dorsal view, distance between eyes about one sixth width of

26 rostrum. Pronotum in lateral view more distinctly arched, posterior constriction evident. Hind femora not projecting or only slightly projecting beyond elytral apex. Abdomen always elongate and cylindrical. Males with internal sac of aedeagus with four pairs sclerites.

2.4.2 Life history

Allard (1990) observed a distinct preoviposition period of 3 days, in a population of laboratory-reared weevils originally collected from Western Kenya. From 2 days post-emergence, females laid eggs singly on the root surface, but after 5 days eggs were laid in an excavation plugged with frass. Eggs laying continued up to 60 days, but most eggs were laid in the first 30 days. Eggs laid in stems and roots hatched after 3-5 days under laboratory conditions. After four larval instars, adult emergence occurred approximately 22-25 days after egg laying. Experiment also revealed that newly-emerged adult weevils can survive for up to 8 days in the absence of any food source and for up to 90 days if fed on sweet potato foliage. Mean adult longevity was 42.5 days. The sex ratio did not differ from a 1 : 1 ratio. Braun and van de Fliert, (1999) stated that adult females excavate cavities for their egg in vines or roots exposed by rain washing soil away, or by soil cracking in dry conditions. Dawes et al., (1987) said that because immature stages of sweetpotato weevils are hidden within roots, the actual time of death of these stages could not be determined. The biology of immature stages as well as the fecundity and longevity of C. puncticollis were studied in the laboratory on TIb4 at 25ºC-30ºC and 79% relative humidity. The development period from egg to adult of C. puncticollis averaged 20.2 days, the

27 preoviposition period 3.6 days and oviposition period 71.4 days. A female lived an averaged of 80.5 days, and laid an average of 329.8 eggs. The male lived an average of 54.8 days (Anota and Leuschner, 1983). Schmutterer, (1969) and Geisthardt and van Harten, (1992) reported that the female lays its eggs in small hollows which are eaten into the base of the stems or in tubers, when the latter can be reached. The larvae hatched after approximately one week and fed on the tubers and vines, causing holes symptoms. The larval period last for 2- 3 weeks, depending on temperature. Pupation takes place either in the tuber or in the soil near by and last for approximately I week. The adult weevils remain within the pupal chamber for some days before leaving the plant, to reach above-ground, they tunnel through the stems or make their way through the soil. Adults are long-lived and activities of more than one month have been observed, even in storage. C. puncticollis prefers drier climates and larval development lasts longer in damp climates or during rainy season, and in such conditions the activity of adults is at considerably lower level. Moyer et al., (1989) reported that eggs are laid singly at the base of the vines, or in roots. After 5-8 days, white legless larvae hatched, feed inside the roots or vines for 15-20 days and then pupate. Adults emerge from the pupal cases about 7 days latter, but remain inside the plant for further 6-9 days. Egg laying begins 2-3 days after emergence and lasts throughout 70-90 days of adult life.

Smit and van Huis, (1998) studied the biology of C. puncticollis and C. brunneus in laboratory experiments carried out at 27±1ºC, 45±5% relative humidity and 12 h photo phase. C. puncticollis females lived longer than C. brunneus (141±10 and 92±12 days,

28 respectively),developed faster (egg to adult 20-28 days, and 32-41 days, respectively) and had a lower oviposition rate (1.10±0.04 and 1.33±0.06 eggs per female per day, respectively). The total egg production per female average (101), sex ratio (1:1) and proportion of eggs surviving to adulthood (average 89%) were similar for both species. The intrinsic rate of increase was higher for C. puncticollis 10.533 per 10 day period compared to 0.521 for C. brunneus. C. puncticollis will benefit from its longer longevity during less favourable conditions as females can survive extended periods when no oviposition sites are available and then resume egg laying when conditions improve.

Ring (1999) stated that following egg laying holes are covered by a grayish mass which hardens to form protective caps over developed eggs. Depending on the environmental conditions, incubation of eggs varies from 4-56 days, larval development occurs inside the root and can range from 12-154 days; pupae occur within the sweet potato, and this stage lasts for 5 to 11 days. Newly emerged adults wait 1 to 3 days before leaving the root. Adults mate soon after emergence from tuber but egg laying does not occur for 4-7 days. Larvae tunnel throughout the root and also through the vine to the soil. All stages of weevil can be found in the root of the sweet potato. Sweet potato infested with weevils are not unsightly, but they taste bitter.

Virtually, all available information on the biology of Cylas weevils relates to C. formicarius. Therefore the biology of the African Cylas species was studied under laboratory conditions. Laboratory experiments revealed that weevil can not dig down through soil.

29 Under field conditions females will reach roots for oviposition through soil cracks when roots are exposed above soil; C. puncticollis seems to be a better competitor during less favorable conditions due to its longer longevity (Smit, 1997).

Sherman and Tamashiro, (1954) after detailed measurements of 964 larval head capsules demonstrated three instars and concluded that frequent handling of larvae would interfere with feeding and increase the number of instars; thus explaining the greater numbers described by other workers.

2.4.3. Effect of temperature on the development of the sweetpotato weevil

Effects of temperature on the development and survival of sweetpotato weevil, Cylas puncticollis were studied in the laboratory at six constant temperatures (16.03, 18.60, 24.11, 26.38, 31.23 and 35.82ºC). As expected, development rate was slower at lower temperatures. At 16.03ºC there was no development beyond the first larval instar. The larval period was longer than other developing stages at all temperatures. A significant difference in total development rate of adults was observed between the two treatments (disturbed and undisturbed), except at 18.6ºC. Mortalities were highest at 16.03, 18.6 and 35.82ºC. Temperature had no effect on the sex ratio of C. puncticollis (Nteletsana et al., 2001). The effect of temperature on the development period of sweetpotato weevil was studied on T1b4 tubers kept at 4 constant temperatures 20ºC, 23.5ºC, 27ºC and 34ºC. Eggs laid by actively ovipositing females were observed for adult emergence and immature stages survival. A significant delay in the development period of the insect at 20ºC and 23.5ºC occurred (33.6

30 and 33.6 days, respectively) as compared to 27ºC and 34ºC the development period was shortened (22.2 and 16.8 days, respectively). High mortality (89.3%) occurred at 20ºC. These results suggest that low temperature extends the development period and drastically affects survival. With increase in the temperature the development period shortens and survival rate (immature stages) increases (Hahn and Anota, 1983). Maily, (1996) concluded that the biology of Cylas spp. is well documented and indicates that weevil development was temperature dependent.

2.5 Effect of sweetpotato root characters on the infestation of sweetpotato weevil

There is great variation in foliage and root characters of sweet potato varieties in Uganda. In addition, varieties vary in taste, food value, consumer acceptance and maturity period (Jana, 1982). Chalfant et al., (1990) explained that characteristics which apparently make tubers less susceptible to weevil attack have been documented for many years and include deep rooting, thick skin, elongated shape, root density and chemistry, dry matter and starch content. It is possible that traditional, local varieties have developed tolerance, selected over time. As lowland farmers grow a diversity of crops, rotations, and mixtures may also indirectly contribute to weevil control.

Smit and Odongo, (1995-96) stated that short growing season varieties can be harvested early before weevil population build up. Deep rooted varieties escape weevil damage; because their roots are less accessible for females to lay eggs. Most varieties mature within 4 to 6 months depending on climate, variety and local customs

31 (Mwanga and Wanyera, 1988). Early maturing and deep storage roots help sweet potato escape weevil damage. Shallow rooting varieties are four times more infested than varieties that have roots 8cm below the soil surface. Early maturing varieties (90-120 days) are three or four times less infested than late varieties (180 day or more)(Cisneros et al., 1995). Jayaramaiah, (1975b) reported that varieties of sweet potato used in India have thin tubers, scattered within the ground and well below the surface. These varieties are less severely damaged than those with large tubers near the surface. Singh et al., (1987) stated that during a field trial in Bihar, India the response of 11 varieties of sweet potato to Cylas formicarius indicated varying levels of infestation and yield. Weevil infestation was found to be linked to factor associated with tolerance/resistance. Tuber neck length and vine thickness were negatively correlated with incidence, where as a positive correlation was observed in case of a tuber girth. Round tubers were more affected than elongate and spindle shape ones. Teli and Salunke (1994) found that round and oval tubers were more susceptible to infestation by weevils in the field than long stalk, spindle and elongate ones. Tuber damage in the field was negatively correlated with stalk length and positively with tuber girth. Pink and red coloured cultivars were generally less susceptible than white and brown coloured ones. Cultivars with thin foliage and lobed leaves with purple colouration at emergence were less susceptible.

Lagnaoui et al., (2000) stated that selection of early and deep rooting varieties seem to help reduce the levels of weevil infestation. However, breeding for resistance to sweetpotato weevil did not result in useful levels of resistance. Research data indicates various levels of

32 resistance to sweetpotato weevil, but these levels are too low to withstand pest pressure. The advisability of using tuber characteristics when screening for weevil resistance has been put in doubt by Sutherland, (1986c) who has shown that damage to vine by weevils can significantly reduce yields of sweetpotato, even when direct damage to tubers is low. Talekar, (1982) found the absence of any correlation between the numbers of sweetpotato weevils in crowns and roots, it means that knowing of the number of insects feeding in crowns can not be used to predict the root damage. Weevil infested crowns were thicker, indicating that adventitious root growth replaced the damaged tissue, thus allowing proper plant development.

Wide variation in weevil infestation of any particular sweet potato accession (cultivar or variety) for each season and each location is common. Despite 12 years of continuous research not a single accession that is consistently resistant to the weevil has been found. Other research groups had similar difficulties (AVRDC, 1987).

Considerable research on sweet potato, Ipomoea batatas Lam. has been done at several institutes in the U.S. from 1939, and at the International Institute of Tropical Agriculture (IITA), Nigeria and the Asian Vegetable Research and Development Center (AVRDC), Taiwan since their establishment in the early 1970's. Nevertheless, despite these efforts, not a single sweet potato cultivar has been bred using previously identical source of resistance, and which is grown in any appreciable scale specifically to control sweetpotato weevil species Cylas formicarius (F.) or C. puncticollis Boh. Effects have been thwarted by instability of resistance as expressed by the differences in weevil infestation among trials, locations, seasons and

33 at times among replicates of a single accession in a trial among plants in the same plots, and even among storage roots within one plant (Talekar, 1987c). The same author added that sweetpotato weevil has no clear-cut seasonality. As long as a weevil source is available in the neighborhood, sweet potato will be infested no matter when planted. Cisneros et al., (1995) reported that planting infested sweet potato stem cuttings is a primary way to distribute sweetpotato weevil. More than 95% of the eggs are deposited in the first 35cm of stem by discarding the basal stem portion the stem makes a healthy cutting.

Institute to Nacional de Investiga Ciones de Viandas Tropicales (INIVIT) recommended harvesting mature crops before the level of infestation reaches 3%.

2.6 Influence of irrigation on sweetpotato weevil infestation

The sweetpotato weevil has been particularly devastating, severely reducing yield and greatly affecting the quality of damaged tubers. The weevil is the single most serious threat to sweetpotato production globally. However, dry periods at the end of the season may cause the soil to crack. Such cracks provide a favourable environment for sweetpotato weevil infestation. Irrigation is recognized as an effective control measure and is widely used by the growers (Lagnaoui et al., 2000).

Braun and van de Fliert, (1999) stated that sweetpotato weevil is considered a dry season pest and it is known that dry soil conditions result in soil cracking and increase the access of weevils to roots leading to higher damage level. Sutherland, (1986b) mentioned that the importance of maintaining soil moisture to prevent soil cracking is emphasized by some authors who quoted unpublished trial work

34 which demonstrated the reduction in weevil damage caused by the irrigation of dry soils. The use of lighter soil types for sweet potato cultivation was recommended as these do not crack under dry weather conditions.

Relatively little is known about water requirements and yield responses to water of sweet potato, few studies have been carried out. Studies in USA, Cuba and Nigeria suggest that water requirement over the total growing season is between 350 and 450 mm. In general review articles, the sweet potato is invariably described as drought tolerant, but sensitive to water-logging. There is usually little scientific evidence cited to support or quantify these statements (Gomez and Carr, 2003). Lenne, (1991) reported that in Indonesia, irrigation at 10 days interval has been shown to reduce weevil infestation, irrigation during dry season has been found to greatly reduce weevil damage. This is relevant to both commercial producers and also to small farmers. If irrigation is not used in the dry season in low lands, losses can be as high as 100%. Further research on the frequency and amount of irrigation needed for adequate control would be worthwhile. There was no significant difference in weevil infestation in three irrigation interval treatments (10, 20 and 30 days interval) in both seasons (1985-1986) and (1986-1987). There was, however, a tendency for the number of weevils per unit root weight to increase, with increasing interval between two consecutive irrigations. More frequent irrigation obviously kept the soil moist and prevent the soil from cracking, thus reducing the weevils access to the roots. The same treatments adversely affect the root yield possibly due to

35 reduced aeration. However, this is expected to vary for each soil type (AVRDC, 1987).

Anioke, (1996) showed that in Nigeria the amount and distribution of rainfall affects sweet potato foliage, root tubers and damage by Cylas puncticollis. Highest yields were obtained when the crop was planted in the month when rainfall between 200 and 250 mm. Delayed planting resulted in reduced yields because of increasing amounts of rainfall. Although, the yield of tubers increased with delayed harvest, increase in C. puncticollis damage as a result of reduced rainfall did not make harvest beyond 20 weeks after planting profitable.

Lenne, (1991) recorded that farmers may delay harvest after physiological maturity to increase yield or to get higher prices at a late date. But in Cuba, postponing harvest 30 days mean a fourfold increase in damage. Soil moisture is essential for plant growth and it has a clear effect on weevil infestation levels. Cracking of the soil because of drought or deficient irrigation water facilitates female weevils reaching the sweet potato fleshy roots to deposit their eggs. Well irrigated fields are commonly 4-5 times less infested than those suffering from moisture deficit.

The influence of rainfall and soil moisture on the level of sweet potato infestation has been well established in experiments in Cuba, the Dominican Republic and Uganda. In Cuba infestation during the dry season was 4-5 times higher than during the rainy season or when irrigation was available. Weevil infestation is favoured by soil cracking, which becomes more severe 80-90 days after planting, at the time of storage root bulking. Proper hilling and irrigation were found

36 to be effective at that time in avoiding direct access of the weevil to sweet potato through soil cracks (CIP, 1995). In 3 districts of Orissa, India the sweetpotato weevil was not important in the kharif season (Bhat, 1987).

2.7 Control

2.7.1 Cultural control

Cultural controls for sweetpotato weevil have been recommended since the early 1900's. Because of its concealed feeding habits C. puncticollis can be difficult to control with conventional insecticides application. However, because of its limited or almost non-existent flying activity, which implies that the insect is carried from place to place via movement of the plant material, host specifity to the genus Ipomea, and characteristic mode of entry and damage to the plant, the pest is amenable to suppression by crop rotation, clean cultivation, mulching and similar cultural practices. Among various control measures attempted, modification of cultural practices has the greatest potential in combating the sweetpotato weevil at very little cost. Cultural pest control involves changing or modifying cultivation practices which directly or indirectly reduced the pest population (Talekar, 1987c).

Allard et al., (1991) described the following techniques that have been used in the management of Cylas spp. in sweet potato, planting only in the fields that have had no weevil infestations within the last 12 months and preferable more than 1 km away from any infested land, planting resistant or tolerant cultivars, selecting deep rooting cultivars with long necks between the roots and stems, planting early maturing cultivars which can escape serious damage,

37 earthing up of plants (hilling), particularly those cultivars with the tendency to push out of the ground, removal of all plant debris and volunteer plants after harvest, reridging approximately 30 days after planting as this places the roots deeper and out of reach of the weevils, planting non-infested materials and the use of intercropping.

2.7.1.1 Crop rotation

Crop rotation appears to be the most effective method of preventing infestation of C. puncticollis, since the adult can not move rapidly from one plantation to anther because of their limited flight activity (Geisthardt and van Harten, 1992). Anioke et al., (1993) studied the effects of K fertilizer with constant levels of N and P on C. puncticollis damage in a sweet potato crop in Nigeria during 1987- 1988. No-fertilizer plots exhibited the least pest damage, and were less attractive to C. puncticollis due to the poor vegetative development. Although K supplements aid some crops to exhibit higher mechanical resistance, due to thicker cell walls and cuticle, no such effects were observed in sweet potato. A survey of farmers' cultural practices in Kenya by Smit and Matengo, (1995) suggested that crop protection workers should concentrate their research and extension efforts on crop sanitation and the avoidance of adjacent planting of successive crops. Crop rotation was also recommended by Lenne, (1991) in Papua New Guinea, and Dalip, (2000).

Rotations of crops, such as growing sweet potato in a field only once every 5 years (TAC, 1954), avoiding planting of sweet potatoes in the same area for two successive years (Holdaway, 1941) have long been suggested. The usefulness of crop rotation with rice in controlling the weevil was investigated in two experiments, each

38 lasting 17-18 months in Taiwan (Talekar, 1983). The results obtained were variable dependent on the proximity of the source of weevil infection. Sweetpotato weevil control was acceptable in a field planted away from weevil-infested field, where as the tubers were heavily infested when the fields were adjacent to each other.

2.7.1.2 Intercropping

Little research information is available on this approach for the management of sweetpotato weevil. In one experiment in Taiwan, sweet potato was planted between two rows of each of 68 crop species and weevil infestations of the roots were monitored. Intercropping with chickpea (Cicer arietinum), coriander (Coriandrum sativum), pumpkin (Cucurbita moschata), radish (Raphanus sativus), fennel (Foeniculum vulgare), blackgram (Vinga mungo) and yardlong bean (Vinga unguiculata) reduced weevil infestation considerably. However, intercropping with blackgram, fennel, pumpkin and yardlong bean also reduced sweet potato yields (AVRDC, 1988). Similarly, Singh et al., (1984) observed reduced weevil damage when sweet potato was intercropped with proso millet (Panicum miliaceum) and sesame (Sesamum indicum). It is uncertain if the reduced yield (smaller and fewer roots) contributed to the lower weevil infestations. More research on the effect of intercropping on weevil damage and root yield is needed.

2.7.1.3 Earthing up the soil (hilling)

Soil cracks are the major route of weevil access to roots. The enlargement of roots, especially in cultivars which set roots near the soil surface, and soil moisture stress can produce cracks and increase exposure of roots to the weevil. The absence of cracks denies the

39 weevil access to the roots. For example, in Taiwan, less damage by C. formicarius occurs during the rainy season when soil cracks are minimal. Similarly, the African sweetpotato weevil (C. puncticollis) which causes damage similar to that by C. formicarius in Nigeria is less damaging during the wet season than during the dry season (Hahn and Leuschner, 1982). This is presumed to be due to the absence of soil cracks due to adequate soil moisture in the wet season as opposed to the dry season. Other workers have reported similar findings (Leuschner, 1982; Rajamma, 1983 and Sutherland, 1986b). Prevention of soil cracking by hilling the area around the plant or irrigating frequently, are also suggested as an important methods of reducing weevil damage (Franssen, 1935; Holdaway, 1941; Sherman and Tamashiro, 1954; Macfarlane et al., 1987 and Lenne, 1991). Palaniswami and Mohandas, (1994) investigated the efficacy of reridging sweet potato crop as a cultural practice for reducing C. formicarius over two seasons at Vellayani, Kerala. Treatment consisted of up to seven reridgings at 10 day intervals between 30 and 90 days after planting. Reridging significantly reduced the weevil damage to the tubers; the damage was lowest with 7 reridgings, which was not significantly different from 5 reridgings between 50 and 90 days after plantings.

2.7.1.4 Sanitation and destruction of crop residues

Sanitation practices or clean cultivation, especially for the control of an insect that has limited flying activity, may help protect the crop from insect infestation. These practices played an important role in pest control until the introduction and widespread use of chemical insecticides. A variety of sanitation methods have been

40 recommended for weevil control and in some locations they are even legally enforced (Karr, 1984; Lenne, 1991 and Dalip, 2000).

Destroying any crop residues left in the field after harvest is important because weevils survive in roots and stems and infest succeeding or neighbouring sweet potato planting (Franssen, 1935 and Dalip, 2000).

2.7.1.5 Clean cuttings

C. puncticollis lays eggs in the vines, especially older portions in the absence of storage roots or when the roots are inaccessible. Planting infested vines may spread the weevil infestation. Therefore, the use of weevil-free sweet potato cuttings is often advised (Lenne, 1991; Lagnaoui et al., 2000 and Dalip, 2000). Weevil-free cuttings can be produced by dipping them in a suitable insecticide solution before planting. In Taiwan, Talekar, (1983) obtained substantial reduction in weevil damage when the cuttings were dipped in carbofuran (0.05% a.i.), even though the crop was planted in close proximity to a weevil source. The same dip treatment provided complete control of the weevil when the crop was planted away from the weevil sources.

Recent findings in Taiwan showed that cuttings (25-30 cm long) taken from fresh terminal growth, even from an infested crop, were rarely infested with weevils, whereas older portions of the stem were. The probability of finding weevils inside the stems decreased in younger cuttings (AVRDC, 1990). This was further confirmed in a related study where 1 to 8 week-old weevil-free plants were exposed to the weevil in the field. The numbers of weevils in the vines increased with increase in vine age (r = 0.92**)(AVRDC, 1990).

41 Other cultural practices which may help reduce weevil damage and which are often advocated are: flooding (Talekar, 1990), control of alternative hosts (Cockerham, 1943; Ho, 1970; Sutherland, 1986b and Dalip, 2000), planting cuttings deep in the soil (Macfarlane et al., 1987; Talekar, 1987a and Lenne, 1991), use of deep-rooted cultivar (Franssen, 1935, Macfarlane et al., 1987 and Lenne, 1991), and harvest the crop as soon as it has developed roots of acceptable size (Sherman and Tamashiro, 1954; Sutherland, 1986b; Talekar, 1987a and Dalip, 2000). Planting weevil-resistant sweet potato cultivars also represents a potential cultural control method, however, a cultivar with a reliable level of resistance to weevil is not yet available (Talekar, 1987b).

Sweet potato producers are mostly small scale, resource-poor farmers and in developing countries management of sweetpotato weevil relies mainly on cultural control practices with low levels of material input (Smit et al., 2001). Most of the management measures involved against sweetpotato weevil are cultural practices, other management tactics may not be feasible (Dalip, 2000).

2.7.2 Host-plant resistance

Talekar, (1982) reviewed the history of the research for resistance of Cylas spp. weevil, field and control procedures have been developed at AVRDC for screening for resistance to Cylas formicarius are being used in many regions of the tropics. Most initial screening work was done in the field and produced inconsistent results. The failure to breed a commercial cultivar utilizing parent with known sources of resistance to either weevil species despite years of research indicates the possibility that an adequate source of

42 resistance to weevil may not exist in sweet potato germplasm. This has created serious doubts as to value of resistance in sweet potato germplasm and feasibility of continuing to search for it. Some entomologists, however, have criticized Talekar methodology as inappropriate for host-plant resistance studies (Lenne, 1991).

A strategy put forward by Raman, (1989) for international development of sweet potato varieties with resistance to weevil includes developing a database of information on screening methods, species of weevils, mechanism of resistance, important environmental factors and varieties with resistance, assembling identified resistant germplasm for systematic evaluation, and developing an appropriate standardized, international screening methodology.

Stathers et al., (2003) investigated the response of the sweetpotato weevil C. puncticollis to roots of different sweet potato cultivars as part of project to examine the factor that affect susceptibility of sweet potato cultivars to infestation in the field. Laboratory experiments were conducted at two sites (Ukiriguru and Kibaha) in Tanzania and at one site (Serere) in Uganda to determine if the harvested storage roots of sweet potato cultivars differed in their acceptability to C. puncticollis or if any root antibiosis towards C. puncticollis existed. For all experiments, cultivar effects for the total number of emerging adults were significant to at least 10% and in most cases were much more significant. At Ukiriguru and Kibaha, the results showed reasonable consistency between years, and of the four cultivars used at both sites, fewer C. puncticollis adults emerged from roots of Sinia and Budagala than from SPN/O and Mwanamonde on all occasions. A relationship between laboratory experiments and

43 crown damage by Cylas spp. in the field suggests that cultivar differences in attraction/deterrence for Cylas spp. exist. However, correlation between adult emergence in laboratory antibiosis experiment and field infestation levels were generally not strong. Although this indicates that cultivar selection by laboratory experiments is not a useful strategy for reducing field infestation, there may be potential for using such techniques to select cultivars that are resistant to attack during long-term storage.

Wang and Kays, (2002) reported that attempts to develop host- plant resistance have been only moderately successful due in part to deficiencies in parent and progeny selection methods. Host-plant phytochemicals play critical roles in insect behaviour, modulating a cross-section of key behavioural decision. Thus identification of the phytochemicals, the female weevil uses in decision making could greatly facilitate development of host-plant resistance. The volatile chemistry of the sweet potato (cultivars Jewel, Centennial, Resisto and Regal) was studied in relation to the host-finding behaviour of the female weevil in Athens, Georgia, USA. Critical biologically active volatiles were determined via isolation (Tenax trapping), fractionation (gas chromatography-thermal conductivity detector), identification (gas chromatography and gas chromatography-mass spectroscopy), and bioassay (olfactometry). Differences in volatile chemistry among sweet potato clones that may relate to differences in resistance or susceptibility to the female sweetpotato weevil were assessed. Volatile extracts from storage roots (site of oviposition) and aerial plant parts were attractive to female sweetpotato weevil, the former being substantially greater. In total 33 compounds were identified from

44 storage roots and aerial plants parts, including 23 terpenes. Three oxygenated monoterpenes (nerol, Z-citral, and methyl geranate), found in storage roots but not aerial plant parts, were identified as attractants. The sesquiterpene volatile fraction was repellent to female sweetpotato weevil with alpha-gurjunene, alpha-humulene, and xylangene active in the concentration range emanating from storage roots. The aerial plant parts emanated a higher composite concentration of sesquiterpenes than storage roots. Differences in the relative attraction among four sweetpotato cultivars to female sweet potato weevil was inversely correlated with the composite concentration of headspace sesquiterpenes. Selection of clones with decreased volatile attractants and/or increased deterrents using an analytical means of quantification may significantly facilitate developing resistance to sweetpotato weevil.

Considerable research has been done on breeding and evaluating sweet potato germplasm for resistance. The development of insect resistance is seen as a viable component of IPM programmes. Mechanism of resistance to Cylas spp. in sweet potato include antibiosis, antixenosis (non-preference) and escape (for example, long and thin storage roots set deep in the soil and scattered within growing hills). Resistance characters identified as under polygenic inheritance include fleshy root density, dry matter and starch content, root depth, vine thickness and tuber chemistry (Allard et al., 1991).

Anota and Odebiyi, (1984) found no evidence that nitrogen, starch, dry matter or moisture content played a role in tuber resistance of five resistant sweet potato cultivars tested in Nigeria, but carotene content was identified as a major factor. No oviposition preference for

45 tubers or vines was apparent. There was a lower survival rate in all life stages, smaller body weights and a longer developmental period of C. puncticollis raised on resistant cultivars.

2.7.3 Biological control

Jansson et al., (1992) reviewed the biological approaches for management of C. puncticollis and other tuber pests of sweet potatoes. It is unlikely that Cylas spp. or other weevil pests of sweet potato are appropriate targets for introductions of exotic biological control agents. There are no recorded releases of parasitoids or predators in Africa.

The subterranean habitat of C. puncticollis, whilst making it less accessible to predators and parasitoids may enhance the impact of fungal pathogens which require a protected cool, humid environment for survival and reproduction; conditions generally found under the dense foliage of sweet potato. The eggs are also well protected as they are laid within vines, or in tubers and the egg cavity is sealed with a fecal plug that preserves moisture, disguises location and protects the eggs from predatory mites. Potential candidates for use as biological insecticides include Beauveria bassiana and Metarhizium anisopliae, isolates of the former have been collected from laboratory reared adults originally collected in Kenya (Allard et al., 1991).

Jansson et al., (1991) gave an up-to-date list of predators, parasites, pathogenic fungi, bacteria and nematodes that attack Cylas species Hardly any efforts have been made to introduce these natural enemies to combat sweetpotato weevils. Lagnaoui et al., (2000) mentioned several control components that were identified and tested, the most important being Beauveria bassiana and predatory ants.

46 Palaniswami, (1989) has documented a wide range of parasites and entomopathogenic fungi on sweetpotato weevil both in India and elsewhere. Natural enemies of sweetpotato weevil which have been recorded world-wide include braconid ectoparasites on larvae. Microbracon cylasovorus and Bassus cylovorus from the Philippines, Microbracon mellitor, M. punctatus and Metaplena spectabilis from Louisiana, USA and Rhaconotus spp. and Bracon spp. from Trivandrum, India, ectopathogenic fungi on adults including Isaria sp. from Java and the East Indies, Fusarium species and Beauveria bassiana from Cuba; entomogenous nematodes on larvae and pupae including Neoplectana spp., Rhabditis sp. and Aphelenchus sp. from Louisiana, Heterorhabditis heliothidis from Cuba and predators including Drapetis exitis larvae in Trivandrum and Argentine, big- headed ant Pheidole megacephala from Cuba.

In Kenya IIBC has identified Beauveria bassiana on C. puncticollis adults in various parts of Kenya and other neighbouring countries. Collection and testing of isolates of B. bassiana is in progress. Another species of this fungus B. brongniartii, has been identified on adults of the rough sweetpotato weevil, Blosyrus spp. which is prevalent in part of Kenya. This will also be tested as a biological control fungus on Cylas spp. (Lenne, 1991). There are no reports of successful biological control of C. formicarius and only few records of parasites, predators and pathogens (Sutherland, 1986b).

2.7.4 Chemical control

When considering the use of insecticides against a pest insect, it is important to define the precise target (Matthews, 1979). C. puncticollis is a difficult target for conventional pest control measures

47 as the larvae feed in the storage roots in the ground, or inside the woody base of the stems. This means that with possible exception of systemic insecticides, which are costly and pose the risk of residual contamination of the tubers, there is no effective chemical control of the larvae, nor of the other stages found within the plant tissue (Dawes et al., 1987 and Allard et al., 1991). Early attempts of chemical control were to some extent thwarted by the lack of systemic insecticides (Sutherland, 1986b). He listed 59 different insecticides, including botanical of unknown chemical composition, that were tested against sweetpotato weevil. These chemicals, most of which were applied as post-planting foliar sprays, resulted in varying levels of control.

Pre-plant insecticide applications have been used to exterminate weevils from the planting material (vine cuttings) before planting. Insecticides with adequate water solubility are presumably transported through the vine and kill the weevils in that plant part. This type of treatment is usually more economical than post-plant insecticide applications, and if combined with proper sanitation and other measures to prevent immigration of weevils from infested plants may result in satisfactory control of the weevil (Sherman, 1951; Sherman and Mitchell, 1953; Wolcott and Perez, 1955 and Talekar, 1983).

