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Open Access
Bionomics of pareuchaetes pseudoinsulata rego barros (lepidoptera:arctiidae) and its interaction with the siam weed chromolaena odorata king and robinson (asteraceae)
(Department of Agricultural Entomology, College of Horticulture, Vellanikkara, 1995) Lyla, K R; KAU; Abraham, C C
Studies were undertaken on the biology, morphometrics, feeding habits, factors affecting fecundity and fertility of Pareuchaetes pseudoinsulata King and Robinson (Arctiidae : Lepidoptera) and also the plant response of the weed host Chromolaena odorata L. at the College of Horticulture, Vellanikkara during 1990 – 1993. The morphometrics and morphology of the various immature stages and adults have been described. The total life-cycle of P. pseudoinsulata took a total of 46.75 days and the various developmental stages lasted for 5.5 days in eggs, 21.30 days for larvae (seven instars) 1.5 days for pre-pupa and 10.15 days for pupae at a mean ambient temperature of 28.40 C. In feeding trials to assess the relative preference of tender, mature, semi yellow and yellow leaves of C. odorata, it was found that the I instar larvae showed district preference to tender leaves as compared to mature leaves. The I and II instar larvae did not feed on semi-yellow and yellow leaves and they died of starvation when these types of leaves were offered for feeding. Consumption indices decreased as the age of larvae advanced and thus early instars consuming all the types of leaves recorded high indices. The rate of increase in larval weight gain was higher in later instars (VI and VII). Caterpillars feeding on mature, semi-yellow and yellow leaves showed higher Relative Growth Rate during IV to V stage, but during I to II stage, a high RGR was seen on larvae which fed tender leaves. Yellow. leaf diet for late instar larvae adversely affected their development and adult emergence. Highest fecundity was recorded when the parental sex-ratio of moths was kept at 1:1 level followed by 1:2 ratio and 2:1 in that order. Egg production and viability were significantly higher at 250 C and 75 per cent RH as compared to 300 C and 60 per cent RH. Adult food did not show any influence on fecundity but in respect of improvement of egg viability the treatments were advantageous. Total nitrogen content in leaves was maximum on the sixth day of release of four larvae per cage. Leaf nitrogen showed a declining trend when the larval load per plant was increased from the eighth day of release onwards. Soluble nitrogen content in leaves showed an increasing trend with increase in larval load per plant, but this however failed to reach significant levels. Chlorophyll content in leaves got reduced significantly at increased larval population loads and with passage of time of confinement. The natural enemies of P. pseudoinsulata consisted of avian fauna, spiders and ants and parasitoids. Predatory species of ants recorded in association with the insect included Lioponera sp. Oecophylla smaragdina Fabr. Solenopsis sp.and Monomorium sp. Occasionally NPV infection occurred in the laboratory as well as in field cultures causing substantial mortality. The implications of the various findings in reorienting the biocontrol strategies involving P. pseudoinsulata against C. odorata have been discussed.
Open Access
Monitoring and management of the pest complex of bitter gourd (Momordica Charantia L.)
