Biological Studies on Raoiella indica Hirst and Phyllotetranychus aegyptiacus Sayed Infesting Date Palm Trees in U. A. R.

(Acarina - Tenuipalpidae)

By M. A. ZAHER, A. K. WAFA and A. A. YOUSLI:

Introduction

Date palm trees are widely cultivated in the LJ.A.R. and considered one ot the main horticultural crops. SAYED 1938, 1940 and 1942, recorded the occurrence of the two mite species Phyllotetvanychus aegyptiacus Sayed and Raoiella indica Hirst as pests infesting these trees. He added that the former was inore widely spread all over the country than the latter which was also found in lower and upper Egypt but rather confined to certain areas.

Thus, because of the importance of the date fruits as one of the main crops in Egypt, it was found necessary to throw light on the biology of these acarine pests before carrying out any control program.

Material and Method

Small pieces of palm fronds, each of 25 cm. with one or two shortened leaflets, were partly inserted in test tubes full of water and plugged with cotton wool. Not less than 25 newly hatched larvae of every experimented species were confined singly, each to a palm frond by a circle of a mixture of Canada balsam and castor oil at about 12 cm. from the top. Water was changed daily and mite individuals were transferred to fresh host when needed till reaching adults. Emerged females were put with males for copu- lation and left to deposit eggs.

A life cycle of each species was investigated in an insectary under natural climatic conditions during summer and observations were made twice daily.

Infestation

Field observations showed that the individuals of the two species infest palm fronds beside the midrib of both leaflet surfaces, but preferring the upper

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one. They sucli tlie plant x ~ p causing the r e m o \ a l of the chlorophyll and 'IS a result infested areas turn to yellowish green. I11 heavy infestation these areas change to dark b r o ~ . i i and the leaflets dr>-.

Symptoiiis of infest:~tion caused b y each mite species could easily be dif- ferentiated. For Raoielln indicn Hirst, dark reddish blotches appeared while f o r P h y 11 o tc tyan y chus ac y y p tin cus Say ed these blotches 11 ad di r t y u'hi t i sh appearance which resulted from tlie aggregation of mite individuals with whitish fan-like setae. Also investigations proved that none of the tlvo ex- perimented mites had an overwintering stage as eggs, immatures and adults were observed during winter.

Description

Ruoiellu indicu Hirst

Adult female and male were described by SAYED 1942. Larva (Fig. 1 A) Body dark red; broadly ovate; 125.011 long and 93.011 wide.Dorsuin smooth with incomplete suture between propodosoma and hysterosoma; all dorsal setae clavate and plumose. Propodosoma with 3 pairs of setae, the second

F i g . 1. Dorsal view of immature stages of Raoielln indicn I-Iirst. - A = Larva, B = Proto- nymph, C = Deutonymph

longer than any dorsal ones. Hysterosoma with 3 pairs of centrals, 4 sub- laterals, 1 huineral and 5 laterals; centrals longer than the laterals and both decrease in length posteriorly; first and second sublaterals longer than the third and the fourth and any of the laterals but similar to the first and second centrals.

Protonymph (Fig. 1 B) Body dark red; nearly rounded; 210.0 ( I long and 159.0 .tr wide. Dorsal chaetotaxal pattern differs from that of the larya in having the humeral, first arid second laterals longer than the sublateral5 a n d any o t 11 er h y s t erosonia 1 s .

Deutonymph (Fig. 1 C) Body dark red; broadly ovate; 272.0 ( I long and 179.0 /( wide. Dorsal chaetotaxal pattern similar to that of protonymph and adult.

Phyltotetranychus aegyptiacus Sa yed

Adult female and male were described by SAYEU 1940. long and

104.0 ,u wide. Dorsum with a suture between propodosoina and hysterosoma not reaching the margins. Propodosonia with 3 pairs of dorsal setae; first fan-like and larger than any dorsal setae; second and third smaller and lanceolate. Hysterosoina with 3 centrals, 1 humeral, 3 sublaterals and 6 laterals; centrals lanceolate, decreasing in length posteriorly, the first broTder

than the second and both lon- ger than any hysterosomals; humeral and first sublateral lanceolate and equal in length, first lareral equal to second sublateral und both longer than other laterals and sub- laterals. All humeral, laterals

A and sublaterals lanceolate. Median part of hysterosoma

Nymphy (Fig. 2 B) body Nymph broadly ovate; dark red;

200.0 ,u long and 138.0 ,u wide. Dorsum with suture between propodosoma and hysterosoma, the latter with transverse striae; dorsal setae have the same number of the larval but longer and larger in size. Propodosoma with first pair large and fan-like, the second lanceolate and longer than the third spatulate seta. Hysterosoma with the first central broadly leaf-like and larger than the third; the second whiplike; first lateral long lanceolate; second, third and fifth spatulate and decreasing in length posteriorly; the fourth and the sixth the smallest; first sublateral and the humeral long spatulate and equal in length; second and third sublaterals short, but the former spatulate and wider than the latter (lanceolate).

Larva (Fig. 2 A) Body dark red; nearly rounded; 133.0

Ezg. 2. Dorsal view of immature stages of Phyllo- tetpanychus aegyptzacus Sayed. - A = Larva, B =

with transverse striae-

Life Cycle

Females of both species usually deposit their eggs singly in preferable places such as depressions or near leaflet veins and as a result these eggs appear in groups.