Control of the weevil is difficult with conventional spraying, dusting, fumigation or side-dressing of insecticide granules with presently available insecticides, once weevils are present within the crown or the tuberous root. Control achieved by post-planting applications appears to be due to mortality of weevil adults searching for feeding or oviposition sites. Movement of adult weevils may

48 facilitate the contact between the toxicant and the insect, thereby resulting in insect mortality. Several researchers have obtained satisfactory control of the weevil by spraying vines or soil around stems (Wadill, 1982 and Rajamma and Padmaja, 1983).

In Ethiopia, insecticidal screening trials tested the use of foliar spray applied 3 months after planting, followed by four applications at fortnightly intervals, and also root dipping prior to planting. Deltamethrin and primiphos methyl gave good control of sweet potato pests (Allard, 1990). Cabangbang and Rodriguez, (1989) reported that sweet potatoes cv. BNAS SI and Balikbayan were grown in Paniqui, Tarlac 1983/84 with no fertilizer, or with 30, 30, 30 or 90, 60, 60 kg NPK/ha. The crops were grown using farmers' practices (no insect or disease control, weed control by hilling up one month after sowing) or various combinations of recommended insect control 10.5 kg Furadan 3G (carbofuran)/ha. at sowing and spray application of thiodan 35EC (endosulfan), recommended disease control (1.04 g Benlate WP "benomyl"/litre), and hand weeding. BNAS S1 generally, produced higher tuber yields, and responded more to increased fertilizer rates and crop protection inputs, than the local cv. Balikbayan. Yields increased with each fertilizer increment and were highest with recommended insect, disease and weed control. Insect control alone generally produced greater marketable yield increases than weed or disease control alone. The main insect pest was sweetpotato weevil (Cylas formicarius).

Workers at the Asian Vegetable Research and Development Centre (AVRDC) in Taiwan have evaluated a large number of insecticides, and carbofuran, methomyl and triazophos have proved

49 consistently effective (Sutherland, 1986a). Sherman, (1951) used vine dipping soil drenching and foliar sprays in a series of combinations. From this he concluded that vine dips alone would not give control but when used with foliar sprays both parathion and DDT were effective.

Soil application of carbofuran at planting to control C. puncticollis increased tuber yield of the susceptible cultivar TIb1 in both wet and dry seasons (IITA, 1974). Recommendations for the use of 19 insecticides for the control of Cylas spp. are provided by PANS (1978). Rajamma, (1990) tested seven insecticides for the control of Cylas formicarius on sweet potatoes in the field in Kerala, India during 1982-1983. Fenvalerate (0.03%), 0.03% permethrin and 0.003% deltamethrin were the most effective insecticides with 0.05 heptachlor, chlordane and fenthion and 0.1% carbaryl plus molasses being less effective.

Low-volume rates of application of several insecticides were found to be economic for weevil control in Papua New Guinea especially when associated with early harvest. Significantly higher undamaged yields were obtained. In sharp contrast with most other developing countries, commercial sweet potato farmers in Thailand depend on insecticides for weevil control. In the past, farmers used chlorinated hydrocarbons for controlling weevil which left toxic residues in tubers. Subsequent trials with harmful insecticides as soil treatments with carbosulphan 20% EC (at 5.55 kg a.i/ha) and carbofuran 3G (7.14 kg a.i/ha), spraying with carbosulphan (0.5 kg a.i/ha), cutting dipping treatments of carbosulphan (5% solution) and combination of these were effective in controlling weevil and did not leave toxic residues in tubers in several experiments, there was no

50 significant differences between cutting dipping alone, and dipping combined with soil and spray treatments. Effective insecticides have been identified for control of the most important pests of sweet potato in Kenya, but the economics of the crop may preclude the use of insecticides except under serious pest outbreaks as pre-planting dips (Lenne, 1991).

When synthetic insecticides were first used to control sweetpotato weevil, workers spoke of "taint-free" tubers to indicate the lack of harmful residues (Sherman, 1951; Sherman and Mitchell, 1953; Wolcott and Perez, 1955). After that chemical analysis have been performed on sweet potato tubers that have been treated with systemic and contact insecticides showing low levels for fenthion disulfoton, carbofuran, aldicarb and carbaryl (Sutherland, 1986b).

2.7.5 Integrated pest management (IPM)

IPM is a decision support system for the selection and use of best control tactics singly or harmoniously coordinated into a management strategy, based on cost/benefit analysis, that take into account the interests of and impacts on producer, society and the environment (Kogan, 1998).

The determination of the levels of tolerable damage by the pest is an essential prerequisite to the development of integrated pest control programme, so the economic threshold level concept is a very important economic concept, and injury level must be studied carefully to take the decision of pest control (Stering, 1959). The economic control is achieved when economic damage is avoided thus the economic injury level (EIL) is always below the economic threshold level (ETL) to allow for the control measures to prevent the

51 pest population from exceeding the (EIL). Rogers, (1976) claimed that, the economic threshold level (ETL) is not static, it may fluctuate with so many factors, such as local climatic condition, time of the year, the stage of plant growth and development, the type of the crop, plant variety, cropping system, market situation of the crop, the taste of the consumer and the cosmetic quality of the product.

The fact that weevils attack stems, crowns and tubers render them difficult to control (Sutherland, 1986a) and the cryptic habit of the Cylas weevils reduces the effectiveness of control by chemical insecticides and parasites. Although the fungal pathogen Beauveria bassiana has been used with apparent success in Cuba, in combination with other control methods (Alcazar et al., 1997) in the drier regions of Africa, pathogen like B. bassiana have limited potential for control (Smit, 1997). Despite years of intensive research, no varieties with significant levels of resistance are available yet (Collins et al., 1991). Sweet potato producers are mostly small-scale, resource-poor farmers (Bashaasha et al., 1995) and in developing countries management of sweetpotato weevil relies mainly on cultural control practices with low level of material inputs (Smit and Matengo, 1995). IPM is an attractive method.

IPM is widely accepted as the most appropriate control strategy for sweetpotato weevil particularly in developing countries. Talekar, (1988, 1989) has developed an IPM programme for sweetpotato weevil at AVRDC. This approach emphasizes the use of cultural and chemical control strategies including weevil-free planting material either selected naturally or by chemical dipping treatments, crop rotation, control of alternative Ipomoea hosts around fields, frequent

52 hilling up of plants to prevent oviposition, sanitation and continuous use of sex pheromone to male weevils. The programme has been tested successfully in Taiwan and is being promoted throughout Asia where C. formicarius is a serious pest. In some cases, for example in the Philippines it is being modified to include local cultural practices.

In Kenya IIBC's programme for control of sweetpotato weevil C. puncticollis includes development of biocontrol to be included with cultural controls and host-plant resistance in an IPM programme. Although low cost pesticides could also play a role in weevil control (Sutherland, 1986c), chemical control, even as cutting dips is not going to be considered in this programme.

53 3. MATERIALS AND METHODS

The field experiments were conducted for two consecutive seasons (2001/02 and 2002/03) in the Demonstration Farm of the Faculty of Agriculture, University of Khartoum-Shambat which is located at latitude 15º 40' N, longitude 32º 32' E and altitude 380 m above sea level.

The climate of the area is semi-arid and tropical with low relative humidity (Oliver, 1965); and hot summer with a mean maximum temperature of 41.9ºC in May, short rainy season (July- September) and has a wide variation in both temperature and rainfall. The solar radiation is about 400-500 cal cm-2day-1 (El Nadi and Kheir, 1969). The soil is heavy deep cracking montmorillonitic clay with 48- 54% clay, 25-29% silt and 17-25% sand. The soil reaction (pH) is moderately alkaline, with a pH about 8.4, hence it has low permeability due to high clay content and is also characterized by having a high exchange sodium percentage (E.S.P) in the sub-soil.

3.1 Survey

Preliminary survey was done in April and May 2001, in El Rahad, Gezira and El Saleit Schemes, to know the situation and to monitor the status of the sweetpotato weevil, Cylas puncticollis Boh. infestation in these areas.

3.2 Laboratory experiments (first season 2001/02)

These experiments were conducted to estimate the duration of the developing stages of sweetpotato weevil, Cylas puncticollis Boh. during the growing season of sweet potato which extended from July

54 2001 to June 2002. Temperature and relative humidity at which the experiments were carried out are given in Appendices (A and B).

3.2.1 Life history of sweetpotato weevil

3.2.1.1 Duration of development of immature stages

This laboratory work was started by establishing a laboratory insect culture. Infested sweetpotato storage roots were collected from fields in Gezira and El Saleit Schemes and from the Demonstration Farm, Faculty of Agriculture, University of Khartoum-Shambat. Some storage roots were put in glass boxes (15.5 × 15.5 × 15.5 cm covered with perforated papers tightly fitted by solo-tape) till adults emerged. Others were cut into small pieces using a sharp knife, and larvae and pupae picked from them were reared in Petri-dishes (Plate 1), in clean sweet potato slices, 3-5mm thick.

After a suitable stock of adult insects was available, adults were sexed by the shape of the distal antennal segments which is filiform in males and club-like in females. Then each pair of insects (a male + a female) was put in separate jam-jar closed with muslin-cloth (Plate 2) and a leaf of sweet potato and a sound, medium to small size storage roots were supplied every 48 hrs. Twenty four jam-jars each containing a pair of insects were used during this study. Every 48 hrs; 24 storage roots were removed from the jars and divided into two equal groups, each one was put in a separate glass box and labelled. One glass box was put under room ambient conditions and the other was placed in an incubator adjusted to 30ºC and 65% relative humidity (Buxton, 1931, Buxton and Mellanpy, 1934 and Solomon, 1957). This process started on 20th April 2002 and continued to the

55

Plate 1. Petri-dish and sweetpotato slice where immature stages reared under laboratory conditions.

Plate 2. Glass-jars used in rearing of sweetpotato weevil, Cylas puncticollis.

56 end of the month (i.e. 5 boxes under room ambient conditions and 5 boxes in the incubator).

Daily each box was examined to see if there are any eggs hatched. Three days after hatching onwards from each box two storage roots were cut into pieces with a sharp knife. Larvae which were found were transferred to Petri-dishes with perforated cover for aeration containing slices of sweet potato and put either under room temperature conditions or in the incubator at the fixed temperature 30ºC and relative humidity 65% according to the source of the storage roots they found in (room or incubator). The Petri-dishes were labelled and kept under daily observation. Records were taken for the developing stages until emergence. Sweet potato slices were changed daily (using healthy fresh storage roots, knives, camel's hair brush, forceps, needles and soap water to clean the knives) during the rearing of larval stage and as was needed during the pupal stage. From every box two or more storage roots remained undisturbed until adults emerged.

3.3 Field experiments (first season 2001/02)

3.3.1 The influence of irrigation intervals and sweetpotato clones on sweetpotato weevil infestation (autumn transplanting experiment)

A field experiment was conducted in the Demonstration Farm, Faculty of Agriculture, University of Khartoum from July 2001 to April 2002 to assess the influence of irrigation intervals and clone types on sweetpotato weevil infestation. Sweet potato clones were brought from the Agricultural Research Corporation (ARC), Shambat

57 Station. Three clones were selected Baladi yellow (BY), Baladi red (BR), and imported clone TIS2544. These clones were planted in a nursery within the Faculty premises on 13th May 2001, later transplanted to the field on 24th July 2001. The design followed was a split plot design with two factors, irrigation in the main plots with three levels of irrigation intervals 7, 14 and 21 days and clones in the subplots with three types BY, BR and TIS2544. The whole treatments were replicated four times. Four buffer zones (one meter a part) were made around each main plot to avoid water sewage. The lay out of this experiment is illustrated in Fig. 1.

Land was prepared and ridges were arranged east-west, 75 cm apart. The area of a replicate 22 X 13 m and the subplot 6 X 4 m. Twenty to 30 cm long stem cuttings were used, each stem cutting had three to four nodes, planted in the shoulder of a ridge. Cultural practices were raised as recommended. After 40 days different irrigation intervals began (viz. 7, 14 and 21 days gap). The first sample to monitor the infestation was taken rather late as no infestation started on the aerial parts of the plants (after four months). Sample size was one square meter containing the vines and the underground parts was harvested; from each sub-plot the following parameters were recorded:

1. Stem thickness up to 10 cm from soil surface using vernier scale.

2. Storage root neck length in cm (from the stem base to the tip of the storage root).

3. Storage root girth (diameter) in cm using also the vernier scale.

58 N

Buffer zone Buffer zone 6 m

main plot Subplot 4 m

Buffer zone Buffer zone

Buffer zone Buffer zone Buffer zone

Fig.1. Layout of autumn field experiment 2001/02

59 4. Percentage of infested and non-infested storage roots.

5. Weight of infested and non-infested storage roots.

6. Observation on the shape of the storage roots.

After the first 4 months sample, sampling continued monthly, until a total of four samples was taken. For reason of late infestation development, nine months after transplanting other two successive samples were taken over half year period. Data collected were statistically analyzed.

3.3.2 The influence of irrigation intervals and sweetpotato clones on sweetpotato weevil infestation (winter transplanting experiment)

The same above experiment was repeated during the period 15th November 2001 to 15th June 2002, but replicated three times and the subplot size was 4 X 4 m instead of 6 X 4 m because of the tedious harvesting of the storage roots and overlapping of the running experiments. Sampling procedure was followed as described in the first experiment (autumn experiment 2001). Stem cuttings were brought from autumn experiment.

3.3.3 Sweetpotato weevil management

The experiment was conducted close to the winter experiment to assess the effects of different control measures on storage root infestation by sweetpotato weevil. An area of 520 m2 was prepared and divided into four main blocks, each block further divided into 6 plots 4 X 4 m with 4 buffer zones in a Randomized Complete Block Design (RCBD). The stem cuttings were transplanted on 20th November 2001, they were brought from El Saleit Scheme (farmers'

60 clone). The stem cuttings confined to deltamethrin treatment were immersed in 20 ml/l Decis (deltamethrin) solution for 20 minutes before transplanting, Furadan (carbofuran) 1 kg/fed was applied around the stem cuttings immediately after transplanting. Six treatments were applied earthing (hilling) up the soil after 6 weeks from transplanting and earthing up the soil plus application of insecticides as follows :-

1. Earthing (hilling) up the soil alone.

2. Stem cuttings were dipped for 20 minutes in a container with deltamethrin aqueous solution (20 ml/l).

3. Stem cutting were dipped in 20 ml/l deltamethrin solution for 20 minutes plus earthing up the soil.

4. Applying of Furadan (1 kg/fed) around the stem cuttings.

5. Applying of Furadan (1 kg/fed) around the stem cuttings plus earthing up the soil.

6. The check (control).

Cultural practices were raised as recommended, after six months from transplanting, samples were taken and the following parameters were measured

1. Stem thickness in cm.

2. Storage root neck length in cm.

3. Storage root girth in cm.

4. Percentage of infested and non-infested storage roots.

5. Total weight of storage roots.

61 The data collected from the above experiments were subjected to analysis of variance.

3.4 Laboratory experiments (second season 2002/03)

3.4.1 Life history of sweetpotato weevil

3.4.1.1 Duration of development of immature stages

The same procedures used in the first season 2001/02 was repeated during this season, to estimate the duration of the developing stages of sweetpotato weevil, Cylas puncticollis Boh.

3.4.1.2 Preoviposition period

From the above experiment (3.4.1.1) newly emerged adults of the same age were collected immediately after emergence, the individuals were sexed by the shape of distal antennal segments; a male and a female were put in a jam-jar and a fresh leaf and a storage root were added and covered with a piece of cloth and labelled, three pairs of insects were used in this experiment. This experiment was replicated 4 times. Every day the old storage roots and the leaves were replaced by fresh ones and the storage roots labelled and kept in a glass box. Daily, the glass boxes were observed and after 12 days from removal from the jam-jars the storage roots were cut into small pieces to find out if there were any eggs hatched or immature stages and adults present. It is impracticable to detach the eggs, the first days of eggs laying were recorded and the preoviposition period calculated.

3.4.1.3 Oviposition rate

To obtain newly laid eggs, adults were collected from the insect culture and sexed, each pair of insects ( a male + a female) transferred to a jam-jar containing non-infested storage root and a fresh leaf, three

62 pairs of insects were used in this experiment, females were allowed to lay eggs on the storage roots. Every 48 hrs the storage roots and the leaves were replaced by new ones and the storage root labelled. It is impracticable to detach the eggs; after that the storage roots were cut in small pieces and the immature stages were counted. This process continued for 8 days and repeated again for another 8 days; hence the eggs laid by each female per day were calculated.

3.4.1.4 Sex ratio

From experiment (3.4.1.1) duration of development of immature stages; every emerged adult from the undisturbed storage roots was sexed by the shape of the distal antennal segments which is filiform in males and club-like in females, the number of males and females was recorded and the sex ratio was calculated. Three pairs of insect progeny were used in this experiment.

3.5 Field experiments (second season 2002/03)

3.5.1 The influence of irrigation intervals and sweetpotato clones on sweetpotato weevil infestation (autumn transplanting experiment)

This experiment was conducted in the Demonstration Farm, Faculty of Agriculture, University of Khartoum, from 27th August 2002 to 27th March 2003 to assess the influence of irrigation intervals and clone types on sweetpotato weevil infestation. Stem cuttings Baladi yellow, Baladi red and imported TIS2544 clones were transplanted from the previous winter planting on 27th August. The design followed was the same as in autumn experiment 2001/02, but

63 the experiment was replicated three times and the subplot area was 4 X 4 m.

Land preparation, cultural practices and sampling were the same as in the autumn experiment 2001/02. Parameters recorded were also the same as in autumn transplanting experiment season (2001/02) in addition to that percentage of infested stems was recorded.

The first sample was taken after 4 months from transplanting and sampling continued monthly until a total of 4 samples were taken over a half year period.

3.5.2 The influence of irrigation intervals and sweetpotato clones on sweetpotato weevil infestation (winter transplanting experiment)

The procedure followed in the previous winter experiment was repeated during the period from 15th November 2002 to 15th June 2003.

3.5.3 Sweetpotato weevil management

The procedure followed in 3.3.3 experiment was repeated during the period from 20th November 2002 to 20th May 2003, and the same parameters were considered. The data from the above experiments were statistically analyzed.

64 4. RESULTS

4.1 Survey

A survey was carried out in April and May, 2001 at Elrahad, Gezira and Elsaleit Agricultural Schemes to identify the abundance and occurrence of sweetpotato weevil Cylas puncticollis Boheman in these areas. It was found that SPW was present, and causes extensive damage to sweetpotato crop.

4.2 Laboratory experiments (first season 2001/02)

4.2.1 Life history of sweetpotato weevil, Cylas puncticollis Boheman

4.2.1.1 Duration of development of immature stages

Eggs were found laid singly in cavities in the roots and stems of sweetpotato and each cavity or hole was then covered with a white or grayish material. The eggs were pale yellow in colour, oval in shape and hardly seen without scratching the hard material that covers them. The incubation period was found to be on average 3.0 ± 0.71 and 3.0 ± 0.0 days under room conditions and under a constant temperature of 30ºC and 65% relative humidity (RH), respectively (Table 1a and Table 2a). The same eggs that hatched were followed to determine the larval period that was found to be 10.37± 1.06 and 13.83 ± 0.96 days under room conditions and the constant temperature and the RH respectively (Table 1b and Table 2b). The mean larval mortality was slightly high and approximately the same under room conditions and the constant temperature and RH; it was equal to 37.60 ± 22.62% and 36.00 ± 22.48%, respectively.

65 Table 1 ( a, b and c). Development in days of pre-imaginal stages of sweetpotato weevil, Cylas puncticollis Boh. under room conditions (April /May,2002).* a. Incubation period Cage No. No. of eggs hatched after (days) Average 2 3 4 (days) 1 0.0 0.0 11** 4 2 17** 0.0 0.0 2 3 0.0 11** 0.0 3 4 0.0 26** 0.0 3 5 0.0 17** 0.0 3 Mean ± S.E. 3.0 ± 0.71 *See Appendix A for room conditions records **Duration of incubation period based on first egg hatched-total based on larvae found. b. Larval period Cage No. of No. of larvae developed to pupae after Average Mortality No. hatched (days) larval % eggs 7 8 9 10 11 12 13 period 1 11 1.0 2.0 0.0 4.0 1.0 0.0 1.0 9.67 18.18 2 17 0.0 0.0 0.0 1.0 0.0 1.0 2.0 12.00 76.47 3 11 1.0 2.0 0.0 3.0 1.0 0.0 1.0 9.63 27.27 4 26 0.0 0.0 1.0 6.0 7.0 2.0 2.0 10.89 30.77 5 17 0.0 3.0 3.0 1.0 3.0 1.0 0.0 9.64 35.29 Mean 16.4 ± 10.37 ± 37.60 ± ± 6.15 1.06 22.62 S.E.

c. Pupal period Cage No. of No. of adults emerged after (days) Average Mortality No. pupae 2 3 4 5pupal % observed period 1 9 0.0 6.0 2.0 0.0 3.25 11.11 2 4 0.0 4.0 0.0 0.0 3.0 0.0 3 8 0.0 6.0 0.0 0.0 3.0 25.0 4 18 1.0 11.0 4.0 1.0 3.29 5.56 5 11 1.0 6.0 3.0 0.0 3.2 9.09 Mean 10 ± 5.15 3.15 ± 10.15 ± ±S.E. 0.14 9.31

66 Table 2 (a, b and c). Development in days of pre-imaginal stages of sweetpotato weevil, Cylas puncticollis Boh. under a constant temperature of 30ºC and 65% RH (April / May, 2002)*.

a. Incubation period Cage No. No. of eggs hatched after (days) Average 2 3 4 (days) 1 0.0 8.0* 0.0 3.0 2 0.0 31.0* 0.0 3.0 3 0.0 26.0* 0.0 3.0 4 0.0 32.0* 0.0 3.0 5 0.0 22.0* 0.0 3.0 Mean± S.E. 3.0 ± 0.0 *Duration of incubation period based on first egg hatched-total based on larvae found.

b. Larval period No. of No. of larvae developed to pupae after (days) Averag Mort- Cage hatche e larval ality No. d eggs 9 10 11 12 13 14 15 16 17 18 19 20 period % 1 8.0 0.0 0.0 0.0 3.0 0.0 0.0 1.0 1.0 1.0 1.0 0.0 0.0 14.57 12.50 2 31 0.0 0.0 5.0 1.0 1.0 1.0 0.0 6.0 1.0 0.0 1.0 0.0 14.13 48.39 3 26 2.0 0.0 3.0 2.0 6.0 3.0 2.0 0.0 1.0 0.0 0.0 1.0 13.10 23.08 4 32 0.0 0.0 0.0 0.0 3.0 4.0 0.0 1.0 0.0 1.0 1.0 0.0 14.80 68.75 5 22 0.0 5.0 4.0 2.0 0.0 1.0 1.0 1.0 0.0 1.0 0.0 1.0 12.56 27.27 Mean± 23.8 ± 13.83 ± 36.0 ±

S.E. 9.7 0.96 22.48

c. Pupal period Cage No. of No. of adults emerged after (days) Average Mortality No. pupae 2 3 4 5 6 pupal % observed period 1 7.0 0.0 1.0 4.0 1.0 0.0 4.00 14.29 2 16 0.0 7.0 6.0 1.0 0.0 3.57 12.50 3 20 1.0 10.0 9.0 0.0 0.0 3.40 0.0 4 10 0.0 5.0 4.0 1.0 0.0 3.60 0.0 5 17 0.0 7.0 6.0 0.0 1.0 3.64 17.65 Mean 14 ± 5.34 3.64 ± 8.89 ± 0.22 8.32 ± S.E.

67 The larva is leg less, white in colour. It tunnels deep into the storage roots or stems of sweetpotato, these tunnels were usually filled with larval fecal material as it feeds and grows. Damage by sweetpotato weevils, results mainly from larval feeding on the tissues of roots and stems. The duration of pupal stage of sweetpotato weevil, Cylas puncticollis took on average 3.15 ± 0.14 and 3.64 ± 0.22 days under room conditions and the constant temperature and RH, respectively (Table 1c and Table 2c). The pupal mortality was 10.15 ± 9.31% and 8.89 ± 8.32% under the room conditions and the constant temperature and RH, respectively. The mature larva creates a small pupal chamber in the storage root in which pupa stays during pupal period. Initially the pupa is white in colour, but with time the eyes and the legs (under formation) become darker in colour. The total life cycle was found to be on average 16.52 ± 1.03 days under room conditions and 20.47 ± 1.08 under the constant temperature and the RH (Table1a,b and c and Table 2a,b and c).

Tables (3) and (4) show the duration in days of the total development of sweeopotato weevil, Cylas puncticollis from egg laying to adult emergence when insects were reared without disturbance under room conditions and a constant temperature of 30ºC and 65% RH, it was 20.03 ±1.10 and 21.87 ± 0.48 days on average, respectively.

68 Table 3. Duration of the development of sweetpotato weevil, Cylas puncticollis Boh. in days from egg laying to adult emergence under room conditions (undisturbed) in (April / May, 2002).

Date of Adults emerged after (days) Total egg development- laying 15 16 17 18 19 20 21 22 23 24 25 28* al period (days) 21.4.2002 0.0 0.0 1.0 1.0 3.0 3.0 2.0 1.0 1.0 0.0 0.0 0.0 19.92

23.4 2.0 1.0 2.0 0.0 5.0 12.0 4.0 4.0 6.0 2.0 0.0 0.0 20.34

25.4 0.0 0.0 0.0 6.0 6.0 4.0 2.0 4.0 2.0 1.0 0.0 0.0 20.08

27.4 0.0 0.0 0.0 1.0 3.0 7.0 7.0 6.0 1.0 1.0 1.0 2.0 21.45

30.4.2002 0.0 0.0 16.0 7.0 5.0 5.0 2.0 1.0 1.0 0.0 0.0 0.0 18.38

Mean 20.03 ±1.10 ± S.E. * No emergence was observed on the 26th and 27th day.

53

Table 4. Duration of the development of sweetpotato weevil, Cylas puncticollis Boh. in days from egg laying to adult emergence under a constant temperature of 30° C and 65% relative humidity (undisturbed) in (April / May, 2002).

Date of Adults emerged after (days) Total egg developmental laying 18 19 20 21 22 23 24 25 26 27 28 29 30 period (days)

21.4.2002 0.0 2.0 5.0 21.0 3.0 7.0 0.0 1.0 0.0 0.0 0.0 0.0 0.0 21.31

23.4 3.0 8.0 10.0 5.0 4.0 1.0 0.0 0.0 3.0 1.0 1.0 1.0 1.0 21.42

25.4 0.0 2.0 3.0 8.0 5.0 1.0 3.0 3.0 0.0 2.0 0.0 0.0 0.0 22.22

27.4 0.0 5.0 4.0 8.0 2.0 4.0 0.0 3.0 1.0 1.0 1.0 1.0 1.0 22.39

30.4.2002 1.0 2.0 9.0 5.0 2.0 1.0 4.0 0.0 1.0 4.0 0.0 0.0 0.0 22.00

Mean ± 21.87± 0.48

S.E.

54

55 A highly significantly difference in the total developmental period of sweetpotato weevil, Cylas puncticollis was found between the disturbed and the undisturbed rearing under room conditions and also a significant difference between disturbed and undisturbed rearing of sweetpotato weevil at 30°C and 65% RH was noted (Table 5). A significant difference on the rearing of SPW under room conditions and at the constant temperature and RH was recorded.

4.3 Field experiments (first season 2001/02)

4.3.1 The influence of irrigation intervals and sweetpotato clones on sweetpotato weevil, Cylas puncticollis infestation (autumn transplanting experiment)

Sweetpotato harvesting was carried out six times and counts for the mentioned parameters (details of counts described in materials and methods section) were started on 24th November, 2001. The 2nd, 3rd, 4th harvesting counts were done at about monthly intervals; the 5th and the 6th counts followed on the 20th and 29th April, respectively. In all the counts, besides the effect of mentioned parameters on the percentage of the damaged storage roots (insect build up), some agronomical characters on the crop in relation to watering were considered as they may affect infestation. Hence, measurements of stem thickness, storage root neck length, storage root girth and storage root weight were taken during different harvesting times.

Table (6a) shows no significant differences among irrigation intervals 7, 14 and 21 days and sweetpotato clones TIS2544, Baladi yellow (BY) and Baladi red (BR) upon stem thickness of sweetpotato. The same observation was recorded for Table (6b) but, a highly significant difference was obtained for mutual effect between the

55 Table 5. Duration of the total development period of Cylas puncticollis Boh. in days under room conditions and a constant temperature of 30°C and 65% RH (disturbed and undisturbed) in (April / May, 2002).

Rearing Means of the total developmental period (days) Average of the conditions Rep. 1 Rep. 2 Rep. 3 Rep.4 total Rep.5 developmental period (days) Room temp. 16.92 17.00 15.63 17.18 15.84 16.51d (disturbed)

Room temp. 19.92 20.34 20.08 21.45 18.38 20.03bc (undisturbed)

Constant 21.57 20.70 19.50 21.20 19.20 20.47bc 30°C & 65% RH (disturbed)

Constant 21.31 21.42 22.22 22.39 22.00 21.87a 30°C & 65% RH (undisturbed) *Means followed by similar letters are not significantly different at 0.05 level of probability.

LSD0.05 = 1.1869 CV = 4.49%

56 Table 6 (a to e). Effect of irrigation intervals, sweet potato clones and their interaction on stem thickness (cm) of sweet potato grown during the period (July 2001/April 2002). a. First count 4 months after transplanting. b. Second count 5 months after transplanting. Clones Irrigation intervals (days) Mean* Clones Irrigation intervals (days) Mean* 7 14 21 7 14 21 a 0.967c 1.263bc 1.334٭TIS 1.831 1.1112 0.950 1.065 ٭TIS 1.318 BY 0.979 1.377 1.263 1.2062 BY 1.112bc 1.163bc 1.555ab 1.277 BR 1.292 1.229 1.454 1.3251 BR 1.306bc 1.236bc 1.467ab 1.336 Mean** 1.1966 1.2237 1.2237 Mean** 1.416 1.122 1.428 S.E.± for irrigation intervals = 0.0699 S.E.± for irrigation intervals = 0.1042 S.E.± for clones = 0.0847 S.E.± for clones = 0.0788 S.E.± for irrigation intervals X clones (interaction) = 0.1467 S.E.± for irrigation intervals X clones (interaction) = 0.1364 c. Third count 6 months after transplanting. d. Fourth count 7 months after transplanting. Clones Irrigation intervals (days) Mean* Clones Irrigation intervals (days) Mean* 7 14 21 7 14 21 1.696 1.690 1.765 ٭TIS 1.633 1.496 1.496 1.502 ٭TIS 1.490 BY 1.503 1.546 1.725 1.575 BY 1.654 1.710 1.943 1.769 BR 1.942 1.742 1.698 1.794 BR 1.754 1.831 2.460 2.682 Mean** 1.645 1.597 1.640 Mean** 1.680 1.769 2.031 S.E.± for irrigation intervals = 0.0922 S.E.± for irrigation intervals = 0.1857 S.E.± for clones = 0.1312 S.E.± for clones = 0.0731 S.E.± for irrigation intervals X clones (interaction) = 0.2272 S.E.± for irrigation intervals X clones (interaction) = 0.1265

57 Table 6. (Continued) e. Fifth count 9 months after transplanting. Clones Irrigation intervals (days) Mean* 7 14 21 1.681 1.670 1.693 ٭TIS 1.681 BY 1.675 1.724 1.765 1.721 BR 1.606 1.475 1.783 1.621

Mean** 1.654 1.630 1.739 S.E.± for irrigation intervals = 0.1102 S.E.± for clones = 0.0655 S.E.± for irrigation intervals X clones (interaction) = 0.1134

A foot note for Table 6 (a to e) -TIS=TIS2544, BY= Baladi yellow, BR=Baladi red (figures in this square are means of interaction effect (irrigation intervals X clones=٭ ,Mean*= of clones, Mean**= of irrigation intervals- - Means followed by similar letters are not significantly different at 0.05 level of probability according to Duncan’s multiple range test (DMRT).

