Phytoseiidae

Sahraoui, H., Kreiter, S., Lebdi-Grissa, K. & Tixier, M. - S., 2016, Sustainable weed management and predatory mite (Acari: Phytoseiidae) dynamics in Tunisian citrus orchards, Acarologia 56 (4), pp. 517-532 : 520-524

Phytoseiidae on citrus trees. Three Phytoseiidae species were found on citrus trees: Euseius stipulatus (Athias-Henriot) , Neoseiulus californicus (McGregor) and Typhlodromus (Anthoseius) rhenanoides Athias-

Henriot ( Table 1); the most abundant was E. stipulatus whatever the weeding management. Considering the overall dataset, mean densities were significantly lower in the Mod.2 (herbicide treatment) than in the three others (H (3, 4800) = 15.30, P = 0.001) ( Figure 3a ). These differences were observed on 09- VI (H (3, 4800) = 23.12, P = 0.00) and 23-VI (H (3, 4800) = 11.27, P = 0.01). After this latter date, Phytoseiidae densities decreased in all the modalities, and no more significant difference was observed.

Phytoseiidae on weeds. Eight Phytoseiidae species were collected on weeds; two are new for the Tunisian fauna ( Kreiter et al. 2010): Typhlodromus (Anthoseius) pegazzani Ragusa and Swirski and Amblyseius meridionalis Berlese ( Tables 1, 2 ). Euseius stipulatus clearly dominates whatever the weed management strategy; N. californicus and T. (A.) rhenanoides are the second and third prevalent species on weeds. Euseius stipulatus was found on nine plants with the highest densities observed on Amaranthus retroflexus L. ( Amaranthaceae ). Neoseiulus californicus was collected on seven plants and was particularly abundant on Cynodon dactylon (L.) Persoon ( Poaceae ). Finally, T. (A.) rhenanoides was collected on five plants ( Table 2 ). Although the total number of Phytoseiidae collected during all the experiment was higher in the modalities wild cover (Mod.1) and mown weeds (Mod.3), mean densities were not statistically different between the four modalities (H (3, 160) = 7.41, P = 0.06) ( Figure 3b ). No significant difference was either observed at each date.

Phytoseiidae captured. The three most abundant species found on trees and weeds were also caught; the most captured was E. stipulatus (67 %) whatever the weeding modality ( Table 1). Species dispersing downwards and upwards were the same. Female was the most captured stage (75 %) followed by immature (21 %) and males (4 %). Higher densities were caught in the direction "weeds to tree" than in the direction "tree to weeds" ( Figure 3c ) (H (1,32) = 8.07, P = 0.004). Considering each modality separately, this trend was only significant for the Mod.1 (wild cover) (H (1, 80) = 4.97, P = 0.026) and the Mod.4 (ploughed ground) (H (1, 80) = 5.26, P = 0.021). In this latter modality, the mean number of Phytoseiidae moving upwards was significantly higher than in the other modalities (H (3, 160) = 23.29, P <0.01), especially at 09-VI (H (1, 32) = 5.38, P = 0.02) and 16-VI (H (1, 32) = 5.56, P = 0.01). Phytoseiidae densities dispersing from trees to the weeds were not significantly different between the four modalities (H (3, 160) = 2.25, P = 0.52).

Relationships between Phytoseiidae densities on trees, weeds and in traps. A positive linear significant correlation was observed between Phytoseiidae mean densities on citrus and weeds for the Mod.1 (wild cover) (R 2 = 0.51, P = 0.018). Positive

significant correlations were found between Phytoseiidae mean densities on weeds and those moving upwards in the Mod.3 (mown weeds) (R 2 = 0.42, P = 0.03) and Mod.4 (ploughed ground) (R 2 = 0.53, P = 0.01). No significant correlation was observed between Phytoseiidae mean densities in weeds and those moving downwards, whatever the modality considered. A significant correlation between densities on trees and those moving downwards was observed for the Mod.1 (wild cover) (R 2 = 0.57, P = 0.01). A positive significant correlation was also found between Phytoseiidae mean densities on trees and those moving upwards for the Mod.2 (glyphosate) (R 2 = 0.59, P <0.01) and Mod.4 (ploughed ground) (R 2 = 0.59, P <0.01) (Table 3).

Figures

FIGURE 3: Mean Phytoseiidae densities per date (a) per citrus leaf, (b) per weed quadrat and (c) per trap for the four weeding modalities in the experimental site 1.

Tables

TABLE 2: Number of specimens of Phytoseiidae species collected on weeds in the inter-rows of the citrus orchards studied in two experimental sites.

		Amblyseius * meridionalis	Euseius * stipulatus	Iphiseius * degenerans	Neoseiulus * barkei	Neoseiulus * californicus	Neoseiulus * cucumeris	Neoseiulus * longilaterus	Neoseiulus * paspalivorus	Phytoseiulus *persimilis	Typhlodromus . * (A.) * rhenanoides	Typhlodromus * (T.)* exhilaratus	Typhlodromus * (T.)* phialatus
Experimental,site,1	Amaranthus * retroflexus		35			3					2
	Beta * arvensis		19
	Bromus *diandrus		1
	Chenopodium * murale										2
	Convolvulus * arvensis	1	8			4					2
	Conyza *canadensis		12			6
	Cynodon * dactylon					12	1				5
	Hordeum *murinum					13
	Malva ,sp.		1								2	5
	Mercurialis *annua		5
	Solanum * nigrum		9							2
Experimental,site,2	Strobilanthes ,sp.		2			2
C.*limetta	Amaranthus *blitum		7	3			1					61	7
	Arisarum *vulgare		1	2
	Beta * vulgaris *			4
	Chenopodium * murale							1	1				2
	Convolvolus * arvensis		2	11								3
	Conyza *canadensis											1	3
	Cynodon * dactylon						4	3
	Ecballium *Elatrium											10
	Malva * sp.											6
	Solanum * nigrum		3	75								9	2
C.*clementina	Bromus *rigidus*Roth.		3			4		2				1
	Chenopodium * murale											36
	Convolvolus * arvensis		7	1		7	3			34		7
	Conyza *canadensis												4
	Cynodon * dactylon							1				3
	Hordeum *murinum											3
	Lolium ,sp.		1					1
	Malva * sp.		1							5		1	3
	Mercurialis *annua		5									29
	Solanum * nigrum		16	22		3				2		34	3
C.*sinensis	Amaranthus *blitum		2										7
	Bromus *hordeaceus							1
	Chenopodium * murale		132			1	7	4				225	25
	Convolvolus * arvensis		11		2	2	1	1		4		8	5
	Conyza *canadensis											14
	Cynodon * dactylon						3					1
	Ecballium *Elatrium											9
	Emex * spinosa		13									7
	Lolium * sp.		1
	Mercurialis *annua									1		23
	Phalaris *brachystachys		2
	Phaseolus * vulgaris											2
	Solanum * nigrum			2						1		1