(Department of Agricultural Entomology, College of Agriculture, Vellayani, 1999) Nandakumar, C; KAU; Saradamma, K
Surveys were conducted in 1995-96 among one hundred bitter gourd farmers in Thiruvananthapuram district. Information on the personal and socio- economic characteristics of the farmers was gathered. Field visits indicated that among the pests at flowering, the jassid, H.phycitis and leaf feeder, D. indica were important. At early harvest, the jassid and fruitfly B. cucurbitae were the major pests. Among the natural enemies observed, the potential ones were Cjohnsoni (parasite on Hseptima), I.scutellare, Msexmaculatus and Snubilis . (predators on A.gossypii). Mosaic was severe in 12 per cent of the plots. Sixty two per cent of the farmers used a combination of mechanical, cultural and chemical measures against pests. Most common pesticides used belonged to the organophosphate group. Farmers in general adopted injudicious methods of chemical control. Seventy per cent farmers relied on mass media and interpersonal cosmopolites for information on plant protection. The most important constraint perceived by farmers was the high cost of inputs viz., plant protection chemicals, manures and fertilizers. Monitoring of fruit fly incidence using Biosense stikatrap (lure) indicated the maximum catch at eleven weeks after sowing. Ten carbofuran smeared banana fruit traps (in yellow coloured coconut shell) were found to be more efficient than one Biosense trap in trapping the fruit fly. 2 Studies on seasonal incidence of the pests and their natural enemies from 1995 to 1996 indicated that they were more from November '95 to April '96. In studies on the assessment of potential natural enemies of pests, the biology and efficacy of Cjohnsoni against epilachna beetle was observed. Among the predators viz., Iscutellare, Msexmaculatus and S.nubilis whose biology and feeding potential was studied, Msexmaculatus was observed as the most efficient predator of aphids. In another set of experiments, the effects of botanicals and chemical pesticides on pests and their natural enemies were studied. The antifeedant effect of botanicals on third instar Hseptima grubs indicated that neem seed oil (three per cent) and nimbecidine (0.40 per cent) were effective. Estimation of the comparative effect of chemical pesticides against the fourth instar Hseptima grubs showed that carbaryl and dimethoate were more effective than quinalphos and malathion. Toxicity studies of botanicals and chemical pesticides to Msexmaculatus grubs and Cjohnsoni adults as well as parasite emergence from treated larval! pupal Hseptima hosts indicated that botanicals were safe whereas, the chemicals were toxic to the natural enemies. Based on the above experiments, the botanicals viz., neem seed oil three per cent, nimbecidine 0.40 per cent and the chemical pesticides,carbaryl 0.15 per cent and dimethoate 0.05 per cent were selected for the pest management trial in bitter gourd. The reaction of five bitter gourd varieties viz., Priya, Arka Harit, Preethi, Priyanka and local to pests was tested in a field trial. Based on pest infestation and yield, Preethi was selected for the pest management trial. 3 The pest management trial was conducted for two seasons (January to April, 1996 and 1997). The results indicated that combination of botanical with chemical pesticide was the best in pest control. Based on the results the following recommendations were suggested as part of IPM strategies in bitter gourd. 1. Use variety 'Preethi' (MC-84) for planting 2. Basal drenching of combination of nee m seed oil three per cent soap emulsion with either dimethoate (0.025 per cent) or carbaryl (0.075 per cent) prior to seeding. This is recommended in areas where pests like pumpkin beetles are endemic. 3. Need based application of above till fruit set to control pests. 4. Apply fungicide (Mancozeb) to control foliar disease (downy mildew). 5. Monitor fruit fly incidence using lure trap. Set yellow painted coconut shell trap's containing carbofuran smeared banana (palayankodan) alternated with carbofuran poisoned ocimum I jaggery (2m spacing) at flowering till final harvest. 6. After fruit set, use (need based) a combination of neem seed oil three per cent soap emulsion and dimethoate 0.025 per cent.
Open Access
Insect pest natural enemy- host plant interaction studies with special reference to the brown planthoper nilaparvata lugens(Stal.)