58 irrigation intervals and the clones, TIS2544-7 days irrigation interval (DII) gave the thickest stem 1.83 cm. Table (6c, d and e) shows the same trend as expressed in Table (6a). Generally 21 DII and BR clone show the thickest stems of sweetpotato during all the harvesting times. No clear relationship between stem thickness and percentage of the infested storage roots was observed; a weak positive correlation was found (r = 0.34) among the irrigation intervals and between the clones (r = 0.02) when the data was pooled.

Mean storage root neck length varied considerably among treatments and over harvest times (Table 7a to e). Significant differences were obtained among irrigation intervals 4 months after transplanting (MAT); 21 DII showed the longest storage root neck 9.73 cm, and 7 DII recorded the shortest one 6.03 cm (Table 7a). Table (7b, c and e) shows a highly significant difference between sweetpotato clones, BR clone showed the longest storage root neck 11.90, 16.30 and 13.09 cm for the 5, 6 and 9 MAT counts respectively, whereas BY and TIS2544 showed no statistical difference between them. Table (7d) shows no significnt difference among all treatment means. The interaction effect was observed 4 MAT, BY-21 DII showed the longest storage root neck 13.94 cm while, TIS2544-7 DII and BR-21 DII showed the shortest storage root necks 4.53 and 2.70 cm, respectively. Generally speaking we can say that, irrigation intervals had no effect on storage root neck length except at the beginning of the harvesting time (4 MAT). However, sweetpotato clones had great effect upon storage root neck length, BR gave the longest storage root neck followed by BY and then TIS2544.

59 Table 7 (a to e). Effect of irrigation intervals, sweet potato clones and their interaction on storage root neck length (cm) of sweet potato grown during the period (July, 2001/April, 2002). a. First count 4 months after transplanting. b. Second count 5 months after transplanting. Clone Irrigation intervals (days) Mean* Clone Irrigation intervals (days) Mean* 7 14 21 7 14 21 7.713b 8.420 8.174 ٭c 7.513bc 12.552ab 8.199 TIS 6.546٭TIS 4.532 BY 7.478bc 9.265bc 13.938a 10.227 BY 8.386 7.316 7.532 7.745b BR 6.071bc 8.150bc 2.700c 5.640 BR 13.811 13.225 8.675 11.904a Mean** 6.027b 8.309ab 9.730a Mean** 9.581 9.572 8.209 S.E.± for irrigation intervals = 0.7805 S.E. for irrigation intervals = 0.8757 S.E.± for clones =1.1792 S.E. for clones = 0.8009 S.E.± for irrigation intervals X clones (interaction) = 2.0424 S.E. for irrigation intervals X clones (interaction) =1.3871 c. Third count 6 months after transplanting. d. Forth count 7 months after transplanting. Clone Irrigation intervals (days) Mean* Clone Irrigation intervals (days) Mean* 7 14 21 7 14 21 9.486 6.860 10.545 ٭10.535b TIS 11.050 13.300 10.825 ٭TIS 7.480 BY 11.925 10.500 18.144 10.556b BY 9.365 8.800 10.344 9.503 BR 14.725 18.144 16.038 16.302a BR 14.306 10.925 9.875 11.702 Mean** 11.377 13.156 15.827 Mean** 11.574 10.090 9.026 S.E.± for irrigation intervals =1.3018 S.E. for irrigation intervals = 0.6458 S.E ± clones =1.0738 S.E. for clones = 0.7049 S.E.± for irrigation intervals X clones (interaction) =1.8598 S.E. for irrigation intervals X clones (interaction) =1.2210

60 Table 7. (Continued) e. Fifth count 9 months after transplanting. Clone Irrigation intervals (days) Mean* 7 14 21 9.180b 9.116 10.698 ٭TIS 7.725 BY 8.979 9.672 9.175 9.275b BR 13.825 12.500 12.929 13.085a Mean** 10.176 10.957 10.407

S.E.± for irrigation intervals = 0.9290 S.E. ± for clones = 0.4369 S.E.± for irrigation intervals X clones (interaction) = 0.7568 A foot note for Table 7 (a to e) -TIS =TIS2544, BY = Baladi yellow, BR = Baladi red (figures in this square are means of interaction effect (irrigation intervals X clones =٭ ,Mean*= of clones, Mean**= of irrigation intervals- - Means followed by similar letters are not significantly different at 0.05 level of probability according to Duncan’s multiple range test (DMRT).

61 There was a weak negative correlation between storage root neck length and percentage of infested storage roots among clones r = -0.10 while a weak positive correlation between irrigation intervals was recorded r = 0.13 when the data was pooled.

There were highly significant and significant variations on sweetpotato storage root girth 4 and 5 MAT among irrigation intervals, respectively. Fourteen days irrigation interval scored the largest storage root girth 4 and 5 MAT (3.16 and 4.14 cm, respectively) (Table 8a and b). Although, there was no significant difference among clones, it was noted that TIS2544 clone possessed the bigger storage root girth than BR and BY.

A moderate positive correlation (r = 0.44) among irrigation intervals could be noticed between storage root girth and percentage of infested storage roots when data was pooled.

Data presented in Table (9a to e) shows the effect of irrigation intervals, sweetpotato clones and their interaction on the infested storage root weight of sweetpotato. No significant differences were observed 4 MAT among irrigation interval treatments, but highly significant differences existed between the clones and their interaction with the irrigation intervals. TIS2544 showed the greater infested storage root weight (0.41 ton/ha) whereas, no statistical difference was recorded between BY (0.13 ton/ha) and BR (0.01 ton/ha). TIS2544-14 DII gave the greatest infested storage root weight 0.85 ton/ha, while BR-7 DII and BR-21 DII reported no infestation. Highly significant difference occurred between irrigation intervals 5 MAT, 14 DII recorded the maximum infested storage root weight 1.70 ton/ha and 21 DII recorded the minimum one 0.57 ton/ha. Highly significant

62 Table 8 (a to e). Effect of irrigation intervals, sweet potato clones and their interaction on storage root girth (cm) of sweet potato grown during the period (July, 2001 /April, 2002). a. First count 4 months after transplanting. b. Second count 5 months after transplanting. Clones Irrigation intervals (days) Mean* Clones Irrigation intervals (days) Mean* 7 14 21 7 14 21 4.020 3.835 4.455 ٭TIS 3.770 3.210 2.836 4.354 ٭TIS 2.439 BY 1.754 1.338 1.430 1.507 BY 2.695 4.368 2.850 3.304 BR 2.439 3.788 0.733 2.320 BR 4.115 3.610 2.373 3.366 Mean** 2.211a 3.160a 1.666b Mean** 3.527b 4.144a 3.019b S.E.± for irrigation intervals =0.1377 S.E.± for irrigation intervals =0.2093 S.E.± for clones =0.4539 S.E.± for clones =0.2823 S.E.± for irrigation intervals X clones (interaction) =0.7863 S.E.± for irrigation intervals X clones (interaction) =0.4889 c. Third count 6 months after transplanting. d. Fourth count 7 months after transplanting. Clones Irrigation intervals (days) Mean* Clones Irrigation intervals (days) Mean* 7 14 21 7 14 21 5.381 5.185 5.863 ٭TIS 5.095 4.992 4.680 5.790 ٭TIS 4.505 BY 4.275 4.435 4.330 4.852 BY 5.055 4.880 6.244 5.393 BR 3.720 4.330 4.143 4.064 BR 5.530 4.930 6.005 5.488 Mean** 4.167 4.852 4.460 Mean** 5.277 5.224 5.811 S.E.± for irrigation intervals = 0.2383 S.E.± for irrigation intervals = 0.5174 S.E.± for clones = 0.2863 S.E.± for clones = 0.3221 S.E.± for irrigation intervals X clones (interaction) = 0.4960 S.E.± for irrigation intervals X clones (interaction) = 0.5579

63 Table 8. (Continued) (e) Fifth count 9 months after transplanting. Clone Irrigation intervals (days) Mean* 7 14 21 5.205 5.095 5.770 ٭TIS 4.750 BY 4.995 4.705 4.860 4.853 BR 4.585 4.535 4.660 4.872 Mean** 4.777 5.005 4.872 S.E. ± for irrigation intervals = 0.3164 S.E. ± for clones = 0.1994 S.E. ± irrigation intervals X clones (interaction) = 0.3454

A foot note for Table 8 (a to e) -TIS =TIS2544, BY = Baladi yellow, BR = Baladi red (figures in this square are means of interaction effect (irrigation intervals X clones =٭ ,Mean*= of clones, Mean**= of irrigation intervals- - Means followed by similar letters are not significantly different at 0.05 level of probability according to Duncan’s multiple range test (DMRT).

64 Table 9 (a to f). Effect of irrigation intervals, sweet potato clones and their interaction on infested storage root weight (ton/ha) by the weevil Cylas puncticollis on sweetpotato grown during the period ( July, 2001/April, 2002). a. First count 4 months after transplanting. b. Second count 5 months after transplanting. Clones Irrigation intervals (days) Mean* Clones Irrigation intervals (days) Mean* 7 14 21 7 14 21 bc 2.9500a 0.2250c 2.1813a٭b 0.8500a 0.0501bc 0.4059a TIS 1.1875٭TIS 0.3175 BY 0.2375bc 0.0751cb 0.0751bc 0.1292b BY 0.6501bc 2.1625ab 0.6125bc 1.1417a BR 0.0001c 0.0376c 0.0001c 0.0126b BR 0.7501bc 0.0001c 0.8752bc 0.5418b Mean** 0.1850 0.3209 0.0417 Mean** 0.8625ab 1.7042a 0.5709b S.E.± for irrigation intervals = 0.0699 S.E.± for irrigation intervals = 0.3507 S.E.± for clones = 0.0471 S.E.± for clones = 0.2742 S.E.± for irrigation intervals X clones (interaction) = 0.0817 S.E.± for irrigation intervals X clones (interaction) = 0.4750 c. Third count 6 months after transplanting. d. Fourth count 7 months after transplanting. Clones Irrigation intervals (days) Mean* Clones Irrigation intervals (days) Mean* 7 14 21 7 14 21 6.1875 3.2500 8.2500 ٭2.9250a 4.7250a TIS 7.0625 7.8750 ٭TIS 3.3750 BY 1.8750 2.0001 1.2751b 1.7167b BY 3.4376 5.6250 2.8250 2.9719 BR 1.0000 0.3751 1.8751b 1.0834b BR 6.1250 2.7501 2.9375 2.9532 Mean** 2.0834 3.4167 2.0250 Mean** 5.5417 5.5417 3.0042 S.E.± for irrigation intervals = 0.6619 S.E.± for irrigation intervals =1.5808 S.E.± for clones = 0.6481 S.E.± for clones = 1.4284 S.E.± for irrigation intervals X clones (interaction) =1.1226 S.E.± for irrigation intervals X clones (interaction) =2.4741

65 Table 9. (Continued) (e) Fifth count 9 months after transplanting. f. Sixth count 9 months after transplanting. Clone Irrigation intervals (days) Mean* Clone Irrigation intervals (days) Mean* 7 14 21 7 14 21 d 47.250b 46.812b 40.479b٭abc 33.25abc 24.125abc 27.625 TIS 27.375٭TIS 24.875 BY 38.250ab 25.875abc 41.250a 35.125 BR 62.875a 44.375bc 48.750b 52.000a BR 38.750ab 16.375c 21.500bc 25.542 BR 32.000cd 43.625bc 39.750bc 38.458b Mean** 33.958 25.167 28.958 Mean** 40.750 45.083 45.104 S.E.± for irrigation intervals = 4.0242 S.E. for irrigation intervals = 24.7597 S.E.± for clones = 3.2866 S.E. for clones = 22.1815 S.E.± for irrigation intervals X clones (interaction) = 5.6926 S.E. for irrigation intervals X clones (interaction) = 38.4195 A foot note for Table 9 (a to e)

-TIS =TIS2544, BY = Baladi yellow, BR = Baladi red (figures in this square are means of interaction effect (irrigation intervals X clones =٭ ,Mean*= of clones, Mean**= of irrigation intervals- - Means followed by similar letters are not significantly different at 0.05 level of probability according to Duncan’s multiple range test (DMRT)

66 difference was obtained among the clones, TIS2544 scored the maximum infested storage root weight 2.18 ton/ha, whereas BR registered the minimum infested storage root weight 0.54 ton/ha. A significant interaction effect was also observed, TIS2544-14 DII showed the greater infested storage root weight 2.95 ton/ha while BR- 14 DII was not infested. There were no statistical differences regarding infested storage root weight among irrigation intervals and their interaction 6 MAT. But a highly significant difference was reported among clones, TIS2544 recorded the maximum infested storage root weight 4.73 ton/ha (Table 9c). Seven months after transplanting no significant difference was observed between the treatment means (Table 9d). The results in Table (9e) show the interaction effect between the irrigation intervals and the clones BY- 21 DII manifested the maximum infested storage root weight 41.25 ton/ha, whereas BR-14 DII recorded the minimum infested storage root weight 16.38 ton/ha. A highly significant difference occurred between the clones 9 MAT (Table 9f), BY gave the highest infested storage root weight 52.00 ton/ha, no significant difference reported between TIS2544 and BR. The mutual effect between irrigation intervals and clones showed a highly significant difference, BY-7 DII gave the maximum infested storage root weight 62.88 ton/ha and TIS2544-7 DII registered the minimum one 27.38 ton/ha. Generally up to 7 MAT, 14 DII scores the greater infested storage root weight followed by 7 DII and 21 DII (Fig. 2); TIS2544 gave the highest infested storage root weight followed by BY and BR. The infested storage root weight 9 MAT was too big among the treatments and economically unprofitable (Fig. 3).

67 50 7 day irrigation intervals 45 14 day irrigation interval 40 21 day irrigation interval 35 30 25 20 15 10 5

Infested torage root weight (ton/ha) 0 4 MAT5 MAT6 MAT7 MAT9 MAT9 MAT Time of harvest (months after transplanting)

Fig. 2. Effect of irrigation intervals and time of harvest on infested storage root weight by the weeil Cylas puncticollis on sweetpotato (autumn 2001/2002).

60 TIS2544 BY BR

50

40

30

20

Storage root weight (ton/ha) 10

0 4 MAT5 MAT6 MAT7 MAT9 MAT9 MAT

Time of harvest (months after transplanting)

Fig. 3. Effect of sweetpotato clones and time of harvest on infested storage root weight by the weevil Cylas puncticollis on sweetpotato (autumn 2001/2002).

68 Positive correlations were noticed between the infested storage root weight and percentage of the infested storage roots among the irrigation intervals 7, 14 and 21 DII (r = 0.41, 0.74 and 0.89 respectively). Also, positive correlations were recorded among the clones TIS2544, BY and BR (r = 0.42, 0.32 and 0.58, respectively).

Results presented in Table (10a to f) show the effects of irrigation intervals, sweetpotato clones and their interaction on the total weight of sweetpotato storage roots. Four months after transplanting highly significant differences among clones were obtained, TIS2544 produced the maximum storage root weight 4.89 ton/ha followed by BY 1.04 ton/ha and BR 0.94 ton/ha. Highly significant differences among both the clones and their interaction with irrigation intervals were shown in Table (10b), TIS2544 gave the largest yield 15.23 ton/ha followed by BY 8.36 ton/ha and BR 7.28 ton/ha. TIS2544-7 DII produced the higher yield 22.94 ton/ha, while BR-21 DII scored the smallest yield 3.76 ton/ha. As shown in Table (10c) a significant difference between clones was noticed, TIS2544 and BY produced the maximum yield 29.85 and 29.72 ton/ha respectively, BR gave the minimum yield 15.21 ton/ha. No significant difference was obtained among the treatments 7 and 9 MAT (Table 10d and e). The interaction effect showed a significant difference latter in the season 9 MAT (Table 10f), TIS2544-14 DII and BY-7 DII produced the maximum yield 70.75 and 68.25 ton/ha, respectively whereas TIS2544-7 DII gave the minimum yield 45.25 ton/ha.

69 Table 10 (a to f). Effect of irrigation intervals, sweet potato clones and their interaction on total storage root weight (ton/ha) of sweet potato grown during the period (July, 2001/April, 2002). a. First count 4 months after transplanting. b. Second count 5 months after transplanting. Clones Irrigation intervals (days) Mean* Clones Irrigation intervals (days) Mean* 7 14 21 7 14 21 a 15.075b 7.675cd 15.229a٭4.885a TIS 22.938 3.525 4.850 ٭TIS 6.280 BY 1.375 0.888 0.863 1.042b BY 8.075cd 9.325c 7.666cd 8.356b BR 1.750 0.813 0.250 0.938b BR 11.270bc 6.800cd 3.763d 7.279b Mean** 3.135 2.183 1.546 Mean** 17.763 10.400 6.368 S.E.± for irrigation intervals = 0.7946 S.E.± for irrigation intervals = 1.8152 S.E.± for clones = 0.4912 S.E.± for clones = 0.8038 S.E.± for irrigation intervals X clones (interaction) = 0.8519 S.E.± for irrigation intervals X clones (interaction) =1.3922 c. Third count 6 months after transplanting. d. Fourth count 7 months after transplanting. Clones Irrigation intervals (days) Mean* Clones Irrigation intervals (days) Mean* 7 14 21 7 14 21 65.229 40.875 74.000 ٭29.850a TIS 80.813 20.675 29.375 ٭TIS2544 39.500 BY 34.000 33.875 21.275 29.715a BY 62.375 44.500 46.500 51.125 BR 19.250 16.750 9.625 15.208b BR 73.250 38.750 24.125 45.375 Mean** 30.917 26.667 17.192 Mean** 72.146 52.417 37.167 S.E.± for irrigation intervals = 5.500 S.E.± for irrigation intervals =7.9554 S.E.± for clones = 3.9364 S.E.± for clones = 6.2726 S.E.± for irrigation intervals X clones (interaction) = 6.8181 S.E.± for irrigation intervals X clones (interaction) = 10.8645

70 Table 10. (Continued) e. Fifth count 9 months after transplanting. f. Sixth count 9 months after transplanting. Clones Irrigation intervals (days) Mean* Clones Irrigation intervals (days) Mean* 7 14 21 7 14 21 b 70.750a 55.500ab 57.167٭TIS 45.250 27.625 24.125 33.250 ٭TIS 25.500 BY 38.250 25.875 41.250 35.125 BY 68.250a 52.625ab 48.125ab 56.330 BR 38.750 16.375 21.500 25.541 BR 56.500ab 58.875ab 49.875ab 55.083 Mean** 34.167 25.167 28.958 Mean** 56.667 60.750 38.375 S.E.± for irrigation intervals = 5.8714 S.E.± for irrigation intervals = 4.4030 S.E.± for clones = 2.8347 S.E.± for clones = 3.4694 S.E.± for irrigation intervals X clones (interaction) = 4.9098 S.E.± for irrigation intervals X clones (interaction) = 6.1823

A foot note for Table 10 (a to e) -TIS =TIS2544, BY = Baladi yellow, BR = Baladi red figures in this square are means of interaction effect (irrigation intervals X =٭ ,Mean*= of clones, Mean**= of irrigation intervals- clones) - Means followed by similar letters are not significantly different at 0.05 level of probability according to Duncan’s multiple range test (DMRT).

71 Generally we can conclude that 7 DII gives the highest yield followed by 14 DII and 21 DII among irrigation interval treatments; TIS2544 clone produces the greatest yield, while BR produces the least one among the clones. A positive correlation between the total storage root weight and percentage of infested storage roots existed between the irrigation intervals (r = 0.23) and the clones (r = 0.31). Figures (4 and 5) show the relationship between the infested storage root weight and the total storage root weight among irrigation intervals and clones, respectively.

There was no significant difference in the percentage of infested storage roots of sweetpotato caused by sweetpotato weevil, Cylas puncticollis among irrigation interval treatments (Table 11a to f and Fig. 6). There was, however, a tendency for the percentage of the infestation to increase 9 MAT among irrigation intervals. A significant difference on percentage of the infested storage roots between clones was found 4 MAT, TIS2544 showed the highest percentage of infestation 12.42% and BR scored the lowest percentage of infestation 3.08% (Table 11a). Latter in the season 9 MAT a highly significant difference on the percentage of infested storage roots was noted among clones, BY clone reported the highest percentage of infestation 93.24% followed by TIS2544 76.09% and BR showed the least percentage of infestation 63.25%. Usually sweetpotato weevil, Cylas puncticollis infests TIS2544 clone more severely than BY and BR up to 7 MAT. But, thereafter BY was severely infected (Fig. 7). It is worth mentioning that, data in Table (11) was transformed. A square root or arcsin transformation was used where possible.

72 80 Infested storage root w eight (ton/ha) Total storage root w eight (ton/ha) 70 60 50 40 30 20 10 Storage root weight(ton/ha) 0 ) ) ) ) ) ) ) ) ) ) T T T) T T T A A M MA MA MA M MAT 6 MAT MAT MAT 6 7 ( 7 9 (7 9 9 I ( II I ( I I ( I D I II ( I I D DII ( DII (9 MAT) D D D D 7 DII (47 DIIMAT) (57 7 7 7 DII (9 MAT) 1 DII (6 MA 14 DII14 (4 DIIMAT) 14(5 MAT) 14 14 14 DII21 (9 DIIMAT21 (4 DIIMAT)2 (5 MAT)21 21 21 DII ( Irrigation intervals

Fig. 4. Relationship between infested storage root weight and total storage root weight of sweetpotato among irrigation intervals during different harvest times (autumn 2001/2002).

70 Infested storage root w eight (ton/ha) Total storage root w eight (ton/ha) 60

50

40

30

20

Storage root weight (ton/ha) 10

0 ) ) ) ) ) ) ) ) T) T) T T T T A A A A A A MAT MAT) M MAT) 9 MAT (5 MAT (7 MAT 5 (7 9 (4 M (6 M (9 M 4 (4 M4 4 (6 M4 4 ( ( ( 4 4 4 Y R 54 54 BY (4 MAT)BY BY (6 MAT)BY B BY (9 B BR (5 MAT)BR BR (7 MAT)BR BR (9 MAT) 2 IS IS2 IS25 TIS25 T TIS25 T TIS2544T (9 MAT) Sweetpotato clones

Fig. 5. Relationship between infested storage root weight and total storage root weight of sweetpotato clones during different harvest times (autumn 2001/2002).

73 Table 11 (a to f). Effect of irrigation intervals, sweet potato clones and their interaction on percentage of infested storage roots by the weevil Cylas puncticollis on sweet potato grown in the period (July, 2001/April, 2002). a. First count 4 months after transplanting. b. Second count 5 months after transplanting. Clones Irrigation intervals (days) Mean* Clones Irrigation intervals (days) Mean* 7 14 21 7 14 21 10.59 5.31 19.12 ٭TIS 7.34 12.42 4.93 25.10 ٭TIS 7.23 (2.78) (5.05) (2.33) (3.39)a (2.80) (4.43) (2.41) (3.21) BY 8.26 1.93 2.70 4.30 BY 5.60 3.26 13.56 7.47 (2.96) (1.56) (1.79) (2.11)ab (2.47) (1.94) (3.75) (2.72) BR 0.0 9.23 0.0 3.08 BR 5.40 0.0 1.11 2.17 (0.71) (3.11) (0.71) (1.51)b (2.43) (0.71) (1.27) (1.47) Mean** 5.16(2.15) 12.09(3.24) 2.54(1.61) Mean** 6.11(2.57) 7.46(2.36) 6.67(2.48) S.E.± for irrigation intervals = 0.6936 S.E.± for irrigation intervals = 0.6829 S.E.± for clones = 0.4737 S.E.± for clones = 0.4878 S.E.± for irrigation intervals X clones (interaction) = 0.8204 S.E.± for irrigation intervals X clones (interaction) = 0.8450 c. Third count 6 months after transplanting. d. Fourth count 7 months after transplanting. Clones Irrigation intervals (days) Mean* Clones Irrigation intervals (days) Mean* 7 14 21 7 14 21 7.53 4.38 7.01 ٭TIS 11.20 12.33 8.56 17.22 ٭TIS 11.20 (3.42) (4.20) (3.01) (3.54) (3.42) (2.74) (2.21) (2.79) BY 7.12 4.34 3.70 5.05 BY 3.74 7.40 4.70 5.28 (2.76) (2.19) (2.05) (2.33) (2.06) (2.81) (2.28) (2.39) BR 10.86 0.0 8.32 6.49 BR 5.95 1.54 15.5 7.66 (3.37) (0.71) (2.87) (2.32) (2.54) (1.43) (4.00) (2.66)

74 Mean** 9.73(3.18) 7.19(2.37) 6.96(2.64) Mean** 6.96(2.67) 5.32(2.33) 8.19(2.83) S.E.± for irrigation intervals = 0.5894 S.E.± for irrigation intervals = 0.3498 S.E.± for clones = 0.4295 S.E.± for clones = 0.3722 S.E.± for irrigation intervals X clones (interaction) = 0.7439 S.E.± for irrigation intervals X clones (interaction) = 0.6446 Table 11. (Continued). e. Fifth count 9 months after transplanting. f. Sixth count 9 months after transplanting. Clones Irrigation intervals (days) Mean* Clones Irrigation intervals (days) Mean* 7 14 21 7 14 21 97.47 100.0 100.0 ٭TIS 92.43 76.09 85.69 83.00 ٭TIS 59.58 (54.53) (72.02) (70.85) (65.80)b (9.64) (10.0) (10.0) (9.87) BY 87.50 92.98 99.24 93.24 BY 100.0 100.0 100.0 100.0 (75.00) (80.42) (89.22) (81.55)a (10.0) (10.0) (10.0) (10.0) BR 47.09 81.44 61.22 63.25 BR 95.30 100.0 100.0 98.43 (43.32) (67.69) (51.64) (54.22)c (9.70) (10.0) (10.0) (9.92) Mean** 64.72 85.81 82.05 Mean** 95.91 100.0 100.0 (57.61) (73.38) (70.57) (9.79) (10.0) (10.0) S.E.± for irrigation intervals = 5.7080 S.E.± for irrigation intervals = 0.1742 S.E.± for clones = 3.4152 S.E.± for clones = 0.0767 S.E.± for irrigation intervals X clones (interaction) = 5.9152 S.E.± for irrigation intervals X clones (interaction) = 0.1329

A foot note for Table 11 (a to e) -TIS =TIS2544, BY = Baladi yellow, BR = Baladi red

75 ;(figures in this square are means of interaction effect (irrigation intervals X clones =٭ ,Mean*= of clones, Mean**= of irrigation intervals- data between parenthesis are transformed. - Means followed by similar letters are not significantly different at 0.05 level of probability according to Duncan’s multiple range test (DMRT).

76 120 7 day irigation intervals 14 day irrigation intervals 100 21 day irrigation intervals

80

60

40 %of infested storage roots

20

0 4 MAT 5 MAT 6 MAT 7 MAT 9 MAT 9 MAT Time of harvest (months after transplanting) Fig. 6. Effect of irrigation intervals and time of harvest on % of infested storage roots by the weevil Cylas puncticollis ons weetpotato (autumn 2001/2002).

120 TIS2544 Baladi yellow 100 Baladi red

80

60

40 %of infested storage roots 20

0 4 MAT 5 MAT 6 MAT 7 MAT 9 MAT 9 MAT Time of harvest (months after transplanting) Fig. 7. Effect of sweetotato clones and time of harvest on % of infested storage roots by the weevil Cylas puncticollison sweetpotato (autumn 2001/2002).

76 4.3.2 The influence of irrigation intervals and sweetpotato clones on sweetpotato weevil infestation (Winter transplanting experiment)

Neither irrigation intervals nor their interaction with clones significantly affect stem thickness of sweetpotato (Table 12a, b, c and d). A significant difference was found between clones 5 MAT, BY (1.15 cm) and BR (1.14 cm) exceeded TIS2544 (0.99 cm) in stem thickness (Table 12b). Six months after transplanting, there was a highly significant difference between these two clones BR (1.23 cm) and BY (1.18 cm) and TIS2544 clone (1.02 cm) in stem thikness (Table 12c). Also a significant diffrence was reported 7 MAT among clones BR had a thicker stem (1.30 cm) than both BY (1.06 cm) and TIS2544 (1.02 cm) 7 MAT (Table 12d). Generally, BR possessed thicker stems among clones followed by BY and then TIS2544.

A moderate to strong positive correlation between stem thickness and percentage of infested storage roots was observed among irrigation intervals 7, 14, and 21 DII (r = 0.63, 0.49 and 0.98, respectively). Also a weak to strong positive correlation was noted among clones TIS2544, BY and BR (r = 0.81, 0.11 and 0.97, respectively).

