Part 1.11

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PROSTEPHANUS TRUNCATUS - A PEST OF STORED PRODUCTS IN NIGERIA: PHEROMONE TRAPPING IN WESTERN PARTS OF NIGERIA

T.N.C. ECHENDU¹ & B.J. OJO²

1	National Bio-control Programme, National Root Crop Research Institute (NRCRI), Umuahia, Nigeria
2	International Institute of Tropical Agriculture (IITA), Ibadan, Nigeria

Introduction

Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae), otherwise known as the Larger Grain borer (LGB), was accidentally introduced into Africa from Central America in the late 1970's.

The presence of the pest has been reported in Africa in Tanzania, Kenya, Burundi, Zambia, Rwanda, Guinea-Conakry, Ghana, Burkina Faso, Togo, Benin and Nigeria (Anonymous, 1994; Pike et al., 1992). From these reports, the pest attacks a variety of stored products. However, it is the damage caused to maize and cassava in storage that is the most important.

Although found principally in maize, P. truncatus feeds and reproduces in various trees (Detmers et al., 1991). Losses due to the activities of P. truncatus can be high. Estimates in Tanzania show up to 9% loss after only 3-6 months storage. In dried cassava roots, losses can also be high, as the dried roots are readily reduced to dust by the boring adults. Weight losses of 70% or more have been reported after just 4 months of storage (Hodges et al., 1985).

In Nigeria the earliest reports of P. truncatus indicated its presence in areas of Oyo, Ogun and Lagos States, mostly in areas near the border with the Republic of Benin (Pike et al., 1992). The extent of spread, degree of damage are yet to be elucidated.

The objective of the present survey was to update some of the information on P. truncatus in view of the current widespread but unsubstantiated reports of its continued spread into newer areas of the country. This is intended to be a first step towards the correct ascertainment of its damage potential and yield loss over the areas where its presence has been confirmed.

Methodology

Surveys were undertaken between July 22nd and September 28th 1997. The team criss-crossed the States of Lagos, Ogun, Oyo, Osun, Kwara, Niger and Kebbi. A total of 50 villages were selected for the trapping exercise (Fig. 1. & Tab. 1). Distances between the traps ranged from 20-50 km along the major roads used. Delta traps were used for the surveys. These traps are made of waxed card-board with the three internal surfaces covered with sticky material. To make the trap functional, pheromone lures contained in polyethene capsules were placed inside the sticky traps. One capsule only was used for each trap. The traps were then hung on trees or shrubs approximately 1-2 m from the ground. The placement of the traps was also diverse but generally near places of human habitation.

Fig. 1.

Survey sites in south- and northwestern Nigeria, July to September 1997.

In most of the villages, the traps were left in the custody of farmers to ensure their safety. After 14 days, the traps were retrieved and the presence or absence of P. truncatus noted. Records were also taken of insects other than P truncatus that were caught in the traps. The pheromone lures remain generally active for up to 14 days and continued stay outside would not lead to much improvement in the trapping. After completing the survey, 5 sites were selected for further trapping. These were:

1.	Ikorodu (Lagos State),
2.	Iwo (Osun State),
3.	Oyo (Oyo State),
4.	Okeho/Iseyin (Oyo State), and,
5.	Kisi (Oyo State).

Traps were replaced every 2 weeks for the next 6 weeks to assess the population trends over a period of time. Maize cobs were also purchased from a few markets in Lagos, Ogun, Oyo and Niger States and assessed for P. truncatus infestation. The cobs were later brought to the laboratory and the number of P. truncatus together with other insects present recorded.

Results

The results of the survey show the presence of the larger grain borer in Lagos, Ogun, Oyo, Kwara and Osun States. Twenty-seven out of the 50 sites recorded P. truncatus (Tab. 1). There were no recoveries in Niger and Kebbi States. The highest number of P. truncatus occurred in Otu, Oyo State (Tab. 1).

The recovery in Iwo was interesting and marked the eastern boundary of the pest distribution in the area surveyed. It also highlights the fact that the pest has moved away from the states bordering the Republic of Benin from where they probably first entered the country.

Catches were heaviest in the traps set at Okeho/Iseyin, Oyo State. Oyo State also recorded the highest number of sites with P. truncatus. This result is very similar to those of Pike et al. (1992) who recorded 60% of their total survey catch from this area alone.

Tab. 1.

Survey sites in south- and northwestern Nigeria between July and September 1997, and numbers of trapped P. truncatus.