(Department of Agricultural Entomology, College of Horticulture, Vellanikkara, 1999) Haseena, Bhaskar; KAU; Joy, P J
Field surveys were conducted in Kole land and Kuttanad to assess the population of rice BPH, Nilaparvata lugens (Stal) and its natural enemies. Field investigations on the population dynamics of BPH and its natural enemies were carried out on susceptible (Jaya), moderately resistant (Jyothi) and resistant (Kanakom) rice varieties at the rice fields of Rice Research Station, Moncompu during 1997-98. The influence of these varieties on the biology of the pest, the biocontrol efficiency of the major natural enemies and the biology of the mirid predator Cyrtorhinus lividipennis Reuter was studied in the laboratory. Histological and chemical investigations were undertaken to evaluate the factors that contribute to the resistance/susceptibility in them. Results of field survey in Kole land revealed that the population of BPH was far below the economic threshold level (ETL). In Kuttanad, in kayal area during Rabi season and in karappadam tract during Kharif season outbreaks of BPH occurred in some localities due to the indiscriminate use of insecticides resulting in the mortality of natural enemies. The results of the study on population dynamics revealed that the BPH population was significantly high on the susceptible J aya and low on the resistant Kanakom with the population reaching a peak from February to March. The predatory complex of the BPH comprised of the rnirid Cyrtorhinus lividipennis, Lycosa pseudoannulata, Tetragnatha maxillosa, Atypena formosana, Microvelia douglasi atrolineata, Pseudogonatopus sp. and Ophionea nigrofasciata. C. lividipennis was the most predominant predator regulating the hopper population and there exists a density dependent host-predator relationship. The population of the mirid predator on Jaya and Kanakom did not differ significantly. The prey-predator ratio was lowest on the resistant variety and highest on the susceptible variety. Of the weather parameters studied, the minimum -. temperature showed a highly significant negative correlation with the population of N. lugens in all the varieties. BPH reared on the resistant variety recorded longer nymphal duration, decreased nymphal survival and shorter adult longevity indicating the prevalence of antibiosis in the variety. Lesser number of eggs laid, longer pre-oviposition period and shorter oviposition period recorded on Kanakom indicate the antixenosis factor in it. Macrpterous forms of BPH did not develop on the variety . The predator C. lividipennis and Micraspis sp. fed more BPH when reared on the resistant variety. The veliid bug M. d. atrolineata, the spider L. pseudoannulata and the dryinid Pseudogonatopus sp. predated significantly more BPH nymphs on resistant variety at a higher prey density only. However, the dryinid parasitoid consumed significantly fewer number of hoppers on Kanakom at the higher host density. C. lividipennis recorded longer nymphal duration, shorter adult longevity and low fecundity when fed on BPH reared on Kanakom which can be attributed to the low fecundity of N. lugens on Kanakom leading to less availability of food to the mirid. Nymphal duration and adult longevity of C. lividipennis did not vary between the varieties Jaya and Jyothi. Well developed bundle sheath with more frequently distributed schlerenchyma tissue in the culm of the resistant variety seemed to impart resistance in Kanakom along with thicker cuticle. Higher amounts of silica, Zn and Mn and lower amounts of N, K, Ca and Mg were recorded in the culm of the resistant variety compared to moderately resistant and susceptible varieties. The findings strongly suggest the mechanism of antibiosis and antixenosis in the resistant variety Kanakom.
Open Access
Distribution and bio-ecology of phytophagous mites of vegetables,medicinal plants and ornamentals in Thiruvananthapuram District
(Department of Agricultural Entomology, College of Agriculture, Vellayani, 1996) Sudharma, K; KAU; Madhavan Nair, G
A detailed survey on phytophagous mites and their predators associated with vegetables, medicinal plants and ornamentals was conducted for the first time in Thiruvananthapuram District, Kerala during premonsoon, monsoon seasons of 1992 and 1993. The centres selected for the survey were the college of Agriculture, Vellayani; Ayurvedic research Centre, poojappura; University Centre, Kariavattom; Tropical Botanical Garden and Reserch Institute, Palode and the District Agricultural Farm, Peringammala. The survey revealed the presence of phytophagous and predatory mites belonging to six families each. The families under the former group were Tetranychidae, tarsonemidae, Tenuipalpidae, Eriophyidae, Galumnidae and Oribatidae and under the latter group were phytoseiidae, Ascidae, Bdellidae, Cheyelitidae Cunaxidae and Stigmaeidae. Phytophagous mites belonging to the families Tetranychidae, Tenuipalpidae, and Tarsonemidae were the most widespread and the dominant species of these families were commonly found on all the three groups of plants. The survey further helped to identify eighteen new host plants of phytophagous mites which are new reports. The phytophagous mites T.cinnabarinus, T.ludeni, T.neocaledonicus , B.phoenicis,T.pacificus R. indica, P. latus and a few species under the genera tetranychus, Brevipalpus and Tarsonemous were the important species infesting vegetables, medicinal plants and ornamentals in the District. Among the acarine predators of phytophagous mites , the species belonging to the family phytoseiidae in general and in the family phytoseiidae, species of the genus Amblyseius in particular were the most widespread .The mites