Table (13a, b, c and d) shows the effects of irrigation intervals, sweetpotato clones and their interaction on storage root neck length of sweetpotato. Highly significant differences were obtained between clones 4 MAT, BR had the longest storage root neck (10.52 cm), whereas TIS2544 attained the shortest one (5.08). No significant difference was observed among irrigation intervals and their interaction with the clones. Table (13b) represents a highly significant

77 Table 12 (a, b, c and d). Effect of irrigation intervals, sweetpotato clones and their interaction on stem thickness (cm) of sweetpotato grown during the period (November, 2001/June, 2002). a. First count 4 months after transplanting. b. Second count 5 months after transplanting. Clones Irrigation intervals (days) Mean* Clones Irrigation intervals (days) Mean* 7 14 21 7 14 21 0.987b 0.947 1.047 ٭TIS 0.967 0.950 1.050 0.900 ٭TIS 0.900 BY 1.020 1.040 0.990 1.020 BY 1.140 1.160 1.140 1.147a BR 1.110 1.110 1.160 1.130 BR 1.053 1.320 1.047 1.140a Mean** 1.010 1.020 1.060 Mean** 1.053 1.177 1.043 S.E.± for irrigation intervals = 0.1078 S.E.± for irrigation intervals = 0.0356 S.E.± for clones = 0.0750 S.E.± for clones = 0.0418 S.E.± for irrigation intervals X clones (interaction) = 0.1300 S.E.± for irrigation intervals X clones (interaction) = 0.0724 c. Third count 6 months after transplanting. D. Fourth count 7 months after transplanting. Clones Irrigation intervals (days) Mean* Clones Irrigation intervals (days) Mean* 7 14 21 7 14 21 1.023b 0.980 1.047 ٭1.017b TIS 1.043 1.000 1.060 ٭TIS 0.993 BY 1.130 1.190 1.210 1.180a BY 1.140 1.080 0.953 1.058b BR 1.210 1.210 1.270 1.230a BR 1.307 1.377 1.200 1.295a Mean** 1.111 1.153 1.160 Mean** 1.163 1.168 1.044 S.E.± for irrigation intervals = 0.0546 S.E.± for irrigation intervals = 0.0497 S.E.± for clones = 0.0447 S.E.± for clones = 0.0512 S.E.± for irrigation intervals X clones (interaction) = 0.0774 S.E.± for irrigation intervals X clones (interaction) = 0.0887

A foot note for Table 12 (a to d) -TIS=TIS2544, BY= Baladi yellow, BR=Baladi red (figures in this square are means of interaction effect (irrigation intervals X clones=٭ ,Mean*= of clones, Mean**= of irrigation intervals-

78 - Means followed by similar letters are not significantly different at 0.05 level of probability according to Duncan’s multiple range test (DMRT).

79 Table 13 (a, b, c and d). Effect of irrigation intervals, sweetpotato clones and their interaction on storage root neck length (cm) of sweetpotato grown during the period (November, 2001/June, 2002). a. First count 4 months after transplanting. b. Second count 5 months after transplanting. Clones Irrigation intervals (days) Mean* Clones Irrigation intervals (days) Mean* 7 14 21 7 14 21 5.627c 5.210 5.300 ٭5.075c TIS 6.367 5.733 4.767 ٭TIS 4.725 BY 6.900 6.900 9.700 7.833b BY 8.033 10.700 8.267 9.000b BR 12.192 9.677 9.700 10.523a BR 12.833 11.367 13.040 12.413a Mean** 7.939 7.114 8.378 Mean** 9.078 9.122 8.839 S.E.± for irrigation intervals = 0.4361 S.E.± for irrigation intervals = 0.6279 S.E.± for clones = 0.7983 S.E.± for clones = 0.4652 S.E.± for irrigation intervals X clones (interaction) = 1.3827 S.E.± for irrigation intervals X clones (interaction) = 0.8058 c. Third count 6 months after transplanting. d. Fourth count 7 months after transplanting. Clones Irrigation intervals (days) Mean* Clones Irrigation intervals (days) Mean* 7 14 21 7 14 21 5.270c 5.617 5.413 ٭d 4.457d 5.200cd 4.578b TIS 4.780٭TIS 4.077 BY 7.333bc 8.770b 10.500b 8.868a BY 8.247 6.690 8.933 7.960b BR 10.493b 14.750a 6.413cd 10.552a BR 12.047 10.767 10.333 11.050a Mean** 7.301 9.326 7.371 Mean** 8.358 7.623 8.294 S.E.± for irrigation intervals = 0.9769 S.E.± for irrigation intervals = 0.6569 S.E.± for clones = 0.6419 S.E.± for clones = 0.5306 S.E.± for irrigation intervals X clones (interaction) = 1.1117 S.E.± for irrigation intervals X clones (interaction) = 5.270 A foot note for Table 13 (a to d) -TIS=TIS2544, BY= Baladi yellow, BR=Baladi red (figures in this square are means of interaction effect (irrigation intervals X clones=٭ ,Mean*= of clones, Mean**= of irrigation intervals-

80 - Means followed by similar letters are not significantly different at 0.05 level of probability according to Duncan’s multiple range test (DMRT).

81 difference between clones, BR showed the longest storage root neck (12.41cm) and TIS2544 showed the shortest one (5.63 cm). Six months after transplanting highly significant differences were observed among clones and their interaction with irrigation intervals; BR (10.55 cm) and BY (8.87 cm) had no statistical difference between them, whereas TIS2544 (4.58 cm) attained the shortest storage root neck; BR-14 DII scored the longest storage root (14.75 cm) while TIS2544-7 DII scored the shortest one (4.08 cm) (Table 13c). Latter in the season 7 MAT, a highly significant difference was obtained among clones; BR produced the longest storage root neck (11.05 cm) followed by BY (7.96 cm) and then TIS2544 (5.27cm) (Table 13d). It is worth mentioning that local clones BR and BY had longer storage root necks than the exotic clone TIS2544 (Fig. 8). A weak negative correlation between storage root neck length and percentage of infested storage root was recorded among clones (r = -0.18), and between irrigation intervals (r = -0.30) when data was pooled. There was no significant difference on storage root girth among irrigation intervals throughout the growing season of sweetpotato, but the different performance of 7 DII from others was obvious (Table 14a, b, c and d). on the contrary, among the clones highly significant differences were observed. Table (14a) shows that TIS2544 and BR recorded the largest storage root girth (4.07 and 3.48 cm, respectively) compared to BY (2.97 cm). Five months after transplanting TIS2544 obtained the largest storage root girth (4.09 cm), while BR (3.35 cm) was not significantly different from BY (2.78 cm) (Table 14b). All clones were significantly different from each other; TIS2544 produced

80

14 TIS2544 Baladi yellow Baladi red

12

10

8

6

4

2 Storageroot neck length (cm)

0 4 MAT 5 MAT 6 MAT 7 MAT Time (months after transplanting)

Fig. 8. Effect of sweetpotato clones and time of harvest on storage root neck length of sweetpotato (winter 2001/2002).

81 Table 14 (a, b, c and d). Effect of irrigation intervals, sweetpotato clones and their interaction on storage root girth (cm) of sweetpotato grown during the period (November, 2001/June, 2002). a. First count 4 months after transplanting. b. Second count 5 months after transplanting. Clones Irrigation intervals (days) Mean* Clones Irrigation intervals (day) Mean* 7 14 21 7 14 21 4.091a 4.173 3.307 ٭4.071a TIS 4.793 3.880 4.080 ٭TIS 4.253 BY 3.313 2.807 2.800 2.973b BY 2.927 2.793 2.627 2.782b BR 3.627 4.040 2.757 3.475a BR 3.060 3.537 3.460 3.352b Mean** 3.731 3.642 3.146 Mean** 3.593 3.212 3.420 S.E.± for irrigation intervals = 0.2828 S.E.± for irrigation intervals = 0.2780 S.E.± for clones = 0.2195 S.E.± for clones = 0.2385 S.E.± for irrigation intervals X clones (interaction) = 0.3758 S.E.± for irrigation intervals X clones (interaction) = 0.4132 c. Third count 6 months after transplanting. D. Fourth count 7 months after transplanting. Clones Irrigation intervals (days) Mean* Clones Irrigation intervals (days) Mean* 7 14 21 7 14 21 a 4.347ab 4.020abc 4.298a٭4.474a TIS 4.527 4.247 4.347 ٭TIS 4.827 BY 3.407 3.193 2.580 3.060c BY 3.680cd 3.250d 4.160abc 3.697b BR 4.707 4.413 3.413 4.178b BR 3.937bc 4.420ab 4.147abc 4.168ab Mean** 4.314 3.984 3.413 Mean** 4.048 4.006 4.109 S.E.± for irrigation intervals = 0.2794 S.E.± for irrigation intervals = 0.2992 S.E.± for clones = 0.0891 S.E.± for clones = 0.1043 S.E.± for irrigation intervals X clones (interaction) = 0.1543 S.E.± for irrigation intervals X clones (interaction) = 0.1807 A foot note for Table 14 (a to d) -TIS=TIS2544, BY= Baladi yellow, BR=Baladi red (figures in this square are means of interaction effect (irrigation intervals X clones=٭ ,Mean*= of clones, Mean**= of irrigation intervals-

82 - Means followed by similar letters are not significantly different at 0.05 level of probability according to Duncan’s multiple range test (DMRT).

83 the biggest storage root girth (4.47 cm) and BY had the smallest storage root girth (3.06 cm) (Table 14c). The sweetpotato clones and their interaction with irrigation intervals were highly significantly different 7 MAT, TIS2544 gave the largest storage root girth (4.30 cm) whereas, BY showed the smallest one (3.70 cm); TIS2544-7 DII possessed the larger storage root girth (4.53 cm) and BY-14 DII possessed the smaller storage root girth (3.25 cm) (Table14d). It was clearly observed that TIS2544 clone had the largest storage root girth and BY showed the smaller one throughout the growing season (Fig. 9).

A strong positive correlation between storage root girth and percentage of infested storage roots was noted among clones TIS2544, BY and BR (r = 0.90, 0.87 and 0.99, respectively).

No significant difference was detected among irrigation intervals; clones and their interaction effects on the infested storage root weight throughout the growing season of sweetpotato except 6 MAT (Table 15a, b, c and d). Seven days irrigation interval scored the maximum infested storage root weight 16.72 ton/ha while, 14 DII registered the least one 10.67 ton/ha. TIS2544 obtained the largest infested storage root weight 22.28 ton/ha whereas, no significant difference was found between BY 11.33 ton/ha and BR 7.42 ton/ha. TIS2544-7 DII recorded the largest infested storage root weight 32.67 ton/ha and BR-21 DII recorded the smallest infested storage root weight 5.0 ton/ha. Generally 21 DII had more infested storage roots weight than other irrigation interval treatments. The exotic clone TIS2544 always exceeds BY and BR on the infested storage root weight.

83 5 TIS2544 Baladi yellow Baladi red 4.5

4

3.5

3

2.5

2

1.5 Storage root girth (cm) 1

0.5

0 4 MAT 5 MAT 6 MAT 7 MAT

Time of harvest (months after transplanting)

Fig. 9. Effect of sweetpotato clones and time of harvest on sweetpotato storage root girth (winter 2001/2002).

84 Table15 (a, b, c and d). Effect of irrigation intervals, sweetpotato clones and their interaction on infested storage root weight (ton/ha) by the weevil Cylas puncticollis on sweetpotato grown during the period ( November, 200 /June, 2002). a. First count 4 months after transplanting. b. Second count 5 months after transplanting. Clones Irrigation intervals (days) Mean* Clones Irrigation intervals (days) Mean* 7 14 21 7 14 21 2.278 3.833 3.83 ٭TIS 0.001 1.478 2.334 2.100 ٭TIS 0.001 BY 0.001 0.001 1.334 0.445 BY 0.001 1.333 1.634 0.989 BR 0.001 0.001 0.001 0.001 BR 0.001 0.001 0.867 0.290 Mean** 0.001 0.701 1.223 Mean** 0.001 1.723 1.834 S.E.± for irrigation intervals = 0.4132 S.E.± for irrigation intervals = 0.6562 S.E.± for clones = 0.6252 S.E.± for clones = 0.5396 S.E.± for irrigation intervals X clones (interaction) = 1.0828 S.E.± for irrigation intervals X clones (interaction) = 0.9347 c. Third count 6 months after transplanting. d. Fourth count 7 months after transplanting. Clones Irrigation intervals (days) Mean* Clones Irrigation intervals (days) Mean* 7 14 21 7 14 21 22.894 22.233 28.200 ٭a 14.000bcd 20.167b 22.278a TIS 18.250٭TIS 32.667 BY 7.000de 11.250cde 15.750bc 11.333b BY 20.000 17.500 21.000 19.500 BR 10.500cde 6.750de 5.000e 7.417b BR 16.5000 18.833 23.667 19.667 Mean** 16.722a 10.667b 13.639ab Mean** 18.250 21.511 22.300 S.E.± for irrigation intervals = 0.8890 S.E.± for irrigation intervals = 1.5247 S.E.± for clones = 1.4658 S.E.± for clones = 1.5834 S.E.± for irrigation intervals X clones (interaction) = 2.5390 S.E.± for irrigation intervals X clones (interaction) = 2.7426 A foot note for Table 15 (a to d) -TIS=TIS2544, BY= Baladi yellow, BR=Baladi red (figures in this square are means of interaction effect (irrigation intervals X clones=٭ ,Mean*= of clones, Mean**= of irrigation intervals-

85 - Means followed by similar letters are not significantly different at 0.05 level of probability according to Duncan’s multiple range test (DMRT).

86 A strong to weak positive correlation between infested storage root weight and percentage of infested storage roots was noted among irrigation intervals intervals 7,14 and 21 DII (r = 1.0, 0. 97 and 0.37, respectively); and among clones TIS2544, BY and BR (r = 1.00, 0.99 and 0.73, respectively).

Neither irrigation intervals nor their interaction with clones revealed significant differences on the total storage root weight of sweetpotato 4 MAT (Table 16a). But, a highly significant difference was observed among clones. TIS2544 produced the maximum yield 19.64 ton/ha while, no statistical difference was found between BY 11.0 ton/ha and BR 8.44 ton/ha. The same above trend among clones was repeated 5 MAT, TIS2544 produced the highest yield 35.17 ton/ha compared to BR 18.86 ton/ha and BY 15.66 ton/ha clones. The interaction effect was significant, TIS2544-7 DII scored the maximum yield 44.50 ton/ha whereas; BR-7 DII and BY-21 DII gave the least total storage root weight 5.83 and 9.63 ton/ha, respectively (Table 16b). Seven days irrigation interval produced the greatest yield 24.95 ton/ha, while 21 DII produced the lowest yield 15.34 ton/ha. The clones repeated the same above pattern; TIS2544 was significantly different from the other clones (25.87 ton/ha), but no significant difference was found between BY (18.41 ton/ha) and BR (16.42 ton/ha). TIS2544-7 DII and BR-21 DII gave the highest and the lowest yield 36.50 and 7.00 ton/ha respectively (Table 16c). There were no significant differences among irrigation intervals, clones and their interaction 7 MAT (Table 16d). A weak positive correlation between the total storage root weight and percentage of infested storage roots

86 Table 16 (a, b, c and d). Effect of irrigation intervals, sweetpotato clones and their interaction on total storage root weight (ton/ha) of sweetpotato grown during the period (November, 2001/June, 2002). a. First count 4 months after transplanting. b. Second count 5 months after transplanting. Clones Irrigation intervals (days) Mean* Clones Irrigation intervals (days) Mean* 7 14 21 7 14 21 a 33.000b 28.000bc 35.167a٭19.644a TIS 44.500 18.833 23.767 ٭TIS 16.333 BY 11.167 14.167 7.667 11.000b BY 22.000c 15.333d 9.633de 15.656b BR 7.500 9.500 7.333 8.444b BR 5.833e 33.750b 17.000d 18.861b Mean** 11.667 15.811 11.278 Mean** 24.111 27.361 18.211 S.E.± for irrigation intervals = 2.9894 S.E.± for irrigation intervals = 1.6930 S.E.± for clones = 1.8219 S.E.± for clones = 1.5721 S.E.± for irrigation intervals X clones (interaction) = 3.1557 S.E.± for irrigation intervals X clones (interaction) = 2.7230 c. Third count 6 months after transplanting. d. Fourth count 7 months after transplanting. Clones Irrigation intervals (days) Mean* Clones Irrigation intervals (days) Mean* 7 14 21 7 14 21 26.533 22.233 33.467 ٭a 19.167b 21.933b 25.867a TIS 23.900٭TIS 36.500 BY 17.667`bc 20.467b 17.083bc 18.406b BY 30.667 21.733 24.167 25.522 BR 20.667b 21.583b 7.000c 16.417b BR 26.833 22.833 23.667 24.444 Mean** 24.945a 20.406ab 15.339b Mean** 27.133 26.011 23.356 S.E.± for irrigation intervals = 1.9712 S.E.± for irrigation intervals = 3.0125 S.E.± for clones = 2.0111 S.E.± for clones = 2.0016 S.E.± for irrigation intervals X clones (interaction) = 3.4833 S.E.± for irrigation intervals X clones (interaction) = 3.4669 A foot note for Table 16 (a to d) -TIS=TIS2544, BY= Baladi yellow, BR=Baladi red (figures in this square are means of interaction effect (irrigation intervals X clones=٭ ,Mean*= of clones, Mean**= of irrigation intervals-

87 - Means followed by similar letters are not significantly different at 0.05 level of probability according to Duncan’s multiple range test (DMRT).

88 was observed among irrigation intervals (r = 0.28) and clones (r = 0.38) when data was pooled. Figures (10 and 11) show the relationship between the infested storage root weight and the total storage root weight among irrigation intervals and the clones, respectively. Table (17a, b, c and d) shows the effects of irrigation intervals, sweetpotato clones and their interaction on the percentage of infested storage roots of sweetpotato. Four months after transplanting, no significant difference was detected among the different treatment means. On the contrary a high significant difference was observed 5 MAT between the treatments; 21 DII and 14 DII scored the highest percentage of infested storage roots 10.21% and 9.58%, respectively while 7 DII was not infested. TIS2544 and BY manifested the higher percentage of infested storage roots 9.56 and 7.52%, respectively while BR scored the least percentage of infested storage roots 3.43%. TIS2544-14 DII represented the highest percentage of infested storage roots 14.32% whereas, TIS2544-7 DII, BY-7 DII, BR-7 DII and BR- 14 DII showed no sign of sweetpotato weevil infestation. Six months after transplanting no significant difference was obtained among the different treatment means. Seven months after transplanting a considerable variation between irrigation intervals was existed, 21 DII represented the higher percentage of infested storage roots 95.5% and 7 DII showed the least one 61.63%. Figures (12 and 13) show the percentage of infested storage roots during different harvest times among irrigation intervals and sweetpotato clones respectively. It is worth mentioning that sweetpotato weevil infestation was lower at early harvesting times (4 and 5 MAT), but increased drastically at late harvesting times (6 and 7 MAT) regardless of irrigation intervals or clones. Generally speaking we can conclude that

88 35 Infested storage root w eight (ton/ha) Total storage root w eight (ton/ha) 30 25 20

15 10 5 Storage root weight(ton/ha) 0 ) ) ) ) ) ) ) ) ) ) ) ) T T T T T T T T T T T T A A A A A A A A A A A A M M M M M M M M M M M M 4 5 6 7 4 5 6 7 4 5 6 7 ( ( ( ( ( ( ( ( ( ( ( ( II II II II II II II II II II II II D D D D D D D D D D D D 7 7 7 7 4 4 4 4 1 1 1 1 1 1 1 1 2 2 2 2 Irrigation intervals

Fig. 10. Relationship between infested storage root weight and total storage root weight of weetpotato among irrigation intervals during different harvest times (winter 2001/2002).

40 Infested storage root w eight (ton/ha) Total storage root w eight (ton/ha) 35

30

25

20

15

10

Storage root weight (ton/ha) 5

0 ) ) ) ) T T ) T) T) T) T T AT) AT) MA M MA MA MA 6 MAT) 4 MAT 5 MA 6 4 ( (5 (6 (7 4 (4 MA 4 (5 MA 4 ( 4 (7 M Y ( Y ( R R R 4 4 BY B B BY (7 MAT) BR ( B B B

TIS25 TIS25 TIS254 TIS354 Sweetpotato clones

Fig. 11. Relationship between infested storage root weight and total storage root weight of sweetpotato clones during different harvest times (winter 2001/2002).

89 Table 17 (a, b, c and d). Effect of irrigation intervals, sweetpotato clones and their interaction on percentage of infested storage root by Cylas puncticollis on sweetpotato grown during the period (November 2001/June 2002). a. First count 4 months after transplanting. b. Second count 5 months after transplanting. Clones Irrigation intervals (days) Mean* Clones Irrigation intervals (days) Mean* 7 14 21 7 14 21 c 14.32 (3.85)a 13.64(3.76)a 9.56(2.77)a٭(TIS 0.0 (0.71 (1.55) 3.33 (0.71) 0.0 (3.24) 10.0 ٭(TIS 0.0 (0.71 b BY 0.0 (0.71) 0.0 (0.71) 14.71(3.9) 4.90 (1.77) BY 0.0 (0.71)c 13.71 8.14 (2.94)b 7.52(2.47)a (3.77)ab BR 0.0 (0.71) 0.0 (0.71) 0.0 (0.71) 0.0 (0.71) BR 0.0 (0.71)c 0.0 (0.71)c 8.86 (3.06)b 3.43(1.49)b Mean* 0.0 (0.71) 3.33(1.55) 4.90(1.77) Mean* 0.0 (0.71)c 9.58(2.78)a 10.21(3.25)a * * S.E.± for irrigation intervals = 0.5210 S.E.± for irrigation intervals = 0.7060 S.E.± for clones = 0.4442 S.E.± for clones = 0.1421 S.E.± for irrigation intervals X clones (interaction) = 0.7694 S.E.± for irrigation intervals X clones (interaction) = 0.2462 c. Third count 6 months after transplanting. d. Fourth count 7 months after transplanting. Clones Irrigation intervals (days) Mean* Clones Irrigation intervals (days) Mean* 7 14 21 7 14 21 TIS 66.04(59.5) 88.92(71.3 92.99(77.9 82.65(69.6 TIS 69.94(61.8) 93.59 (81.34) 100.0 87.84(77.7 (4 (90.0) ٭ (1 (2 (7 ٭ BY 30.05(32.9 53.78(47.4 64.64(58.5 49.49(46.2 BY 73.96 79.25 86.53 79.91(65.7 4) 1) 2) 9) (61.28) (67.40) (68.5) 3) BR 61.70(57.0 37.68(37.7 70.37(66.4 56.58(53.7 BR 41.0 70.74 100.0 60.58(64.0 2) 0) 9) 4) (39.70) (62.47) (90.0) 6)

90 Mean* 52.6(49.84) 60.13(52.1 76.0(67.65) Mean* 61.63(54.29) 81.19(70.40) 95.51(82.83 6) b ab )a * * S.E.± for irrigation intervals = 9.1791 S.E.± for irrigation intervals = 6.2217 S.E.± for clones = 6.5994 S.E.± for clones = 5.0979 S.E.± for irrigation intervals X clones (interaction) = 11.4305 S.E.± for irrigation intervals X clones (interaction) = 8.8297 A foot note for Table 17 (a to d) -TIS=TIS2544, BY= Baladi yellow, BR=Baladi red; data between parenthesis were transformed. (figures in this square are means of interaction effect (irrigation intervals X clones=٭ ,Mean*= of clones, Mean**= of irrigation intervals- - Means followed by similar letters are not significantly different at 0.05 level of probability according to Duncan’s multiple range test (DMRT).

91 90 7 day irrigation intervals 80 14 day irrigation intervals 70 21 day irrigation intervals

60 50 40 30

20 % of infested storage roots 10 0 4 MAT5 MAT6 MAT7 MAT Time (months after transplanting)

Fig. 12. Effect of irrigation intervals and time of harvest on % of infested storage roots by the weevil Cylas puncticollis on sweetpotato (winter 2001/2002).

90 TIS2544 80 Baladi yellow Baladi red 70

60

50

40

30 % of infested storage roots 20

10

0 4 MAT 5 MAT 6 MAT 7 MAT Time of harvest (months after transplanting) Fig. 13. Effect of sweetpotato clones and time of harvest on %of infested storage roots weight ofsweetpotato (winter 2001/2002).

91 21 DII suffered severe infestation by sweetpotato weevil than 14 and 7 DII; also TIS2544 was severely affected than local clones BY and BR.

4.3.3 Sweetpotato weevil management

Integrating different cultural control practices has specific potential upon managing weevils Cylas spp., taken into account that the insects have a limited flight activity, restricted host range and characteristic mode of entry into the plant. Table (18) shows the effects of different control treatments applied against sweetpotato weevil, Cylas puncticollis during the period from November, 2001 to May, 2002. The results indicated that, there were no significant differences between controls and stem thickness, storage root neck length, storage root girth and the total storage root weight of the harvested storage roots. But, there was a significant difference on the percentage of infested storage roots between control 64.17% and earthing up the soil 34.85%, deltamethrin plus earthing up the soil 30.52%, carbofuran plus earthing up the soil 31.45% and deltamethrin 31.97% whereas, no significant difference was observed between carbofuran (47.44) and the control.

It is worth mentioning that the total storage root weight (yield) of sweetpotato was greater when earthing up was practiced on the soil, carbofuran plus earthing up the soil then deltamethrin and deltamethrin plus earthing up the soil, while carbofuran produced the smaller amount of storage root moreover, it suffered high percentage of sweetpotato weevil infestation compared to other treatments.

92 Table 18. Effect of different control treatments on some sweetpotato vegetative and yield characters and on the percentage of infestation of sweet potato weevil, Cylas puncticollis Boh. during the period (November, 2001/May, 2002).

Sweetpotato characters Stem thickness Storage root neck Storage root Total storage % of (cm) length (cm) girth (cm) root weight infested Treatments ton/ha storage root Carbofuran plus earthing up 0.8083 6.1643 4.9675 20.750 31.45* Earthing up the soil 0.8143 6.9028 4.5218 23.125 34.85* Deltamethrin plus earthing up 0.0893 7.0873 4.3573 21.375 30.52* Deltamethrin 0.8256 5.9950 4.2020 18.375 31.97* Carbofuran 0.8140 5.0310 4.0075 13.500 47.44ns Control 0.8623 6.4140 4.3385 13.750 64.17 SE± 0.0444 1.0387 0.4322 0.3574 8.9201 LSD 0.05 0.0946 2.2135 0.9984 0.7616 28.106 LSD 0.01 0.01308 3.0610 1.2737 1.0532 39.7966

ns = not significant * = significant at 0.05 level of probability

93 4.4 Laboratory experiments (second season, 2002/03)

4.4.1 Life history of sweetpotato weevil, Cylas puncticollis Boh.

4.4.1.1 Duration of development of immature stages

Table (19a, b and c ) and Table (20a, b and c) show the results of some experiments which were carried out as continuation of the life history studies to estimate the duration of the developing stages of sweetpotato weevil, Cylas pucticollis under room conditions and a constant temperature of 30°C and 65% RH. Tables (19a) and (20a) show the incubation period of sweetpotato weevil eggs which averaged 3.0 ± 0.58 and 3.43 ± 0.53 days under room conditions and the constant 30°C and 65% RH, respectively. The larval period was found to be 10.82 ± 1.57 and 11.96 ± 0.76 days under room conditions and the constant 30°C and 65% RH, respectively. The larval mortality was 15.18 ± 8.54% under room conditions and 26.42 ± 13.86% under 30°C temperature and 65% RH (Table 19b and Table 20b). The pupal period was recorded to be 3.26 ± 0.27 and 3.98 ± 0.18 days under room conditions and 65% RH, respectively. The pupal mortality was 7.67 ± 6.94% under room conditions and 4.95 ± 7.23% under 30°C and 65% RH.

When the insects were reared without disturbance, both under ambient room conditions and under a constant temperature of 30°C and 65% RH, the total life cycle durations were 20.22 ± 1.45 and 23.01 ± 1.96 days, respectively (Tables 21 and 22). There was a highly significant difference in the total developmental stages of sweetpotato weevil between disturbed and undisturbed rearing under

94 Table 19 (a, b and c). Development in days of pre-imaginal stages of sweetpotato weevil, Cylas puncticollis Boh. under room conditions (May/June, 2003)*. a. Incubation period Cage No. No. of eggs hatched after (days) Average 2 3 4 (days) 1 0.0 33.0** 0.0 3.0 2 0.0 0.0 15.0** 4.0 3 0.0 57.0** 0.0 3.0 4 0.0 38.0** 0.0 3.0 5 0.0 43.0** 0.0 3.0 6 32.0** 0.0 0.0 2.0 7 0.0 33.0** 0.0 3.0 Mean ± S.E. 3.0 ± 0.58 *See Appendix B for room conditions records. **Duration of incubation period based on first egg hatched-total based on larvae found. b. Larval period Cage No. of No. of larvae developed to pupa after (days) Average Mortality No. eggs larval % hatched period 8 9 10 11 12 13 14 15 16 17 1 33 0.0 0.0 0.0 3.0 3.0 3.0 6.0 5.0 3.0 1.0 13.83 27.27 2 15 10.0 4.0 0.0 0.0 1.0 0.0 0.0 0.0 0.0 0.0 8.53 0.0 3 57 7.0 5.0 8.0 16.0 10.0 3.0 0.0 0.0 0.0 0.0 10.53 14.04 4 38 3.0 9.0 6.0 10.0 5.0 0.0 0.0 0.0 0.0 0.0 10.15 13.16 5 43 0.0 6.0 12.0 8.0 3.0 2.0 0.0 3.0 0.0 0.0 10.85 20.93 6 32 0.0 0.0 10.0 10.0 5.0 1.0 0.0 0.0 0.0 0.0 10.88 18.75 7 33 0.0 2.0 9.0 8.0 7.0 3.0 0.0 0.0 0.0 0.0 11.00 12.12 Mean 35.86 10.82± 15.18 ± 8.54 ± S.E. ±12.71 1.57 c. Pupal period Cage No. of No. of adults emerged after Average Mortality No. pupae (days) pupal % observed 2 3 4 5 6 period 1 24 3.0 14.0 3.0 3.0 1.0 3.38 0.00 2 15 3.0 5.0 4.0 0.0 0.0 3.08 20.0 3 49 3.0 34.0 7.0 1.0 0.0 3.13 8.16 4 33 1.0 23.0 6.0 0.0 1.0 3.26 6.06 5 34 2.0 23.0 1.0 4.0 0.0 3.23 11.76 6 26 0.0 14.0 1.0 9.0 0.0 3.79 7.69 7 29 3.0 25.0 0.0 1.0 0.0 2.97 0.0 Mean 30.14 3.26 ± 7.67 ± ± S.E. ±10.43 0.27 6.94

95 Table 20 (a, b and c). Development in days of pre-imaginal stages of sweetpotato weevil, Cylas puncticollis Boh. under a constant temperature of 30°C and 65% relative humidity (May/June, 2003). a. Incubation period Cage No. No. of eggs hatched after (days) Average (days) 3 4 1 0.0 9.0* 4.0 2 0.0 10.0* 4.0 3 27.0* 0.0 3.0 4 30.0* 0.0 3.0 5 30.0* 0.0 3.0 6 27.0* 0.0 3.0 7 0.0 41.0* 4.0 Mean ±S.E. 3.43 ± 0.53 *Duration of incubation period based on first egg hatched-total based on larvae found.

b. Larval period No. of No. of larvae developed to pupae after (days) Avera Cag eggs ge Mortal e 1 1 1 1 1 1 17 2 hatch 8 9 12 larval ity % No. 0 1 3 4 5 6 * 1 ed period 0. 1. 0. 0. 0. 0. 0. 0. 0. 0. 1 9.0 3.0 11.25 55.56 0 0 0 0 0 0 0 0 0 0 0. 0. 0. 2. 3. 3. 0. 0. 0. 0. 2 10.0 0.0 12.88 20.00 0 0 0 0 0 0 0 0 0 0 0. 0. 0. 1. 6. 1. 3. 1. 0. 0. 3 27.0 8.0 13.00 25.93 0 0 0 0 0 0 0 0 0 0 0. 0. 5. 4. 11. 2. 2. 1. 0. 0. 0. 4 30.0 11.80 16.67 0 0 0 0 0 0 0 0 0 0 0 1. 1. 5. 4. 2. 0. 1. 0. 0. 0. 5 30.0 7.0 11.24 30.00 0 0 0 0 0 0 0 0 0 0 0. 4. 5. 6. 1. 1. 0. 0. 0. 1. 6 27.0 5.0 11.30 14.81 0 0 0 0 0 0 0 0 0 0 2. 4. 2. 4. 9. 3. 2. 0. 3. 0. 7 41.0 3.0 12.25 21.95 0 0 0 0 0 0 0 0 0 0 Mea 24.86 11.96 26.42 ± n ± ±10.6 ± 0.76 13.86 S.E. 6 *No larvae developed to pupae on the 18th ,19th and 20th day. c. Pupal period Cage No. of No. of adults emerged Average Mortality No. pupae after (days) pupal % observed 3 4 5 period 1 4.0 0.0 4.0 0.0 4.0 0.0 2 8.0 1.0 6.0 1.0 4.0 0.0 3 20.0 5.0 9.0 3.0 3.88 15.0

96 4 25.0 1.0 19.0 4.0 4.13 4.0 5 21.0 0.0 20.0 1.0 4.05 0.0 6 23.0 1.0 17.0 5.0 4.17 0.0 7 32.0 13.0 11.0 3.0 3.63 15.63 Mean ± 19.0 ± 9.04 3.98 ± 0.18 4.95 ±7.23 S.E.

