Spatial Distribution of Different Life Stages of Monosteira alticarinata (Hemiptera: Tingidae) in Birjand Region

The jujube, Ziziphus jujuba Mill. is a well-known medicinal plant with various nutritional values and pharmacological properties which grows in South Khorasan province, Iran, as the major producer of jujube in Iran. The jujube lace bug, Monosteira alticarinata Ghauri (Hemiptera: Tingidae) is the second most important pest of jujube trees after the jujube fruit fly, Carpomyia vesuviana Costa (Diptera: Tephritidae) in South Khorasan province. Its occurrence in Iran was reported for the first time in 2012 by Moodi from Birjand in South Khorasan province. Adults of M. alticarinata overwinter on the bark of trees, under fallen leaves and in spring they move to young jujube leaves where they feed and lay eggs on the underside, thus starting infestations. Both M. alticarinata adults and nymphs feed on underside of leaves and produce small chlorotic stippling on the upper leaf surface. Leaf undersides appear specifically black varnish spotted due to lace bug excrement. Their injury reduces photosynthesis and respiration and also causes aesthetically displeasing injured leaves. As a result, foliage becomes bronzed and leaves may drop early. The accumulation of excrements on the leaves, also results in reduction of the gas exchange like other lace bugs. Distribution pattern of an insect population is an important aspect as it represents the interaction between individuals of the species and their habitat. The importance of spatial distribution comes from its central role in ecological theories and its practical role in population sampling theory as well as in the development of rational pest management strategies. For these reasons, a great deal of effort has been invested in characterizing the spatial distribution of insect populations. Spatial dispersion of a population usually follows one of three models: aggregated (or contagious), random (or by chance) or uniform (or regular). To determine the spatial distribution pattern of a given species it is necessary to obtain data on the count of individuals in the ecosystem to be considered. Despite the importance of M. alticarinata in the region, no study has been conducted on the distribution of this pest in jujube plant in Iran. Knowledge of spatial distribution of M. alticarinata is useful for designing, pest management and development of population models and assessment of levels of its damage.

To investigate the spatial distribution pattern of different life stages of M. alticarinata, samplings were done weekly of jujube trees in 2020. Jujube leaf was selected as sampling unit and the reliable sample size with maximum relative variation of 20% was obtained 50. The number of egg, nymph and adult was recorded in three heights of jujube trees (1.5, 2, and 3 meters). The spatial distribution pattern of different life stages of lace bug was determined using mean-variance ratio, Lloyd's mean crowding index, Taylor´s power low and Iwao´s patchiness regression model.

Spatial distribution of an insect is affected by various environmental factors such as food, temperature, light, habitat condition, and other biotic and abiotic factors. The results of the study indicated an aggregated pattern for the spatial distribution of M. alticarinata in almost all heights of jujube. In other words, different heights of jujube did not have any marked effect on the distribution pattern of this pest. Information on spatial distribution of M. alticarinata can be used in estimating the number of samples required from an area to reliably estimate pest infestation levels to develop effective management programs. Similar to our results, the change in plant height did not affect the spatial distribution pattern of Agonoscena pistaciae and Diaphorina citri nymphs and in both cases the pattern of distribution was reported to be aggregated. Aggregated distribution is the most common pattern of spatial distribution in the world of harmful insects which is consistent with the results of this research.

M. alticarinata presented an aggregated spatial distribution in different life stages. The causes of aggregation in these lace bugs might be due to their inherent active aggregative behavioral response such as in a situation where the presence of one individual attracts the others, perhaps for the purpose of feeding and reproduction. Knowledge of the spatial distribution of this pest can be useful in designation of suitable sampling programs and it makes us estimate the density of this pest faster with low cost.