Laboratory as well as field investigation are very essential to predict the occurrence of insect pests. In current laboratory studies, the developmental rates of different stages of bollworms were increased with the rise in constant temperatures. Cotton bollworm [Heliothis armigera (Hub)] completed its developmental- period (from egg to pupa) in the minimum of 14.7 days at 35°C as compared to 18.9,31.3, 54.2 and 7.9 days at 30,25, 20 and 15°C, respectively. The minimum generation period 17.3 days was observed at 35°C as compared to 22.0 at 30, 35.3 at 25, 60.4 at 20 and 94.1 days at 15°C. The pink bollworm [(Pectinophora gossypiella (Saund.)] got the maximum period of 68.2 days to develop from egg to pup followed by 49.3 at 20, 26.4 at 25, 15.7 at 30 and 12.6 days at 35°C. A generation was completed in 78.2 days at 15°C followed by 55.0 at 20, 30.6 at 25, 1 .7 at 30 and 14.8 at 35°C. Results on spotted bollworm [(Earias vitella (F)] showed that it completed its development in a minimum period of 16.6 days at.35°C followed by 19.3 at 30,27.7 at 25,44.1 at 20 and 77.3 days at 1°C. Generation was completed in 19.2 at 35°C as compared to 22.3, 31.7, 50.1 and 88.3 days at 30, 25, 20 and 15°C, respectively. The spiny bollworm [(Earias insulana (Boisd)] completed its development in a minimum period of 14.7 days at 35°C, whereas the maximum in 79.9 days at 35°C. Its generation was 17.3 at 35 and 94.1 days at15 °C.
The overall data on growth versus temperature confirmed that the developmental rate for all bollworms was a linear function in the range of moderate temperatures (15-30oC). It was concluded that the upper and lower temperature developmental thresholds of all bollworm varied from each other. The upper optimum threshold temperature was 30°C for all bollworms, whereas the lower developmental threshold temperatures were 12.5°C for cotton bollworm, 12.6°C for pink bollworm, 10.0°C for spotted bollworm and 11.7°C for spiny bollworm. Degree days (DD) for different: stages of bollworms were determined above their lower developmental thresholds. For complete development (egg to pupa), cotton, pink, spotted and spiny bollworms required 333.7, 281.8,408.7 and 310.2 DD and for generation periods they needed 382.9, 324.4, 468.7 and 362.7 DD, respectively. Under field conditions, degree days of bollworms were calculated for each day using minimum and maximum temperatures for three consecutive years using the rectangle or simple average method. Then degree day were accumulated over a period of year starting from 1st January as a biofix to forecast the appearance of bollworms. Accumulated degree days tables were developed for each bollworm.
A computer model was developed to determine DD for each day after the input of minimum and maximum temperatures, lower and upper thresholds of any insect. These DD accumulations were targeted to predict the occurrence of different levels of bollworms population that was monitored through pheromone baited traps at NIAB and farmers fields and through visual observations on their percent infestations. The overall mean results for 3 years achieved through traps indicated significantly high population of cotton bollworm on 15th September 1998 followed by 8th September 1999 and 21st July 2000 in insecticide free cotton at NIAB. Field infestation studies showed significantly high infestation on 22nd September 1998 followed by 4th August 1999 and 15th September 2000. The cyclic patterns of moth population/trap/night and percent infestations for three years showed positive relationships with their corresponding accumulated DD. After comparing the results on moths captured per trap/ night and their average per week from 1998 to 2000 with those on DD accumulations it was concluded that the first peak population occur from 21st July to 28th July that accumulate 1906 to 2071 DD. Similarly, the comparisons showed that the first peak infestation occur from 4th August to 11th August that collect 2131 to 2202 DD, starting from 1st January over a threshold 12.45°C. The cumulative data over three years showed that 50% population occurs between 2398 and 2509 DD and 50% infestation 'occurs between 2347 and 2642 DD. These trends varied to some extent in farmers insecticides sprayed field: The comparisons between threshold levels and DD accumulations showed that DD or the capture of 8 moths nearly equal 5% infestation. Three years data indicated that accumulation of 1713 -1825 DD in period from 9-13th July for 8 moths/trap/night equals and follows 1679-1921 DD in period from 7 -19th July for 5% infestation. Similarly, accumulation of 1937-1988 D from 21-23rd July for 12 moths/trap/night follow the range of 2004-2153 DD from 28th July to 2nd August for 10% infestation. Field infestation usually folio s moth population. Therefore, the capture of 4 moths/trap/night that needs 679-1774 DD from 6-9th July predict the occurrence of 5% infestation that require more DD from 7-19th July.
