Context-Dependent Suppression of Thrips by Insect-Proof Nets in Greenhouse Eggplant and Potato

Insect-proof nets provide a non-chemical alternative within integrated pest management (IPM), but their effectiveness against thrips may depend on crop species, season, mesh size, and treatment-associated microclimate conditions. We compared an uncovered and unframed control (CK) and 40-, 60-, and 80-mesh insect-proof nets on thrip abundance in eggplant and potato across two planting seasons in a single-span plastic greenhouse. Weekly plot-level thrip surveys were conducted using a five-point sampling method. Thrips were not identified to species, and the response variable therefore represented total thrip abundance. Treatment effects were estimated with negative binomial (NB1) generalized linear mixed models incorporating a random intercept for plot and an offset for sampling effort; microclimate variables were analyzed with linear mixed models, and exploratory analyses additionally adjusted the NB1 model for measured microclimate covariates to examine whether accounting for these variables altered the estimated net-cage treatment associations. Net-cage treatments generally reduced thrip abundance relative to the control, but the magnitude and consistency of suppression varied markedly with crop and season. The 60-mesh net showed the most consistent direction of suppression, with estimated reductions ranging from 36.0% to 44.4% across the four crop–season contexts; this suppression was statistically supported in both eggplant contexts, but only marginal in the two potato contexts, and this directional consistency did not imply universal superiority in all contexts. The 80-mesh net produced stronger suppression in some cases but was inconsistent, with no detectable suppression in eggplant during the second season. Treatment-related differences in 7-day temperature and relative humidity were generally statistically uncertain, whereas illuminance showed some treatment-associated variation. Adjustment for the measured microclimate covariates did not consistently attenuate the estimated treatment associations, indicating that the measured variables did not provide a simple statistical explanation for the observed context-dependent pattern. Overall, the 60-mesh treatment showed the most consistent estimated suppressive direction under the tested conditions, whereas increasing nominal mesh count did not produce a simple monotonic increase in suppression. The microclimate-adjusted analysis was exploratory and did not provide a causal decomposition of net-cage effects.