In addition to egg stage both sexes of Raoiella indica Hirst pass through active and quiescent larval, protonymphal and deutonymphal stages before

Hatching

The egg of the former is oval, dark red and measures about 11 8.0 ic long and 89.0 / / wide. As the incubation period proceeds the egg becomes pale and just before hatching a split encirles it near the top, then the hatching larva pushes this part of the egg shell to crawl outside.

The egg of the latter is spherical, dark red and measures 98.5 (( in dia- meter. Before hatching it turns to reddish pink and a split surrounds most of the egg from which the larva crawls outside leaving t h e egg shell.

Moulting

Before moulting every active immature of both species enters a quiescence during which it stops feeding and movement, stretching its fore legs forward and posterior legs backward. Phyllotetranychus aegyptiacus Sayed inserts the mouth parts into the plant tissues.

During these quiescent stages the skin becomes gliininering reddish purple with glassy appearance. A transverse rupture of the skin occurs on the venter between the podosoma and opisthosoma of Raoiella indica Hirst, then the iininature withdraws itself posteriorly then forwardly to get rid of the exu- via. For Phyllotetranychus aegyptiacus Sayed the rupture of the skin en- circles the larval body behind the posterior legs, then it disengages itself only from the anterior part of the old skin (that of prosoma). It is of interest to note that the emerging adult gets rid from the all the nymphal exuvia with that remained of the larval posterior part.

Mating

Newly emerged females generally accepted copulation immediately after emergence while the male spent a period which lasted 0.5 day for Raoiella irzdica Hirst and 1.5 days for Phyllotetranychus aegyptiacus Sayed under the natural climatic conditions of the experiment at average temperature 24.0° C for the former and 28.0° C for the latter.

In this process the male and female of the two species behave as that mentioned by MANGLITZ and CORY (1953) and ZAHER et a1 (1968) concern- ing other tenuipalpid mites Brevipalpus austvalis (Tucker) ( = B. califovnicus [Banks]) and Cenopdpus lanceolatisetae (Attiah) respectively. The male manipulates itself beneath the female, bending its posterior end upward and forward to contact that of the female.

Duration of the developmental stages

Under the natural climatic conditions of the experiment in suinmer, the periods of incubation, larval and nymphyal stages, life cycle, preoviposition

and generation of t h e tivo species are given i n t,ibles 1 and 2. A s usunll) heippens i n tetiuipalpid and tetranj&id mites males reachcd the adult st'igc be f o re fern a les . A 1 t 11 o u gli Ph y I1 o t e t ra n ~ ) ch M s aeg y p tiu C L I s S ,I !.ed has on 1 y one nymphal stage, yet its life cycle lasted for about fii-e da!,s niore than that of

TdblC I

Average duration of the different stages of Raoiefb indica Hirst

I t i CLI ba tio ti LArva Prom ymph I>cutotiymph

6.1 26.6 i.7 2i.C 5.4 27,s 4.1 25.2

-57. I 60.4 53.7 61.0

21.4 ii 21.0 26. I 57.9 Lifc c y c l e A

Preovipositioti 3.3 23.7 61.2 Generation 24.7 25.7 58.3

Table 2

Average durat ion of the different stages of Phyllotetranyrhus aegyptiacus Sayed

A \ . c r q e Averaqc Per iod ( U , l j c j T u m p e r n r u r e oc: R.1 I. 0;o

Incubation 9.4 26.5 58.6 Larva 6.3 25.6 47.4 Nymph 10.2 29.0 46.1

26.4 24.8 26.9 52.7 4.5 28.3 46.8 Preoviposition

Geiicratioii 30.9 27.0 51.8

Life cycle Q d

Raoieila indica Hirst. This however could partly be attributed to the differ- ence in average temperature and relative humidity during the immature stages. But there is a great evidence that the incubation period of the former lasted for about three and a half days more t!ian the latter as averages tem- perature and relative humidity were similar. On the other hand the only one nymphal stage durated as much as or little longer than the proto- and deuto- nymphal stages of the other species.

Summary

Infestation, description of immature stages, and biological aspects which in- cluded hatching, moulting, and mating of Raoiella indica Hirst and Phyllo- tetranychus aegyptiacus Sayed were studied. Life cycle of the two species proved that the former has two nymphal stages while the latter has only one. Also adult male emerged ahead of the female. The generation period of the former durated shorter than the latter. This could partly be due to the longer incubation period of Phyllotctuanychs aegyptiacus Sayed. Field observa- tions showed that the two investigated mites continued their development and reproduction during winter but with slow activity.

Zusammenfassung

Es wurden dic Morpliologie, Biolcgie iind Schadens\<reise der beiden an Dat- telpaimen schXdliclicii Milhen Raoiel!iL zriciku Hirst und Ph~il lotet ,ar~j ,c~~Ms ~ r g y p t i m u s Sayed in Agypten untersucht. Die erstgenannte Ar t hat zwei Nympheristadien, die letztere n u r eiiis. Ph?/llotet,arz2ic/~Ms hat eine langere Gt.samtentwick1ui~g '11s Ruoiellu, was z. T. in der liiingereii Inkubationszeit begriindet ist. Freilandbeobncht~iiigeii crgaben, dai3 die zwei Artcn ihrc Ent- wiclilung uiid Reproduktion %war im Winter fortsetzen, jedoch in verlang- samter Form.

References

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