Inoculate Release of Stethorus gilvifrons Mulsan (Coleoptera: Coccinellidae) for Biological Control of Date Palm Spider Mite, Oligonychus afrasiaticusMcGregor (Prostigmata: Tetranychidae)

The spider mite, Oligonychus afrasiaticus feeds by sucking the sap from the immature fruits tissue. The natural color of fruits changes to pale yellow or gray by mite's feeding. Damaged fruit are cracked and its damage can dry out the fruits. Because of resistance to pesticides, resurgence of date palm spider mite causes to disrupt the natural balance of their population. Tiny black ladybird beetle, Stethorous gilvifrons is the most important and active lady beetle species in Khuzestan province and is very effective on biological control of the spider mite. Determination of the amount and release time of the lady beetles are the most important factors in the implementation of biological control programs of date palm spider mite. So, careful monitoring, time of the release and the ability of deployment of predatory ladybird are essential steps to success in the programs of biological control.
This research was conducted in Shadegan region of Khuzestan province. The nested design was used to compare the efficiency of different inoculate release methods of the predator, S. gilvifrons. The main niches include three release times which were at the time of emergence, three days and one week after emergence of date palm spider mite in date palm plantation. Sub nesting including three different levels of predator release including minimum, moderate and maximum release with 0.5, 1 and 3 predator /m2 per day and were continued for two weeks. The two or three-days ladybirds were used to release. First, the infected clusters were covered by mesh fabric and ladybirds were released under them. After a week, mantles were opened up to the establishment of ladybird run on the normal condition of date palm plantations. This experiment was repeated three times, and each replication consists of a quarter- hectare plantation with dominant cultivar Sayer.Three date Palm trees from each release and control were randomly selected. One hundred fruits from10 major's of each bunches were randomly selected and the number of spider mite (prey) and coccinellid (predator) were counted in different developmental stages. The relationship between predator and prey was calculated by using Pearson's correlation in different treatments as an index of density-dependent reaction of the predator to prey density and its establishment.
Results showed that there were significant difference between treatments of release on seasonal mite and lady beetle populations and the average seasonal growth reduction rate at 1% probability level. The maximum difference in the number of mite – infested treatment and control occurred at maximum release with predatory mite. The maximum density of the lady beetle population was observed around mid to late June. Date palm fruits were been at Kharg phonological growth at this time and they had the greatest sensitivity to the mite population. The highest correlation coefficient occurred in terms of release time coincided with the moderate and maximum release of spider mite´s predator. So, the predator showed density - depend reaction and its establishment were occurred. Release of three and one lady beetle/m2 and simultaneously with the appearance of spider mite had powerful and significant correlation. In those circumstances, the density-dependent response of lady beetle was observed. The prey and the predator population densities have several fluctuations around their equilibrium level during the season. Number of predator population declines and prey population increases from their equilibrium levels were reduced by the simultaneous release of the predator to start prey activities. The predatory failure establishment is zero in the maximum release.The highest control of date palm spider mite was about 83.28% at release treatments. In all releasing treatments, the level of biological control was increased with increasing the number of coccinelid releases per unit.
The highest predator efficiency were calculated in the maximum release (3 coccinellid per square meter) and simultaneously with the appearance of spider mite in date palm plantation. The control performance was 83.27 percent in this condition. Understanding of the fluctuations of the date palm pests and their natural enemies and the effect of climatic factors on the fluctuations are necessary to operate the proposed models for biological date palm pest control. The success of this predator is high in terms of the date ecosystem, and the susceptibility of palm fruit to pests decreased at the end of the season.