97 Table 21. Duration of development of Cylas puncticollis Boh. in days from egg laying to adult emergence under room conditions (undisturbed) in (May/June, 2003).

Date of Adults emerged after (days) Total egg 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 developmental laying period (days) 11.5.2003 0.0 0.0 0.0 0.0 0.0 13.0 1.0 5.0 3.0 1.0 4.0 1.0 1.0 0.0 0.0 20.97

13.5 0.0 0.0 0.0 0.0 0.0 6.0 0.0 21.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 19.29

15.5 0.0 0.0 0.0 0.0 0.0 1.0 2.0 1.0 3.0 0.0 1.0 0.0 1.0 2.0 1.0 23.17

17.5 2.0 3.0 0.0 5.0 11.0 18.0 3.0 3.0 4.0 2.0 2.0 2.0 0.0 2.0 0.0 19.42

19.5 0.0 0.0 1.0 10.0 3.0 15.0 3.0 7.0 6.0 6.0 2.0 1.0 2.0 1.0 1.0 19.34

21.5 0.0 0.0 2.0 7.0 4.0 4.0 11.0 5.0 5.0 6.0 0.0 1.0 0.0 0.0 1.0 20.12

23.5.2003 0.0 0.0 6.0 6.0 4.0 8.0 8.0 3.0 1.0 1.0 3.0 0.0 1.0 0.0 0.0 19.22

Mean ± 20.22 ± 1.45 S.E.

97 Table 22. Duration of development of Cylas puncticollis Boh. in days from egg laying to adult emergence at a constant temperature of 30°C and 65% relative humidity (undisturbed) in (May/June, 2003).

Date of Adults emerged after (days) Total egg 17 18 19 20 21 22 23 24 25 26 27 28 29 30* 32 developmental laying period (days) 11.5.2003 0.0 0.0 0.0 0.0 0.0 2.0 2.0 0.0 2.0 0.0 0.0 0.0 2.0 5.0 0.0 26.77

13.5 0.0 0.0 0.0 0.0 0.0 0.0 1.0 5.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 23.83

15.5 0.0 0.0 3.0 5.0 6.0 4.0 2.0 4.0 4.0 0.0 1.0 1.0 1.0 2.0 0.0 22.94

17.5 2.0 1.0 2.0 4.0 1.0 6.0 2.0 0.0 2.0 0.0 2.0 2.0 1.0 1.0 2.0 23.29

19.5 2.0 9.0 7.0 8.0 8.0 6.0 5.0 2.0 2.0 2.0 4.0 2.0 1.0 0.0 0.0 21.50

21.5 0.0 4.0 11.0 3.0 2.0 1.0 3.0 6.0 6.0 2.0 1.0 1.0 0.0 0.0 0.0 21.88

23.5.2003 2.0 4.0 8.0 6.0 11.0 9.0 2.0 2.0 3.0 1.0 0.0 0.0 0.0 0.0 0.0 20.88

Mean ± 23.01 ± 1.96 S.E. *No adult emerged on 31th day.

98 room conditions and at the constant temperature of 30°C and 65% RH; also a significant difference was recorded between rearing under room ambient conditions and the constant temperature and RH conditions (Table 23).

4.4.1.2 Preoviposition period

The duration between adults’ emergence and the first egg laid was recorded for 12 pairs of sweetpotato weevil, Cylas pucticollis. It ranged from 2 to 7 days with an average of 4.33 ± 1.23 days (Table 24).

4.4.1.3 Oviposition rate

Table (25) shows the oviposition rate of three pairs of sweetpotato weevil, Cylas pucticollis reared for 16 days. The mean number of eggs laid per female per day was found to be 3.90 ± 1.67 eggs.

4.4.1.4 Sex ratio

The sex ratio of the progeny of three pairs of sweetpotato weevil reared for 16 days was 1: 0.9 (female: male).

4.5 Field experiments (second season 2002/03)

4.5.1 The influence of irrigation intervals and sweetpotato clones on sweetpotato weevil infestation (autumn transplanting experiments)

Table (26a, b, c and d) shows the effect of irrigation intervals, sweetpotato clones and their interaction on stem thickness. No significant difference was detected on stem thickness among the

99 Table 23. Duration in days of the total development of Cylas puncticollis Boh. in days under room conditions and a constant temperature of 30°C and 65% RH (disturbed and undisturbed).

Rearing Mean total developmental period (days) Average of the conditions Rep.1 2 3 4 5 6 7 total developmental period (days) Room temp. 20.21 15.61 16.45 16.41 17.08 16.67 61.97 17.06c (disturbed)

Room temp. 20.97 19.29 23.17 19.42 19.34 20.12 19.22 20.22b (undisturbed)

Constant 19.25 20.88 19.88 18.93 18.29 18.47 19.88 19.37b 30°C and 65% RH (disturbed)

Constant 26.77 23.83 22.94 23.29 21.50 21.88 20.88 23.01a 30°C and 65% RH (undisturbed)

*Means followed by similar letters are not significantly different at 0.05 level of probability. LSD 0.05 = 1.6473 CV = 7.5%

100

Table 24. Preoviposition period (days) of Cylas puncticollis Boheman under room conditions (May/June, 2003).

Insect pair No. Date adults caged Date of first egg Preoviposition laid period 1 31.5.2003 4.6.2003 4

2 31.5 5.6 5

3 31.5. 7.6 7

4 1.6.2003 5.6 4

5 1.6. 5.6 4

6 1.6. 5.6 4

7 2.6. 5.6 3

8 2.6. 7.6 5

9 2.6. 7.6 5

10 3.6. 5.6 2

11 3.6. 8.6 5

12 3.6.2003 7.6.2003 4

Range 2-7 Mean ± S.E. 4.33 ± 1.23

101

Table 25. Oviposition rate of the sweetpotato weevil, Cylas puncticollis Boheman.

Cage No. No. of eggs No. of eggs laid/female/ 8 days laid/female/day

Replicate 1 Replicate 2 Replicate 1 Replicate 2

1 40 36 5.00 4.50

2 45 32 5.63 4.00

3 7 27 0.88 3.38

Mean ± 31.27 ± 13.38 3.90 ± 1.67

S.E.

102 Table 26 (a,b,c and d). Effect of irrigation intervals, sweetpotato clones and their interaction on stem thickness (cm) of sweetpotato grown during the period (August, 2002/March, 2003). a. First count 4 months after transplanting. b. Second count 5 months after transplanting. Clones Irrigation intervals (days) Mean* Clones Irrigation intervals (days) Mean* 7 14 21 7 14 21 1.097c 1.110 1.080 ٭TIS 1.100 1.268 1.383 1.233 ٭TIS 1.187 BY 1.293 1.353 1.387 1.344 BY 1.340 1.220 1.290 1.283b BR 1.473 1.240 1.510 1.427 BR 1.260 1.530 1.720 1.503a Mean** 1.318 1.276 1.427 Mean** 1.233 1.278 1.373 S.E.± for irrigation intervals = 0.0505 S.E.± for irrigation intervals = 0.0526 S.E.± for clones = 0.0782 S.E.± for clones = 0.0495 S.E.± for irrigation intervals X clones (interaction) = 0.1354 S.E.± for irrigation intervals X clones (interaction) = 0.0857 c. Third count 6 months after transplanting. d. Fourth count 7 months after transplanting. Clones Irrigation intervals (days) Mean* Clones Irrigation intervals (days) Mean* 7 14 21 7 14 21 1.060 1.120 1.013 ٭TIS 1.047 1.153 1.233 1.120 ٭TIS 1.107 BY 1.393 1.213 1.307 1.304 BY 1.260 1.200 1.100 1.187 BR 1.287 1.173 1.377 1.279 BR 1.133 1.313 1.253 1.233 Mean** 1.262 1.169 1.306 Mean** 1.147 1.176 1.164 S.E.± for irrigation intervals = 0.0454 S.E.± for irrigation intervals = 0.0413 S.E.± for clones = 0.0514 S.E.± for clones = 0.0518 S.E.± for irrigation intervals X clones (interaction) = 0.0891 S.E.± for irrigation intervals X clones (interaction) = 0.0897 A foot note for Table 26 (a to d) -TIS=TIS2544, BY= Baladi yellow, BR=Baladi red figures in this square are means of interaction effect (irrigation intervals X=٭ ,Mean*= of clones, Mean**= of irrigation intervals- clones)

103 - Means followed by similar letters are not significantly different at 0.05 level of probability according to Duncan’s multiple range test (DMRT).

104 different treatment means 4 months after transplanting (MAT). For stem thickness, all the sweetpotato clones were highly significantly different from each other 5 MAT; BR had a thicker stem (1.50 cm) followed by BY (1.28 cm) and then TIS2544 (1.10 cm). But, no significant difference was found between irrigation intervals and their interaction with clones. Table (26c and d) reflected similar trend as shown 4 MAT, no significant differences were observed among the different treatment means. Generally speaking we can say that 21 DII had thicker stems than the other irrigation interval treatments. Baladi red clone exceeded both BY and TIS2544 regarding the stem thickness. A moderate negative correlation was obtained between stem thickness and percentage of infested storage roots among irrigation intervals (r = - 0.52) and between clones (r = -58).

Table (27a, b, c and d) indicates the effect of irrigation intervals, sweetpotato clones and their interaction on storage root neck length. The clones had highly significant differences on storage root neck length throughout the growing season of sweetpotato, while no significant difference was observed among irrigation intervals and their interaction with clones. Four months after transplanting, BR gave the longest storage root neck (19.24 cm ) compared to BY (11.24 cm) and TIS2544 (5.98 cm). Table (27b and c) manifested similar trend, all clones were highly significantly different from each other ,BR possessed the longest storage root neck and TIS2544 showed the shortest one. A month latter 7 MAT, BR (11.10 cm) and BY (9.69 cm) were not statistically different from each other but, differed from TIS2544 (4.92 cm). It can be noticed that BR always has the longest storage root neck whereas; TIS2544 had the shortest one.

105 Table 27 (a,b,c and d). Effect of irrigation intervals, sweetpotato clones and their interaction on storage root neck length (cm) of sweetpotato grown during the period (August, 2002/March, 2003). a. First count 4 months after transplanting. b. Second count 5 months after transplanting. Clones Irrigation intervals (days) Mean* Clones Irrigation intervals (days) Mean* 7 14 21 7 14 21 5.373c 5.37 4.53 ٭5.98b TIS 6.22 6.36 6.46 ٭TIS 5.13 BY 18.10 7.18 8.44 11.24b BY 10.49 9.91 9.40 9.933b BR 17.23 22.82 17.68 19.24a BR 12.73 15.67 16.60 15.00a Mean** 13.23 12.15 10.83 Mean** 9.816 10.036 10.456 S.E.± for irrigation intervals = 1.6948 S.E.± for irrigation intervals = 0.8777 S.E.± for clones = 1.4561 S.E.± for clones = 0.6003 S.E.± for irrigation intervals X clones (interaction) = 2.5221 S.E.± for irrigation intervals X clones (interaction) = 1.0398 c. Third count 6 months after transplanting. d. Fourth count 7 months after transplanting. Clones Irrigation intervals (days) Mean* Clones Irrigation intervals (days) Mean* 7 14 21 7 14 21 4.917b 4.98 5.07 ٭6.233c TIS 4.70 5.83 7.10 ٭TIS 5.77 BY 7.87 11.80 8.09 9.253b BY 9.35 10.33 9.39 9.689a BR 13.27 16.93 12.31 14.17a BR 11.59 11.30 10.40 11.098a Mean** 8.967 11.943 8.747 Mean** 8.549 8.864 8.257 S.E.± for irrigation intervals = 11.9433 S.E.± for irrigation intervals = 0.9887 S.E.± for clones = 8.9667 S.E.± for clones = 0.5888 S.E.± for irrigation intervals X clones (interaction) = 1.5339 S.E.± for irrigation intervals X clones (interaction) = 1.0199

A foot note for Table 27 (a to d) -TIS=TIS2544, BY= Baladi yellow, BR=Baladi red figures in this square are means of interaction effect (irrigation intervals X=٭ ,Mean*= of clones, Mean**= of irrigation intervals- clones)

106 - Means followed by similar letters are not significantly different at 0.05 level of probability according to Duncan’s multiple range test (DMRT).

107 There was a negative correlation between storage root neck length and percentage of infested storage root among clones TIS2544, BY, and BR (r = -0.77, -0.34 and -0.92 respectively) and between irrigation intervals (r = -0.82, -0.79 and -0.76 respectively).

Neither irrigation intervals nor their interaction with clones significantly affected storage root girth during the four harvesting periods of sweetpotato (Table 28a, b, c and d). The storage root girth of sweetpotato varied continuously among clones over time. At the early harvest (4 MAT) TIS2544 recorded the largest storage root girth 4.0 cm that is significantly different from BR (2.44 cm) and BY (2.22 cm). Five months after transplanting BR (4.45 cm) and TIS2544 (4.08 cm) clones were highly significantly different from BY (2.91 cm). A month latter a significant difference was recorded among clones, also BR (4.57 cm) obtained the largest storage root girth whereas, BY (3.74 cm) recorded the smaller one. At the late harvest (7 MAT) no significant difference was recorded among all treatment means. Usually TIS2544 and BR clones have bigger storage root girth than BY.

Strong to moderate positive correlations between storage root girth and percentage of infested storage roots of sweetpotato were noticed among irrigation intervals 7, 14 and 21 days (r = 0.92, 0.58 and 0.65, respectively) and also between clones TIS2544, BY and BR (r = 1.0, 0.74 and 0.82).

Data presented in Table (29a, b, c and d) shows the effects of irrigation intervals, sweetpotato clones and their interaction on the infested storage root weight. At the early harvest (4 MAT) no SPW infestation occurred, therefore hardly infested storage roots weight

106 Table 28 (a,b,c, and d). Effect of irrigation intervals, sweetpotato clones and their interaction on storage root girth (cm) of sweetpotato grown during the period (August, 2002/ March, 2003). a. First count 4 months after transplanting. b. Second count 5 months after transplanting. Clones Irrigation intervals (days) Mean* Clones Irrigation intervals (days) Mean* 7 14 21 7 14 21 4.077a 4.55 4.03 ٭4.00a TIS 3.65 2.83 5.51 ٭TIS 3.66 BY 2.74 2.32 1.61 2.22b BY 3.05 3.04 2.63 2.907b BR 2.93 1.39 3.00 2.44b BR 3.47 5.12 4.77 4.453a Mean** 3.11 3.07 2.48 Mean** 3.391 4.062 3.983 S.E.± for irrigation intervals = 0.3352 S.E.± for irrigation intervals = 0.1573 S.E.± for clones = 0.2710 S.E.± for clones = 0.1895 S.E.± for irrigation intervals X clones (interaction) = 0.4694 S.E.± for irrigation intervals X clones (interaction) = 0.3282 c. Third count 6 months after transplanting. D. Fourth count 7 months after transplanting. Clones Irrigation intervals (days) Mean* Clones Irrigation intervals (days) Mean* 7 14 21 7 14 21 5.517 5.47 5.55 ٭4.187ab TIS 5.53 4.04 4.23 ٭TIS 4.29 BY 3.61 4.37 3.23 3.738b BY 3.78 3.90 4.74 4.140 BR 4.34 5.65 3.72 4.570a YR 5.58 4.59 5.84 5.337 Mean** 4.08 4.75 3.66 Mean** 4.963 4.680 5.35 S.E.± for irrigation intervals = 0.2387 S.E.± for irrigation intervals = 0.3613 S.E.± for clones = 0.2052 S.E.± for clones = 0.4448 S.E.± for irrigation intervals X clones (interaction) = 0.3553 S.E.± for irrigation intervals X clones (interaction) = 0.7705 A foot note for Table 28 (a to d) -TIS=TIS2544, BY= Baladi yellow, BR=Baladi red (figures in this square are means of interaction effect (irrigation intervals X clones=٭ ,Mean*= of clones, Mean**= of irrigation intervals-

107 - Means followed by similar letters are not significantly different at 0.05 level of probability according to Duncan’s multiple range test (DMRT).

Table 29 ( a,b,c and d). Effect of irrigation intervals, sweetpotato clones and their interaction on infested storage root weight (ton/ha) by the weevil Cylas puncticollis on sweetpotato grown during the period (August, 2002/ March, 2003). a. First count 4 months after transplanting#. b. Second count 5 months after transplanting. Clones Irrigation intervals (days) Mean* Clones Irrigation intervals (days) Mean* 7 14 21 7 14 21 0.0778 0.0667 0.0667 ٭TIS 0.00 0.00 0.00 0.00 TIS 0.100 BY 0.00 0.00 0.00 0.00 BY 0.0001 0.0834 0.0001 0.0278 BR 0.00 0.00 0.00 0.00 BR 0.0001 0.0001 0.0834 0.0278 Mean** 0.00 0.00 0.00 Mean** 0.0334 0.0501 0.0501 # No infestation observed. S.E.± for irrigation intervals = 0.0364 S.E.± for clones = 0.0333 S.E.± for irrigation intervals X clones (interaction) = 0.0577 c. Third count 6 months after transplanting. d. Fourth count 7 months after transplanting. Clones Irrigation intervals (days) Mean* Clones Irrigation intervals (days) Mean* 7 14 21 7 14 21 8.1111a 12.8333 10.6667 ٭TIS 0.8334 2.5278 2.4167 5.1667 ٭TIS 0.0001 BY 0.0001 3.6667 0.0001 1.2223 BY 0.0001 2.3334 8.3333 3.5556b BR 0.0001 2.1667 0.1667 0.7778 BR 0.0001 0.1667 0.1667 0.1112b Mean** 0.0001 3.6667 0.8612 Mean** 0.2779 4.3889 7.1111 S.E.± for irrigation intervals = 0.8688 S.E.± for irrigation intervals = 1.8315 S.E.± for clones = 0.8986 S.E.± for clones = 1.3911

108 S.E.± for irrigation intervals X clones (interaction) = 1.5565 S.E.± for irrigation intervals X clones (interaction) = 2.4095 A foot note for Table 29 (a to d) -TIS=TIS2544, BY= Baladi yellow, BR=Baladi red (figures in this square are means of interaction effect (irrigation intervals X clones=٭ ,Mean*= of clones, Mean**= of irrigation intervals- - Means followed by similar letters are not significantly different at 0.05 level of probability according to Duncan’s multiple range test (DMRT).

109 Records were obtained. For both harvest times 5 and 6 MAT no significant difference was observed among the different treatment means. Latter in the season (7 MAT) the clones effect on infested storage roots weight was highly significant, TIS2544 recorded the higher infested storage root weight 8.11 ton/ha than both BY (3.56 ton/ha) and BR (0.11 ton/ha). It worth mentioning that 21 DII and 14 DII had more infested storage root weight than 7 DII even though no significant difference was obtained. TIS2544 gave greater infested storage root weight compared to BY and the latter had more infested storage roots than BR during the different harvest times. When data was pooled, strong positive correlations were recorded between infested storage root weight and percentage of infested storage root among irrigation intervals (r = 0.92) and the clones (r = 0.95).

The results of the total storage root weight were summarized in Table (30a, b, c and d). There was no significant difference among irrigation interval treatments throughout the growing season of sweetpotato except after 7 months from transplanting where, 7 DII gave the highest yield (60.5 ton/ha) while14 DII produced the lowest one (24.50 ton/ha). A highly significant difference was obtained between clones 4 MAT, TIS2544 produced the highest yield (9.94 ton/ha) while BY and BR gave the lowest yield (2.67 ton/ha and 2.61 ton/ha, respectively). A significant effect was induced by the interaction TIS2544-7 DII produced the highest yield (14.67 ton/ha) whereas BR-14, BY-21 DII and BY-14 gave the lowest yield (0.33, 1.0 and 2.50 ton/ha, respectively) (Table 30a). As shown in Table (30b), a significant variation between clones can easily be observed

109 Table 30 (a,b,c and d). Effect of irrigation intervals, sweetpotato clones and their interaction on total storage root weight (ton/ha) of sweetpotato grown in the period (November, 2002/June, 2003). a. First count 4 months after transplanting. b. Second count 5 months after transplanting. Clones Irrigation intervals (days) Mean* Clones Irrigation intervals (days) Mean* 7 14 21 7 14 21 24.1722a 17.3333 20.0833 ٭a 9.8333ab 5.3333bc 9.9444a TIS 35.1000٭TIS 14.6667 BY 4.5000bc 2.5000c 1.0000c 2.6667b BY 8.5000 5.7333 6.5000 6.9111b BR 4.1667bc 0.3334c 3.3333bc 2.6111b BR 11.8333 26.3333 14.8333 17.6667a Mean** 7.7778 4.2222 3.2222 Mean** 18.4778 17.3822 12.8889 S.E.± for irrigation intervals = 1.6872 S.E.± for irrigation intervals = 2.1332 S.E.± for clones = 1.1771 S.E.± for clones = 3.6977 S.E.± for irrigation intervals X clones (interaction) = 2.03 88 S.E.± for irrigation intervals X clones (interaction) = 6.4047 c. Third count 6 months after transplanting. d. Fourth count 7 months after transplanting. Clones Irrigation intervals (days) Mean* Clones Irrigation intervals (days) Mean* 7 14 21 7 14 21 59.5556a 59.6667 29.5000 ٭a 32.0000b 15.0000cd 33.5000a TIS 89.5000٭TIS 53.5000 BY 12.3333cd 18.3333bc 5.9167d 12.1944c BY 28.6667 24.6667 21.1667 24.8334b BR 23.8333bc 26.7000bc 21.0000bc 23.8444b BR 63.3333 19.3333 45.5000 42.7222ab Mean** 29.8889 25.6778 13.9722 Mean** 60.5000a 24.5000b 42.1111b S.E.± for irrigation intervals = 3.4060 S.E.± for irrigation intervals = 4.6243 S.E.± for clones = 2.7159 S.E.± for clones = 6.5716 S.E.± for irrigation intervals X clones (interaction) = 4.7040 S.E.± for irrigation intervals X clones (interaction) = 11.3824 A foot note for Table 30 (a to d) -TIS=TIS2544, BY= Baladi yellow, BR=Baladi red (figures in this square are means of interaction effect (irrigation intervals X clones=٭ ,Mean*= of clones, Mean**= of irrigation intervals-

110 - Means followed by similar letters are not significantly different at 0.05 level of probability according to Duncan’s multiple range test (DMRT).

111 TIS2544 and BR produced the higher yields (24.17 and 17.67 ton/ha) than BY (6.91 ton/ha). A remarkable difference among clones on the total storage root weight can be noticed 6 MAT (Table 30c) TIS2544 gave the highest yield (33.50 ton/ha) followed by BR (23.84 ton/ha) and BY produced the least yield (12.19 ton/ha). Also a significant interaction effect between treatments was recorded TIS2544-7 DII gave the greatest yield (53.50 ton/ha) while; BY-21 DII scored the smallest yield (5.92 ton/ha). A considerable variation was found between clones, TIS2544 produced the highest yield (59.56 ton/ha) and BY recorded the lowest one (24.83 ton/ha) (Table 30d). It was obvious that the exotic clone TIS2544 surpassed the local clones BY and BR on the yield. A positive correlation between the total storage root weight and percentage of infested storage roots existed among irrigation intervals (r = 0.43) and the clones (r = 0.70) when data was pooled. Figures (14 and 15) show the relationship between the infested storage root weight and the total storage root weight among sweetpotato clones and irrigation intervals respectively.

The results in Table (31a, b, c and d) show the effects of irrigation intervals, sweetpotato clones and their interaction on the percentage of infested storage roots of sweetpotato. Four months after transplanting no sweetpotato weevil infestation was recorded among the treatments. A month latter, a slight infestation was recorded, but did not show any significant difference between the treatments. There was a significant variation among irrigation intervals 6 MAT, 21 DII (5.24%) and 14 DII (6.70%) were equally infested whereas, no infestation was observed in the 7 DII treatment. The clones and their interaction with irrigation intervals had no great influence on

111 70 Infested storage root w eight (ton/ha) Total storage root w eight (ton/ha) 60

50

40

30

20

Storage root weight (ton/ha) 10

0 ) ) ) ) ) ) ) ) ) ) ) ) T T T T T T T T T T T T A A A A A A A A A A A A M M M M M M M M M M M M 4 5 6 7 4 5 6 7 4 5 6 7 ( ( ( ( ( ( ( ( ( ( ( ( 4 4 4 4 Y Y Y Y R R R R 54 54 54 54 B B B B B B B B 2 2 2 2 IS IS IS IS Sweetpotato clones T T T T

Fig. 14. Relationship betyween infested storage root weight and total storage root weight of sweetpotato clones during different harvest times (autumn 2002/2003).

70 Infested storage root w eight (ton/ha) Total storage root w eight (ton/ha) 60

50

40

30

20

10 Storage root weight (ton/ha) 0

) ) ) ) T) T) T) T) T) T) T) T) AT AT AT AT A A A A A A A A M M M M M M M M M M M M (4 (5 (6 (7 (4 (5 (6 (7 (4 (5 (6 (7 II II II II II II II II II II II II D D D D D D D D D D D D 7 7 7 7 14 14 14 14 21 21 21 21 Irrigation intervals

Fig. 15. Relationship between infested storage root weight and total storage root weight of sweetpotao among irrigation intervals during different harvest times (autumn 2002/2003).

112 Table 31(a,b,c and d). Effect of irrigation intervals, sweetpotato clones and their interaction on percentage of infested storage root by the weevil Cylas puncticollis on sweetpotato grown during the period (November, 2002/June, 2003). a. First count 4 months after transplanting#. b. Second count 5 months after transplanting. Clones Irrigation intervals (days) Mean* Clones Irrigation intervals (days) Mean* 7 14 21 7 14 21 (1.03)1.74 (1.15)0.83 (1.00) 0.50 ٭(TIS 0.0 0.0 0.0 0.0 TIS 0.41(0.95 BY 0.0 0.0 0.0 0.0 BY 0.0 (0.71) 2.08 (1.61) 0.0 (0.71) 0.69(1.01) BR 0.0 0.0 0.0 0.0 BR 0.0 (0.71) 0.0 (0.71) 0.89(1.18) 0.30(0.86) Mean** 0.0 0.0 0.0 Mean** 0.14(0.79) 0.86(1.10) 0.57 (1.01) #No infestation observed. S.E.± for irrigation intervals = 0.1921 S.E.± for clones = 0.2193 S.E.± for irrigation intervals X clones (interaction) = 0.3798 c. Third count 6 months after transplanting. d. Fourth count 7 months after transplanting. Clones Irrigation intervals (days) Mean* Clones Irrigation intervals (days) Mean* 7 14 21 7 14 21 a(26.88)25.68 (47.85)49.37 (28.31)26.11 ٭(TIS 1.56(4.47 (2.45)7.24 (3.87)14.44 (2.79) 7.27 ٭(TIS 0.0(0.71 BY 0.0 (0.71) 8.57 (3.01) 0.0 (0.71) 2.86(1.48) BY 0.0 (0.57) 7.86 (13.31) 32.12(34.55) 13.33(16.14)ab BR 0.0 (0.71) 4.25 (2.18) 1.29 (1.34) 1.85(1.41) BR 0.0 (0.57) 2.38 (5.72) 3.04 (6.37) 1.81 (4.22)b Mean** 0.0(0.71)b 6.70(2.66)a 5.24(3.21)a Mean** 0.53(1.89) 12.12(15.78) 28.21(29.59) S.E.± for irrigation intervals = 0.2887 S.E.± for irrigation intervals = 5.9648 S.E.± for clones = 0.4701 S.E.± for clones = 5.2322 S.E.± for irrigation intervals X clones (interaction) = 0.8142 S.E.± for irrigation intervals X clones (interaction) = 9.0662

A foot note for Table 31 (a to d) -TIS=TIS2544, BY= Baladi yellow, BR=Baladi red; data between parenthesis were transformed. -Mean*= of clones, Mean**= of irrigation intervals, `=figures in this square are means of interaction effect (irrigation intervals X clones)

113 - Means followed by similar letters are not significantly different at 0.05 level of probability according to Duncan’s multiple range test (DMRT).

114 sweetpotato weevil infestation (Table 31c). At the late harvest 7 MAT a significant variation in sweetpotato weevil infestation could be noticed among clones, TIS2544 was severely infested 25.68% and BR showed the lowest infestation (1.81%). It was clear that sweetpotato weevil infestation was negligible during autumn planting up to 6 MAT. Infestation was less than 7.24% (Table 31c), but it increased suddenly to a maximum of 28.21% (Table 31d). It is worth mentioning that, the imported clone TIS2544 was more susceptible to sweetpotato weevil infestation than the local clones (BR and BY) throughout the growing season of sweetpotato. Figures (16 and 17) show the relationship between percentage of infested storage roots and different harvest times among irrigation intervals and clones, respectively.

