Mealybug Control Studies on Pineapples

It is now generally accepted, as pointed out by Westgate (1945), that the pineapple mealybug, Pseudococcus brevipes (Ckll.), is present in Florida, causing wilt as in other, pineapple growing areas. Control of the pine apple mealybug and/or of the ants infesting the soil and plants is, furthermore, usually considered to effect control of the wilt of pineapples, as shown by Illingworth (1931). Both oil emulsion sprays and tobacco dust treatments provide control measures of the mealybug and ants, and therefore of the wilt, although growers are still trying to learn of other, cheaper and more efficient means of wilt control. It is hoped that some of the more recently developed insecticides may be found more practicable for all Florida pine apple growers. Before describing recent exploratory tests for ant and mealybug control, however, it ap pears desirable to discuss briefly some often underemphasized factors concerning the pine apple mealybug. It is desired to note, first, that the ants and the mealybugs may be infesting plants for weeks or months before any but a careful examination would disclose their presence. This fact was a source of confusion to early workers on the pineapple wilt, and it may cause lack of sufficient and early attention by present-day growers. A plant may wilt three months or so after mealybugs attack it. In the meantime it has been a reservoir of mealy bugs, some of which have moved or been moved by ants to healthy plants. Time periods for the development of wilt symptoms were reported by Carter (1945) to vary from 43 to 295 days, depending somewhat on the age of the plant at the time of infestation. He re ported that recovery from early stages of wilt could occur with complete loss of symptoms and that recovery from advanced stages oc curs. Other factors reportedly affecting wilt are nitrogen fertilization, mealybug reinfestation or addition of other mealybug colonies, and different qualities or quantities of light. Mealybug infestations may originate through one or more of three means. Infestations may arise from planting materials, slips or suck ers, used to start new beds. The insects are often present in the soil at the time the beds are started. A third method is the dispersion into beds from sources outside. Repeated ob servations have indicated that plants around the bed margins often begin wilting before those in the centers of the beds. Although the 'mealybugs are able to disperse without aid from other agencies, ants undoubtedly carry mealybugs to favorable locations and aid in more rapid and widespread mealybug distri bution. The rate of mealybug growth is considered rather slow, requiring two months or more from young larvae to female ready for repro duction. They give birth to living young, how ever, and males are not required for repro duction. Mealybug host plants are numerous, so that the exclusion of pineapple plants from an area for a period of time cannot be expected to provide wilt control. Only a few mealybugs per plant are nec essary to produce wilt. One per plant may do so but there are usually many more per plant inducing wilt. In an experiment involv ing thousands of plants, Carter (1935) re ported on the percentage of plants wilting as the result of different mealybug population levels per plant. This report includes plants wilting 75 to 105 days after insect infestation. His experiments showed that five insects in duced wilt in 7 percent, 25 insects induced wilt