THE ORANGE THRIPS. 



Ecirs. lnrva\ iiiiil adults are found on the trees, and pupie in the 

 deaci leaves under them, from early ^lay until early Xovember, all 

 four forms l)ein.i!: present durin<>- tlif culirc period. 'ri)e broods thus 

 overlap so closely that it is very dillieult to se|)arate them. 



IX'rKKKKI.ATlON (IF AlUNDANCK OK TIIHII'S AND FOOD IM.ANTS. 



The orange thrips feed only on very tender plant tissues, namely, 

 the young leaves, shoots, and tender fi-uit. This makes it necessary 

 for them to pass from foliage to fruit and from plant to j^lant as the 

 suitability of the tissues as food ehanges. They first make their 

 appearance in April and May on the new growth of the Navel orange, 

 reaching the first maximum of abundance about the time four-fifths 

 of the petals are off. When most of the petals have fallen a few 

 thrips pass to the more advanced fruit and the number feeding on 

 the latter rapidly increases as the first growth of foliage becomes 

 hardened and distasteful. The thrips continue feeding on the fruit 

 until the latter, in turn, becomes somewhat tough, and reach a second 



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Fig. 1. — Diagram illustrating the relative abundance of orange thrips on oranges, on 

 orange foliage, and on other plants during the season. (Original. I 



and greater maximum in May. June, and July. They then pass 

 once more to the succulent growth which has come on in the mean- 

 time, and reach the third and final maximum of concentration in 

 Augu.st and September. 



As the first citrus growths are becoming tough and before the fruit 

 is quite tender, the thrips begin to work on the leaves of the grape, 

 pepper tree, umbrella tree, and some uncultivated plants, reaching 

 a minor maxinuim of abundance on these at the time of greatest 

 al)undance of tender leaves and stems. A second maximum of concen- 

 tration is reached on some of these secondary food plants in the fall, 

 when most all of the siunmer growths on citrus trees have become 

 tough. 



Tlie relative abundance of the orange thrips on its various food 

 plants, at different times during the season, is shown diagramnuitic- 

 ally in the accompanying chart (fig. 1) ; the diagram represents the 

 results of observations made at regular intervals in tl.ifferent parts 

 of the Tulare County citrus belt. 