Table (32a, b, c and d) shows the effect of irrigation intervals, sweetpotato clones and their interaction on percentage of infested stem of sweetpotato. There was no significant difference between the treatment means 4 and 5 MAT. But for 6 MAT, a remarkable difference among clones can be observed BY (46.67%) was severely infested than TIS2544 (15.55%) and BR (13.33%); it has been equally observed that a significant difference among irrigation intervals occurred, 21 DII scored the highest percentage of infestation 40.0% followed by 14 DII (17.78%) and 7 DII (17.78%); no interaction effect was observed. Late in the season 7 MAT a highly significant difference on stems infestation was recorded among clones, BY showed the highest percentage of infestation 48.89% whereas, BR and TIS2544 showed the least percentage of infestation 8.89 and 8.89%, respectively. A significant difference between irrigation intervals was

114 35 7 day irrigation intervals 14 day irrigation intervals 30 21 day irrigation intervals

25

20

15

10

5 % of infested storage root

0 4 MAT 5 MAT 6 MAT 7 MAT Time of harvest (months after transplanting) Fig. 16. Effect of irrigation intervals and time of harvest on % of infested storage root by the weevil Cylas puncticollis on sweetpotato (autumn 2002/2003).

30 TIS2544 Baladi yellow Baladi red 25

20

15

10 % of infested storage roots 5

0 4 MAT 5 MAT 6 MAT 7 MAT Time of harvest (months after transplanting)

Fig. 17. Effect of sweetpotato clones and time of harvest on % of infested storage root by the weevil Cylas puncticollis on sweetpotato (autumn 2002/2003).

115 Table 32 (a,b,c and d). Effect of irrigation intervals, sweetpotato clones and their interaction on percentage of infested stem by the weevil Cylas puncticollis on sweetpotato during the period (November, 2002/June, 2003). a. First count 4 months after transplanting. b. Second count 5 months after transplanting. Clones Irrigation intervals (days) Mean* Clones Irrigation intervals (days) Mean* 7 14 21 7 14 21 TIS 40.02(38.86 31.68(29.2 33.33(30.43 35.01(32.85 (6.90)4.55 18.1)13.35 (1.28)0.05 ٭ (TIS 0.05(1.28 ( ( (8 ٭( (3 BY 41.27(39.99 54.02(43.38 76.67(65.7 57.32(49.70 BY 40.02(38.86 73.33(59.2 53.33(46.92 55.56(48.33 ) ) 2) ) ) 2) ) ) BR 33.45(31.15 23.35(24.28 29.18(27.3 28.66(27.59 BR 33.37(30.43 46.67(43.0 33.33(34.63 37.79(36.05 ) ) 3) ) ) 8) ) ) Mean* 28.1(24.14) 25.81(22.98 39.18(37.0 Mean* 37.86(36.05 50.56(43.8 40.00(37.33 * ) 6) * ) 6) ) S.E.± for irrigation intervals = 3.5741 S.E.± for irrigation intervals = 10.5314 S.E.± for clones = 11.313 S.E.± for clones = 5.6053 S.E.± for irrigation intervals X clones (interaction) = 19.595 S.E.± for irrigation intervals X clones (interaction) = 9.7087 c. Third count 6 months after transplanting. d. Fourth count 7 months after transplanting. Clones Irrigation intervals (days) Mean* Clones Irrigation intervals (days) Mean* 7 14 21 7 14 21 b(9.59)8.89 (9.71)6.67 17.78)20.0 ٭(TIS 13.33(13.93 13.33(13.93 20.0(23.28 15.55(16.83 TIS 0.0(1.28 ( b( ( ( ٭( BY 40.0(34.65) 40.0(38.85) 60.0(51.15 46.67(41.88 BY 33.33(30.43 33.33(35.0 80.0(68.07) 48.49(44.50 ) )a ) 1) )a BR 0.0(1.28) 0.0(4.05) 40.0(38.85 13.33(13.80 BR 0.0(1.28) 6.67(9.71) 20.0(26.56) 8.89(12.52) ) )b b Mean* 17.78(16.62 17.78(18.02 40.0(37.54 Mean* 11.11(11.00 20.0(20.83 35.56(34.78 * )b )b )a * )b )b )a S.E.± for irrigation intervals = 2.666 S.E.± for irrigation intervals = 3.1582 S.E.± for clones = 5.208 S.E.± for clones = 5.7832

116 S.E.± for irrigation intervals X clones (interaction) = 9.092 S.E.± for irrigation intervals X clones (interaction) = 10.0168 A foot note for Table 32 (a to d) -TIS=TIS2544, BY= Baladi yellow, BR=Baladi red; data between parenthesis were transformed. (figures in this square are means of interaction effect (irrigation intervals X clones=٭ ,Mean*= of clones, Mean**= of irrigation intervals- - Means followed by similar letters are not significantly different at 0.05 level of probability according to Duncan’s multiple range test (DMRT).

117 detected, 21 DII was severely infested 35.56% followed by 14 DII (20.0%) and 7 DII (11.11) (Table 32d). Generally 7 DII was least infested among irrigation intervals. Local clone stems were more susceptible to sweetpotato weevil infestation than exotic TIS2544 clone. A weak positive correlation between percentage of infested storage roots and percentage of infested stems was observed among irrigation intervals (r = 0.08); and a weak negative correlation between clones existed (r = - 0.21).

4.5.2 The influence of irrigation intervals and sweetpotato clones on sweetpotato weevil infestation (winter transplanting experiment).

Table (33a) indicates that, there were no significant differences on stem thickness among the treatment means. A higher significant difference on stem thickness was recorded between clones 5 MAT, BR had a thicker stem (0.93 cm) than both BY (0.79 cm) and TIS2544 (0.78 cm) (Table 33b). It can clearly be seen that no statistical variation among both the irrigation intervals and their interaction effect with clones. There was a significant difference between irrigation intervals 6 MAT, 7 DII showed the thicker stems (0.87 cm) whereas, 14 DII showed the thinner ones (0.75 cm). There was a marked difference among clones, BR (0.96 cm) exceeded both TIS2544 (0.76 cm) and BY (0.71 cm) in stem thickness, no interaction effect existed (Table 33c). Seven months after transplanting, a noticeable difference among irrigation intervals was recorded, 7 DII attained the thickest stems (0.94 cm) compared to 14 DII (0.76 cm) and 21 DII (0.76 cm) (Table 33d). Generally 7 DII possessed thicker stems than 14 DII and 21 DII. Baladi red clone recorded the biggest stem thickness than both BY and TIS2544.

117 Table 33 (a,b,c and d). Effect of irrigation intervals, sweetpotato clones and their interaction on stem thickness (cm) of sweetpotato grown during the period (November, 2002/June, 2003). a. First count 4 months after transplanting. b. Second count 5 months after transplanting. Clones Irrigation intervals (days) Mean* Clones Irrigation intervals (days) Mean* 7 14 21 7 14 21 0.7756b 0.7400 0.7333 ٭TIS 0.8533 0.682 0.693 0.667 ٭TIS 0.687 BY 0.773 0.628 0.680 0.694 BY 0.8600 0.7467 0.7500 0.7867b BR 1.000 0.9000 0.867 0.922 BR 0.9067 0.9000 0.9800 0.9289a Mean** 0.820 0.731 0.747 Mean** 0.8733 0.7933 0.8244 S.E.± for irrigation intervals = 0.0214 S.E.± for irrigation intervals = 0.0267 S.E.± for clones = 0.0601 S.E.± for clones = 0.0270 S.E.± for irrigation intervals X clones (interaction) = 0.1042 S.E.± for irrigation intervals X clones (interaction) = 0.0468 c. Third count 6 months after transplanting. d. Fourth count 7 months after transplanting. Clones Irrigation intervals (days) Mean* Clones Irrigation intervals (days) Mean* 7 14 21 7 14 21 0.790 0.830 0.700 ٭0.762b TIS 0.840 0.833 0.693 ٭TIS 0.760 BY 0.833 0.627 0.673 0.711b BY 0.980 0.680 0.650 0.770 BR 1.010 0.920 0.940 0.957a BR 1.000 0.890 0.790 0.890 Mean** 0.868a 0.747b 0.815ab Mean** 0.940a 0.760b 0.760b S.E.± for irrigation intervals = 0.0217 S.E.± for irrigation intervals = 0.0114 S.E.± for clones = 0.0258 S.E.± for clones = 0.0407 S.E.± for irrigation intervals X clones (interaction) = 0.0447 S.E.± for irrigation intervals X clones (interaction) = 0.0705 A foot note for Table 33 (a to d) -TIS=TIS2544, BY= Baladi yellow, BR=Baladi red (figures in this square are means of interaction effect (irrigation intervals X clones=٭ ,Mean*= of clones, Mean**= of irrigation intervals-

118 -Means followed by similar letters are not significantly different at 0.05 level of probability according to Duncan’s multiple range test (DMRT).

119 A weak negative correlation between stem thickness and percentage of infested storage roots among irrigation intervals was noticed (r = -0.22) while a very weak positive correlation (r = 0.04) among clones was recorded. Referring to Table (34a, b, c and d) effect of irrigation intervals, sweetpotato clones and their interaction on storage root neck length of sweetpotato was evaluated. No statistical variation was observed among irrigation interval treatments and their interaction with clones throughout the growing season of sweetpotato. A considerable variation between clones was observed, BR had longer storage root necks (11.71 cm) compared to BY (8.72 cm); and the latter had a longer storage root neck than TIS2544 (5.02 cm) (Table 34a). Five months after transplanting, BR (8.70 cm) and BY (8.26 cm) were highly significantly different from TIS2544 (5.75 cm). It can clearly be observed that, considerable variations among clones occurred, BR obtained the longest storage root neck (10.19 cm) while, TIS2544 had the shortest ones (4.47 cm) (Table 34c). The same trend was continued 7 MAT as previously described; BR clone had the longest storage root neck (8.89 cm) and TIS2544 had the shortest one (5.17 cm) (Table 34d). Moderate to strong negative correlation were observed between storage root neck length and percentage of infested storage roots among irrigation intervals 7, 14 and 21 day (r = -0.74, -0.92 and -0.73, respectively) whereas, a weak to strong negative correlation was recorded among clones TIS2544, BY and BR (r = -0.35, -0.95 and - 0.45, respectively). As shown in Table (35a, b, c and d) irrigation interval treatments and their interaction with clones had no significant effect

119 Table 34 (a,b,c and d). Effect of irrigation intervals, sweetpotato clones and their interaction on storage root neck length (cm) of sweetpotato grown during the period (November, 2002/June, 2003). a. First count 4 months after transplanting. b. Second count 5 months after transplanting. Clones Irrigation intervals (days) Mean* Clones Irrigation intervals (days) Mean* 7 14 21 7 14 21 5.753b 6.533 6.427 ٭5.019c TIS 4.300 4.693 5.860 ٭TIS 4.503 BY 9.033 7.500 9.617 8.717b BY 8.980 7.157 8.640 8.259a BR 11.773 10.550 12.817 11.713a BR 10.533 9.177 6.397 8.702a Mean** 8.437 7.970 9.042 Mean** 7.838 7.587 7.190 S.E.± for irrigation intervals = 0.3775 S.E.± for irrigation intervals = 0.8444 S.E.± for clones = 0.3128 S.E.± for clones = 0.6318 S.E.± for irrigation intervals X clones (interaction) = 0.9687 S.E.± for irrigation intervals X clones (interaction) = 1.0944 c. Third count 6 months after transplanting. d. Fourth count 7 months after transplanting. Clones Irrigation intervals (days) Mean* Clones Irrigation intervals (days) Mean* 7 14 21 7 14 21 5.167c 4.500 4.033 ٭4.474c TIS 6.967 5.093 4.010 ٭TIS 4.320 BY 8.447 6.250 6.600 7.099b BY 6.820 6.433 6.067 6.440b BR 11.133 9.567 9.877 10.190a BR 8.813 9.000 8.843 8.886a Mean** 7.967 6.609 7.190 Mean** 7.533 6.489 6.470 S.E.± for irrigation intervals = 0.3689 S.E.± for irrigation intervals = 0.3173 S.E.± for clones = 0.5060 S.E.± for clones = 0.3427 S.E.± for irrigation intervals X clones (interaction) = 0.8774 S.E.± for irrigation intervals X clones (interaction) = 0.5936 A foot note for Table 34 (a to d) -TIS=TIS2544, BY= Baladi yellow, BR=Baladi red (figures in this square are means of interaction effect (irrigation intervals X clones=٭ ,Mean*= of clones, Mean**= of irrigation intervals-

120 - Means followed by similar letters are not significantly different at 0.05 level of probability according to Duncan’s multiple range test (DMRT).

121 Table 35 (a,b,c and d). Effect of irrigation intervals, sweetpotato clones and their interaction on storage root girth (cm) of sweetpotato grown during the period (November, 2002/June, 2003). a. First count 4 months after transplanting. b. Second count 5 months after transplanting. Clones Irrigation intervals (days) Mean* Clones Irrigation intervals (days) Mean* 7 14 21 7 14 21 4.141a 3.647 3.913 ٭3.382a TIS 4.863 3.317 3.120 ٭TIS 3.710 BY 2.487 2.273 2.479 2.479b BY 3.007 2.603 2.320 2.643b BR 3.643 2.713 2.353 2.903b BR 5.103 3.273 3.700 4.026a Mean** 3.280 2.702 2.782 Mean** 4.324 3.263 3.222 S.E.± for irrigation intervals = 0.1225 S.E.± for irrigation intervals = 0.2800 S.E.± for clones = 0.1499 S.E.± for clones = 0.1227 S.E.± for irrigation intervals X clones (interaction) = 0.2596 S.E.± for irrigation intervals X clones (interaction) = 0.2125 c. Third count 6 months after transplanting. d. Fourth count 7 months after transplanting. Clones Irrigation intervals (days) Mean* Clones Irrigation intervals (days) Mean* 7 14 21 7 14 21 5.1756a 5.620 4.360 ٭4.312a TIS 5.547 4.293 3.753 ٭TIS 4.890 BY 3.117 2.587 2.687 2.797b BY 3.713 2.953 3.293 3.3200b BR 5.667 3.617 4.640 4.641a BR 3.493 2.767 3.573 3.2778c Mean** 4.558 3.319 3.873 Mean** 4.251a 3.360b 4.162a S.E.± for irrigation intervals = 0.2792 S.E.± for irrigation intervals = 0.1820 S.E.± for clones = 0.1421 S.E.± for clones = 0.2021 S.E.± for irrigation intervals X clones (interaction) = 0.2461 S.E.± for irrigation intervals X clones (interaction) = 0.3501

A foot note for Table 35 (a to d) -TIS=TIS2544, BY= Baladi yellow, BR=Baladi red (figures in this square are means of interaction effect (irrigation intervals X clones=٭ ,Mean*= of clones, Mean**= of irrigation intervals-

122 - Means followed by similar letters are not significantly different at 0.05 level of probability according to Duncan’s multiple range test (DMRT).

123 on storage root girth up to 6 MAT. A month latter, a remarkable difference among irrigation intervals was recorded on storage root girth, 7 DII (4.25cm) and 21 D II (4.16cm) exceeded 14 DII (3.36cm).

The interaction showed no significant effect on storage root girth throughout the growing season of sweetpotato. Table (35a) shows that, there was a high significant difference between clones TIS2544 scored the greater storage root girth (3.38 cm) than both BR (2.90 cm) and BY (2.48 cm). It can be noticed that, there was a high significant difference between clones 5 MAT, TIS2544 (4.14 cm) and BR (4.03 cm) clones both surpassed BY (2.64 cm) on storage root girth. Six months after transplanting, BR (4.64 cm) and TIS2544 (4.31 cm) clones recorded the larger storage root girths than BY (2.80 cm). Latter in the season 7 MAT significant differences between clones were obtained; TIS2544 attained the bigger storage root girth 5.18 cm followed by BY (3.32 cm) and BR (3.28 cm) (Table 35d). Generally, it was clear that 7 DII had greater storage root girth among irrigation interval treatments. Whereas, TIS2544 obtained the larger storage root girth among clones followed by BR and then BY clone. A weak positive correlation between storage root girth and percentage of infested storage roots were recorded among irrigation intervals (r = 0.23) and clones (r = 0.37) when data was pooled. Table (36a, b, c and d) shows the effect of irrigation intervals, sweetpotato clones and their interaction on the infested storage root weight. There were no statistical differences between all treatment means 4 MAT on the infested storage root weight. It was obvious that, there was a significant difference among irrigation intervals 14 DII (1.56 ton/ha) and 21 DII (1.44 ton/ha) exceeded 7 DII (0.17 ton/ha); also a highly significant difference was observed between clones, TIS2544 (2.22 ton/ha) recorded the highest infested storage root

122 Table 36 (a,b,c and d). Effect of irrigation intervals, sweetpotato clones and their interaction on infested storage root weight (ton/ha) by the weevil Cylas puncticollis on sweetpotato grown during the period (November, 2002/June, 2003). a. First count 4 months after transplanting. b. Second count 5 months after transplanting. Clones Irrigation intervals (days) Mean* Clones Irrigation intervals (days) Mean* 7 14 21 7 14 21 2.2225a 2.8333 3.8333 ٭TIS 0.001 0.2785 0.001 0.8334 ٭TIS 0.001 BY 0.001 0.001 0.100 0.0340 BY 0.500 0.6667 1.1667 0.7778b BR 0.001 0.001 0.1670 0.0563 BR 0.001 0.1667 0.3334 0.1670b Mean** 0.001 0.2785 0.0891 Mean** 0.1673b 1.5556a 1.4444a S.E.± for irrigation intervals = 0.1419 S.E.± for irrigation intervals = 0.1856 S.E.± for clones = 0.1628 S.E.± for clones = 0.3713 S.E.± for irrigation intervals X clones (interaction) = 0.2820 S.E.± for irrigation intervals X clones (interaction) = 0.6431 c. Third count 6 months after transplanting. d. Fourth count 7 months after transplanting. Clones Irrigation intervals (days) Mean* Clones Irrigation intervals (days) Mean* 7 14 21 7 14 21 9.9447a 4.1667 10.00 ٭bc 16.667a 14.6667a 10.7224a TIS 15.6667٭TIS 0.8334 BY 0.001c 4.3333bc 2.5000bc 2.2781b BY 7.6667 2.1667 0.9000 3.5778b BR 0.001c 5.5000b 4.5000bc 3.3337b BR 10.6667 4.8333 3.1667 6.2222b Mean** 0.2785 8.8333 7.2222 Mean** 11.3334a 5.6667b 2.7445b S.E.± for irrigation intervals = 1.9923 S.E.± for irrigation intervals = 0.8602 S.E.± for clones = 0.9010 S.E.± for clones = 0.6861 S.E.± for irrigation intervals X clones (interaction) = 1.5610 S.E.± for irrigation intervals X clones (interaction) = 1.1884 A foot note for Table 36 (a to d) -TIS=TIS2544, BY= Baladi yellow, BR=Baladi red (figures in this square are means of interaction effect (irrigation intervals X clones=٭ ,Mean*= of clones, Mean**= of irrigation intervals-

123 -Means followed by similar letters are not significantly different at 0.05 level of probability according to Duncan’s multiple range test (DMRT).

124 weight than BY (0.78 ton/ha) and BR (0.17 ton/ha); no significant interaction effect was observed (Table 36b). Six months after transplanting, no significant differences were noticed between irrigation interval treatments but, a highly significant difference was recorded among clones, TIS2544 showed higher infested storage root weight (10.72 ton/ha) than both BR (3.33 ton/ha) and BY (2.28 ton/ha) ; a significant interaction effect was found, TIS2544-14 DII (16.67 ton/ha) and TIS2544-21 DII (14.67 ton/ha) recorded the highest infested storage root weight whereas, BY-7 DII and BR-7 DII showed no infested storage root weight (Table 36c). At the end of the season a remarkable difference between irrigation intervals was noticed, 7 DII (11.33 ton/ha) had more infested storage root weight than both 14 DII (5.67 ton/ha) and 21 DII (2.74 ton/ha). The clones recorded a significant difference on the infested storage root weight, TIS2544 attained the larger infested storage root weight (9.94 ton/ha) than BR (6.22 ton/ha) and BY (3.58 ton/ha); no significant interaction effect between treatments occurred (Table 36d). Generally speaking early in the season 14 DII and 21 DII recorded more infested storage root weight than 7 DII, but at the end of the season 7 DII recorded more infested storage root weight. TIS2544 always attains higher infested storage root weight than BR and BY clones. Fig. (18) shows the effects of irrigation intervals and time of harvest on the infested storage root weight of sweetpotato. Fig. (19) shows the effect of sweetpotato clones and time of harvest on the infested storage root weight.

A moderate positive correlation was found between infested storage root weight and percentage of infested storage roots among the irrigation intervals (r = 0.65) and the clones (r = 0.78) when data was pooled.

124 12 TIS2544 Baladi yellow Baladi red 10

8

6

4

2 Storage root weight (ton/ha)

0 4 MAT 5 MAT 6 MAT 7 MAT Time of harvest (months after transplanting)

Fig. 18. Effect of sweetpotato clones and time of harvest on the infested storage root weight by the weevil Cylas puncticollis on sweetpotato (2002/2003).

12 7 day irrigation intervals 14 day irrigation intervals 10 21 day irrigation intervals

8

6

4

2 Storage root weight (ton/ha)

0 4 MAT 5 MAT 6 MAT 7 MAT Time of harvest (months after transplanting)

Fig. 19. Effect of irrigation intervals and time of harvest on the infested storage root weight by the weevil Cylas puncticollis on sweetpotato (winter 2002/2003).

125 As shown in Table (37a, b, c and d), it can well be seen that there was no variation between irrigation interval treatments on the total storage root weight of sweetpotato at the early harvest 4 MAT. But considerable variations were noticed among clones, TIS2544 produced the highest yield (13.72 ton/ha) compared to BR (8.50 ton/ha) and BY (5.53 ton/ha). The interaction effect between the clones and irrigation intervals on the total storage root weight was noticeable; TIS2544-7 DII gave the highest yield (19.17 ton/ha). The results in Table (37b), 5 MAT show a significant difference on the total storage root weight between clones, TIS2544 and BR scored the highest yield 19.67 and 19.61 ton/ha respectively,whereas BY gave the lowest one (8.72 ton/ha). No significant differences were observed between irrigation intervals and their interaction with clones. But the same pattern among the clones was repeated 6 MAT as mentioned previously for 5 MAT, TIS2544 and BR produced the highest yield 29.56 and 25.33 ton/ha, respectively and BY attained the lowest yield 12.72 ton/ha. Seven days irrigation interval scored the highest yield 40.67 ton/ha whereas, no significant difference between 21 DII (14.89 ton/ha) and 14 DII (12.06 ton/ha). The interaction effect between clones and irrigation intervals on the total storage root weight was highly significant, BR-7 DII (54.0 ton/ha) and TIS3544-7 DII (47.83 ton/ha) gave the highest yield while, BY-14 DII, BR-14 DII, BY-21 DII and BR-21 DII produced the lowest yield (8.0-13.67 ton/ha). Referring to Table (37d) a marked difference between irrigation intervals was recorded, 7 DII scored the highest

126 Table 37 (a,b,c and d). Effect of irrigation intervals, sweetpotato clones and their interaction on the total storage root weight (ton/ha) of sweetpotato grown during the period (November, 2002/June, 2003). a. First count 4 months after transplanting. b. Second count 5 months after transplanting. Clones Irrigation intervals (days) Mean* Clones Irrigation intervals (days) Mean** 7 14 21 7 14 21 19.6667a 13.8333 13.1667 ٭TIS 19.1667a 11.3333b 10.6667bc 13.722a TIS 32.0000 BY 8.8333bc 3.3333c 4.4333bc 5.533b BY 16.3333 4.0000 5.8333 8.7222b BR 9.6667bc 7.0000bc 8.8333bc 8.500b BR 25.6667 15.3333 17.8333 19.6111a Mean** 12.5556 7.2222 7.9778 Mean* 24.6667 10.8333 12.500 S.E.± for irrigation intervals = 3.0738 S.E.± for irrigation intervals = 3.2494 S.E.± for clones = 1.2924 S.E.± for clones = 2.8540 S.E.± for irrigation intervals X clones (interaction) = 2.2385 S.E.± for irrigation intervals X clones (interaction) = 4.9432 c. Third count 6 months after transplanting. d. Fourth count 7 months after transplanting. Clones Irrigation intervals (days) Mean* Clones Irrigation intervals (days) Mean 7 14 21 7 14 21 27.1667a 4.1667 10.0000 ٭TIS 47.8333a 19.8333b 21.0000b 29.5555a TIS 67.3333 BY 20.1667b 8.0000c 10.0000bc 12.7222b BY 32.1667 3.0000 0.9000 12.0222b BR 54.0000a 8.3333c 13.6667bc 25.3333a BR 36.5000 4.83330 3.1667 14.8333b Mean** 40.6667a 12.0555b 14.8889b Mean** 45.3333a 5.9444b 2.7445b S.E.± for irrigation intervals = 3.5257 S.E.± for irrigation intervals = 0.9756 S.E.± for clones = 1.5047 S.E.± for clones = 3.1504 S.E.± for irrigation intervals X clones (interaction) = 2.6062 S.E.± for irrigation intervals X clones (interaction) = 5.4567

A foot note for Table 37 (a to d) -TIS=TIS2544, BY= Baladi yellow, BR=Baladi red

127 ---figures in this square are means of interaction effect (irrigation intervals X clones=٭ ,Mean*= of clones, Mean**= of irrigation intervals- -Means followed by similar letters are not significantly different at 0.05 level of probability according to Duncan’s multiple range test (DMRT).

128 yield (45.33 ton/ha), while no significant difference between 14 DII (5.94 ton/ha) and 21 DII (2.74 ton/ha) was observed. A significant variation occurred between clones, TIS2544 produced the highest yield (27.17 ton/ha) compared to BR (14.83 ton/ha) and BY (12.02 ton/ha). No interaction effect was recorded.

A weak to moderate positive correlation between total storage root weight and percentage of infested storage roots was recorded among clones TIS2544, BY and BR (r = 0.65, .60 and 0.26 respectively). Figures (20 and 21) show the relationship between total storage root weight and infested storage root weight among irrigation intervals and sweetpotato clones, respectively.

Data presented in Table (38a) show that no great influence on the percentage of infested storage roots caused by both the irrigation intervals and the clones. Five months after transplanting a significant variation on the percentage of infested storage roots between clones was noticeable, TIS2544 (12.73%) and BY 8.71%) were more infested than BR (0.93%). However, no significant difference was observed between the irrigation intervals and their interaction effect with the clones (Table 38b). Table (38c) reflects a clear difference on the percentage of infested storage roots between irrigation intervals, 21 DII (49.15%) and 14 DII (48.63%) scored higher percentage of infested storage roots than 7 DII (0.38%). A considerable variation between clones was also recorded, TIS2544 was severely infested (41.09%) than BY (28.54%) and BR (21.13%). But, no significant interaction effect between the treatments was noticed. Seven months after transplanting a significant difference on the percentage of infested storage roots among irrigation intervals was recorded, 21 DII

128

50 Infested storage root w eight (ton/ha) 45 Total storage root w eight (ton/ha) 40 35 30 25

(ton/ha) 20 15

Storage rootweight 10 5 0 ) ) ) ) ) ) ) ) ) ) ) ) AT AT AT AT AT AT AT AT AT AT AT AT M M M M M M M M M M M M 4 5 6 7 (4 (5 (6 (7 (4 (5 (6 (7 II ( II ( II ( II ( II II II II II II II II D DFig. 20. D Relationship D D between D D infested D Dstorage D root D weight D 7 7 7 7 14 14 14 14 21 21 21 21 and Irrigation intervals total storage root weight by the weevil Cylas puncticollis among irrigation intervals during different harvest times (winte 2002/2003).

35 Infestestorage root w eight (ton/ha) Total storage root w eight (ton/ha) 30

25

20

15

10

Storage root weight (ton/ha) 5

0 ) ) ) ) ) ) ) T T T T) T) A A A A A M MAT MAT (5 MAT (6 M (7 MAT) 5 6 M 6 7 (7M (4 MAT (5 M ( ( 4 R 44 44 BY (4 MAT)BY ( BY ( BY B BR BR BR IS254 IS25 S25 TIS2544 (4T MAT) T TI Sweetpotato clones

Fig. 21. Relationship between infested storage root weight and total storage root weight by the weevil Cylas puncticollis on sweetpotato clones during different harvest times (winter 2002/2003).

129 Table 38 (a,b,c and d). Effect of irrigation intervals, sweetpotato clones and their interaction on percentage of infested storage root by the weevil Cylas puncticollis on sweetpotato grown during the period (November, 2002/June, 2003). a. First count 4 months after transplanting. b. Second count 5 months after planting. Clones Irrigation intervals (days) Mean* Clones Irrigation intervals (days) Mean* 7 14 21 7 14 21 (3.19)12.73 (4.30)17.99 (4.55)20.2 ٭(TIS 0.0(0.71) 2.16(1.63) 8.74(3.04) 3.63(1.79) TIS 0.0(0.71 a ٭ BY 0.0 (0.71) 0.0 (0.71) 8.99(3.08) 3.00(1.50) BY 2.67(1.78) 9.3(3.12) 14.17(3.83) 8.71(2.91)a BR 0.0 (0.71) 0.0 (0.71) 6.82(2.71) 2.27(1.37) BR 0.0(0.71) 1.16(1.29) 1.36(1.46) 0.93(1.15)b Mean* 0.0 (0.71) 0.72(7.22) 8.18(2.94) Mean* 0.89(1.06) 10.22(2.99) 33.29(3.20) * * S.E.± for irrigation intervals = 0.2601 S.E.± for irrigation intervals = 0.4580 S.E.± for clones = 0.2403 S.E.± for clones = 0.5559 S.E.± for irrigation intervals X clones (interaction) = 0.4162 S.E.± for irrigation intervals X clones (interaction) = 0.9628 c. Third count 6 months after planting. d. Fourth count 7 months after planting. Clones Irrigation intervals (days) Mean* Clones Irrigation intervals (days) Mean* 7 14 21 7 14 21 TIS 1.15(3.97) 61.56(52.22 76.49(67.08 46.40(41.09) TIS 43.23(41.08) 100.0(90.00 100.0(90.0) 81.08(73.6 ) ) a ) 9) BY 0.0(0.57) 44.01(41.49 47.89(43.57 30.63(28.54) BY 31.44(33.72) 88.89(78.25 100.0(90.0) 73.44(67.3 ) ) b ) 2) BR 0.0(0.57) 40.33(39.27 23.06(30.22 21.13(23.35) BY 38.57(38.19) 100.0(90.00 100.0(90.0) 79.52(72.7 ) ) b ) 3)

129 Mean* 0.38(1.70) 48.63(44.32 49.15(46.96 Mean* 37.75(37.66) 96.30(86.08 100.0(90.0) b )a )a b )a a * * S.E.± for irrigation intervals = 5.8685 S.E.± for irrigation intervals = 2.6703 S.E.± for clones = 2.8549 S.E.± for clones = 2.7018 S.E.± for irrigation intervals X clones (interaction) = 4.9448 S.E.± for irrigation intervals X clones (interaction) = 4.6797

A foot note for Table 38 (a to d) -TIS=TIS2544, BY= Baladi yellow, BR=Baladi red; data between parenthesis were transferred. (figures in this square are means of interaction effect (irrigation intervals X clones=٭ ,Mean*= of clones, Mean**= of irrigation intervals- -Means followed by similar letters are not significantly different at 0.05 level of probability according to Duncan’s multiple range test (DMRT).

