Sudha Nagarkatti

Modeling Development in Grape Berry Moth (Lepidoptera: Tortricidae)

Abstract We modeled development in grape berry moth, Endopiza viteana (Clemens), which exploits wild and cultivated Vitis. Laboratory experiments were used to derive the temperature-dependent developmental curve for eggs, larvae, and pupae. We used linear interpolation to estimate stage-specific base temperature thresholds and degree-day requirements under laboratory conditions. We also estimated parameters of the Logan and Lactin nonlinear developmental models. Lastly, we conducted field experiments to evaluate the conventional degree-day model, which has a base threshold of 10°C; an improved degree-day model that was based on our laboratory observations; and nonlinear developmental models in predicting seasonal grape berry moth development. We concluded that the Logan nonlinear model provided the best estimates of grape berry moth field development, and an improved degree-day model should use 8.41°C as a minimum base temperature threshold and 423.9 as the egg-to-adult degree-day requirement. Also, after comparing degree-day accumulation estimates using the maximum-minimum method and trapezoidal integration to hourly temperature measurements, we concluded that the two approaches provided similar estimates during June–September.

Phenology of Grape Berry Moth (Lepidoptera: Tortricidae) in Cultivated Grape at Selected Geographic Locations

Abstract The grape berry moth, Endopiza viteana (Clemens) feeds on wild and cultivated Vitis spp., causing economic damage in the latter. We studied incidence of pheromone trap catch data, and combined this with previous work on development and diapause to construct a comprehensive model of the temporal dynamics of E. viteana. We explored the behavior of this model in six eastern United States locations along Lakes Erie and Michigan, the Finger Lakes in New York, and in Missouri and Virginia. Voltinism of E. viteana is influenced by the accumulated growing degree-days before the postsummer solstice photoperiod at which eggs develop exclusively into diapausing pupae. Our model generally predicted two full and a partial third generation in Geneva, NY, whereas partial fourth generations existed in vineyards along Lakes Erie and Michigan. In more southern latitudes, such as Missouri and Virginia, the absence of a partial fourth generation would be rare. Also, our model suggested the presence of clinal latitudinal variation in diapause induction, with southern populations of E. viteana responding to shorter daylengths than northern populations. These predictions, based on average 10-yr surface temperatures (1991–2000), are supported by past observations and explain the variability in voltinism from year to year that has been reported in the northeastern United States and Niagara Peninsula of Canada.

Diapause Maintenance and Termination in Grape Berry Moth (Lepidoptera: Tortricidae)

Abstract We studied pupal diapause maintenance and termination in Endopiza viteana, a pest of commercially grown grapes. We observed considerable variation in diapause intensity, which ranged from 5.5 to 10 mo under natural temperatures and photoperiods. Adult males tended to emerge from diapause slightly earlier than females, suggesting that E. viteana may be protandrous. In the field, low temperatures maintained diapause in overwintering pupae, and adult emergence began at ≈148 degree-days accumulated from 1 January. Photoperiod did not influence diapause termination in E. viteana. Overall, most adults emerged in spring at roughly the same time, regardless of the date at which pupae entered diapause; however, emergence was extended over a 6-wk period. Moreover, eggs oviposited by late-emerging females may experience photoperiods that would lead to diapause in pupae. Under natural conditions, extended adult emergence may result in overlapping generations; accordingly, coordinating the timing of control tactics with peak oviposition is very difficult for this insect pest.

Diapause induction in the grape berry moth (Lepidoptera : Tortricidae)

Abstract Photoperiod influences diapause induction in the grape berry moth, Endopiza viteana (=Polychrosis viteana), and eggs and neonates (<12 h) were the most sensitive to decreasing photoperiod. When held at photoperiods of 7–14 h, eggs produced mostly diapausing pupae, whereas at 15 h, development proceeded without diapause. Neonate larvae also showed sensitivity to short photoperiods, but responsiveness of larvae decreased rapidly with age, so that instars greater than 12 h old exposed to a short photoperiod of 8 h developed into adults without diapause. Eggs held at a high temperature (30°C) and 8-h photoperiod also produced diapausing pupae, suggesting that diapause induction in E. viteana is independent of temperature. Field studies showed considerable population variation in diapause induction, and an exponential saturation model predicted that 50 and 90% of individuals entered diapause at photoperiods of 14 h, 45.5 min and 14 h, 21.1 min, respectively.