belonging to the family Cunaxidae and the coccinellidae, Stethorus sp . were also found to be important predators of phytophagous mites. The mean percentage of mite infested leaves and the mean population counts were also assessed to study the distribution and abundance of different groups of mites on different host plants in different seasons. The species, T.ludeni, T cinnabarinus, T neocaledonicus and P.latus on vegetables, T.ludeni and B.phoenicies on ornamentals and B.phoenicis, T.cinnabarinus, T.ludeni, T.neocaledonicus and P.latus on medicinal plants were found to be numerically dominant species capable of causing serious damage to the crops. The mean percentage of mite infested leaves and the mean population counts of phytophagous mites were the least in the monsoon season as compared to the premonsoon and postmonsoon seasons in vegetables, medicinal plants and ornamentals. The mean population counts of predators in different seasons also showed trends similar to those of phytobhagous mites, the monsoon season having the least or no predatory populations. In the postmonsoon season also their numbers were negligible. The phytoseiids were numerically the most dominant predators on vegetables, ornamentals and medicinal plants. The coccinellid predator, Stethorus and acarine predator cunaxids were also found to be important to a lesser extent. The results of replicated field trials conducted in the College of Agriculture, vellayani on selected vegetables, medicinal plants and ornamentals also revealed that, in general, the mite population was the least in the monsoon season as compared to the premonsoon and postmonsoon season. In general, the population development was found to be positively correlated with maximum temperature and relative humidity. The nature and symptoms of damage of T.cinnabarinus on Adhatoda ;T.ludeni and T.neocaledonicus on rosea; T.pacificus on Dendrobium; R.indica on T.alata; B.phoenicis on the medicinal plants G.sylestre,S.ciliates O.sanctum, and on Caladium, Maranta and Dendrobium and P.latus on chilli, bittergourd , ridegorud and T. erecta were studied and described in detail. The biology and biometrics of T. cinnabarinus, T.ludeni, T neocaledonicus, T.pacificus and B.phoenicis were studied on selected host plants and described in detail. Crop loss studies conducted on bhindi and chilli by releasing different population levels of T.ludeni and P.latus revealed that , the stage of the crop at which infestation commenced was an important factor which determind the crop loss. It was also found that there was crop to crop variation on the levels of tolerance to different mite loads. No significant difference was noticed in the distribution of T.ludeni on the top, middle and bottom strata of bhindi plants while in chillies the mite P.latus preferred the top stratum indicating a preference for young growing tissues for feeding and oviposition.
Open Access
Resurgence potential of the rice leaf folder. Cnaphalocrocis.medinalis Guen. as influenced by the soil application of carbofuran granules
(Department of Agricultural Entomology , College of Horticulture, Vellanikkara, 1991) Baby, P Skaria; KAU; Abraham, C C
In investigations on the changes taking place in the extent of feeding, growth and development of the rice leaf folder, Cnaphalocrocis medinalis Guen. on rice plants receiving soil application of carbofuran granules at 0.50, 0.75 and 1.00 kg ai/ha/application at 20, 50 and 20 and 50 days after transplanting, the extent of larval feeding on leaves did not show any variations as a result of carbofuran treatments. In the third, fourth and fifth larval instars and pupae, carbofuran treatments led to their weight gain due to possible enhancement of the digestibility and more effective conversion of ingested food into body matter, under .influence of factors mediated by the metabolites of carbofuran in leaf tissues. In respect of mean larval and pupal mortality, the insecticidal treatments did not show any impact, but the metabolites showed a negative correlation with the mortality levels thereby indicating the favourable influence of the metabolites on the development of C. medinalis. There was improvement in female emergence as a result of treatment with 1.00 kg ai/ha of carbofuran applied at 20 as well as 50 DAT as compared to untreated control, but the sex-ratio variations as a result of treatments were not pronounced. The first instar larval emergence (F1 generation) showed a positive influence by different metabolites of carbofuran. Carbofuran treated plants showed distinctly positive orientational stimulus to C. medinalis adults due to positive olfactory stimuli probably due to emission of vapour-phase admixture of carbofuran metabolites, but there was no improvement in fecundity under such treatments. There was distinct improvement in progeny production from females developing from carbofuran treated rice plants. This is mainly due to the ingress of more female moths and the resultant increase in overall ovipositional output rather than increase in fecundity'. Carbofuran treatments caused increase in the density of leaf hairs in a dose-dependent manner, but such variations were not significant as compared to untreated control. The positive relationship between ovipositional preference on the one hand and leaf hair density of treated plants .on the other brings to focus the role of tactile stimuli provided by leaf hairs in the acceptance of host plants for oviposition. The residues and metabolites of carbofuran in leaves favourably influenced most of the growth and developmental attributes of the rice leaf folder. None of the plant biochemicals showed any changes under influence of carbofuran treatments.
