Experimental & Applied Aearology, 18 (1994) 581-585 581

Dispersal of the broad mite, Polyphagotarsonemus latus (Banks)

(Heterostigmata: Tarsonemidae), by the greenhouse whitefly, Trialeurodes vaporariorum

(Westwood) (Homoptera: Aleyrodidae)

Russell Parker ~ and Uri Gerson b* aQueenstand Department of Prinutry Industries, Meiers Rd., lndooroopiUy, Qld. 4068, Australia.

bFaculty of Agriculture, Hebrew University q[ Jerusalem, Rehovot 76-100, Israel.

(Accepted 27 October 1994)

ABSTRACT

P',n'ker. R. and Gerson, U., 1994. Dispersal of the broad mite, Polyphagotarsonemus latus (Banks) (Heterostigrnata: Tarsoqemidae), by the greenhouse whitefly, Triateurodes vaporariorum (Westwood) (Homoptera: Aleyrodidae). Exp. Appl. Acarol., 18: 581-585.

Key words: Greenhouse whitefly, broad mite.

The greenhouse whitefly, Trialeurodes vaporariorum (Westwood), (Homoptera: Aleyrodidae) was found to disperse the broad mite, Polyphagotarsonemus latus (Banks) (Heterostigmata: Tarsonemidae). Mite presence on whiteflies was highly aggregated. This is the second whitefly species reported to disperse the broad mite, suggesting some recognition of the insects by P. latus.

The broad mite, Polyphagotarsonemus latus (Banks) (Heterostigmata: Tarson- emidae) is a major, cosmopolitan pest of many crops. Its biology and control were reviewed by Gerson (1992), while damage and chemical control in Australia were discussed by Gough and Qayyum (1987). Long-distance dispersal of the pest is through human transport of infested plants, by prevailing winds, and on insects, especially whiteflies (Homoptera: Aleyrodidae). Natarajan (1988) and Flechtmann et al. (1990) reported that sweet potato whitefly, Bemisia tabaci (Gennadius), served as a vector of the broad mite in India and in South America, respectively. Flechtmann et al. (1990) provided scanning electron microscopic (SEM) evidence showing many mites clasping the leg of a single B. tabaci. Herein we report on the dispersal of P. latus by another species of whitefly.

The broad mite was reared on potted potato plants in a greenhouse under con- ditions of 18-28°C, close to saturation humidity and prevailing mid-summer, south

*To whom correspondence should be addressed.

© Science and Technology Letters+ All rights reserved.

582 R. PARKER AND U. GERSON

Queensland, photoperiods (14L: 10D). In early November the plants became infested by the greenhouse whitefly, Trialeurodes vaporariorum (Westwood), a major, polyphagous pest in greenhouses (van Lenteren and Woets, 1988). Three whitefly samples were taken (by randomly aspirating the adults off infested plants) during late 1992 and early 1993. Most whitefly immatures were then attacked by the hymenopterous parasite Encarsia formosa (Gahan), and sampling had to be discontinued. Seven additional collections were made almost weekly from the same colony from mid-November 1993 to early January 1994, when most T. vaporariorum were again parasitized. An additional batch of ca 200 whiteflies was collected on 19 January, 1994, from gerberas grown out of doors at Wynnum, S.E. Queensland, to record phoresy in the field. Aspirated whiteflies were immediately placed in a freezer for one hour and then transferred to lactic acid for examination. Individual mite-carrying insects were deep-frozen with diethylether for 30 min, air-dried, coated with platinum and scanned by means of a Phillips 505 SEM. Members of another polyphagous plant feeder, the green peach aphid, Myzus persicae (Sulzer) (Homoptera: Aphididae), found on these plants, were sporadic- ally collected and similarly examined. Relationships between log variance and log mean of mites counted on whiteflies were calculated for all data (Taylor's power law) in order to determine mite distribution on whiteflies (Taylor, 1961 ).

The broad mite occurred on ca 10% (range: 2.5-23.9%) of the greenhouse- collected whiteflies (Table 1). Rates of phoresy in the greenhouse were high in late November and then declined; we cannot explain this trend because greenhouse conditions remained the same. All phoretic mites were females. Most occurred singly on the insects, although as many as i 1 were seen on one whitefly (November 17 sample). A significant regression was obtained between log variance and log mean (Fig. 1), and the slope significantly exceeded unity (one tailed t-test, t=2.755;

T A B L E 1

Phoresy of the broad mite, Polyphagotarsonem~ latus, on adult greenhouse whiteflies, Trialeurodes vaporariorum.

