MANAGEMENT OF COTTON WHITEFLY BEMISIA TABACI (GENN.) AND BOLLWORMS PECTINOPHORA GOSSYPIELLA (SAUND) AND HELICOVERPA ARMIGERA (HUB) IN THE PUNJAB, PAKISTAN

Abstract

wmTEFL Y (Bemisia tabaci) On Cotton Bemisia tabaci adults were most active from 0600 to 0700 hours in July, from 0600 to 0800 hours in August, between 0800 to 1000 hours in September and from 0900 to 1000 hours in October. During the present survey whitefly was recored from 145 plant specIes ill Multan and Khanewal Districts. These included 41 crops, 41 ornamentals, 45 weeds and 18 fruit and forest trees. Based on the rate of infestation and duration of feeding, hosts have been categorised as major, minor and incidental hosts. In the crops 15 in ornamentals 13 in fruit and forest trees six and in weed 14 plant species were regarded as major host others were minor or incidental. Of the 145 host plants B. tabaci was found on 114 hosts during winter. These include 32 crops, 31 ornamentals, 16 fruit and forest trees and 35 weeds. After winter maximum population was found on Vigna radiata, V cylindrica, Glycine max, Lens culinaris, Helianthus annuus, Solanum melongena, Cucurbita p epo var. melopepo, Cucumis melo, Citrullus lanatus var. listulosus, C. melD var. phut from crops, Althaea rosea, Chrysanthemum morifolium, Lantana camara and Hibicus mutabilis among ornamentals, Euphorbia prostata, Citrullus tetragona, Xanthium strumarium, Malvastrum tricuspidatum, Solanum nigrum and Achyranthes aspera from weeds, Morus alba and Albizzia lebbek from fruit and forest trees. These hosts seem to play an important role for its shifting and build up on cotton. Maximum oviposition took place on S. melongena followed by G. hirsutum , X strumarium,. L. camara, A. aspera and C. tetragona. The most suitable host for development was S. melongena followed by L. camara, C. tetragona, G. hirsutum, A. aspera and X strumarium in descending order. In studies on vertically distribution maximum whitefly nymphs and pupae were found on leaves on node number nine in July and as the plant grew it shifted upwards or downwards and was maximum on leaves of node ten in August on the main stem. On side branches population trends were similar to on the main stem. Within the branch leaves close to main stem were more susceptible than the young leaves. Monocrotophos and lambda-cyhaluthrin gave higher mortality with high volume of application than with low and ultra low volumes. Monocrotophos proved better than lambda-cyhaluthrin. Acetamiprid and diafenthiuron gave highest mortality than monocrotophos and lambda-cyhaluthrin. From the non-conventional insecticide biosal (neem extract) gave higher mortality than the Eruca sativa oil + detergent or Eruca sativa oil + neem soap or detergent alone. Encarsia species and Eretmocerus species were common parasitoids of whitefly nymphs and pupae. Among the alternate host plants maximum parasitism was on A. rosea, A. aspera, Ipomoea batatas, X strumarium and S. melongena. On cotton its maximum parasitism was 40% in the plot where natural enemies were conserved compared with 5% where insecticide were used. The important predators associated with the whitefly infestation on all the plants were coccinellids, Chrysoperla carnea, Orius · sp., Geocoris and unidentified species of spiders. From these coccinellids, C. carne a and spiders played important role in regulating whitefly infestation. PINK BOLLWORM (Pectinophora gossypiella) The pink bollworm adults continued to emerge throughout the year. It completed four generations and the larvae of the fifth generation entered diapause in the bolls or soil in early November. Larvae of fifth generation have long and short diapause. In the sex pheromone baited traps maximum adults from diapausing population were caught during March-April but continued to emerge up to August. Females laid eggs singly on all pI arts of the plant but maximum eggs were laid on squares and bolls. When bolls were not present, maximum eggs were laid on squares. They prefer less than half-grown squares (I-10-days old). Fecundity of females developed from diapausing larvae, an average was 75 and those developed from the active generations was 125. Infested squares turned into rosette flowers. Most of these were shed. Eight to ten percent bolls that developed from rosette flowers were not normal and shrivelled on one side. Number of seeds and weight of lint produced from rosette were less than from bolls developed from healthy flowers . Fourteen to twentyeight days old bolls were most susceptible. Carry over sources of the pink bollworm such as alternate hosts, ratoon cotton, left over bolls and survival of pink bollworm larvae in the soil, double seeds and ginning waste etc., were studied. There was no major alternate hosts and very negligible infestation was found on Althaea rosea and Hibiscus rosa-sinensis. However, low infestation was found on ratoon cotton. :From diapausing larvae in the soil emergence was completed by May. Afterwards larvae