Open Access
Composting efficency of indigenous and introduced earthworms
(Department of Agricultural Entomology, College of Agriculture, Vellayani, 1997) Jiji, T; KAU; Dale, D
Eight species of earthworm belonging to three families were identified from five different soil types of southern Kerala. The identified species were Megascolex cochinensis, M.konkanensis, M.trivandranus, M.trilobatus, Perionyx, sansibaricus, Pheretima heterochaeta (Megascolecidae), Pontoscolex corethrurus (Glossoscolecidae) and Drawida sp. (Moniligastridae). M.cochinenses and corethrurus were ubiquitous. P. sansibaricus was confined to forest soil and red soil. Forest soil with high water holding capacity, organic carbon content and acidic pH had the highest total count of worms and the highest species diversity. The exotic species Eudrilus eugeniae was more efficient for composting in terms of duration for composting and biomass production. However, the multiplication rate of the indigenous P. sansibaricus was more than that of E.eugeniae. In field conditions, when the same weight of worms was used, the time taken for composting was found equal for E. eugeniae and P. sansibaricus. However, the biomass recovery of earthworm was more in E. eugeniae. Both species performed well in the rainy season, compared to hot summer months. The breeding potential, time required for composting and decomposition rate were significantly superior from june to September. There was posititve correlation between juvenile count and rainfall and negative correlation with maximum temperature with respect to E.eugeniae. In P. sansibaricus adult and juvenile counts expressed positive correlation with rainfall and humidity and negative correlation with maximum temperature. Space was found to be a determining factor in the growth and multiplication earthworms. The cocoons of E.eugeniae required 29+ 1.10 days for hatching. The hatching rate was only 56.25 + 1.19 percent in laboratory condition. The mean number of juvenile hatched /cocoon was 2.88+0.35. The period required to attain reproductive stage was 43.38 + 0.56 days. Cocoons of P.. sansibaricus was elongate and slender. The time required for hatching of cocoon was 16+0.43 days. The hatching rate was 64.06+3.44 percent in laboratory conditions. The juveniles required 38.25 + 0.70 days to become adults. The number of cocoon laid / week was also significantly superior, as compared to E. eugeniae. Vermicompost along with full inorganic fertilizer increased the yield by 21.4 per cent and 19.0 percent in bittergourd and cowpea, respectively. In cowpea, application of vermicompost without inorganic fertilizer was equally effective as that of the recommended manorial schedule. There was significant yield increase when vermicompost was used as a potting mixture in bhindi. However, no significant difference in the biometric characters of plants was observed. Vermicompost along with full inorganic fertilizer increased the yield of bhindi by 15 percent. The effect of in situ vermiculture (250 worms of p. sansibaricus /plot) was on par with that of package of practices recommendations. Neemcake was found beneficial for supporting growth and multiplication of E.eugeniae. Neem cake recorded 102 percent increase in juvenile worm production. Neem leaves and thevetia leaves were equally effective. Mahua cake was not supportive for growth and multiplication. Neem cake was effective in supporting growth and multiplication of P.sansibaricus. Neem cake recorded 52 percent increase in juvenile worm production. Leaves of neem, clerodendron and glyricidia were equally effective in supporting juvenile worm production as that of the control. Calotropis leaves and mahua cake caused significant reduction in adult, juvenile and cocoon production. In a pot culture study, among the treatments, carbofuran, phorate and quinalphos, quinalphos(0.5 kg and 1.0kg ai/ha) was found the least toxic to earthworm and there was total survival after an interval of seven days. The treatments involving earthworms for composting evolved significantly higher Co2 during the period of composting, compared to the control treatment of banana: cowdung mixture without worms. The Co2 evolved by the treatments involving E.eugeniae and P.sansibaricus were on par. Maximum Co2 evolution was observed on the 21st day which was significantly superior to the Co2 evolution estimated at various other intervals. From the 21st day onwards a decline in the CO2 evolution was recorded. The treatment involving earthworms had a significantly higher bacterial, fungal and actinomycetes counts, as against the treatment without worms. The highest fungal count for E.eugeniae was found on the 28th day. Towards compost maturity the fungal counts were more or less steady; however, a slight increase in the count was observed on the 56th day. There was no definite trend with respect to actinomycetes count during the period of composting.
