Heat Unit Accumulation for The Two-Spotted Spider Mite, Tetranychus urticae (Acari: Tetranychidae) On Potato And Tomato Crops Under Climatic Changes

Citation: Egypt. Acad. J. Biolog. Sci. (A. Entomology) Vol.8 (2)pp.103-109(2015) Egyptian Academic Journal of Biological Sciences is the official English language journal of the Egyptian Society for Biological Sciences, Department of Entomology, Faculty of Sciences Ain Shams University. Entomology Journal publishes original research papers and reviews from any entomological discipline or from directly allied fields in ecology, behavioral biology, physiology, biochemistry, development, genetics, systematics, morphology, evolution, control of insects, arachnids, and general entomology. www.eajbs.eg.net Provided for non-commercial research and education use. Not for reproduction, distribution or commercial use.


INTRODUCTION
A well known fact is that members of the Actinedid family Tetranychidae contains more than 1,200 polyphagous mite pest species and Tetranychus urticae Koch (TSSM) might be considered the most important one (Alzoubi and Cobanoglu, 2008).It attacks over 300 host plants including vegetables (e.g., beans, eggplant, peppers, tomatoes, and potatoes), fruits (e.g., strawberries, raspberries, currants, and pear) and ornamental plants ( Le Goff et al., 2009).Defoliation, leaf burning, and even plant death can occur due to direct feeding damage.Indirect effects of feeding may include decreases in photosynthesis, transpiration and can lead to yellow to white discoloration of the leaf often referred to as bronzing, causing loss of quality and yield or the death of the host plants (Park and Lee, 2002).Temperature has been recognized to be a key abiotic factor driving population dynamics of arthropods, which has resulted in a plethora of studies on the relationship between arthropod developmental biology and temperature.To predict developmental rates of poikilothermic arthropods, both linear and nonlinear models have been developed.With warmer temperatures occurring earlier in the spring, pest population can become established and thrive during earlier and more vulnerable crop growth stages.Additional insect generation and greater populations encouraged by higher temperatures and longer growing seasons will require greater efforts of pest management (Stinner et al., 1989).Estimates of future global climate change are necessarily somewhat imprecise, with different models showing substantial remember, however that at least for the next 40 years or so a large amount of this change is already built into the system and cannot be reversed.Climate change beyond this period will be influenced by future emission rates and change models utilize a rage of carbon dioxide and aerosol emission scenarios.Here, we use climate change scenarios effects of climate change in the UK and in sub-Saharan Africa (Chancellor and Kubiriba, 2006).
In the present work, it was planned to study the influence of degree-days units on generation number and days number per generate of Tetranychus urticae Koch (TSSM) infesting the Tomato and potato crops, under Egyptian environmental conditions.

Determination of degree-days units (DDU)
Daily maximum and minimum temperatures which recorded and obtained from CLAC were transformed to heat units using the lower threshold temperature of (TSSM) Tetranychus urticae (where, t0 was 10.0°c with 100 unit for generate according to Herbert (1982).Degree-days units were calculated by applying Richmond et al. (1983)  These experiments were carried out on spider mite T. urticae infesting Potato and Tomato crops, at Beheira, Sohag and Beni Suef governorates, during September-April for ten successive seasons 2003-2015.These mites were (TSSM) two spotted spider mite: Tetranychus urticae.Average temperatures (daily maximum and minimum) were calculated according to the data which recorded and obtained from central Laboratory for Agriculture Climate (CLAC).

Effect of Expected Future Climatic Changes on TSSM:
This study was carried out to predicate numbers and durations of generations and degree-days units (accumulated thermal heat units) in expected future climate change 2050s and 2100s.Climate change scenarios for locations were assessed according to future conditions derived from MAGICC/ SCENGEN software of the University of East Angle (UK).In this study one scenario of climate data was used A1(Table1).The principal of MAGICC/ SCENGEN data were used to explore the consequences of a medium is allowing the user to explore the consequences of a medium range of future emission scenarios.The user selects two such scenarios from library of possibilities.The reason for two scenarios is to able to compare a no action scenario with an action or policy scenario.Thus, in MAGICC/ SCENGEN the tow emissions scenarios were referred to as a reference scenario and policy scenario (Wigley et al., 2000).The data which generated from MAGICC/ SCENGEN are represented in one scenario A1.These scenarios are described by IPCC (2001) as "The A1 scenario describes a future world of very rapid economic growth, global population that peaks in mid-century and declines thereafter, and the rapid introduction of new and more efficient technologies" (Meehl et al., 2007).

