Distribution pattern of sweet potato whitefly Bemisia tabaci (gennadius)‎ on tomato plants

الملخص EN

A field experimen[ was conducted to study the intra plant distribution and temporal dispersion patterns of whitefly (BemisiaGennadius) eggs and nymphs on tomato plants to establish a sampling method which would give accurate estimates of the population size.

From the third week to the ninth week after transplanting, terminal leaflets were collected from the outer and inner canopies of each of the upper, middle, and lower plant strata.

A strong ovipositional preference was found in whitefly adults at an early crop age.

A maximum of 50.6% of the eggs were deposited in the middle stratum followed by upper (36.1% ) and lower strata (13.3%).

However, most of the nymphs (65.5%) were present in the lower stratum followed by middle (32.4%) and upper strata (2.1%).

These findings indicated that when taking observations in egg counts the most preferred site is the upper and middle strata while for nymphal counts it is the lower and middle strata.

There was a sharp decrease in egg and nymphal counts from the seventh week after ' which clearly indicated that, after this age, ٥١٠ crop is not preferred by whitefly.

Egg and nymphal populations of whitefly on tomato plants in the field were distributed in aggregates as evident by high variance to mean ratio.

Values ranged from 2.72 to 14.36 and 4.52 to 2 ).82 for egg counts and nymphal population, respectively.

Aggregation of whitefly eggs and nymphs in all cases might be due to the behaviour of adults to congregate and to the heterogeneity of the environment.

TTie appropriate number of leaflets re؟u؛red for the estimation of egg density at 10% and 20% er،or was found to be 149 and 37, respectively.

In the case of nymphal population the numbers were 163 and 41 at 10% and 20% error, respectively.