Open Access
Distribution of spindle bug of Arecanut, Carvaholia arecae Miller and China in Kerala.Its broecology, suspected role as the vector of yellow leaf disease and control
(Department of Agricultural Entomology, College of Agriculture, Vellayani, 1990) Stanley, Jacob A; KAU; Mohan, Das N
A state wide survey was conducted in Kerala during 1988 with a view to ascertaining the distribution and severity of incidence of C. arecae and yellow leaf disease on arecanut. The pest enjoyed a state wide distribution while the disease was present only in 40 per cent of the locations covered in the survey. Based on the percentage of the infested palms and on adult popula tion of the insect, the southern zone was found as most affected and the nymphal population was more in the northern zone. Based on total population northern and southern zone came on par. The leaf injury caused by the bug was higher in the northern zone and other zones came on par and less effected. Thus on different criteria the severity of the pest infestation in different agroclimatic zone did not show consistency .Vadakkanchery and Palghat in the middle zone were identified for the first time as the only pest free locations in Kerala. In southern zone, Pandianpara, Kattakkada and Ettiruthi had high pest incidence while at Theviyode, Vithura and palode the infestations were found comparatively lower. A consecutive monthly monitoring of the populations in five of the above locations during 1987-89 revealed that places found less affected in the single state wide survey were seen badly affected and vice versa in repeated assessment. In the problem zone Moncompu, Vytilla and Chengannur were much more affected than Karthikaplly, Kumarakom and Karunagapally. In the middle zone, Alwaye, Pattikkad and Peechy were more affected than Vadakkanchery, Palghat and Mukundapuram. In the hill zone Peringamala, Vythiri and Ernadu had much higher population than Vaduvanchal and Kottapady. In northern zone Calicut, Taliparamba, Madhur and Koipady were more infested than Kumbla, Tellichery and Koothuparamba. Since repeated survey over two years reversed the relative position of the locations based on single survey, the latter did not appear conclusive thus suggesting the need for resorting to control measures throughout the state for tackling the pest problem. A new spot of high incidence of yellow leaf disease in north Kerala was detected at Irrikkur near Cannanore. Incidence of C.arecae and yellow leaf disease did not show any association in different agroclimatic zones in Kerala or among different locations within each zone. Continuous monitoring of the population over 24months revealed that the occurrence of immature stages and adults overlapped, indicating continuous breeding of the pest. Period of high/low incidence of pest could not be identified consistently. The occurrence of the symptoms of yellow leaf disease did not coincide with the levels of fluctuating pest population. Maximum temperature and minimum relative humidity showed negative and positive correlation with the pest population respectively. C.arecae fed and multiplied on its alternate hosts A. triandra, C. lutescens and pinanga sp.as favourable as on A catechu. E.guineensis also was found a suitable host since the immature and adult stages of the pest on the host showed more favourable attributes when compared to those on A. catechu. The feeding behavior of the insect relating to the ‘plant surface exploration ‘,’exploratory probes ‘ and ‘imbibing food ‘ agreed with the behavior of other ‘Cimico-morphs’ described by earlier workers. The feeding suppressed the emergence of spindle leaf partly or fully depending on the period of the damage. Total suppression of spindle leaf emergence even choked further growth of the palm. Injury caused by oviposition was observed in detail for the first time .Characteristic ‘pot marks’ made on the rachis of the leaf and the internal damage also were noted in detail for the first time. Histological observations of the leaf along the feeding marks showed that the bug resorted to ‘lacerate and flush’ feeding .Formation of water soaked areas soon after stylet insertion , continuance of plasmolysis after the removal of the insect from the feeding spot and later discolourations and collapse of cells indicated that the action of the saliva would have caused the injury . Histochemical studies of the injured leaf lamina showed accumulation of proteins and lipids in the portion . The above host reactions were detected for the first time . A new technique of warding off C. arecae from the crown of areca palms by keeping phorate /carbofuran granules in perforated polythene sachets , at the leaf axil, was developed and standardized . The technique was evaluated at field level in comparison with the recommended methods of spraying insecticides on the crown or