EFFECTS OF TEMPERATURES AND PLANT HOST SPECIES ON CERTAIN BIOLOGICAL CHARACTERS OF THE CASTOR BEAN WHITEFLY, Tria/eurodes ricin; MISRA (HIMEPTERA: AL YRODIDAE).

Laboratory studies were carried out to determine the influence of
temperature (abiotic) and host plant species (biotic) on the biological characters of the
castor bean white ny, Trialeurodes riCini Misra. Four temperatures namely 15. 20, 25
and 30°C, as well as the three plant species, castor bean (Ricinus communis L),
Papaya (Carica papaya L.), and sweet potato (Ipomoea balatas L.) were tested.
Various temperatures affected greatly Ihe insect development, oviposilion, life cycle
and generation time when reared on castor bean plants. At 30°C., egg incubation
period, development of nymphal instars, adult longevity and life cycle were shortest,
follollled by 25°C., while these characters were longer when the insect reared at 15
DC. The hatchability percentage and female fecundity were greater at both 30 and 25
DC. Meanwhile they were lower at 15°C. The temperature threshold (to) and thermal
accumulative effect (degree·days) were also calculated. The laboratory studies were
confirmed by field applications regarding the relationship between temperatures
among the geographical seasons and the insect populations. The study demonstrates
that T. ricini can, in otherwise unlimited conditions, persist and increase in number
within the range 20-30 aC. Therefore, the pest is well adapted to high temperatures
and may extend its distribution if the mean world temperatures increase because of
global warming. Regarding the plant hosl species, the castor bean was the preferred host
followed by papaya, while the sweet potato was not preferred for insect rearing. This
indicated that the host plant species had a significant effect on egg hatchability,
nymphal survival. female fecundity and the duration of life cycle of T. ricini.