Effect of climatic changes on spider mite, Tetranychus urticae Koch (TSSM) :
The aim of the present experiments is to study the influence of climatic changes on degree-days units, days number per generate and generations number of Tetranychus urticae Koch (TSSM) during current climate for growing seasons of 2011 to 2015 predict in 2050s and 2100s, at Beheira, Beni Suef and Sohag governorates, under environmental Egyptian conditions (Tables 2-4).Generation numbers of TSSM were more under climatic changes comparison with current climate, at different governorates, where generation numbers ranged from 11 to 16.With increasing degree-days units led to increase generation number, where degree-days units increased from 165.2 to 172.3 unit.Also, increasing degreedays units led to decreased days number per generate, where days number per generate decreased from 14.0 to 16.0 days when degree-days units were increased from 165.2 to 172.3 units.
Using degree-days allows for predicting pest occurrence, also can be an aid tool for scheduling sprays and beneficial insect releases at the optimum time to insure the best results and helpful in monitoring pest activity (Farag et al., 2009).The standard degree-days methods to predict by several insects, where degree-days can be defined as the units combining between time and temperature used to measure the development of an organism from one point to another in its life cycle (Wilson andBarnett, 1983 andZalom et al., 1983).Accumulated thermal units have been used to predict the seasonal development and emergence of various insect (Eckenrode et al., 1975;Sevacherian et al., 1977 andFarag et al., 2009).

A -Current climate:
Under current climate for growing seasons 2011-2015 recorded Beheira, Beni Suef and Sohag governorates generations number and degree-days units were less recorded during current climate, but days number per generate were highly recorded during current climate as compared with data of 2050s and 2100s, where in case of current climate degree-days units 170.7, 170.9 and 167.4 unit were recorded and 21.0, 19.0 and 19.0 days at Beheira, Beni Suef and Sohag governorates, respectively (Tables 2-4).
Temperature is usually the environmental factor with the greatest effect on developmental rate of immature mites and other poikilotherms.To quantify the effect of temperature on mite development, life stages of a spider mites T. urticae may be held at constant temperature and the resultant development times can be used to estimate developmental rate curves (Southwood, 1978).From these developmental rate curves, models can be formulated to predict development time as a function of temperature.These models are useful in making pest management decisions, or to be used as components of more comprehensive models for the investigation of population dynamics (Riahi et al., 2013).

B -Future predicting in 2050s and 2100s:
Climate changes scenarios for Beheira, Beni Suef and Sohag governorates were assessed according to future conditions derived from MAGICC/SCENGEN Software of the University of East Angle (UK) and these relation with TSSM.Generation number increased from 13 to 15 in 2050s and from 14 to 16 in 2100s, respectively.Days number per generate decreased to 17.0, 16.0 and 15.0 days in 2050s, but it decreased to 15.5, 15.0 and 14.0 days in 2100s, respectively.Also, degree-days units increased to 165.2,169.3 and 170.1 units in 2050s, but increased to 169.6,166.1 and 172.3 units for TSSM (Tables 1-3).
The Intergovernmental Panel on Climatic Changes (IPCC) found that predicted an increment in mean temperature from 1.1 to 5.4°c toward the year 2100 (Meehl et al., 2007).Kriticos et al. (2007) mentioned that climate change scenarios for the 2080s indicate that in the central pacific, the change in potential distribution is relatively minor for oriental fruit fly.Estay et al. (2009) predict a change in the equilibrium density of the confused flour beetle from 10 to 14% under the moderate B2 scenario and 12 to 22% under the extreme A2 scenario to the period 2017-2100.

Table 1 :
Simple model results of the climate change versus the current level of climate.Global mean temperature change for the illustrative SRES scenarios (A1).

Table 4 :
Influence of heat units on generation numbers and generation periods of Tetranychus urticae Koch (TSSM), at Sohag governorate during current climate (2011-2015) and climate change (2050s-2100s) under environmental emption condition.