keeping granules directly in leaf axils. On the basis of cost and bioefficacy, the new technique was found far superior to the recommended practices. Salivary glands of C.arecae , exposed on yellow leaf disease affected palms for 20 to 33 days (ensuring acquisi-tion and incubation periods for MLO), were excised , processed , stained and examined under electron microscope for locating mycoplasma like organisms in the acini of the anterior, posterior and lateral lobes, if any . The haemolymph drawn from such insects also was examined under electron microscope . MLOs were absent in all the preparations. This finding in conjunction with the absence of correlations between the pest population and disease incidence ruled out the possibility of the insect being a vector of the disease.
Open Access
Influence of weather and rearing techniques on mulberry silk worm crops in Kerala
(Department of Agricultural Entomology, College of Agriculture, Vellayani, 1998) Krishnakumar, R; KAU; Sasidharan Pillai, K
Investigations were conducted on the effect of weather parameters on the mulberry silkworm crops reared in different seasons and to evolve suitable rearing technology for stress seasons in order to improve the rearing during these seasons and for developing suitable package of practices recommendations for silkworm rearing in Kerala. The study was conducted during 1992-1996 at College of Agriculture, Vellayani. The experiments conducted were  Effect of climatic factors on mulberry silkworm crops in different seasons.  Identifying rearing technology for stress seasons of high temperature and humidity.  Manipulation of feeding schedule with reference to stress seasons and types of silkworm rearing houses. To study the effect of climatic conditions on the mulberry silkworm crop, the silkworms were reared during different identified seasons viz December- January, February-April, May-July, August-September and October-November in 1993-94. The mulberry silkworms used for the study were bivoltine NB4Dz and crossbreed PM x NB4D2. Three brushing were done in each season at fortnightly intervals and fifteen continuous rearings were conducted. The important weather parameters recorded were maximum temperature, minimum temperature, maximum humidity and minimum humidity inside and outside the rearing house. The rearing characters like instarwise larval duration, moulting duration, larval weight, leaf consumption, silk gland weight, disease incidences, missing larval percentage and economic traits like cocoon weight, shell weight, shell ratio, effective rearing rate, filament length, reelability and computed parameters like growth index and growth rate were also recorded. Among the different seasons, August-September and December-January were identified as the favourable seasons. October-November, February-April and May-July seasons were found to be the stress seasons as the biological and economic traits of the different silkworm races during these seasons were not compromising in comparison with other seasons. Maximum temperature and minimum temperature show direct correlations whereas maximum humidity indirectly showed negative correlations with the economic traits like larval weight, silkgland weight, shell ratio, cocoon weight and yield. Second and third experiments were conducted to identify suitable cost effective and efficient rearing house for these stress seasons and also to evolve rearing technology so as to reduce cost of production. The treatments for the second experiment were five different rearing houses along with three different larval spacings. The rearings were conducted by using the same crossbreed and bivoltine race used in the first experiment. The rearings were carried out during 1995 and 1996 in the three stress seasons viz May-July, October-November and February-March. The observations were recorded in terms of the larval characters and economic traits of the silkworms NB4D2 and PM x NB4D2 in these seasons. The results revealed that wider spacing was superior to medium and close spacings in both races. The rearing houses made of mud brick and thatched roof and burnt brick and thatched roof were found superior to other rearing houses in all the three stress seasons during the two year period. Among the different feeding schedules studied in the third experiment, three feeding a day was mostly on par with four feeding a day but was advantageous in terms of convenience of feeding time over other feeding schedules though four feedings recorded higher values for some biological and economic traits in the different silkworm types during different seasons. The incorporation of new techniques of rearing the crossbreed silkworm types in thatched mud wall rearing house, medium spacing of worms and three feeding a day was found to be an ideal profitable package during unfavourable seasons as comparable to that of favourable seasons.
