Shoppers are making fewer food-shopping trips this year but spending more on groceries, according to a study released Thursday by Acosta Sales & Marketing. More than a quarter of respondents said they were making fewer routine shopping trips this year than last, while only 5% said they were making more trips. Average monthly spending on groceries, however, increased 11%, to $309, primarily due to price increases, the study found. The report, which polled a random sample of 1,098 shoppers using an online survey found that 35% of households earning less than $45,000 reporting fewer shopping trips this year, vs. 14% of those making $100,000 or more. The reduction in trips appears to have been exacerbated by higher gas prices, the study found.