did not survive when temperatures were above 400C. In ginning waste most of the double seeds were crushed.The ginning waste when put in the soil increased organic matter and nitrogen in the soil thus improving its fertility. Left over bolls were the only source of carry over. All the larvae were killed in the bolls on the upper part of the sticks kept horizontally in the conventional way in big heap. However, 5% larvae survived on the lower part of heap. Larval mortality was 100% when sticks were kept in small bundles in the upright position (vertically). Pyrethroids proved better than all doses of naturalyte. Residual effect of these chemicals lasted for less than 5-days. The number of larvae in the bolls was higher after 12 days than after 7 days of spary. This indicated that eggs laid 4-5 days after spray hatched and entered the bolls. AMRICAN BOLLWORM (Helicoverpa armigera) H. armigera remained active almost throughout the year. Number of moth caught was lower during January and February than June to August with a peak in April. The females laid eggs on all parts of the plant including terminal buds, leaves, fruiting parts and internodes. About 70-80% eggs were found on the upper part of the plant followed by middle and bottom parts. At low infestation rate 71% eggs were found on the main stem but at medium and high levels of infestation 51-54% eggs were found on side branches. Minimum eggs were found on fruiting parts at all levels of infestation. On main stem more eggs were laid on leaves up to seventh node, highest being on fIrst and second fully developed leaves. On the side branches maximum eggs were laid on fIrst fully expanded leaves and the oviposition decreased towards the main stem. More eggs were found on squares near the tips of branchs. For oviposition squares were preferred to flowers and bolls. Development period and survival varied with the host and temperature. It took 24.5 days on Trifolium aestivum and 34.0 days on Glycine max. Under forced feeding it could developed even on Mangifera indica which is not a recorded host. It was recorded from 61 plant species belonging to 56 genera of 20 families including 31 crops, 14 ornamentals and 16 weed plants. Based on level of infestation and duration of feeding host were categorized as 19 major and 42 minor. Maximum infestation on major hosts was found from March to June. At 27±3°C it completed development in 24-30 days on cotton in the laboratory. It had 7-8 generations in a year. The larvae were recorded from all parts of the cotton plant. Maximum number of young larvae was on top, half-grown on the middle and full-grown on the lower parts of the plant. Maximum young larvae were found on squares followed by vegetative parts. Half-grown larvae preferred flowers and full-grown bolls. No young larva was found on bolls and no full-grown larva was found on vegetative parts. Pupation took place on or in the soil at different depths. Maximum larvae pupated at 2.5 to 5.0 cm below the soil. In sandy soils pupation took place 12.5 to 17.5 cm below the soil. The pupal period was 6-8 days during summer and increased 65 datys in larvae that pupated in October and November, up to 70 days in December and 70-90 days in January. From the field collected pupae in October adults emerged up to after 150 days. First generation life table was prepared in June-July when crop was 30 to 55 days old. Key egg mortality factors during this period were desiccation (42.1 %), dislodging (31.5%) and predation (12.5%). Parasitism remained extremely low being 1.9%. Important mortality factors in the first and second instar larvae were dropping and predation. In the third instal' missing and predation of larvae by chewing insects and birds was 24.1 % followed by predation and parasitism. In the fourth, fifth and sixth instars, predation followed by parasitism were main mortality factors. Maximum pupal mortality was due to decaying because of flood irrigation (15.3%), predation by ants, interculturing and desiccation (26.8%). In the second generation during AugustSeptember loss was 70.8% and in the third generation during October-November 60.0%. Larval and pupal mortality factors were almost the same. However, because of high humidity diseases also caused larval mortality. Pupal mortality due to decaying and other factors was almost the same and caused 56% reduction. After harvest of cotton irrigation, ploughing and planking gave considerable mortality in pupae. Methomyl, profenofos and thiodicarb were effective insecticides on eggs and larvae of H armigera. High parasitism was recorded on Cicer arietinum and Carthamus oxycantha where insecticide were not used in rain-fed areas. In the main cotton belt parasitism was extremely low because of use of insecticides. Chrysoperla carnea is very efficient predator and consumed on an average 241.6 eggs in its life span. It completed its development on 191.2 first instar larvae or 147.3 second instar or 92.0 third instar larvae of H armigera.