Significantly high number of pink bollworm was detected on 6th October followed by 29th September and 1st September. Similarly high percent infestation was recorded on 6th October followed by 30th October and 29th September. The close association of moth population and field infestations over three years with reference to DD showed that the first peak population occurs between 25th August and1st September that accumulate 2477 to 2556 DD. The peak infestation occurs between 1st September and 6th October with the collection of 2586 to 3015 DD. The linear equations and skewed curves confirmed a positive and close link between cumulative percent moth populations and infestations. Data indicated that 50% cumulative moth population occurs between 2473 and 2834 DD and 50% infestation between 2536 and 2849 DD. Three years observations showed that 4 moths/trap/night accumulate 1589 to 1747 DD during 2nd -10th July; 8 moths from 1972 to 2200 DD from 24th July to 10th August and 12 moths from 2348 to 2424 DD from 17-24th August. Comparably, 1973 to 2138 DD were accumulated for 5% infestations from 27th July to 6th August; 2493 to 2639 DD from 26th August to 6th September and 2844 to 3028 DD from 20 to 30th September. It was concluded that 5% infestation follows 4 moths/trap/night. The same relationships were developed between 8 moth and 1 0% infestation and 12 moths and 15% infestation.
The maximum mean yearly captures of spotted bollworm moths/night were recorded at NlAB on 18th August followed by 11th August and 29th September. The 1st high peak population occurs between 11th and 18th August that accumulate 2755-2813 DO starting fro11st January above lower threshold temperature of 10.0oC. The peak infestation was recorded on 25th August that accumulate 2896-3014 DD. Data on cumulative percent moth populations and cumulative percent infestations over three years showed close association for accumulation of DD. Therefore, the skewed curves predict that 50% cumulative population occurs between 3001 and 3041 DD, whereas 50% infestation occurs between 3050 and 3115 DD. It was concluded that various threshold levels of insect require different DD. A number of 4 moths/trap/night accumulate relatively less DD as compared to those with 5% infestation. The field infestation mostly follow the appearance of moths. Therefore, 4 moths/trap/night during 1st to 2nd July will predict the forthcoming infestation level of 5% during 9th to 12th July. In other words the mean yearly DD from 1952 to 2067 forecast the occurrence of 4 moths and 2124 to 2204 DD for the occurrence of 5% infestation. The same trends occur between 8 moths and 10% and between 12 moths and 15% infestation.
Moth population of spiny bollworm at NIAB under un-sprayed conditions was the maximum on 8th September followed by 1st and 15th September. The period from 8th to 22nd September was very favorable for the occurrence of highest field infestations. Significant and positive correlations were determined between the cyclic fluctuations of moth population and percent infestations with reference to degree days in three consecutive years. It was found that the first high peak of moth population occurs at the accumulation of 2720 to 2795 DD during 1st to 8th September. The peak infestation occurs between 8th to 15th September by accumulating 2860 2907 DD. The skewed distribution of cumulative percent month populations and percent infestations showed that these factors are linked very closely on the .basis of DD. The equations and curves predict the. percent occurrence of moths and field infestation in terms of DD. It was concluded that 50% cumulative moth population occurs between 2759 and 2825 DD The 50% cumulative infestations occur between 2849 and 2825 DD. Different expected threshold levels showed different DD. However, DD for 4 moths/trap/night ranged from 1981 to 2055 in period from 16th to 23rd July; for 8 moths from 2309 to 2516 in period from 9th to 19th August and for 2 moths from 2530-2594 in periods from 20th to 23rd August. Comparably, 5% infestation accumulate a range of 2216 to 2309 DD from 29th July to 7th August; 10% infestation a range of 2478 to 2660 DD from 20th to 5th August and 15% infestation a range of 2514 to 2793 DD from 22nd August to 2nd September. It was concluded that DD for 5%, 10% and 15% infestation followed those of 4, 8 and 12 moths/trap/night.
The overall results in this research were converted into prediction models of bollworms for agro-climate of district Faisalabad. In brief, these prediction models allow research workers and farmers to use them according to their own local environments keeping in view the species of bollworm, variable temperature and crop phonology; further-more these models predict the occurrence of bollworms either in DD or moth population/trap or percent infestation or their combinations. Using these models we can predict and control bollworms occurrence well in time, accurately and for a specific area under IPM programmes. Therefore, keeping in view the validity of these models the government research organizations can expand such programmes to other locations of Pakistan.