Whiteflies with mites Number whiteflies Mites per

Date examined Number % Total whitefly

Nov. 6, 1992 53 5 9.4 5 0.09 Dec. I0, 1992 20 2 10.0 4 0.20 Jan, 15, 1993 81 7 8.6 9 0.11 Nov. 17, 1993 56 9 16.1 31 0.55 Nov. 25, 1993 46 I 1 23.9 17 0.37 Dec. 2, 1993 59 3 5.1 3 0.05 Dec. 9, 1993 50 4 8.0 9 (I.18 Dec. 16, 1993 54 2 3.7 5 0.09 Dec. 23, 1993 40 1 2.5 1 0.02 Jan. 6, 1994 44 3 6.8 3 0.07

DISPERSAl. OF THE BROAD MITE., POLYPIIAGOTARSONEMUS 1.41Z/S 583

0 c- 03 ~L

03 >

0

-1

-2

y = 1 . 4 7 8 2 x + 0 . 6 7 2 ~ 3 o o t ,,g, m,te r2=0.90 p<0.001 *l/// ~ .vv jU~ Z0~[BB abundance

/ "

O / • o • ~ 0 1 2 3 4 5 >5

M i tes /wh i t e f l y

A: ::II /• ~ too } l ~ ^ . { ~ Low mite

0 1 2 3 4 5 >5

Mites/whitefly

' -2 -1 0 1

Mean Fig. 1. Aggregation of the broad mite, Polyphagotarsonemus latus, on greenhouse whiteflies, Trialeurodes vaporariorum, shown as log variance on log mean of mite abundance per whitefly. Upper and lower inserts show mite/whitefly frequencies per host at high and low P. latus abundance, respectively.

0.01 < P < 0.025; df=8), indicating the aggregated nature of broad mite distribu- tion on whiteflies. Aggregation appeared to be higher at low mite abundance (~ = 0.07 mites/whitefly; lower insert in Fig. 1) than at high mite numbers (g = 0.349 mites/whitefly; upper insert, Fig. 1), conforming to Taylor's (1984) statement that aggregation decreases as abundance increases. Of the 200 whiteflies collected out of doors, about 20% carried mites, indicating that this phoresy is not restricted to greenhouses.

Mites were seen to clasp the legs of T. vaporariorum (Fig. 2), in a way quite similar as that shown for B. tabaci by Flechtmann et al. (1990, Fig. 2). No mites were seen on the aphids during these observations, nor later, by the junior author in Israel (unpublished data, 1993-94).

The dispersal of P latus on T. vaporariorum, two dissimilar phytophages simultaneously infesting the s0ane plants, could have been opportunistic. However, this is the second instance of an aleyrodid vector for P. latus. And broad mite phoresy on B. tabaci was reported from two different parts of the world (Natarajan, 1988; Flechtmann et al., 1990), indicating that it is probably a common occurrence. Taken together, these cases suggest a closer association between P. latus and white-

584 R. PARKER AND U. GERSON

Fig. 2. Two individuals of the broad mite, Polyphagotarsonemus kttus, clasping legs of the green- house whitefly, Trialeurodes vaporariorum. Insert on left-hand side enlarged on right side.

flies, possibly cvcn some mode of aleyrodid recognition by the broad mite. It is unknown whether other whiteflies "also carry P. latus.

The only other vector reported for P. lares was the aphid M. persicae (Smith, 1935). We failed to corroborate this finding. Such negative rcsults, partial as they may be, tend to support the specificity of whiteflies for the broad mite.

Lindquist (1986) placed Polyphagotarsonemus into the Pseudotarsonemoidini (his Group A). This is a group of insect-associated tarsonemid genera of in- determinate feeding habits, with the exception of the clearly phytophagous Po~,phagotarsonemus. The phoresy of the broad mite on two different species of whiteflies indicates that a vestige of association between P. latus and insects has been retained.

ACKNOWLEDGEMENT

We wish to thank Dr. Marlene M. Elson-Harris and M1,. John E Donaldson (both of QDPI, Brisbane) for SEM micrography and whitefly identification, respectively, and Mr. Sergey Izraylevich (Faculty of Agriculture, Rehovot) tbr statistical expertise. This study was supported in part by the Australia Horticultural Research and Development Corporation.

DISPERSAL OF THE BROAD MITE, POLYPtlAGOE4RSONEMUS L4TUS 585

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