Thz Potential 07 Using Hydrothermal Treatment For Protection Of Stored Cowpeas.Against Callosobruchus Maculatus (F.)

ABSTRACT

Laboratory experiments were carried out to evaluate the

effect of steaming cowpeas on the oviposition and larval

development of the cowpea beetle, Callosobruchus

maculatus (F.). The possibility of oven and solar drying

as well as the effect of the initial temperature of the

cowpeas on the steaming effect were also investigated.

Samples of four cowpea varieties (Soronko, Asontem,

Amantin and US Blackeye) were steamed for 10 and 15

minutes and solar or oven dried. Some initially stored

at 4°C or at room temperature were steamed for ten minutes

while other samples were oven dried, solar dried, treated

with Actellic super dust or untreated.

The results showed that when Soronko, Asontem and Amantin

cowpeas were steamed for 15 minutes and oven dried at 70

°C for 8 hours, oviposition by C. maculatus was not

significantly different from unsteamed beans. Of the

four cowpea varieties tested, US blackeye cowpeas were

most preferred as oviposition substrate and also for

larval development followed by Soronko, Asontem and

Amantin. The drying method (solar or oven drying) did

not affect oviposition of the bruchids. Significantly

fewer eggs were laid on steamed beans compared with

unsteamed beans. When US blackeye were steamed for 10 or

15 minutes and solar dried, the grains were protected

against the development of bruchid larvae comparable to

Actellic Super Dust insecticide. In contrast, steaming

blackeye cowpeas for 10 or 15 minutes and oven drying

delayed adult bruchid emergence for about 4-5 days due to

starch gelatinization and protein denaturation.

Furthermore, steaming cowpeas initially at a lower

temperature of 4°C significantly reduced oviposition in

gravid C. maculatus compared to beans at room

temperature.

Fifteen or ten minutes steaming did not affect damage to

the beans so long as the seeds were solar dried to attain

safe shelf moisture levels before storage. Microscopic

examination of hatched eggs in steamed cowpeas which

failed to develop into adults showed death of larvae due

to non-utilization of the normal nutrition.

All seeds of the four varieties of cowpeas that were

steamed lost the ability to germinate.