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Project description

Vine mealybug and its natural enemies in the San Joaquin Valley. (01FE018)
Program UC IPM competitive research grants program
Principal
investigator
K.M. Daane, Insect Biology, UC Berkeley
Host/habitat Grapes
Pest Vine Mealybug Planococcus ficus
Discipline Entomology
Beneficial
organism
Anagyrus pseudococci; Leptomastix abnormis; parasitoids
Review
panel
Field Ecology
Start year (duration)  2001 (Two Years)
Objectives Determine the seasonal abundance and distribution of the vine mealybug in San Joaquin Valley vineyards.

Determine life history parameters of the vine mealybug in temperature-controlled cabinets.

Conduct field and laboratory studies on the biology and competitive interactions of two vine mealybug parasitoids Anagyrus pseudococci and Leptomastix abnormis.

Final report The vine mealybug (VMB) is rapidly spreading through California and is well-established in some San Joaquin Valley (SJV) regions. We investigated VMB seasonal abundance and distribution and show that, in winter, VMB is found in hidden locations on the lower and upper trunk sections and the cordon. In spring, there is a movement upwards and, by June, VMB infests leaves and grape bunches, although some VMB remain in hidden locations. In summer, generations overlap and all development stages are present; its density increases rapidly during this period. In late summer and fall, the population declines dramatically because of vine senescence and VMB parasitoids. Parasitoid activity is highly seasonal. Few parasitoids were collected from November to May, when the VMB was in protected locations. From June to October, parasitoid density increased rapidly, contributing >80% mortality of exposed VMB by September. Anagyrus pseudococci is the dominant parasitoid species. The SJV abundance and distribution pattern is different from that found in the Coachella Valley, where a greater portion of the VMB population is on the lower trunk and roots and parasitism levels are lower (<20% at their peak). Studies on the VMB and parasitoid biology suggest temperature development and seasonal distribution influence natural controls. For example, Anagyrus pseudococci show egg to adult development required 14 days at 27C, while VMB development was nearly twice as long, suggesting there are two parasitoid generations to each VMB generation. In the laboratory, we also tested for possible competitive interactions between two parasitoid species (A. pseudococci and Leptomastix abnormis). We found that when both parasitoid species are present there was a reduction in A. pseudococci density, but an overall increase in VMB parasitism. Most important for natural regulation is that A. pseudococci overwinter as larvae, inside a mealybug, and there is a biologically-cued delay of adult emergence until April or May. Results suggest that A. pseudococci have a limited ability to suppress VMB early in the season. For this reason, studies are ongoing to develop better biological and chemical controls including mating disruption and importation of new parasitoid species.

Second-year
progress
The vine mealybug (VMB) is rapidly spreading through California and is well-established in some San Joaquin Valley (SJV) regions. We investigated VMB seasonal abundance and distribution and show that VMB overwinters in hidden locations on the lower and upper trunk sections and the cordon. In spring and summer, generations overlap and all development stages are present; its density increases. There is a corresponding movement upwards and, by June, VMB infests leaves and grape bunches, although some VMB remain in hidden locations. In fall, the population declines dramatically because of vine senescence and VMB parasitoids (Anagyrus pseudococci, Leptomastidea abnormis, and Allotropa sp.). Few parasitoids were collected from November to May, when the VMB was in protected locations. From June to October, parasitoid density increased rapidly, contributing >80% mortality of exposed VMB by September. Anagyrus pseudococci was the dominant parasitoid species (>90%), followed by L. abnormis (<10%) and Allotropa sp. (<1%). The "SJV" abundance and distribution pattern SJV is different from that found in the Coachella Valley, where a greater portion of the VMB population is on the lower trunk and roots and parasitism levels are lower (<20% at their peak). Studies on the VMB and parasitoid biology suggest temperature development and seasonal distribution influence VMB suppression. Anagyrus pseudococci show egg to adult development at 11, 14, and 22 days when held at 32, 27, and 22ºC, respectively. VMB development (at 27ºC) was nearly twice as long. Field studies show reduced parasitism when VMB is located under bark. On exposed VMB, we found competitive interactions between A. pseudococci and L abnormis, resulting in a reduction in A. pseudococci density but an overall increase in VMB parasitism. These results suggest resident natural enemies have a limited ability to suppress VMB throughout the season.
First-year
progress
The vine mealybug (VMB) is a new vineyard pest in the San Joaquin Valley (SJV). Our research in 2001 determined the seasonal abundance and distribution of this pest. We found that VMB overwinters in locations throughout the lower and upper trunk sections and in hidden locations of the cordon. As temperatures increase, VMB moves up the vine sections and, by June/July, it is infesting leaves and grape bunches. Still, on any sample date, there was always a portion of the population that remained in concealed locations; therefore, any effective treatment must be able to penetrate the bark. During late spring and throughout summer its density steadily increases, with generations overlapping and all mealybug stages present at any time. The VMB population declines dramatically after harvest as a result of increased parasitism and the natural senescence of the leaves. We have collected data that will serve as a standard for testing more practical mealybug sampling methods. We compared a quick 5-minute per vine count and a more labor intensive 3-minute count of seven vine sections (lower trunk, middle trunk, vine cordon, spurs, canes, leaves and grape bunches) to a "destructive whole-vine sampling." There were very few parasitoids collected from winter until the end of June. From July through October, we found Anagyrus pseudococci as the dominant parasitoid species. Its density increased quickly during the summer, contributing up to 80% mortality of exposed VMB by August and September. The other parasitoid was Allotropa sp., which contributed <1% mortality. We have begun studies on the biology and interactions among two VMB parasitoids: Leptomastidea abnormis and Anagyrus pseudococci. We observed a slightly higher mealybug percent parasitism when A. pseudococci was added four days later than L. abnormis (65%) compared to A. pseudococci (59%) or L. abnormis alone (28%). Future studies will more closely determine the importance of VMB parasitoids.

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