130 (100%) and 14 DII (96.30%) were severely infested whereas, 7 DII had been less infested (37.37%). No significant differences were observed among clones and their interaction with irrigation interval treatments (Table 38d). It is worth mentioning that, at late harvests (6 and 7 MAT) a higher percentage of infested storage roots were recorded compared to the early harvesting times (4 and 5 MAT). It was clearly observed that 21 DII and 14 DII were excessively infested by the sweetpotato weevil than 7 DII in the winter season. The exotic clone TIS2544 was more susceptible to SPW infestation than the local clones BY and BR. Figures (22 and 23) show the relationship between percentage of infested storage roots and harvest times among irrigation intervals and clones, respectively.

Table (39a, b, c and d) illustrates the effect of irrigation intervals, sweetpotato clones and their interaction on the percentage of infested stems of sweetpotato. There was a high significant difference on percentage of infested stems among clones 4 MAT, BY (7.85%) was more infested than TIS2544 (1.14%) and BR showed no infestation (0.0). No significant variation was observed between irrigation intervals and their interaction with clones. Five months after transplanting, the treatments had no influence on the percentage of infested storage roots. Table (39c) indicates that, there was a high significant difference on the percentage of infested stems among clones, BY (30.35%) was more infested than BR (17.78%) and TIS2544 (4.45%). Also an interaction effect was observed between irrigation intervals and the clones, BY-21 DII (66.67%) and BR-14 DII (46.67%) were severely infested. No significant difference was recorded between irrigation intervals. Seven months after

131 100 7 day irrigation intervals 90 14 day irrigation intervals 21 day irrigation intervals 80 70 60 50 40 30 20

%of infestedstorage roots 10 0 4 MAT 5 MAT 6 MAT 7 MAT Time of harvest (months after transplanting)

Fig. 22. Effect of irrigation intervals and time of harvest on% of infested storage root by the weevil Cylas puncticollis during different harvest times (winter 2002/2003).

80 TIS2544 Baladi yellow 70 Baladi red

60

50

40

30

20 % of infested storage root 10

0 4 MAT 5 MAT 6 MAT 7 MAT Time of harvest (months after transplanting)

Fig. 23. Effect of sweetpotato clones and time of harvest on %of infested tubers by the weevil Cylas puncticollis (winter 2002/2003).

132 Table 39 (a,b,c and d). Effect of irrigation intervals, sweetpotato clones and their interaction on percentage of infested stem by the weevil Cylas puncticollis on sweetpotato grown during the period (November, 2002/June, 2003). a. First count 4 months after transplanting. b. Second count 5 months after transplanting. Clones Irrigation intervals (days) Mean* Clones Irrigation intervals (days) Mean* 7 14 21 7 14 21 11.0)11.11 (17.78)20.0 13.9)13.33 ٭(b TIS 0.0(1.28(1.13)1.14 (0.71) 0.0 (1.98) 3.42 ٭(TIS 0.0(0.71 3) 0) BY 3.32(1.98) 10.06(3.25) 10.06(3.25) 7.85(2.83)a BY 13.08(13.93 60.0(51.57) 33.33(30.4 35.47(31.9 ) 3) 8) BR 0.0 (0.71) 0.0 (0.71) 0.0 (0.71) 0.0(0.71)b BR 0.0(1.28) 26.67(26.2 0.0(1.28) 8.89(9.59) 0) Mean* 1.14(1.13) 4.49 (1.98) 3.35 (1.56) Mean* 4.36(5.50) 33.33(30.5 17.78(16.5 7) 0) * * S.E.± for irrigation intervals = 0.6004 S.E.± for irrigation intervals = 6.2796 S.E.± for clones = 0.4586 S.E.± for clones = 6.9074 S.E.± for irrigation intervals X clones (interaction) = 0.7943 S.E.± for irrigation intervals X clones (interaction) = 11.9639 c. Third count 6 months after transplanting. d. Fourth count 7 months after transplanting. Clones Irrigation intervals (days) Mean* Clones Irrigation intervals (days) Mean* 7 14 21 7 14 21 b 6.67(9.71)b 6.67(9.71)b 4.45(6.90)b TIS 33.67(30.03 56.67(48.4 40.0(34.24) 43.45(37.5 ٭(TIS 0.0(1.28 (7 (4 ٭( BY 17.71(18.13 6.67(9.71)b 66.67(54.99 30.35(27.61 BY 63.33(57.29 53.33(46.9 66.67(54.9 61.11(53.0 )b )a )a ) 2) 9) 7) BR 0.0(1.28)b 46.67(42.70 6.67(9.71)b 17.78(17.90 BR 26.67(21.18 60.0(55.78) 30.0(31.92) 38.39(36.2 )a )b ) 9)

133 Mean* 5.90(6.90) 20.0(20.71) 26.67(24.80 Mean* 41.22(36.17 56.67(50.3 45.56(40.3 ) ) 8) 9) * * S.E.± for irrigation intervals = 4.0990 S.E.± for irrigation intervals = 10.1233 S.E.± for clones = 3.5095 S.E.± for clones = 10.2233 S.E.± for irrigation intervals X clones (interaction) = 6.0786 S.E.± for irrigation intervals X clones (interaction) = 17.7073 A foot note for Table 39 (a to d) -TIS=TIS2544, BY= Baladi yellow, BR=Baladi red; data between parenthesis. (figures in this square are means of interaction effect (irrigation intervals X clones=٭ ,Mean*= of clones, Mean**= of irrigation intervals- -Means followed by similar letters are not significantly different at 0.05 level of probability according to Duncan’s multiple range test (DMRT).

134 Transplanting; no significant difference observed between the treatment means. Generally, BY clone stems were more infested than TIS2544 and BR clone. Fourteen days irrigation interval and 21 DII were more infested than 7 DII.

A strong positive correlation between percentage of infested stems and percentage of infested storage roots was found among both treatments the irrigation intervals 7, 14 and 21 day (r = 0.99, 0.76 and 0.93, respectively) and the clones (r = 0.83, 0.82 and 0.76, respectively) Figures (24 and 25).

4.5.3 Sweetpotato weevil management

Data presented in Table (40) show the effect of different control measures on some vegetative and yield components of sweetpotato grown during the period from November, 2002 to May, 2003. Deltamethrin (Decis) application, earthing up the soil, deltamethrin plus earthing up the soil, carbofuran (Furadan) and carbofuran plus earthing up the soil had no influence on stem thickness, storage root neck length, storage root girth, percentage of infested storage roots and percentage of infested stems. However, a high significant difference on the total storage root weight was recorded between the control and earthing up the soil and a significant difference between deltamethrin plus earthing up the soil and control was also recorded.

134 100 %of infested storage root 90 % of infested stem 80 70 60 50

infestation 40 30

% of sweetpotato weevil 20 10 0 ) ) ) ) ) ) ) ) ) ) ) ) AT AT AT AT AT AT AT AT AT AT AT AT M M M M M M M M M M M M 4 5 6 7 (4 (5 (6 (7 (4 5 (6 (7 II ( II ( II ( II ( II II II II II I ( II II D D D D D D D D D D D D 7 7 7 7 14 14 14 14 21 21 21 21 Irrigation intervals Fig. 24. Relationship between % of infested storage roots and % of infested stems by the weevil Cylas puncticollis on sweetpotato among irrigation intervals during different harvest times (winter 2002/2003).

n 80 % of infested storage roots % of infested stems 70 60 50 40 30 20 10 of sweetpotato weevil infestatio 0 ) ) ) ) ) ) T A MAT MAT) MAT MAT MAT) MAT) 6 7 MAT 4 M 6 MAT) 7 MAT 6 7 ( ( ( (4 (5 4 ( 4 ( Y R 4 4 B BY (5 BY BY B BR BR ( BR ( IS2544 (4 MAT) IS25 Sweetpotato clones T TIS2544 (5TIS25 MAT) T

Fig. 25. Relationship between % of infested storage roots and % of infested stems by the weevil Cylas puncticollison sweetpotato clones during different harvest times (winter 2002/2003).

135 Table 40. Effect of different control treatments on some sweetpotato vegetative and yield characters and on the percentage of infestation of sweet potato weevil Cylas puncticollis Boh. during the period (November, 2002/May, 2003). Sweetpotato characters Stem Storage root neck Storage root Total storage % of infested % of thickness length (cm) girth (cm) root weight storage root infested Treatments (cm) ton/ha stems Deltamethrin 0.79 4.64 5.24 16.375ns 48.18 36.59 Earthing up the soil 0.78 5.84 5.07 22.250** 49.44 48.20 Deltamethrin plus earthing up 0.75 4.55 4.92 19.750* 33.07 41.85 Carbofuran 0.75 4.75 4.53 12.625ns 52.50 29.74 Carbofuran plus earthing up 0.74 4.90 4.81 15.125ns 45.42 27.68 Control 0.75 5.28 4.61 12.250 54.69 51.07 SE± 0.0420 0.6396 0.3764 0.1838 10.869 6.4381 LSD 0.05 0.5540 LSD 0.01 0.7662 ns = not significant * = significant at 0.05 level of probability ** = significant at 0.01 level of probability

136 5. DISCUSSION

Many inset pests have the potential to reduce the quality and yield of sweetpotatoes. Pests that damage the root directly are most troublesome and referred to as soil pests. The sweetpotato weevil is a serious pest of sweetpotatoes that can be a problem in the field and in the storage. In this investigation it was noted mainly to attack storage roots under the soil, rarely seem to be associated with floral part or the vines above the soil. Attack appeared in the field during the maturity stage of the crop. 5.1 Laboratory experiments During this study females of sweetpotato weevil, Cylas puncticollis were observed laying eggs on the storage roots in holes excavated by their snouts and covered them by a white or grayish material (plugged with frass). This habit was earlier reported by many workers (Sutherland, 1986a; Allard, 1990; Braun and van de Fliert, 1999 and Ring, 1999). The incubation period of the eggs was the same under room conditions (3.0 ± 0.71 and 3.0 ± 0 .58 Tables 1 and 19) and under a constant temperature of 30°C and 65% R.H. (3.0 ± 0.0 and 3.43 ± 0.54 Tables 2 and 20). This may be attributed to the similar microhabitat inside the storage roots; also it is the same as reported by Allard (1990) and Sathula et al., (1997) who reported that incubation period averaged 3.3 days. Other workers recorded different ranges for the incubation period (Schmutterer, 1969; Moyer et al., 1989 and Ring, 1999). The larval and pupal developmental periods are in accordance with results obtained by Schmutterer (1969); Moyer et al., (1989); and Geisthart and van Harten (1992).The total developmental period partially differed (Tables 5 and 23) from results recorded by Nwana (1979) who recorded that the total developmental period lies between 22-32 days. But in the same line with results recorded by Anota and Leuschner (1983); Anota and Odebiyi (1984) reported that the total developmental period range between 19-25 days.

137 There was a highly significant difference in the duration of the total life cycle of the weevil between the disturbed and undisturbed rearing within each season (Tables 5 and 23), this difference may be attributed to the time that the teneral adults stay inside the storage roots before they emerge, this result is also in the same line with Smit (1997) who indicated that adults eclosion usually occurred 1-4 days before emergence from the root and was dependent on the proximity of the pupal chamber to the surface. According to previous records, the estimated period which adults spend within the storage root after eclosion varies widely from 1-3 days at 27ºC (Mullen, 1981) to 15 days at 26ºC (Yoshida, 1985) and Sugimoto et al., (1996) suggested that many females remain in the storage root for at least 4-6 days after eclosion.

Duration of the total life cycle of sweetpotato weevil under room conditions was significantly shortened compared to those reared at constant temperature of 30°C and 65% R.H. (Tables 3, 4, 21 and 22). High temperature accelerates the development of sweetpotato weevil, these results coincided with conclusion drawn by other authors (Hahn and Anota, 1983 and Nteletsana et al., 2001). It is well known that weevil development is temperature dependant (Maily, 1996 and Ring, 1999). However, the effect of the environment on the insect life cycle and behaviour are also not well understood, although laboratory studies show the importance of temperature on the duration of the total life cycle of C. formicarius (Mullen,1984) and on C. puncticollis and C. brunneus (Smit et al., 1991).

Preoviposition period was not different from findings recorded by earlier investigators (Anota and Leuchner, 1983; Anota and Odebiyi, 1984; Dawes et al., 1987; Moyer et al., 1989 and Allard, 1990). But in contrast with Smit (1997) who reported that it was 13.9 days,

138 considerably longer than 4.33 ± 1.18 days reported in this study (Table 24 ). Jansson and Hunsberger (1991) reported that females’ weevils begin laying eggs about 4 days after adults’ emergence and continue to lay eggs for over 75 days thereafter. Young female insects laid limited number of eggs per day 3.90 ± 0.09; this result was slightly different from that mentioned by Smit and van Huis, (1998). This could probably due to the differences in the experimental conditions. However a study in Uganda by Semwogerere (1999) confirmed our results; he recorded that the average number of eggs laid per day per female of Cylas puncticollis was 2.7 and 2.3 for singly and continuously mated females, respectively.

The sex ratio (female: male) for Cylas puncticollis as found by Allard (1990) and Smit and van Huis, (1998) was 1: 1 is in the same line with the results obtained in this study.

5.2 Field experiments

5.2.1 Autumn transplanting season experiments (2001/02) and (2002/03)

Irrigation intervals 7, 14 and 21days and sweetpotato clones TIS2544, Baladi yellow (BY) and Baladi red (BR) had no significant influence on stem thickness of sweetpotato in both autumn transplanting seasons (2001/02) and (2002/03)(Tables 6 and 26). No clear relationship between stem thickness and percentage of infested storage roots appeared; in the first season a weak positive correlation was found (r = 0.34) among irrigation intervals while in the second season a moderate negative correlation was found (r = -0.52). Also, the same phenomenon was observed among clones between stem thickness and percentage of infested storage roots in the first and the second season (r = 0.02 and r = - 0.58), respectively. Sweetpotato clones that possess thin stems generally are less liable to infestation by sweetpotato weevil, the same observation

139 was mentioned by Cockerham and Deen (1947) and Pole (1988) who reported that cultivars with hard storage roots, thin or hard crowns and stems were also identified as being more resistant to weevil damage.

A very important observation drawn from this study is that, there was a highly significant difference in storage root neck length between clones. Local clones (BY and BR) had longer storage root necks than the exotic clone TIS2544, there was a negative correlation between storage root neck length and percentage of infested storage roots in both seasons (2001/02) and (2002/03) r = -0.1 and r = -0.38, respectively. Hence local clones are less susceptible to sweetpotato weevil infestation; this finding is in agreement with many workers (Singh et al., 1987; Chalfant et al., 1990; Teli and Salunke, 1994; Cisneros et al., 1995; Smit and Odongo, 1995-1996; Smit, 1997 and Lagnaoui et al., 2000).

Although there was no significant difference in storage root girth between irrigation intervals in both seasons except 4 and 5 months after transplanting (MAT) in the first season, where 14 days irrigation interval (DII) had bigger storage root girth. A positive correlation (r = 0.44 and r = 0.65 in the first and the second season respectively) could be noticed between storage root girth and percentage of infested storage roots. Jayaramaiah (1975b); Singh et al., (1987) and Teli and Salunke (1994) recorded similar results. TIS2544 clone showed bigger storage root girth in both seasons notably at the beginning of the season, TIS2544 always equals or exceeds the local clones in storage root girth . Results in both seasons followed a similar pattern. TIS2544 seems to be an early maturing clone whereas local clones are late maturing ones, so TIS2544 suffered high percentage of sweetpotato weevil infestation.

Data recorded on the infested storage roots weight by sweetpotato weevil manifested the same pattern in both seasons. A significant

140 difference was observed between the clones in the first season (Table 9), TIS2544 always has greater infested storage root weight than other clones; but 9 MAT, BY scored the greatest infested storage root weight, as we concluded latter BY clone matures late. The insect population build up with time, hence BY subjected to severe attack at the end of the season, clones which showed less susceptibility early in the season become susceptible as the season progressed. This indicates that this insect floreshes as a store pest. Clones that give higher total storage root weight usually had higher infested storage root weight, this result supports Talekar (1983) results, who mentioned that larger roots which were produced in plants grown after rice rotation may have also helped to increase weevil density. Root number per plot and root weight per plot, were positively associated with infestation levels at Ukiriguru (1997) and Serere (1998) and both parameters differ significantly between cultivars. These two parameters are associated with root yield. It has long been postulated that higher yielding cultivars are likely to be more susceptible to attack by Cylas spp. However, it is important to recognize that this relationship exists (Stather et al., 2003). Sweetpotatoes which were irrigated every 7 or 14 days give higher yield than those irrigated every 21 days. The latter might suffer from water stress. TIS2544 gave the highest yield in both autumn seasons (Tables 10 and 30), it matures early. When harvest was delayed, the infestation of sweetpotato clones by the weevil increased. Lenne (1991) reported that farmers might delay harvest after physiological maturity to increase yield or to get higher prices at a late date. But postponing harvest 30 days means a fourfold increase in damage. Usually a positive correlation between total weight of the storage roots and the percentage of infested storage roots existed (r = 0.23 and r = 0.43) for the irrigation intervals and (r = 0.31 and r = 0.72) for the clones in the first and the second season, respectively.

141 At the beginning of the harvesting time, sweetpotato weevil infestation was low and no significant difference in the percentage of infested storage roots was obtained between irrigation intervals, this may be attributed to the fact that soil was still moist and the crop canopy is too dense, so no soil cracking was available for weevil entry. Insect population density was also low, contrary to the end of the season, when sweetpotato weevil infestation was so high. Although no significant difference among irrigation intervals was observed 7 MAT, 21 DII suffered higher percentage of infestation than 14 and 7 DII (Tables 11 and 31). These results are in agreement with AVRDC report (I987) which indicated that there was no significant difference in weevil infestation in three irrigation interval treatments (10, 20 and 30 days interval) in both seasons (1985-1986) and (1986-1987). There was however, a tendency for the number of weevils per unit root weight to increase, with increasing interval between two consecutive irrigations. Moreover, Bhat (1987) concluded that in 3 districts of Orissa, India, the sweetpotato weevil was not important in the Kharif season. In the first season infestation of sweetpotato by weevils was very low, but when irrigation was stopped 7 MAT infestation of sweetpotato weevil increased drastically and reached 100% (Table 11f). Climate and under ground storage can have a significant effect on the degree of soil cracking; drier soils are more prone to cracking so increasing the chance of weevil infestation. The percentage of infestation in both autumn seasons was similar among clones up to 7 MAT, TIS 2544 was severely infested than the local clones BY and BR (Fig. 17). This may be attributed to the fact that local clones had longer storage root necks than the exotic clone TIS2544; this character was well known to reduce sweetpotato weevil infestation.

142 In the first autumn transplanting season 9 MAT all clones were severely infested by the weevil and loss in yield ranged from 54.21 to 100% (Table 11e and f ). Development of infestation is influenced by many environmental factors such as temperature and rainfall (irrigation) as well as the state of the crop and cultural practices. The situation with sweetpotato weevil is further complicated by the long growing season and cumulative nature of damage as illustrated by general increase in the infestation levels the longer the storage roots were left in the ground (Aldrich, 1963 and Mukibii, 1976). These results are similar to those of CIP report (1995) in Cuba where infestation during the dry season was 4- 5 times higher than during the rainy season or when irrigation was available. Sutherland (1986a) added that damage increased sharply between 24-30 weeks. O’Hair (1991) reported that the relationship between sweetpotato plant growth and weevil attack is complex. There are critical periods during the growth of the plant when it is more vulnerable to attack by these weevils (e.g. late in the season when storage roots are more available) and this relationship is affected by population dynamics of these weevils. In the field, population of Cylas formicarius increase exponentially at a rate of about one weevil per plant per day, with most increase in population density occurring late in the growing season when storage roots are available (Jansson et al., 1990).

Percentage of infested stems was high at the beginning of (2002/03) autumn season. No significant differences between irrigation intervals and among clones were observed. Later in the season, a significant difference was observed between irrigation intervals; 21 DII was severely infested than 14 and 7 DII, BY clone was highly significantly infested and TIS2544 was the least infested. This can be attributed to some phytochemicals found in BY clone. Starr et al., (1991)

143 mentioned that differences in susceptibility to weevil may be largely due to chemical differences among genotypes, which could result in variation in initial attraction (host choice). Positive correlation (r = 0.08) between percentage of infested storage roots and percentage of infested stems was observed among different irrigation intervals and a weak negative correlation (r = -0.21) between clones existed. Cockerham and Harrison (1952) and Talekar (1982) found the absence of any correlation between the numbers of sweetpotato weevil in crowns and roots.

5.2.2 Winter transplanting season experiments (2001/02) and (2002/03)

In both winter transplanting seasons (2001/02) and (2002/03) irrigation intervals had no significant effect on stem thickness except in the second season 6 and 7 MAT, 7 DII had thicker stems and lower percentage of infested storage roots. Generally, BR clone had thicker stem in both seasons followed by BY and TIS2544. A weak positive correlation between stem thickness and percentage of infested storage roots among clones (r = 0.3 and r = 0.04 in the first and the second season, respectively) was obtained. These results confirmed autumn transplanting experiments. However, no clearly defined pattern was obtained between stem thickness and percentage of infested storage root, this result is in line with Talekar (1982) who found the absence of any correlation between the number of sweetpotato weevils in the crowns and roots.

In both winter seasons (2001/02) and (2002/03) no significant differences were observed in storage root neck length between the irrigation intervals, but a highly significant difference was obtained among the clones, BR attained the longest storage root neck in both seasons, this indicated that storage root neck length is a clone character.

144 A negative correlation was recorded between storage root neck length and percentage of infested storage roots among irrigation intervals(r = -0.3 and r = -0.03) and among clones (r = -0.18 and r = -0.30) in the first and the second season, respectively. From these results and results drawn from autumn seasons we can conclude that local sweetpotato clones BR and BY are less susceptible to sweetpotato weevil infestation, they usually set their storage roots deeper in the soil and escape weevil infestation. There is quite clear evidence that deep rooting confers resistance, since the weevil can burrow only very short distances through the soil (Jayaramaiah, 1975b; Smit, 1997 and Stathers et al.,2003) and usually rely on soil cracks to reach the roots (Sherman and Tamashiro, 1954). Selection of longer stalk (neck) lengths can reduce accessibility of storage roots to weevils (O’Hair, 1991).

Irrigation intervals had no significant difference on storage root girth in both winter seasons. But a highly significant difference between clones was obtained. TIS2544 had bigger storage root girth and BY had the smaller ones. This may indicate that storage root girth is a clone character. A positive correlation between storage root girth and percentage of infested storage roots was noted among clones (r = 0.56 and r = 0.37) in season (2001/02) and (2002/03) respectively. Bigger storage root sizes of sweetpotato were more liable to attack by sweetpotato weevils than smaller ones this result is in the line with the results of Singh et al., (1987).

The effect of irrigation intervals on the infested storage root weight was not significant in the first winter season expect 6 MAT (May); in the second winter season the effect of irrigation was significant 5 and 7 MAT and the results did not follow defined pattern and they hard to explain. This might be due to variation in temperature of the months. However, 7

145 DII had the smaller infested storage root weight, as we explained previously 7 DII keeps soil moisture and usually obtained thick plant canopy, hence reduce accessibility of storage roots to the weevil. But a positive correlation was recorded between percentage of infested storage roots and the infested storage root weight among irrigation intervals (r = 0.68 and r = 0.65 in the first and second winter season, respectively). TIS2544 clone had the greater infested storage roots weight than local clones BY and BR in both seasons, and strong positive correlation occurred between percentage of infested storage roots and infested storage root weight (r = 0.96 and r = 0.78) in seasons (2001/02) and (2002/03), respectively. This may be attributed to the fact that TIS2455 was an early maturing variety and had bigger storage root girth which always succumbs to weevil infestation. Insect population build up with time; also local clones had longer storage root neck lengths that enable them to avoid weevil infestation, all these factors exacerbated infestation of TIS2544 clone, these results are in agreement with many workers who were mentioned previously.

Highly significant differences in the total storage root weight among irrigation intervals were recorded at the end of both winter transplanting seasons, 7 DII yielded out 14 DII and 21 DII. In Sudan May and June are dry and hot months, so irrigating every 7 DII keeps soil moist and prevent soil cracking and, hence reducing sweetpotato weevil infestation and increase probability to have un-infested storage roots also crop grows normally without suffering from water stress. These results are in agreement with Sutherland (1986b) and Lagnaoui et al., (2000). TIS2544 clone produced higher yield than local clones in both winter seasons, this is because TIS2544 is an improved and early maturing clone. There is evidence that weevil tend to attack relatively mature

146 storage roots than immature ones NRS (1992). Occitti p’Owoya (1990) reported that some early maturing varieties are highly susceptible while others are low to medium; late maturing varieties appear to be tolerant to pest attack.

There were highly significant differences in the percentage of infested storage roots between irrigation intervals 5 and 7 MAT in the first season and 6 and 7 MAT in the second season, 7 DII was less infested than 14 and 21 DII (Figures 12 and 22). We can conclude that irrigation intervals are important factors in infestation of sweetpotato weevil, this result is partially in accordance with AVRDC (1987) and supports results from Indonesia reported by Lenne (1991). TIS2544 showed higher percentage of infested storage roots in both winter seasons than the local clones due to the reasons mentioned previously. BR clone was the least susceptible to sweetpotato weevil infestation.

Irrigation intervals had no significant effect on the percentage of infested stems in winter season (2002/03), but 7 DII seems to be less infested than other irrigation intervals, the same results were observed in autumn seasons (2002/03). This may be due to setting of thin stem when irrigating every 7 DII (Table ). Talekar (1982) mentioned that weevil- infested crowns were thicker indicating that adventitious root growth replaced the damaged tissue, thus allowing proper plant development. BY clone was more infested than TIS3544 and BR in winter and autumn seasons (2002/03), this may be attributed to some chemical components presents in BY clone. In winter season (2002/03) a strong positive correlation between percentage of infested storage roots and percentage of infested stems existed in the treatments, irrigation intervals (r = 0.84) and clones (r = 0.76) (Figures 24 and 25). These results are in agreement with Talekar (1982) who reported that heavy infestation in vine has been

147 correlated with high damage in storage roots and reduction in total yields and storage root size, although there is evidence that this is not always the case; Mullen et al., (1980) described a negative correlation between crown damage and adult emergence from infested roots. Further studies by Mullen et al., (1982) indicated heavy crown damage reduces yield, although previous studies by Cockerham et al., (1954) and Talekar (1982) reported that the degree of crown infestation had no effect on the total yield. The most probable explanation for the large disparities among the findings is the timing and severity of the infestation (Mullen et al., 1985) and variation in the environmental conditions (Stathers et al., 1999).

In some 75 lines, infestation of crown and roots by Cylas formicarius elegantulus appeared not to be correlated (Jones et al., 1978). Larvae feed inside the vines; the effect of weevil densities in vines on root yield has produced variable and often contradicting results (Cockerham et al., 1954; Mullen, 1984 and Sutherland, 1986b).

The period of peak weevil abundance coincided with the period of drier weather conditions and soil cracking. Significant negative correlations were obtained between weevil numbers and relative humidity, soil moisture content, rainfall and number of rainy days, suggesting that the amount and distribution of moisture over time are critical for the levels of weevil infestation on sweetpotato. Delay in harvesting of storage roots increased the level of weevil infestation damage (Alghali and Moifula, 1996).

5.2.3 Sweetpotato weevil management

At present, in the absence of resistant cultivars, and under conditions where the use of insecticides is not feasible, cultural practices are the only effective means of controlling sweetpotato weevils. Pre-

148 planting insecticides applications have been used to exterminate weevils from planting material (vine cuttings) before planting. During this study different control treatments were applied to control sweetpotato weevil showed no significant effect in both seasons (2001/02) and (2002/03) on stem thickness, storage root neck length and storage root girth. These traits are clone characters and slightly affected by cultural practices. Generally the results followed similar trend in both seasons. Earthing (hilling) up the soil alone or combined with insecticide application (deltamethrin or carbofuran) significantly reduced the percentage of infested storage roots. For whatever variety the farmers chose, rehilling resulted in high yield and reduced pest attack (Odongo et al., 2003). These results are in accordance with many workers (Franssen, 1935; Holdaway, 1941; Sherman and Tamashiro, 1954; Macfarlane, 1987; Lenne, 1991 and Palaniswami and Mohandas, 1994). Deltamethrin alone or when combined with earthing up reduced sweetpotato weevil infestation. Rajamma (1990) tested seven insecticides for the control of Cylas formicarius on sweetpotatoes in the field, Kerala, India during 1982-1983, deltamethrin was found among the most effective insecticides. Carbofuran when applied alone was not different from the control, but when combined with earthing up it was effective, many workers recommended carbofuran for sweetpotato weevil control (Talekar, 1983 and Cabangbang and Rodriguez, 1989). The efficacy of carbofuran may be reduced as the crop harvest is delayed 6 MAT.

149 6. REFERENCES Alcazar, J.; Cisneros, F. and Morales, A. (1997). Large-scale implementation of the IPM for sweetpotato weevil in Cuba. A collaborative effort. Lima, Peru. International Potato Centre: pp 185-190. Aldrich, D. (1963).The sweet potato crop in Uganda. East African Agricultural and Forestry Journal 29: 42-49. Alghali, A.M. and Moifula, A.J. (1996). The influence of weather parameters and plant characters on the relative abundance of the weevil Cylas puncticollis Boheman on two sweet potato cultivars in Sierra Leone. Afr. J. Pl. Prot. 6 : 34-41. Alhag, I.M. (1998). Agricultural and chemical evaluation of sweet potato (Ipomoea batatas) genotypes grown under Shambat conditions. M.Sc. Thesis, University of Khartoum, Sudan. Ali, A.M. and Bushra M.E. (1993a). Response of sweet potato (Ipomoea batatas) cultivars to the time of planting in the semi-arid environment of Shambat, Sudan. University of Khartoum Journal of Agricultural Science, 1 (2): 99-112. Ali, A.M. and Bushra M.E. (1993b). Effects of mineral nutrients on growth and yield of sweet potato (Ipomea batatas) in Shambat area, Sudan. University of Khartoum Journal of Agricultural Science, 1 (2): 113-124. Allrad, G.B. (1990). Integrated control of pests of root crops. November, 1988-December, 1989. Mid-term Report. Nairobi, Kenya: CAB International.