Open Access
Host-specificity, patho-physiology and transmission of the baculovirus(Kerala isolate) infecting Oryctes rhinoceros Linn. (Scarabaeidae:Coleoptera)
(Department of Agricultural Entomology, College of Horticulture, Vellanikkara, 1995) Suma Paulose; KAU; Abraham, C C
The Baculovirus oryctes has been recognized as one of the most promising pathogens against oryctes rhinoceros. Laboratory studies were conducted to evaluate the virus in respect of its patho-physiology, histopathology, mode of transmission, cross-infectivity, effect of physical factors on the virulence of the virus and safety to non –target organisms. The oral inoculation technique has been found to be more effective than the swim method. For long term storage of the virus, the freeze drying method was found to be ideal as it retained viability for more than sixteen months. The viral particles have been found to be bacilliform , measuring 210 to 250nm in length and 75 to 105 nm in width. The main symptoms observed in grubs due to viral infection are loss of appetite, lethargy, pallor, migration to the top of the breeding medium, disintegration of the fat bodies and development of diarrhoea. Adults did not show any pronounced external symptoms. Infected adults refused to take food and they eventually developed diarrhea. All instars of grubs and adults were susceptible to the viral infection .The susceptibility to infection was maximum in the first instar followed by third instar, second instar and the adults in that order. The mean lethal concentration of the viru required to cause fifty per cent mortalities were 0.377 x10-4 , 14.417x10-4, 0.297x10-4 and 1.137x10-4 gut equivalent for the first, second and third instar grubs and adults respectively. The cytology of the midgut contents showed desquamated epithelial cells with nuclear and cytoplasmic vacuolation, nuclear hypertrophy and ring stages nucleus. The midgut and fat bodies have been identified as the major sites of viral multiplication. Transovum and transovarial transmission studies have shown that the virus was not transmitted by any of these method. The studies on transtadial transmission established that the disease was transmitted from first to second and from second to third instar, but not from the third instar to the pupae. The predator platymerus laevicollis did not transmit the disease. The reproductive potential of oryctes was found to be significantly impaired due to viral infection. When both the mating partners were infected, the number of eggs laid was only 19 to 20 as compared to the output of 209 to 219 in the healthy pairs. The cross-infectivity studies have clearly established that the virus was not infective to other important pests of coconut such as Rhyncophorus ferrugineus, Leucopholis coneophora, opisina arenosella and the predator’s p.laevicollis. In studies on the effect of temperature on the viability of the virus, it was found that above fifty per cent mortality took place on incubation of the virus for 21/2 hours at 370c and that the viability was totally lost as a result of exposure for 4 1/2 hours. The number of adults required for release in to the breeding pits of size of 30cmx30cmx30cm to kill fifty per cent of the Rhinoceros grubs at different time intervals were 4.440, 3.668, 3.016 and 2.889. Safety studies have revealed that the virus was absolutely safe to the silkworm Bombyx mori, chick embryo, white mice and white rat.

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