Temperature Dependent Rates of Development and Phenology of the American Bollworm Heliothis armigera (Hub.).

M.F. Gergis and B.A. Ibrahim


 
ABSTRACT

Parameters were estimated for temperature-dependent models of spring emergence, post diapause development, moth population peaks and population growth of the American bollworm, Heliothis armictera (H�bner) in Middle Egypt.

Winter survival and spring emergence data for bollworms were collected over a 5-year period and used to develop a heat unit emergence model for Middle Egypt.

Since temperature is considered as the driving force for Heliothis emergence, simultaneous temperatures were recorded under field conditions and converted to a cumulative degree-day summation. An accumulation of ca. 115 (dd's) from the 1(st) of January was required for emergence of the first moth from overwintering pupae. Accumulating degree days was seen to be an accurate means of forecasting cumulative moth emergence under field conditions. The agreement between predicted and actual emergence was good even though cumulative emergence varied among years in the dates of first and last emergence and the length of emergence period.

Studies, also examined Heliothis post-diapause development under field conditions. From these data, development rates vs. temperature curves are constructed and incorporated into a model predicting Heliothis spring emergence of 10, 50 and 90% of overwintered generations. Degree-days (dd's) accumulation was used as a means of forecasting moth population peaks. Male moths exhibited cyclic population peaks at intervals of ca. 488 (dd's).

The models were validated by using temperature data pheromone trap catches and they provided good predictions at all percentages of emergence.

Rate of development and life table statistics were determined from the field-collected data to examine the effect of favorable and unfavorable temperatures on population growth parameters. Temperature extremes were found to delay development, shorten longevity and reduce fecundity. As a consequence, the net reproductive, intrinsic, and finite rate of natural increase were reduced and the population doubling time lengthened as compared with life table parameters measured under more favorable temperature conditions.

These findings should reduce the monitoring period of Heliothis on cotton by allowing checking of sex pheromone traps only at critical periods and help in controlling decision-making in cotton fields.



Reprinted from 1993 Proceedings Beltwide Cotton Conferences pp. 1059 - 1062
©National Cotton Council, Memphis TN

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Document last modified Sunday, Dec 6 1998