150 Allrad, G.B.; Cock, M.I.W. and Rangi, D.K. (1991). Integrated control of arthropod pests of root crops. Final Report. Nairobi, Kenya: CAB International. Anioke, S.C. (1996). Effect of time of planting and harvesting of sweet potato (Ipomoea batatas (L.) Lam.) on yield and insect damage in South-eastern Nigeria. Entomon., 21(2): 137-141. Anioke, S.C.; Chukwu, G.O. and Nwinyi, S.C.O. (1993). The effect of different rates of potassium application on control of sweet potato pests. Journal of Potassium Research, 9(1): 44-47. Anota,T. and Leuschner, K. (1983). Survival of sweet potato weevil on some promising sweet potato clones. International Institute of Tropical Agriculture (IITA): pp 70-74. Anota, T. and Odebiyi, J.A. (1984). Resistance in sweet potato to Cylas puncticollis Boh. (Coleoptera: Curculionidae). Biologia Africana, 1 (1): 21-30. AVRDC (1987). Progress Report for 1987. Asian Vegetable Reserch and Development Center, Shanhua, Taiwan: 177-189. AVRDC (1988). Progress Report for 1988. Asian Vegetable Research and Development Center, Shanhua, Taiwan: 35-41. AVRDC (1990). Progress Report Summaries for 1989. Asian Vegetable Research and Development Center, Shanhua, Taiwan: 33-39. Bashaasha, B.; Mwanga, R.O.M.; Ocitti p’Owoya, C. and Ewell, P. (1995). Sweet potato in the farming and food systems of Uganda: A farm survey report. CIP, Nairobi, Kenya. 63 pp. *Bhat, P.S. (1987). Annual Progress Report 1986 for the period January- December. Central Storage Root Crops Research Institute, Trivandrum, Kerala, India: 103-104. Borror, D.J. and White, R.E. (1970). A field guide to the insects of America North of Mexico. Houghton Miffling Company, Boston.

151 Braun, R.B. and van de Fliert, E. (1999). Evaluation of the impact of sweet potato weevil (Cylas formicarius) and the effectiveness of Cylas sex pheromone traps at the farm level in Indonesia. International Journal of Pest Management, 45 (2): 101-110. Burns, R. (1999). Sweet potato weevil put an industry at risk in north east Texas. Texas Agricultural Extension Service, Texas, USA. Buxton, P.A. (1931). The measurement and control of atmospheric humidity in relation to entomological problems. Bull. ent. Res., 22: 431-447. Buxton, P.A. and Mellanby, K.(1934). The measurement and control of humidity. Bull. ent. Res., 25: 171-175. *Cabangbang, R.P. and Rodriguez, J.D.C. (1989). Culture and management requirement of sweet potao (Ipomoea batatas L.) in central Luzon. Phillippine Journal of Crop Science, 14(2): 77-82. Calder, A.A. (1989). The alimentary canal and nervous system of Curculioniodea (Coleoptera): Gross morphology and systematic significance. Journal of Natural History, 23(6): 1205-1265. Chalfant, R.B.; Jansson, R.K.; Seal, D.R. and Schalk, J.M. (1990). Ecology and management of sweet potato insects. Ann. Rev. Ent., 35:157-180. CIP (1995). Program Report: 1993-1994 International Potato Center (CIP) Lima, Peru, 192 p. Cisneros, F.; Alcazar, J.; Palacious, M. and Ortiz, O. (1995). A strategy for developing and implementing Integrated Pest Management. CIP circular 21: 2-7. Cockerham, K.L. (1943). The host preference of sweet potato weevil. J. econ. Ent., 36: 471-472. Cockerham, K.L. and Deen, O.T. (1947). Resistence of new sweet potato seedlings to attack by sweeopotato weevil. J. econ. Ent.,45: 132.

152 Cockerham, K.L. and Harrison, P.K. (1952). New sweetpotato seedlings that appear resistant to sweetpotato weevil attack. Ann. Entomol. Soc. Am. 74 : 478-481. Cockerham, K.L. ; Deen, O.T.; Christian, M.B. and Newsom, L.D. (1954). The biology of the sweetpotato weevil. La. Agric. Exp. Stn. Tech. Bull. No. 483: 1-30. Collins, W.W.; Jones, A.; Mullen, M.A.; Talekar, N.S. and Martin, F.W. (1991). Breeding sweet potato for insect resistance: A global overview. In: Jannson, R.K. and Raman, K.V. (eds.), Sweet potato pest management. A global perspective. Westview Press Boulder, San Francisco, Oxford: 379-398. Daiber, K.C. (1994). Injurious insects, spider mites and nematodes on sweet potatoes in Southern Africa. Zeitschrift für Pflazenkrankheiten und Pflanzenschutz. 101(5): 550-557. Dalip, K.M. (2000). Major pests of sweet potato Ipomea batatas (L). Workshop on the Integrated Pest Management of Sweet Potato November 26-30, 2000, Caribbean Agricultural Research and Development Institute. Dawes, M.A.; Saini, R.S.; Mullen, M.A.; Brower, J.H. and Loretan, P.A. (1987). Sensitivity of sweet potato weevil (Coleoptera: Curculionidae) to gamma radiation. J. econ. Ent., 80: 142-146. El Hilo, A.E. and Ahmed, M.A. (1966). Agricultural Research Corporation, Annual Report, Wad Medani, Sudan. El Nadi, A.H. and Kheir, E.M. (1969). Appraisal of the meteorological approach for assessing evaporation under tropical conditions. Sudan Agric. J., 4(2): 38-47. El Shafie, B.E. (1967). Agricultural Research Corporation, Annual Report (1966/67), Wad Medani, Sudan. F.A.O(1999). Production Year Book 1998. vol. 52.

153 Franssen, C.G.H. (1935). Insect pests of sweet potato in Java. Overdruck Landbouw, 10: 205-225. (Original in Dutch, English translation published by Asian Vegetable Research and Development Center, Shanhua, Taiwan 1986). Gapasin, R.M. (1989). Studies on the major diseases and pests of sweet potato at VISCA, the Philippines. In: Makay, K.; Palomar, M. K. and Sanico, R. T. (eds.). Sweet potato research and development for small farmers. Los Banos, Philippines: SEAMEO-SEARCA, IDRC. Geisthardt, M. and van Harten, A. (1992). Noxious of the Cape Verde Islands with additional reference to West Africa. Weisbaden, Germany: Verlag Christa Hemmen, 197-198. Gomez, F. and Carr, M.K.V. (2003). Effects of water availability and vine harvesting frequency on the productivity of sweet potato in southern Mozambique. Expt. Agri. 39: 39-54. Hahn, S.K. and Anota, T. (1983). Mortality pattern of weevils buried in soil at different depth. International Institute of Tropical Agriculture, Annual Report 1983. Ibadan, Nigeria. Hahn, S.K. and Leuschner, K. (1982). Breeding sweet potato for weevil resistance. In: Villareal, R.L. and Griggs, T.D. (eds.). Sweet potato Proc. of the 1st. Inter. Symp. Asian Vegetable Research and Development Center, Shanhua, Taiwan: 331-336. Ho, T.H. (1970). Studies on some major pests of sweet potato and their control. Malysian Agricultural Journal, 47(4): 437-445. Holdaway, F.G. (1941). Insects of sweet potato and their control. Hawaii Agricultural Experiment Station Progress Notes. No. 2. Ibrahim, A.K. (2000). Studies on the sweet potato productivity as influenced by some cultural practices under heavy clays. Ph. D. Thesis, University of Khartoum, Sudan.

154 IITA (1974). Root and storage root improvement programme. International Institute of Tropical Agriculture Report 1972-73. Ibadan, Nigeria: IITA. Jana, R.K. (1982). Status of sweet potato cultivation in East Africa and its future. In: Villareal, R.L. and Griggs, T.D. (eds.). Sweet potato Proc. of the 1st. Inter. Symp. Asian Vegetable Research and Development Center, Shanhua, Taiwan, 63-72. Jansson , R.K. and Hunsberger, A.G.B. (1991). Diet on ontogenic patterns of oviposition in the sweet potato weevil (Coleoptera: Curculionidae). Environ. Entomol. 20: 454-550.

155 Jansson, R.K.; Lecrones, S.H. and Gaugler, R.R. (1991). Comparison of single and multiple releases of Heterorhabditis bacteriophora (Nematoda: Heterorhabditidae) for control of Cylas formicarius (Fabricius) (Coleoptera: Apionidae). Biological Control, 1: 320- 328. Jansson , R.K. and Hunsberger, A.G.B. .; Lecrones, S.H. and O’Hair, K.K. (1990). Seasonal abundance, population growth, and within plant distribution of sweet potato weevil (Coleoptera: Curculionidae) on sweet potato in southern Florida. Environ. Entomol. 19 : 313-321. Jansson, R.K.; Mason, L.J.; Heath, R.R.; Sorensen, K.A.; Hammond, A.M. and Robinson, J.V. (1992). Pheromone-trap monitoring system for sweetpotato weevil (Coleoptera: Apionidae) in Southern United States: effects of trap types and pheromones dose. J. econ. Ent., 85 (2): 416-423. Jayaramaiah, M. (1975a). Bionomics of sweet potato weevil Cylas formicarius (Fabricius), (Coleoptera: Curculionidae). Mysore Journal of Agricultural Science, 9(1) : 99-109. Jayaramaiah, M. (1975b). Reaction of sweet potato varieties to the damage of the weevil Cylas formicarius (Fab.), (Coleoptera: Curculionidae) and on the possibility of picking up of infection by the weevil. Mysore Journal of Agricultural Science, 9(3): 418- 421. Jones, A.; Cuthbert, F.P.Jr.; Schalk, J.M.; Paterson, D.R.; Boswell, E.T.; Eahart, D.R.; Fuqua, M.C.; Mullen, M.A. and Arbogast, T.R. (1978). Field screening for sweet potato weevil resistance: a progress report. Hort. Science, 13: 3, 1, 286. Karr, G.W. (1984). Alabama’s sweet potato weevil quarantine. In : Mullen, M. A. and Sorensen, K.A. (eds.). Proceeding of Sweet

156 Potato Workshop, Raleigh, USA: Department of Entomology, North Carolina State University, 30-35. Kogan, M. (1998). Integrated pest management, historical perspective and contemporary developments. Ann. Rev. Ent., 43: 234-270. Lagnaoui, F.; Cisneros, F.; Alcazar, J. and Morales, F. (2000). A sustainable pest management strategy for sweet potato weevil in Cuba: A success story. Food and Fertilizer Technology Center, 5 pp. Lenne, J.M. (1991). Diseases and pests of sweet potato: South East Asia, the Pacific and East Africa. Chatham, UK Natural Resources Institute Bulletin No.46: 116 pp. Leuschner, K. (1982). Pest control of cassava and sweet potato. Root crops in Eastern Africa. Proceeding of a workshop, 23-27 November, 1980. Kigali Rwanda. Ottawa, Canada: International Development Research Center, 60-64. Macfarlane, R.; Abington, J.B.; Walton, P.D. (1987). Sweetpotato weevil Cylas formicarius insecticide trial. Solomon-Islands, Ministry of Agriculture and Land Research Department, Agriculture Division. Annual Report 1985: 3-6. Maily, A.M. (1996). Root and storage root crops. Review of Kenyan Agricultural Research, 22: 26-34. Matthews, G.A. (1979). Pesticides application methods. Longman, London and New York, 12-25.

May, B.M. (1994). An Introduction to the Immature stages of Australian Curculionoidea. In: Zimmerman, E.C. (ed.). Australian weevils. Volume 2. Melborn, Australia: CSRIO, 365-728.

157 Moriya, S. and Hiroyoshi, S. (1998). Flight and locomotion activity of the mating status, sweetpotato weevil (Coleoptera: Brentidae) in relation to adult age, mating status and starvation. J. econ. Ent., 91(2): 439-443. Moyer, J.W; Jackson, G.V.H. and Frison, E.A. (eds.) (1989). FAO/IBPGR Technical guidelines for the safe movement of sweet potato germplasm. Food and Agricultural Organization of the United Nation/International Board for Plant Genetic Resources, Rome, 29 pp. Mukiibi, J. (1976). Effect of mosaic virus on yield of sweet potato in Uganda, pp. 169-170. In: Proceeding of the Fourth Symposium of the International Society for Tropical Root Crops, IDRC-080, Cock, J. MacIntyre, R. and Giaham, M. (eds.). IDRC, Canada. Mullen, M.A. (1981). Sweetpotato weevil Cylas formicarius elegantulus (Summers): development, fecundity and longevity. Ann. Ent. Soc. Amer. 74 : 478-481. Mullen, M.A. (1984). Influence of sweetpotato weevil infestation on the yield of twelve sweet potato lines. J. Agri. Entomol. 1: 227-230. Mullen, M.A.; Jones, A.; Davis, R.; and Pearman, G.C. (1980).Rapid selection of sweet potato lines resistant to sweetpotato weevil. Hort. Science 15 : 70-71. Mullen, M.A.; Jones, A.; Paterson, D.R. and boswell, T.E. (1982). Resistance of sweet potato lines to the sweetpotato weevil. Hort. Science 17 :931-932. Mullen, M. A.; Jones, A.; Paterson, D.R. and boswell, T.E. (1985). Resistance in sweetpotatoes to the sweetpotato weevil, Cylas formicarius elegantulus (Summers). J. Ent. Sci. 20 (3): 345-350. Mwanga, R.O.M. and Wanyera, N.W. (1988). Sweet potato growing and research in Uganda. In: Improvement of sweet potato (Ipomoea

158 batatas) in East Africa. Report of Workshop on Sweet potato Improvement in Africa, ILRA, Nairobi, Kenya, September- October 1987, Lima, Peru: CIP, 187-198. Nonveiller, G. (1984). Catalogue of the insects of agricultural importance of Cameroon. Belgrade, Yugoslavia: Institute Pour la Protection des Plantes, 15. NRS (1992). Namulonge Research Station 1992. Sweet potato project report 1989-1992.Uganda-GTZ-CIP, 50 PP. *Nteletsana, L. ; Schoeman, A.S. and Mc Geoch, (2001). Temperature effects on development and survival of sweet potato weevil, Cylas puncticollis Boheman (Coleoptera: Aionidae), African Entomology, 9 (1): 1-3. Nwana, I.E. (1979). The biology of the Cylas puncticollis Boheman (Coleoptera: Apionidae) on Ipomoea batatas (Linnaeus) Lamark. Nigeria J. Ent. 3: 2-7. Ocitti p’Obwoya C. (1990). Sweet potato on-farm survey report for Apac and Ambale Districts . Sweetpotato programme 1989-1990. Namulonge Research Station, Kampala, Uganda, 32 pp. Odongo, B.; Heather, K.; Ewell, P.; Stathers, T.; van de Fliert, E.; Mudiope, J.; Ogiro, V. and Lugwana, E. (2003). Technique of re- hilling sweet potato mounds to reduce Cylas spp. weevil infestation and improve sweet potato yield in Soroti District, North East Uganda. Uganda Journal of Agricultural Science 8 :117-122. O’Hair, K.S. (1991). Growth of sweet potato in relation to attack by sweet potato weevils. In : Jansson, R.K. and Raman, K.V. (eds.): Sweet potato pest management: A global perspective. Westview Press, Boulder, San Francisco, Oxford; 59-78.

159 Oliver, J. (1965). The climate of Khartoum Province. Sudan Notes and Records. 46: 90-129. Palaniswami, M.S. (1989). Use of parasitoids and entomopathogenic fungus on sweetpotato weevil. Seminar on pests and diseases of sweetpotato (Ipomoea batatas ), Trivandrum, India, August 1989. Palaniswami, M.S. and Mohandas, N. (1994). Reridging as a cultural methods for the management of sweet potato weevil Cylas formicarius F. Journal of Root Crops, 20 (2): 101-105. PANS (1978). Pests control in tropical root crops. PANS Manual No. 4. London, UK: Center for Overseas Pest Research: pp 85-88. Pfeiffer, H.J. (1982). Sweet potato improvement in Cameron. Root Crops in Eastern Africa. Proceeding of Workshop held at Kigali, Rwanda ,23-27 November, 1980. International Development Research Center Ottawa Canda, 33-38. Pole, F.S. (1988). Vine thickness in sweetpotato Ipomoea batatas: its inheritance and relationship to weevil damage. M.A. Thesis, University of South Pacific, Western Samoa. Rajamma, P. (1983). Biology and bionomics of sweet potato weevil Cylas formicarius Fab. In: Goel, S.C. (ed.). Insects ecology and resource management. Muzaffar, India, Sanatan Dhram college: 87-92. *Rajamma, P. (1990). Evaluation of some newer insecticides for the control of the sweetpotato weevil Cylas formicarius Fab. Entomon., 15: 241-243. Rajamma, P and Padmaja, G. (1983). Pests of sweet potato-varietal resistance, bionomics and control. Annual Progress Report 1982, Trivandrum , India: Central Tuber Crops Research Institute: 108- 112.

160 Raman, K.V. (1989). Strategies to develop sweet potatoes with weevil resistance in developing countries. In: Improvement of sweet potato (Ipomoea batatas) in Asia. Report of the Workshop on Sweet Potato Improvement in Asia, Trivandrum, India. Oct. 1988. Lima, Peru; CIP: 203-211. Ranjith, A.M. (1985). First report for cylas formicarius F. on black pepper, Piper nigrum L. Current Science, 54 (16): 810. Ring, D. (1999). Sweet potato insect pests management. Louisiana State University Cooperative Extension Service, Publication 2620: 92- 96. Rogers, C.E. (1976). Economic Injury level of Contarina taneana on guar. J. econ. Ent., 69: 693-696. Sathula, R.A.; Logman, J. M.; Munthali, D. C. and Nyirenda, G. K. C. (1997). Adult longevity, fecundity and oviposition characteristics of Cylas puncticollis (Boheman) on sweet potatoes. African Crop Science Journal, 5(1): 39-45. Schmutterer, H. (1969). Pests of crops in north east and central Africa with particular reference to the Sudan. Gustav Fisher Verlag Stuttgart, Germany: 296 pp. Semwogerere, T. (1999). Sexual behaviour of Cylas spp. (Coleoptera : Apionidae) with respect to synthetic pheromones. M. Sc. Thesis Makerere University, Uganda. *Setokushi, O. and Nakao, K. (1991). In field damage by sweetpotato weevil Cylas formicarius (Fabricius) to sweetpotato. Proceedings of the Association for Plant Protection of Kyushu: pp 104-106. Sherman, M. (1951). Chemical control of sweet potato insects in Hawaii. J. econ. Ent., 44: 652-656. Sherman, M. and Mitchell, W. (1953). Control of sweet potato weevils and vine borer in Hawaii. J. econ. Ent., 46: 389-393.

161 Sherman, M. and Tamashiro, M. (1954). The sweet potato weevils in Hawaii, their biology and control. Hawaii Agricutural Experimentation Technical Bulletin No. 23. Singh, B.; Yazdani, S.S.; and Hameed, S.F. (1987). Sources of resistance to Cylas formicarius Fab., in sweet potato. 1. morphological characters. Indian Journal of Entomology, 49(3): 414-419. Singh, B.; Yazdani, S.S.; Singh, R. and Hameed, S.F. (1984). Effect of intercropping on the incidence of sweet potato weevil Cylas formicarius Fab., in sweet potato (Ipomoea batatas Lam.). Journal of Entomological Research, 8(2): 193-195. Smit, N.E.J.M. (1997). Integrated pest management for sweetpotato in Eastern Africa. Ph. D. Thesis Landbouw uninversiteit Wageningen, Netherlands. Smit, N.E.J.M. and Matengo, L.O. (1995). Farmers’ cultural practices and their effects on pest control in sweetpotato in south Nyanza, Kenya. International Journal of Pest management, 41(1): 2-7. Smit, N.E.J.M. and Odongo, B. (1995-96). Integrated pest management for sweetpotato weevil in East Africa. International Potato Center Report: 191-197. *Smit, N.E.J.M. and van Huis, A. (1998). Biology of African sweetpotato weevil species Cylas puncticollis (Boheman)and Cylas brunneus (Fabricius) (Coleoptera:Apionidae). Insect Science and its Application 18 (2): 93-100. Smit, N.E.J.M.; Holo, T. and Wilson, J.E. (1991). Sweetpotato seedling for resistance to leaf scab disease (Elsinoe batatas ). Tropical Agriculture (Trinidad), 68: 263-267 Smit, N.E.J.M.; Downham, M.C.A.; Laboke, P.O.; Hall, D.R. and Odongo, B. (2001). Mass-trapping male Cylas spp. With sex

162 pheromones: a potential IPM component in sweetpotato production in Uganda. Crop Protection, 20: 643-651. Solomon, M.E. (1957). Estimation of humidity with potassium hydroxide, sulphuric acid or other solutions. Bull. ent. Res. 42: 543-551. Starr, C.K.; Severson, R.F. and Kays, S.J. (1991). Volatile chemicals from sweet potato and other Ipomoea: effects on the behaviour of cylas formicarius, pp. 235-245. In: Jansson, R.K. and Raman, K.V. (eds.) Sweet potato pest nanagement: A global perspective. Westview Press Boulder, San Francisco, Oxford, 235-246. Stathers, T.E.; Rees, D.; Nyango, A.; Kiozya, H.; Mbilinyi, L.; Jeremiah, S.; Kabi, S. and smit, N. (2003). Sweet potato infestation by Cylas spp. in East Africa: 11. Investigating the role of root characteristics. International Journal of Pest Management, 29(2): 141-146. Stering, S. (1959). Resistant of plant to insects. Ann. Rev. Ent., 3: 353- 365. *Sugimoto, T.; Fukui, H.; Sakuratani, O.; Kiritani, K. and Okada,T. (1996). Estimating the reproductive properties of sweetpotato weevil, Cylas formicarius (Fabricius) (Coleoptera: Brentidae). Appl. Entomonl. Zool. 31 : 357-367. Sutherland, J.A. (1986a). Evaluation of foliar sprays, soil treatment and vine dip for control of sweetpotato weevil Cylas formicarius (Fab.). Journal of Plant Protection in the Tropics, 3: 95-103. Sutherland, J.A. (1986b). A review of the biology and control of the sweetpotato weevil Cylas formicarius (Fab.). Tropical Pest Management, 32(4): 304-315. Sutherland, J.A. (1986c). Damage by Cylas formicarius (Fab.) to sweet potato vines and tubers, and the effect of infestations on total

163 yield, in Papua New Guinea. Tropical Pest Management, 32(4): 316-323. TAC (1954). (Texas Agricultural College). Ways to control weevil (Cylas formicarius elegantulus ) and diseases of sweet potatoes. Texas Agricultural College Extension Leaflet No. 202.

Talekar, N.S. (1982). A search for sources of resistance to sweet-potato weevil. In: Villareal, R.L. and Griggs, T.D. (eds.) Sweetpotato Proceeding of the First International Symposium. Shanhua, Taiwan: Asian Vegetable Research and Development Center, pp 147-156. Talekar, N.S. (1983). Infestation of sweetpotato weevil (Coleoptera: Curculionidae) as influenced by pest management techniques. J. econ. Ent., 76(2): 342-344. Talekar, N.S. (1987a). Influence of cultural pest management techniques on infestation of sweet potato weevil. Insec. Sci. applic., 8(4/5/6): 809-814. Talekar, N.S. (1987b). Feasibilty of the use of resistant cultivar in sweet potato weevil control. Insec. Sci. applic., 8(4/5/6): 815-817. Talekar, N.S. (1987c). Resistance in sweet potato to sweet potato weevil. Insec. Sci. applic., 8(4/5/6): 819-823. Talekar, N.S. (1988). How to control sweet potato weevil: A practical IPM approach. International co-operator guide, AVRDC, Shanhua,Taiwan, 6 pp. Talekar, N.S. (1989). Development and testing of an Integrated pest management technique to control sweetpotato weevil . In: Improvement of sweet potato (Ipomoea batatas) in Asia. Report

164 of the Workshop on Sweet Potato Improvement in Asia, Trivandrum, India. October 1988, Lima, Peru; CIP: pp 117-126.

165 Talekar, N.S. (1990). Integrated control of sweet potato weevil. In: Howler, R. H. (ed.). Proceeding of the 8th Symposium of the International Society for Tropical Root Crops. Bankok, Thailand: Department of Agriculture, Centro Internacional de Agricultural Tropical (CIAT), and Centro Internacional de la Papa (CIP), pp 552-558. Teli, V.S. and Salunke, G.N. (1994). Biology of sweetpotato weevil. Journal of Maharashtra Agricultural Universities, 19(3): 381- 384. Thompson, R.T. (1994). Observation on the morphology and classification of weevils (Coleoptera: Curculionidae) with a key to major groups. Journal of Natural History, 26(4): 835-891. Vietmeyer, N.D. (1986). Lesser-known plants of potential use in Agriculture and Forestry. Science, 232: 1379-1384. Wadill, V.H. (1982). Control of sweetpotato weevil Cylas formicarius elegantulus by foliar application of insecticides. In: Villareal, R.L. and Girggs,T.D. (eds.) Sweet potato Proceeding of the First International Symposium. Shanhua, Taiwan: Asian Vegetable Research and Development Center, 157-159. *Wang, Y. and Kays, S.J. (2002). Sweet potato volatile chemistry in relation to sweetpotato weevil(Cylas formicarius) behaviour. Journal of the American Society for Horticultural Science, 1(4): 656-662. Wolcott, G. N. and Perez, M. (1955). Control of Sweetpotato weevil in Puerto Rico. J. econ. Ent.,49: 486-487.

Wolfe, G.W. (1991). The origin and dispersal of the pest species groups of the world. In: Jansson, R.K. and Raman, K.V. (eds.). Sweet

166 potato pest management: A golobal perspective. Westview Press Boulder, San Francisco, Oxford, 13-44. Youshida,T. (1985). An ecological study of the two weevils, the sweetpotato weevil Cylas formicarius (Fabricius) and the small sweetpotato weevil Euscepes postfasciatus (Fairemaire) (Coleoptera: Curulionidae) in Amami Islands-on life spans of the two species. Res. Bull. PL. Prot. Jpn. 21: 55-59 Zhang, D.P.; Golmirzai, A.; Cipriani, G.; Panta, A.; Ghislain, M.; Smit, N.; Rety, I. and Michaud, D. (1995-96). Developing weevil resistance in sweet potato with genetic transformation, IPC. *Seen as abstract.

167 Appendices

Appendix A. The man monthly records of temperature and relative humidity (RH) in April and May, 2oo2. April May Date Room conditions Incubator Room conditions Incubator Temp. RH Temp RH Temp RH Temp RH 1 - - - - 37.0 55 30 60 2 - - - - 39.0 54 30 65 3 - - - - 32.0 65 32 60 4 - - - - 36.0 75 32 60 5 - - - - 33.0 75 31 68 6 - - - - 37.0 50 30 68 7 - - - - 39.0 50 31 60 8 - - - - 39.0 55 30 65 9 - - - - 35.0 60 30 68 10 - - - - 35.0 60 30 60 11 - - - - 34.0 55 29 65 12 - - - -35.0 50 31 67 13 - - - - 35.0 70 31 65 14 - - - - 36.0 50 29 67 15 - - - - 35.0 75 31 64 16 - - - - 35.0 70 30 60 17 - - - - 34.5 65 31 60 18 - - - - 34.0 55 30 65 19 - - - -30.0 60 30 66 20 - - - - 35.0 65 30 60 21 37 60 30.67 65 34.0 65 30 60 22 39 70 30.33 68 34.0 70 31 68 23 36 67 29.50 72 34.0 75 30 67 24 33 65 31.00 68 34.0 80 31 65 25 37 55 32.00 65 35.0 75 32 65 26 39 54 33.00 62 36.0 70 31 65 27 38 70 30.00 65 37.0 65 31 68 28 38 70 31.00 62 37.0 70 31 65 29 37 65 30.00 64 39.0 60 28 65 30 39 60 32.00 65 35.0 75 32 70 31 - - - - 35.0 65 28 65 35.34 Mean 37.00 63.60 30.95± 65.95 30.42± 67.26 64.0 ±8.87 ±S.E. ±1.83 ±5.75 1.04 ±2.87 ±2.00 1.01 5.05±

Appendix B. The man monthly records of temperature and relative humidity (RH) in April and May, 2oo2.

168 April May Date Room conditions Incubator Room conditions Incubator Temp. RH Temp RH Temp RH Temp RH

1 - - - -35.67 67.67 30.33 65.0 2 - - - -34.50 77.25 31.67 70.0 3 - - - -37.00 57.33 30.00 72.0 4 - - - -37.33 57.33 30.00 65.0 5 - - - -37.67 56.67 30.00 60.0 6 - - - -36.00 65.00 31.00 62.0 7 - - - -37.00 65.50 29.50 65.0 8 - - - -37.33 63.33 30.00 60.0 9 - - - -38.00 57.50 30.00 70.0 10 35.0 50.0 30.0 65.0 35.50 68.50 31.00 70.0 11 35.0 55.0 30.0 70.0 36.50 75.50 32.00 62.0 12 34.0 50.0 30.0 60.0 37.00 69.00 33.00 68.0 13 31.0 55.0 30.0 57.5 34.00 75.00 33.00 64.0 14 32.0 50.0 32.0 67.0 35.00 58.50 30.00 60.0 15 35.5 52.5 32.0 62.0 35.67 55.33 31.00 55.67 16 37.0 47.0 31.0 65.0 36.33 67.67 31.00 66.33 17 35.0 54.0 27.0 68.0 36.33 66.00 32.00 68.0 18 36.0 54.5 29.5 65.0 36.00 66.67 31.00 67.33 19 37.0 55.0 28.5 60.0 36.00 70.00 31.00 68.0 20 37.0 54.0 31.0 62.0 36.00 65.00 30.00 60.0 21 38.0 67.5 32.0 68.0 37.00 66.00 32.00 65.0 22 38.0 50.67 29.7 63.0 35.00 65.00 33.00 62.0 23 39.5 58.5 30.0 65.0 37.00 70.00 32.00 65.0 24 36.0 72.2 32.0 65.0 34.00 81.00 30.00 68.0 25 33.5 80.0 32.0 70.0 36.00 68.67 29.00 68.0 26 36.5 70.0 31.67 60.0 35.00 75.33 30.00 65.0 27 38.0 67.0 31.0 63.0 35.00 74.33 30.00 65.0 28 38.5 69.25 29.75 68.0 36.00 75.67 31.00 65.0 29 38.5 68.0 31.33 65.0 35.00 86.33 30.00 60.0 30 37.0 62.33 29.33 68.0 36.00 81.00 30.00 60.0 31 - - - - 37.00 63.00 31.00 70.0 36.02 Mean 36.05 59.35 30.5 64.84 68.18 30.83 64.71 ±S.E. ±2.16 ±8.81 ±1.27 ±13.51 ±1.02 ±7.70 ±1.06 ±3.82

169