Studies On Diapause Of The Pink Bollworm Pectinophora Gossypiella:


.

Sonia Mohamed Naguib

Author
Ph.D
Type
Benha University
University
Faculty
1989
Publish Year
Pink bollworm. 
Subject Headings

The pink bollworm, Pectinophora 80BByplella (Saunders)are subtropical insect species, which feed on annual plants.Those species are multi-voltine with diapause likely tooccur at any season of the year apparently independentlyon the weather.. Modern methods of insect control requirea detailed knowledge of insects seasonality since accurateforecast of season activity are necessary tor populationmanagemen t.The aim ot the present work is to study the effectof some tactors on the initiation and termination ofdispause stage of the pink bollwora larvae.Samples of larvae were collected at weekly intervalsthroughout the cotton season from flowers, green and drybolls from Kalyobia Governorate. Samples from each stageof plant growth were reared in the laborato~ at a consotent temperature of 27 c. 4!a lnstar larvae were sexedand the sex ratio was estimated. Normal and undersizedpale coloured larvae, referred to as abnormal larvaewere collected and sexed.I.a. Sex ratio during the season of 1985 :Results showed that at the beginning of the seasonin June the sexual ratio was in favour of males () f!: 1 .)in samples collected from infested flowers.The reverSe was true in August where the ratio was(1 rI’: 1.8 f). In Nov”’ber IllldDecember the ratio becameagain in ravour or malee (1.6 0’: 1 f) and (2.5 ~: 1 ’)respectively.r ,b. Normal. and abnormal larvae :Abnormal larvae appeared throughout the August-Novemberperiod, and it Was prOPortionally higher among malee. Thoelarvae invariably railed to enter into diapause stage, eaccordingly they were completely abSent in December whereall the larvae collected were in dlapause.II. Inrluence or temperature on diapause in the 41a instar larvae :The erfect oro three conetant temperatures were etudied,i.e. 15, 20 end 27 C on larval weights, time end percentageof PUpation, malformation inpupaa end adulta, percentagaof diapauee were estimated after 30 days end si% months.There Wae a general loss of lsrval weight at all temperatureeinveatigated snd in both ee%ee, males were moreafrected thllllr”’alee end the 1IIegn1 tUde or loee waeinversoely proportional to temperature being negligible at 27 C.proportional to temperature end at 27oC tha larvalThe duration of the larval period waa inveraelyduration period did not reach the threshold of dispause, owhile the degreeS of 15 and 20 C were conducive todiapause.Pupation incressed with the rise of temperature tooresch a maximum of 100 ~ at 27 c. At lower temperaturemore females pupated than males. oMalformations in pupae occurred at 15 snd 20 C butnot at 27oc. The percentage of malformation was inverselyproportional to temperature and males were more affectedthan females.Low temperatures extended the duration of ths pupalperiod and weight wes reduced by low temperatures theeffect was more noticeable with males.The percentege of eclusion of adults was low at theo temperatures of 15 and 20 C, never reaching 50 %. thisproportion was always lower among males compared withfemaleS. This percentage was 100 ~ in both sexes ato27 c.Diapausing larvae : By lowering the temperature morediap8Useoccurred with a larger proportion among males.statistically the effect of temperature and the inter~action of s8% and temperature were significant.oAt the temperatures of 15 and 20 C. 50 ~ of larvaewent into extended diap8Use for six months with higherpercentage of males than females. Temperature, sex andtheir interaction were found to be statistically signioficant. At 27 C, no extended diapause occurred.At the end of six months the effect ot the threeconstant temperatures on total mortalities throughoutthe experiment was calculated. Percentages at mortalitiesrose at low temperatures with higher percentageo mortalities in males. At 27 0, no mortalities occurred.The effects of temperature and sex on mortalities werefound to be statistically significant.III. Effect of sublethal doses of insecticides on diapause :The above experiment was repeated using 4th instarlarvae dosed with ca. 10 % dosages of one of threeinsecticides; fenvalerate, cypermethrln and chlorpyritos.Log-dose mortality line indicated that the descendingorder of toxicity of the three insecticides wasfenvalerate, cypermethrin and ehlorpyrifos. Statisticalanalysis showed the differences between the susceptibilitiesat males and temales to be not significant.