State - Location

Altitude (in m)

No. of P. truncatus

Kebbi
	400 km to Sokoto (Kontagora) 348 km to Sokoto 296 km to Sokoto 36 km to Sokoto (Kaboji)	1100 800 800 1100	0 0 0 0
Kwara
	Kembi-via Olorun Kaima Gwazero Igbetti	1100 1200 1500 1500	0 0 19 1
Lagos
	Epe Lagos Ikorodu Badagry Jebba Mokwa Robizi 72 km to Kontagora (Mulo) Ibbi 38 km to Wawa Wawa	300 300 300 600 600 600 1300 700 1300 700	0 8 0 0 0 0 0 1 2 0
Ogun
	Ijare Ijebu Idi-Oroko Oke-Odan Otta Iffon Ojo-Odan Ilaro Imeko Aiyetoro Igbo-Ora Iwo Iba (via Ikurun) Ragbiji -Osogbo Gbongan	900 300 200 900 500 400 100 100 100 100 500 1500 1400 900	1 15 13 0 6 7 6 29 0 9 2 0 0 0
Oyo

Abeokuta-Ibadan
Orile-Igun
Moniyan
Fiditi
Oyo
Ogbomosho
Pekee
Kishi
Igboho
Shaki-Idi-Opa
Shaki
Ago Are
11 km to Otu
Otu
12 km to Okeho
Okeho
Iseyin
Fasola Oyo

300
800
1500
1000
1400
1100
1200
1400
1400
1400
1800
900
1000
900
600
1000
600
1200

0
0
0
0
11
2
0
9
12
5
14
6
4
33
31
4
2
1

The results also confirm the spread of the pest into new areas with Iwo (Osun State) and Ijebu-Ode marking the eastern boundaries of the spread, approximately 220 km and 180 km respectively from the border with the Republic of Benin.

Results of the by-weekly trapping exercise are shown in table 2. The catches recorded around Okeho were the highest over the period of study. No further recoveries were made at Iwo after the July trapping. Catches were generally low across the locations during the 6th week of trapping. However, the 8th week showed increased recovery in the four sites, with Okeho location recording the highest numbers.

Tab. 2.

Number of P. truncatus recovered in pheromone traps over 8 weeks in 5 different
locations in Nigeria.

Week of	Trap sites
trapping	Ikorodu	Okeho	Kisi	Oyo	Iwo	Total

2
4
6
8
Total

8
3
1
2
14

31
19
4
20
74

9
2
5
7
23

11
22
3
3
39

2
0
0
0
2

61
46
13
32

The results from the maize cobs obtained from some selected markets also confirm the results of the trapping exercise (tab. 3). In nearly all the markets surveyed, P. truncatus was present in the maize being offered for sale. The number of P. truncatus recovered from the grain was considerably high also.

A lot of inter-border trade takes place between the Republic of Benin and Nigeria, particularly in Oyo, Kwara, and Ogun States where the same tribal groups live on both sides of the border. It is possible that the introductions into Nigeria came through such inter border trade routes. In Gwazero (Kwara State), interview with farmers indicate very huge losses to stored cassava by LGB in this area. Earlier reports did not find LGB in these areas of Kwara State. In Shaki and Iseyin (Oyo State) cassava chips being offered for sale in the markets were also seriously infested by P. truncatus.

Tab. 3.

Recoveries from maize cobs purchased on 20 local markets in Nigeria.

State – Market place

No. of P. truncatus obtained
per kg of maize cobs

Lagos
	Mile 2 Oyingbo Ketu Mushin	50 8 24 14
Ogun
	Lafenwa Ijemo Saw mill Ita Oba	18 0 0 3
Oyo
	Oje Owode Bodija Ojaoba Takki Katika Ojaoba Molete Mojo Ojude	40 95 150 20 0 15 35 179 28 42
Niger
	Sabo Kara	0 11

Conclusion

The surveys indicated that LGB has moved out of the border areas of the south-west from where it probably entered into the country to the hinter-land and spreading eastwards. It is now found in Osun and Kwara States where earlier surveys did not show its presence. It is therefore necessary to initiate practical steps towards its control and containment before it covers the entire country. Practical steps like the introduction of its known natural enemies and mass rearing leading to eventual releases should be initiated.

Acknowledgement

We thank the GTZ for making available the funds for this survey and for their continued support.

References

Anonymous 1994.
	How to use pheromone traps to monitor the Larger Grain Borer. Natural Resources Institute (NRI), Chatham, UK.
Detmers, H.-B., Helbig, J., Laborius, G.-A., Richter, J. & Schulz, F.A., 1990.
	Investigations on the development capability of Prostephanus truncatus (Horn) (Coleoptera; Bostrichidae) on different types of wood, p.7. In 5th International Working Conference on Stored-Product Protection, Bordeaux, France, September 9-14, 1990. Abstract volume.
Hodges, R.J., Meik, J. & Denton, H., 1985.
	Infestation of dried cassava (Manihot esculenta Crantz) by Prostephanus truncatus (Coleoptera: Bostrichidae). Journal of stored Products Research 21: 73-77
Pike, V., Akinnigbagbe, J.J.A. & Bosque-P�rez, N.A., 1992.
	Outbreaks and new records: Larger grain borer (Prostephanus truncatus) outbreak in western Nigeria. FAO Plant Protection Bulletin 40: 170-173.