Studies on the pests of chromolaena in Kerala

Abstract

A detailed survey was conducted in Trichur District and an objective survey in five other selected districts of the Kerala State during November 1980 to October 1981 to study the pests of choromolaena odorata Linn. Observations on the nature of damage and population density have been made during the survey. Details of the insects recorded on the weed are given below. 1. Hemipteran pests 1.1 Aphis spiraecola patch These aphids were recorded in all the areas surveyed and alate and apterous forms were available. There are four instars each occupying one to two days and the adult six to ten days. The alate forms occurred at relatively lower levels compared to apterous form. In both cases, maximum population was in July irrespective of the topographic conditions. Both the nymphs and adults such sap from the tender shoots thereby reducing the vigour of the plant. 1.2 Aphis fabae scopoli Both apterous and alate forms were observed. Here also the aphid population attained peak level in July both in medium hilly areas and plains. The aphid infested leaves presented a crinkled appearance. 1.3 Braschycaudus helichrysi kitb These were noted in higher elevations like Idukki and Wynad areas and were absent in Trichur District. The aphid attacked leaves become folded and rolled longitudinally. 1.4 Coptosoma sp. These bugs were observed throughout the growth phase of the weed. Adults suck sap from tender parts of the plant without causing any serious damage. 1.5 Sepontia nigrofusea Dist. These bugs suck sap from the weed causing negligible damage and were present in very few number at Pananchery Village. 1.6 Tettigella ceylonica melich. These appeared only as casual feeders of C.odorata and their populations were extremely low for affecting any appreciable damage. 1.7 Bemisia tabaci. Gen. The adult suck sap from tender parts of the weed and the population level was very low. 1.8 Leptocorisa acuta thumb. These were found in the Puzhakkal Village and the bugs suck sap from the weed. 1.9 Riptortus pedestris Fb. The adults suck sap from tender shoots and were found in few number. 1.10 Dysdercus koenigii Fb. The adults suck sap from the weed without causing any appreciable damage. 1.11 Leptocentrus sp. These bugs suck sap from the plant throughout the growth phase of the weed, but the population count was very low. 1.12. Cocosterphus minutes Fabricius These insects were present in few numbers and suck sap from the weed. 2. Coleopteran pests 2.1 Apion sp. As a result of feeding of the weevil irregular holes are formed on leaf surface. These feed on the flowers during the flowering season. 2.2 Unidentified curculionid They eat away portions of the leaf creating holes on the surface. 2.3 Astycus aurovittatus Heller The weevil was found feeding the foliage of the weed during December. 2.4 Amblyrrhinus sp. They feed on the leaves and flowers by cutting small holes on them. 2.5 Mylabris sp. These feed on the weed flowers occasionally. 2.6 Corynodes sp. These beetles feed on the leaves making irregular holes here and there. 2.7 Carvedon sp. These insects were found feeding on the flowers occasionally. 3. Lepidopteran pests 3.1Pericallis ricini Fb. The young larvae feed on the surface tissue of young leaves and in the later instars they feed both by scrapping and by eating the whole leaf lamina. 3.2 Discrisia oblicua wlk. Larvae found defoliating the weed 4. Dipteran pest 4.1 Unidentified agromyzid

The larvae mine into the leaves and eat through the mesophyll leaving the two epidermal layers intact. 5. Thysanopteran pest 5.1 Haplothrips gowdeyi franklin Both nymphs and adults feed by lacerating the tissues of the inflorescence and found in numbers. Out of 23 species of insects recorded to occur on c. odorate coptosoma sp.(plataspididae:Hemiptera),Sepontia nigrofusca (Plataspididae: Hemiptera),Tettigella ceylonica (Cicadelliade: Hemiptera)Leptocorisaacuta (Coreidae: Hemiptera)Riptortus pedestris(Coreidae: Hemiptera)Coccosterphus minuts(Membracidae: Hemiptera)Astycus aurovittatus (Curculionidae:Coleoptera) Amblyrinus sp.(Curculionides sp. Coleoptera)Mylabris sp.(Meloidae:Coleoptera)Corynodes sp.(chrysomelidae: Coleoptera) Caryedon sp.(Bruchidae: Coleoptera),pericallia ricini (Arctide:Lepidoptera) and Haplothrips gowdeyi(phloethripidae:Thysanoptera) are reported for the first time. Among the insects, the most widespread and numerous were A.spiraecola and A.fabae in that order.