~ substantial loss at weight occurred one week aftertreatment among treated larvae at the three constanttemperatures investigated. the loss was higher amongfemales than males. Treatment with insecticides didnot prevent diapause at low temperatures, but there wasa reduction of dispausing larvae, the reduction was morenoticeable among males and the most effective insectieideswas :t’envalerate.The lowest percentage of pupation at the two dispauseinducing temperature occurred in male and female larvaeexposed to cypermethrin, while fenvalerate and chlorpyrifoswere comparable in males, in females pupal formationfigures were slightly higher in chlorpyrifos.An increase in the percentage of malformations inpupae Occurred in survivals ot insecticides treatments,the phenomenon was discussed alongsIde reports in thelIterature on morphogenetic effects of pesticides.Insecticidal treatment prolonged pupal duration atthe three constant temperatures used with a more pronouncedeffect on males, and as would be expected pupalweights were adversely affected by insecticidal treatment,the least reduction in weight was brought about bychlorpyrifos.An additional reduction in adult ecluatOD was broughtabout by insecticides, the reductions were larger infemales than in males. Malformations of ada!ts wereincreased among survivals ot insecticidal treatments.Treatment with insecticides reduced the percentageof diapausing larYae, the reduction varied with aeX endinsecticide. Analysis of varience of this par~etershowed that the effect of temperature end insecticideswere significant but the effect of seX waS not.EXpOsure to insectiCides reduced the percentages oflarYae entering extended diepeuse (6 monthS) at the temperaturesof 15 end 20oc. The reduction was more pronouncedin male then in female larvae. Ststistical enalysiS supportedthese observations.Total mortalities after 6 months were computed, itwas evident that insecticidal treatment increased thispercentsge significantly at the three constent temperatureaused end with the three insecticides investigated.IV. Influence of some allelochemicS on the biology of thenewly hatching larYae of Eo. gossYl!1ella (Saund.) IThe newly hatching larvae were reared on diets cont- osining gossypol and coumarin at 21 C suffered mortalitiesthroughout the larval stage. Ilortalities were concentrationadependent, probit analysiS showed that coumarin wasabout 4.56 time more toxic than gossypol at LC50 level.The two compo~ds cansed a slowing down of the rate ofdevelopment of larvae the figpreS were statistical11significant.Weight of larvae and pupae were reduced, the reductionswere proportional to concentration, in coumarin,male larvae were affected more than temales, thosedeductions were verified statistically. There was areduction in the percentage pupation in the two compoundsand the reduction was proportional to concentration.There were substantial increases in malformed pupae,the etfect was more pronounced with coumarin.The two compounds caused elongation ot the pupalduration, coumarin caused more elongation than gossypolfor this period.There were appreciable percentages ot failure toproduce adults from pupae in the two compounds, percentageswere higher in coumarin. Among tormed adults therewere persistant, dose dependent percentages of malformedadults, gossypol was more effective.The two compounds slow down the rate of development,but the figures obtained did not prove the compounds tobe dlapause induces.Adults from larvae reared on the two compounds laidsignificantly less numbers of eggs. The frequency ofmating was adversely affected by the two compounds andhatchability among the eggs laid was reduced, there wssa slight decrease in the proportion of mated females inSeventeen amino acids were identified and quantifiedin the body hydrolysates of larvae in the above conditions.There was 3-4 folds increase in glutamic acid in diapausing,abnormal and coumarin treated larvae in comparisonwith aetive larvae.Similar patterns were found for valine, isoleucineand leueine, the three being reported 8S essential aminoacids to insects and similar in structure, routes orsynthesis and catabolism.There was some defieiency of tyrosine in abnormaland coumarin treated larvae. An increase in ammonia wasnoticed in active males.The overall picture suggested that a lesst part otthe increase in weight of diapeusing larvae may be dueto an increased protein content. 

Abstract
Attachments


Seacrch again