Polyphagous insects, when exposed to different host plants simultaneously,
are often found to experience a difficulty in making a decision when selecting
food and oviposition sites. The tobacco whitefly, Bemisia tabaci, has a
wide host-range with over 700 host plant species having been recorded.
Whiteflies are amongst the most noxious insect pests of field and greenhouse
crops worldwide, partly due to the build up of resistance against pesticides.
Control of whiteflies is thus very difficult.
As part of developing an Integrated Pest Management (IPM) programme, the
behaviour of B. tabaci females was studied in order to find if they show reduced
feeding and fecundity if exposed to different crops or different tomato
cultivars simultaneously, as opposed to the same crop plant (monocrops).
Tests were conducted on three different crops (tomato, bean and cucumber) and
on three different tomato cultivars. Bemisia tabaci showed clear
behavioural preference for cucumber when exposed to the different crops
simultaneously. Cucumber seems to be a host of high ranking for B.
tabaci. This suggests that B. tabaci has no problem in choosing a host
plant, i.e. showing a preference, when one of the plants in the choice test is a
high-ranking host plant. However, when only low-ranking hosts of similar, but
not identical, host plant signatures were present, female whiteflies tended to
have difficulty in making a selection, resulting in increased movement and
reduced fecundity.
If the above results can be confirmed under tunnel and field conditions, the
value of intercropping with different cultivars could contribute towards
controlling pest population build-up in an integrated pest management
programme.
